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Nutritional composition and shelflife of the Lake Victoria Nile perch (Lates niloticus) stored in ice.



INTRODUCTION

Nile perch Nile perch

Large food and game fish (family Latidae) found in the Nile and other African rivers and lakes. The Nile perch (Lates niloticus) has a large mouth and is greenish or brownish above, silvery below. It grows to about 6 ft (1.8 m) and weighs 300 lbs (140 kg).
 (Lates niloticus) is the most important commercial fish species from the Lake Victoria Fishery. In Kenya, it is locally referred to as "Mbuta" and is the most commercialized fish species that finds its way to the competitive European markets. In 2006, a total of 55,706 metric tons of Nile perch were landed. This was 35% of the total fish landed in Kenya the same year. The quantity was second to that of "Omena" (Rastrineobola argentea) with 57,929 metric tons, while the Nile tilapia Nile tilapia

tilapianiloticus (Oreochromis niloticus).
 was ranked third with 19,038 metric tons. The Nile perch export contributed US $ 50 million to Kenya, which is about 67% of the total fish and fishery product export earnings for 2006 [1]. The importance of the Nile perch fishery as a source of food for the local people, export earnings and employment for the riparian riparian adj. referring to the banks of a river or stream. (See: riparian rights)  communities justifies the need for better quality Nile perch products.

The nutritional composition of fish varies greatly from one species and individual to another, depending on age, feed intake, sex and sexual changes connected with spawning, the environment and season [2]. Processors have direct interest in the chemical composition of fish in order to know the nature of the raw material before chilling, freezing, smoking or canning can be correctly applied [3].

The quality of fresh fish is a major concern to the fish industry and consumers. Like marine fish, fresh water fish are perishable commodities. Deterioration in the quality of fish occurs due to the effect of a variety of biochemical and microbial microbial

pertaining to or emanating from a microbe.


microbial digestion
the breakdown of organic material, especially feedstuffs, by microbial organisms.
 mechanisms. However, the rate of loss of quality depends directly on the nature of the fish species and on the handling and storage conditions [4]. Once the fish are caught, on-board storage conditions exert a strong effect on the quality of manufactured fish products and accordingly on their commercial values [5].

Storage time and conditions have great impact on the quality of fish and fish products and the storage stability depends on the composition of the fish [5]. The rate of deterioration of fish is highly temperature dependent and can be inhibited by the use of low storage temperature [6]. Icing reduces temperature to about 0[degrees]C which lowers the growth of spoilage spoilage

decomposition; said of meat, milk, animal feeds especially ensilage.
 and pathogenic micro-organisms and hence their spoilage rate. Ice has a large cooling capacity, and therefore, a comparatively small amount of ice will be needed to cool one Kilogramme of fish. The reason why more ice is needed in practice is mainly because ice melting tends to compensate for thermal losses [7].

Despite the Nile perch being an important foreign exchange earner in the export market, there is little information available on its nutritional composition and shelf life. The objective of this study was, therefore, to assess the effect of storage in ice on the nutritional composition and study the usefulness of selected sensory, microbiological and chemical parameters in determining the shelf life in ice of the Nile perch. The quality index method (QIM QIM Quantization Index Modulation
QIM Quit India Movement
QIM Quality Inspection Management
QIM Quality Instruction Manual
) was used to select and study the sensory parameters and attributes that change most significantly during the deterioration process. Chemical and microbiological parameters were used together with complementary sensory analysis Sensory analysis (or sensory evaluation) is a scientific discipline that applies principles of experimental design and statistical analysis to the use of human senses (sight, smell, taste, touch and hearing) for the purposes of evaluating consumer products.  of cooked fish, to establish a sensory demerit de·mer·it  
n.
1.
a. A quality or characteristic deserving of blame or censure; a fault.

b. Absence of merit.

2. A mark made against one's record for a fault or for misconduct.
 value which would show the end of shelf life and act as a limit of Nile perch acceptability for human consumption.

MATERIALS AND METHODS

Raw material sampling

Fresh Nile perch (Lates niloticus) were purchased from fishermen at Dunga and Ogal fish landing sites situated about 2 and 30 km, respectively, from Kisumu town, Kenya, between April and October, 2008. The time interval between harvesting and arrival of the fish at the landing sites was about 3-4 hours and they were iced on purchase by layering with flaked ice. The control samples were iced immediately after being taken off the nets at the fishing ground by the fishermen according to according to
prep.
1. As stated or indicated by; on the authority of: according to historians.

2. In keeping with: according to instructions.

3.
 our instructions. After taking the weights and lengths of the fish, whole fish were immediately layered with flaked ice and packed in insulated containers. Each sampling time, 60 pieces of fish were purchased. A total of 180 pieces of fish were used in this experiment, including the controls. The whole Nile perch had an average weight of 887.2 [+ or -] 2.9 grams and a total length of 48.6 [+ or -] 0.4 cm. The average weight and length are within the recommended statutory specifications [8]. The iced Nile perch were transported to a nearby chill store and stored at a temperature of 0-2[degrees]C overnight before being transported within 4-5 hours to the Food Chemistry Laboratory at Egerton University Egerton University is a public university whose main campus is located in Njoro, near the city of Nakuru, Kenya. History
The school was founded in 1939 and was originally named Egerton Farm School.
 150 Km away where they were kept under similar conditions. Three fish were randomly sampled on days 3, 6, 10, 14, 18 and 22 while the control was sampled at the same interval up to day 30 of storage in ice. The average temperature of the sampled fish was 1.4 [+ or -] 0.14[degrees]C. During the storage period, any melted ice was replaced. All experimental and control samples were analyzed using the sensory, biochemical and microbiological tests as described below.

Proximate Analysis (Chem.) an analysis which determines the proximate principles of any substance, as contrasted with an ultimate analysis.

See also: Proximate
 

Three Nile perch samples were analyzed in triplicate for proximate proximate /prox·i·mate/ (prok´si-mit) immediate or nearest.

prox·i·mate
adj.
Closely related in space, time, or order; very near; proximal.



proximate

immediate; nearest.
 composition at each sampling time. The protein content was analyzed according to the Kjeldhal Method [9].

The lipid content was determined by Soxhlet Method according to AOAC [9]. The lipid content was determined by the following formula: % crude lipid = (wt of residue/original wt of sample) x 100.

Moisture content was determined by the standard AOAC method with oven drying of 5 g of fish at 105[degrees]C until a constant weight was reached [9]. The moisture content was determined as the loss in moisture. Ash content was determined by the standard AOAC method [9].

Sensory evaluation

Sensory evaluation was conducted on whole fish using a quality index scheme developed by a panel of three experts following the guidelines for sensory evaluation for fish species proposed by Martinsdottir et al. [10]. The sensory characteristics of Nile perch were assessed over the storage period of 22 days by a panel of ten previously trained assessors belonging to the Department of Dairy and Food Science and Technology of Egerton University, Kenya. The panelists were trained in order to familiarize them with the sensory scheme for Nile perch freshness evaluation. The appearance of the skin; slime color; clarity and shape of the eyes; elasticity; the belly texture; gill color, odor and gill slime appearance were assessed based on the scores of 0 to 3 (Table1).

The attributes of cooked fish (odor, taste and texture) were evaluated by the same panel on each sampling day simultaneously. The sensory assessment score sheet for cooked fish was adopted from Huss [7], with slight modifications (Table 2). The fish samples (50 g) were wrapped in aluminium foil Noun 1. aluminium foil - foil made of aluminum
aluminum foil, tin foil

foil - a piece of thin and flexible sheet metal; "the photographic film was wrapped in foil"
 and cooked in hot potable potable /pot·a·ble/ (po´tah-b'l) fit to drink.

po·ta·ble
adj.
Fit to drink; drinkable.



potable

fit to drink.
 water at a temperature of 95[degrees]C for 25 minutes, cooled and immediately presented to the panelists. The odor, taste and texture were evaluated using a structured acceptability scale of 0-10. The rejection threshold was set at [less than or equal to] 4 (Table 4).

Biochemical analyses

pH

Ten grams of Nile perch flesh from the tail region were homogenized in 50 mL of distilled water Noun 1. distilled water - water that has been purified by distillation
H2O, water - binary compound that occurs at room temperature as a clear colorless odorless tasteless liquid; freezes into ice below 0 degrees centigrade and boils above 100 degrees centigrade;
 and the mixture filtered using Whatman filter paper No.1. The pH of the filtrate filtrate /fil·trate/ (fil´trat) a liquid or gas that has passed through a filter.

fil·trate
v.
To put or go through a filter.

n.
 was measured using a CRISON Model 507 pH meter at ambient temperature after calibration using standard buffers of pH 7 and 4 at 25[degrees]C. The pH meter is made to read measurements accurately to [+ or -] 0.01 pH units [11].

Total volatile basic nitrogen (TVBN TVBN Total Volatile Basic Nitrogen (index of freshness)
TVBN Tech Venture Business Network (Los Altos, CA) 
)

Approximately ten grams sample of skinless fish flesh from the tail region was homogenized with 50 mL of distilled water. The mixture was centrifuged in Sorval RC-285 centrifuge centrifuge (sĕn`trəfyj), device using centrifugal force to separate two or more substances of different density, e.g., two liquids or a liquid and a solid.  (Dupont, Wilmington, Delaware, U.S.A) at 400 rpm for 5 minutes and the supernatant supernatant /su·per·na·tant/ (-na´tant) the liquid lying above a layer of precipitated insoluble material.

supernatant

the liquid lying above a layer of precipitated insoluble material.
 filtered through a Buchner funnel using Whatman No.1 filter paper. Two grams of MgO was added followed by one drop of antifoaming agent. A 250-mL Erlenmeyer flask containing 25 mL of 3% aqueous solution of boric acid boric acid, any one of the three chemical compounds, orthoboric (or boracic) acid, metaboric acid, and tetraboric (or pyroboric) acid; the term often refers simply to orthoboric acid. The acids may be thought of as hydrates of boric oxide, B2O3. , 0.04 mL of a mixture of methyl red and methylene blue methylene blue
n.
A basic aniline dye that forms a deep blue solution when dissolved in water and is used as a bacteriological stain and as an antidote for cyanide poisoning.
 indicators was used as the indicator. Distillation was continued until a final distillate dis·til·late
n.
A liquid condensed from vapor in distillation.



distillate

a product of distillation.
 volume of 125 mL was obtained. The distilled TVBN was titrated with an aqueous 0.1N HCL HCl

hydrochloric acid.
 solution. TVBN content was expressed as mgN/100 g of fish flesh [11].

TVBN = (V x C x 14 x 100) /10, where V is the volume of hydrochloric acid hydrochloric acid: see hydrogen chloride.
hydrochloric acid
 or muriatic acid

Solution in water of hydrogen chloride (HCl), a gaseous inorganic compound.
 added and its concentration (C), 10 represent the weight of the sample while 14 is the molecular weight of nitrogen.

Free Fatty Acids (FFA FFA free fatty acids. ) determination

Percent free fatty acids were determined by the standard AACC Method [12]. The FFA was expressed as percent oleic acid oleic acid /ole·ic ac·id/ (o-le´ik) a monounsaturated 18-carbon fatty acid found in most animal fats and vegetable oils; used in pharmacy as an emulsifier and to assist absorption of some drugs by the skin.  equivalent.

Microbiological analysis

Fish samples (25 g) from the tail region with skin on were mixed with 225 mL of peptone peptone /pep·tone/ (pep´ton) a derived protein, or a mixture of cleavage products produced by partial hydrolysis of native protein.pepton´ic

pep·tone
n.
 water diluent diluent /dil·u·ent/ (dil´oo-int)
1. causing dilution.

2. an agent that dilutes or renders less potent or irritant.


dil·u·ent
adj.
Serving to dilute.

n.
 and homogenized. The fish samples were analyzed with skin on to estimate the total viable counts that could be responsible for deterioration in quality both as a result of cross contamination cross contamination Medical practice The passsage of pathogens indirectly from one Pt to another due to use of improper sterilization procedures, unclean instruments, or recycling of products  due to poor handling and autolysis autolysis /au·tol·y·sis/ (aw-tol´i-sis)
1. spontaneous disintegration of cells or tissues by autologous enzymes, as occurs after death and in some pathologic conditions.

2.
. Further serial dilutions were made in tubes before plating. The TVC TVC Traditional Values Coalition
TVC Televisió de Catalunya (Catalan Public Broadcasting Company, Catalonia, Spain)
TVC Television Commercial
TVC Thrust Vector Control
TVC Texas Veterans Commission
TVC Total Variable Cost
 and [H.sub.2]S producing bacteria counts were done on Iron Agar Agar, in the Bible
Agar (ā`gər), the same as Hagar.
agar, substance obtained from seaweed
agar (ä`gär, ā`–, ăg`är) 
 (Oxoid, UK) by pour plate technique with an overlay as described by Gram et al. [13]. The plates were incubated at 22[degrees]C for 3 days. The total viable count (TVC) was obtained by registering all bacterial colonies on the incubated plates from each dilution of the sample showing growth. The number of colonies showing a clear dark color represented the bacterial population able to produce H2S, while the white colonies represented the TVC.

Data analysis

ANOVA anova

see analysis of variance.

ANOVA Analysis of variance, see there
 was performed on the treatment means for each parameter studied using Statistical Package for Social Scientists (SPSS A statistical package from SPSS, Inc., Chicago (www.spss.com) that runs on PCs, most mainframes and minis and is used extensively in marketing research. It provides over 50 statistical processes, including regression analysis, correlation and analysis of variance.  15, Chicago, Ill, USA) to examine whether there were significant differences in the parameters analyzed with storage time in ice. Correlations between the sensory, chemical and microbiological parameters were also done and are presented in Table 6.

RESULTS

Proximate composition

As shown in Table 5, lipid, moisture and ash contents varied between 0.59 and 0.63%, 78.5 and 79.6%, and 0.55 and 0.63%, respectively. Total crude protein decreased with storage time (p<0.05), from an initial value of 19.8% on day 3 of storage to 17.7% on day 22 of storage in ice.

Sensory evaluation

The scores given by the panellists according to the QIM scheme for each parameter are presented in Table 3. The demerit points were calculated for each storage day of sampling and showed an increase with storage time. The panellists scored 3.3 points on day 3 of storage and there was a significant increase (p<0.05) in the scores as storage in ice progressed. On day 22, the total demerit point score (quality index score QI), as determined by the panelists was 18.1 points (out of a maximum of 20 points).

The results of the analysis of cooked fish as determined by the same panel members showed a good score of 8.3 [+ or -] 0.1 points for odor, 8.3 [+ or -] 0.2 for taste and 8.7 [+ or -] 0.5 points for texture on day 3 of storage in ice. These scores tended to decrease with storage time in ice (p<0.05). On day 22 when the panellists perceived the fish were unacceptable, the scores were 4.4 [+ or -] 1.2, 4.3 [+ or -] 0.8 and 3.6 [+ or -] 0.5 for odor, taste and texture, respectively (Table 4).

pH

Changes in the pH of Nile perch stored in ice are shown in Table 5. On day 3 of storage in ice, the fish had a pH of 6.85. During the storage period, there was no significant increase in the pH up to the 10th day of storage in ice when the pH increased to 6.94. On day 22 the pH was 7.18. The overall pH values increased significantly (p<0.05), with storage time in ice.

TVBN

The TVBN values of Nile perch stored in ice are given in Table 5. The TVBN showed an increase with storage time in ice. The initial value of TVBN was 8.4 mgN/100 g of flesh on day 3 of storage in ice. It increased to 9.3 mgN/100g, 12.8 mgN/100 g, 16.6 mgN/100 g and 21.9 mgN/100 g on day 6, 10, 14 and 18 of storage in ice, respectively. On day 22 of storage, the TVBN content was 26.0 mgN/100 g of flesh. For the controls, the final value on day 28 was 26.8 mgN/100 g of flesh.

Free Fatty Acids

The changes in FFA in Nile perch muscle during iced storage are shown in Table 5. On day 3 of storage in ice, the FFA was 1.9%. No changes in FFA content were observed on day 3 and 6 of storage in ice. However, a gradual increase was evident from day 10 up to day 18 and the highest percent FFA content (2.7%) was obtained on day 22 for the experimental samples.

Microbiological analysis

The TVC and hydrogen sulphide producing bacterial counts increased with storage days in ice (p<0.05) as shown in Figure 1. The initial TVC was 6.6 log cfu/g on day 3 of storage in ice, which increased to 7.6 log cfu/g and 8 log cfu/g on day 14 and 22, respectively. The initial hydrogen sulphide producing bacterial count bacterial count Public health The concentration of coliform bacteria in water, a quantity that loosely correlates with the level of contamination of drinking and recreational waters. See Public water.  was 4.3 log cfu/g and this increased to 5.2 log cfu/g and 7.3 log cfu/g on the 14th and 22nd day of storage in ice, respectively, for the experimental sample lot.

[FIGURE 1 OMITTED]

DISCUSSION

Proximate composition

The lipid, ash and moisture contents which varied between 0.59 and 0.63%, 0.55 and 0.63%, and 78.5 and 79.5%, respectively, were not significant with storage time (p>0.05 (Table 5). Total crude protein decreased with storage time from the initial value of 19.8-17.7% at the end of the storage period. The decrease in the total crude protein content of fish flesh was possibly due to a decrease in salt soluble protein and water soluble protein [14]. This loss could also be due to autolytic au·tol·y·sis  
n.
The destruction of tissues or cells of an organism by the action of substances, such as enzymes, that are produced within the organism. Also called self-digestion.
 deterioration associated with the actions of endogenous enzymes and bacteria [15]. From the observations made, there was a decrease in protein content with an increase in TVBN content in the flesh. These changes coincided with an increase in the number of bacterial counts and this could be due to the proteolytic pro·te·o·lyt·ic
adj.
Relating to, characterized by, or promoting proteolysis.


proteolytic (pro″teolit´ik),
adj
 breakdown of the protein molecules to release volatile nitrogenous nitrogenous /ni·trog·e·nous/ (ni-troj´e-nus) containing nitrogen.

ni·trog·e·nous
adj.
Relating to or containing nitrogen.



nitrogenous

containing nitrogen.
 compounds determined as TVBN.

Sensory evaluation

The demerit points after day 3 of storage showed an increase with storage time. This was evident as deterioration in the quality of the Nile perch. The panellists scored an average of 3.3 points on day 3 of storage and there was significant increase (p<0.05) in the scores as storage progressed thereafter. On day 22, the average sum of demerit points (QI) as determined by the panellists was 18.1 points and this was the point of rejection of this fish. At this time, the skin appearance was dull, the eyes were opaque and concave Concave

Property that a curve is below a straight line connecting two end points. If the curve falls above the straight line, it is called convex.
 in shape, the texture of the fish was clearly marked by pressure, the belly was very soft, the gill colour was discolored, the odour was off normal and the slime was cloudy. These observed changes related positively with the pH, TVBN, FFA content, TVC and H2S bacterial counts, at which points the levels were 26.0 mgN/100 g, 2.7%, 8.0 log cfu/g and 7.3 log cfu/g, respectively. The corresponding correlations were 0.97, 0.97, 0.96, 0.84 and 0.74, respectively. These findings showed that the deterioration in the quality of the Nile perch as evidenced by the considerable values of these factors was in agreement with other authors [16, 17].

The results of the analysis of cooked fish as determined by the same panel members showed a high score of 8.3 points for both odour and taste and 8.7 points for texture on day 3 of storage. These scores tended to decrease with storage time in ice. On day 22 when the panellists felt the fish were unacceptable for human consumption, the scores were 4.4, 4.3 and 3.6 points for odour, taste and texture, respectively. The high scores observed on day 3 of storage showed the odour of the cooked fish was fresh to sea-weedy while the taste was sweet with a characteristic meaty flavor. The texture was firm and juicy. At the point of rejection there was a strong ammoniacal smell, the taste was sour, fishy fish·y  
adj. fish·i·er, fish·i·est
1. Resembling or suggestive of fish, as in taste or odor.

2. Cold or expressionless: a fishy stare.

3.
 and musty, while the flesh texture was very soft and mealy meal·y  
adj. meal·i·er, meal·i·est
1. Resembling meal in texture or consistency; granular: mealy potatoes.

2.
a. Made of or containing meal.

b.
. These characteristics corresponded with the high levels of pH (7.18), TVBN (26.0 mgN/100 g flesh), FFA (2.7%), TVC (8 .0 log cfu/g) and H2S bacterial counts (7.3 log cfu/g).

pH

The pH of live fish muscle is close to the value 7.0 [18]. However, post mortem [Latin, After death.] Pertaining to matters occurring after death. A term generally applied to an autopsy or examination of a corpse in order to ascertain the cause of death or to the inquisition for that purpose by the Coroner .  pH varies from 6.0 to 7.1 [19]. The pH of the Nile perch stored in ice increased with storage time. On day 3, the pH was 6.85. However, there was no significant increase in the pH until the 10th day when it increased to 6.94. On day 22 when the fish was considered unacceptable for human consumption, the pH was 7.18. Increases in pH may indicate the accumulation of alkaline compounds such as ammonia mainly derived from microbial actions. The increase may also be due to an increase in volatile bases from the decomposition of nitrogenous compounds by endogenous or microbial enzymes [18].

Although this index is not very important in determining the quality of fish, it can be used as a guide [19]. The pH of fish flesh has an important influence on its freshness because of its influence on bacterial growth. The lower the pH of fish flesh, the slower the bacterial growth, and vice versa VICE VERSA. On the contrary; on opposite sides. . The high correlation between the pH and TVC and H2S producing bacterial counts (0.82 and 0.74, respectively), confirms this relationship.

TVBN

The TVBN showed an increase with storage time, results that were similar to those of other studies of the Nile perch [13, 20]. The values for this index increased slowly until day 10 of storage when a sharp and significant increase was observed. This increase corresponded to the increase in the pH, TVC, [H.sub.2]S bacterial counts and the QI and is supported by the high correlations of 0.98, 0.97, 0.82 and 0.75, respectively. This increase detected from the 10th day, coincided with the onset of spoilage and the logarithmic logarithmic

pertaining to logarithm.


logarithmic relationship
when the logs of two variables plotted against each other create a straight line.
 phase of microbial growth.

The formation of TVBN is generally associated with the activity of micro-organisms and tends to be high at high microbial population [21, 22]. In this study, TVBN was 26.0 mgN/100 g of flesh on day 22 of storage in ice, a time when the cooked fish was considered unfit for human consumption. At this point, the TVC and [H.sub.2]S bacterial counts were high (8.0 log cfu/g and 7.3 log cfu/g, respectively) similar to the high pH value of 7.18. Since TVBN is produced mainly by bacterial decomposition of proteins in fish flesh, the high values of TVC and [H.sub.2]S bacterial counts on the 22nd day could explain the considerable value of TVBN in Nile perch flesh at this time of storage.

The changes in TVBN content may also be related to changes in pH [15]. The initial lower levels of TVBN observed could be due to lower levels of endogenous ammonia due to reduced microbial activity during the first 10 days of storage of the fish in ice [19]. The increase in the TVBN could also be due to bacterial and enzymatic activity, especially the psychrophylic bacteria [7].

Free Fatty Acids

There was a gradual increase in the FFA content with increasing storage time. The levels had a high correlation with the QI, TVBN and pH (Table 5) showing that it could act as a good indicator for the assessment of the freshness of the Nile perch. Lipid hydrolysis hydrolysis (hīdrŏl`ĭsĭs), chemical reaction of a compound with water, usually resulting in the formation of one or more new compounds.  occurred to a great extent at the end of the storage period. Hydrolysis of glycerol-fatty acid esters is one important change that occurs in fish muscle lipids post mortem with the release of fatty acids [23]. This is catalyzed by lipases and phospholipases [19]. The accumulation of FFA could be attributed to lipases and phospholipases activity in Nile perch muscle, digestive organs as well as microorganisms which were enhanced with extended storage. In addition, extracellular lipases produced by certain micro-organisms such as Pseudomonas spp. may have also contributed to lipolysis lipolysis /li·pol·y·sis/ (li-pol´i-sis) the splitting up or decomposition of fat.lipolyt´ic

li·pol·y·sis
n. pl. li·pol·y·ses
The hydrolysis of lipids.
 in the Nile perch tissue [23]. This is demonstrated by the moderate correlations observed between the FFA, and the TVC and [H.sub.2]S producing bacterial counts (0.82 and 0.69, respectively).

The formation of FFA does not lead to nutritional losses [24]. However, its examination was deemed important since it has been shown that the accumulation of FFA is related to texture deterioration by FFA interacting with proteins [25]. This is supported by the very soft and mealy texture that was observed when the FFA levels reached 2.66% on day 22 of storage, at which point the fish was perceived by the sensory panel to be unacceptable for human consumption. The FFA had a high correlation of 0.74 with the QI.

Microbiological analysis

The TVC and [H.sub.2]S producing bacterial counts increased throughout the storage period. There was no considerable increase in the TVC for the first 10 days, after which a significant increase was observed. This increase coincided with the rise in pH, TVBN and [H.sub.2]S producing bacterial counts. It may be explained that the high post mortem pH and the chilled storage temperature were favourable factors that could have contributed to the sharp increase in the TVC [10]. The increase in the TVC could also have led to an increase in the breakdown of nitrogenous components resulting in increased TVBN. This was shown by the high correlation with pH and TVBN of 0.81 and 0.82, respectively.

The increase in the bacterial counts also manifested itself in the changes in the sensory characteristics resulting in an increase in demerit points. The correlation between the TVC and the demerit points was high (0.84) indicating that the microbial growth could have contributed to the observed sensory changes.

At the end of the storage in ice, [H.sub.2]S producing bacteria dominated the bacterial flora (7.3 log cfu/g) and this could primarily have been responsible for most of the spoilage [5]. This is supported by the rejection of the cooked Nile perch when a rotten odor with a strong ammoniacal smell, a sour, fishy and musty taste, and a very soft and mealy texture was detected at this point of fish storage.

CONCLUSIONS

The nutritional composition of Nile perch shows that it has high content of protein of 19.8% when fresh which tended to slightly reduce to 17.7% as the sensory quality deteriorated. The fish is lean and had a low lipid content of 0.59-0.63%. The moisture and ash content varied between 78.5 and 79.6%, and 0.55 and 0.63%, respectively. It was demonstrated in this study that the shelf life of iced ungutted Nile perch with a 3-4 hour delay before icing is 22 days and this is the point at which the sensory panel perceived that the fish was unacceptable for human consumption. However, the ungutted control which was iced immediately it was taken on board had a shelf life of 28 days under the environmental conditions in the fishery. The high correlations between the sensory, chemical and microbiological parameters studied showed that these parameters are related to each other when applied in determining the shelf life of the L. Victoria Nile perch. At the point of rejection, the level of TVBN was 26.0 mgN/100 g of flesh, FFA was 2.7%, TVC was 8.0 log cfu/g), the [H.sub.2]S producing bacterial count was 7.3 log cfu/g), the pH was 7.18, the total demerit points were 18.1 out of a possible 20. The scores for texture, taste and odour were 3.6, 4.3 and 4.4, respectively, in the cooked fish as determined by the panellists.

ACKNOWLEDGEMENTS

We are grateful to the Research and Extension Division of Egerton University for funding this study. We also wish to thank staff of the Ministry of Fisheries Many states have set up government departments, usually called ministries, which regulate fisheries management within the state's exclusive economic zone. Examples include:
  • Ministry of Agriculture, Food and Fisheries (Sweden)
 Development, Kisumu, Kenya, for useful discussions, and the Beach Management Units in Dunga and Ogal, as well as the individual fishermen who willingly participated in the study.

REFERENCES

[1.] Fisheries Department. Fisheries Annual Statistical Bulletin. Nairobi, Fisheries Department, 2006; pp 1-50.

[2.] Silva JJ and RS Chamul Composition of marine and fresh water finfish finfish

fish with fins, that is teleosts, elasmobranches, holocephalids, agnathids and cephalochordates; also a fish marketer's term used to include that section of marketable fish which is neither shellfish nor molluscs.
 and shellfish species and their products. In: RE Martin, EP Carter, EJ Flick and LM Davis (Eds.), Marine and fresh water products handbook, Lancaster, Pennsylvania, U.S.A: Technomic Publishing Company, 2000; pp 31-46.

[3.] FAO FAO,
n See Food and Agriculture Organization.
. The composition of fish. Available from http://www.fao.org/wairdoes/tan/ x5916e/x5916co1.htm. 2004;1-80. Accessed on October 15, 2008.

[4.] Olafsdottir G, Martinsdottir E, Oehlenschlager J, Dalgaard P, Jensen B, Undeland I, Mackie I.M, Henehan G and J Nielsen Methods to evaluate fish freshness in research and industry. Trends Food Sci. Technol. 1997, 8: 258-265.

[5.] Ashie I, Smith J and B Simpson Spoilage and shelf life extension of fresh fish and shellfish. Crit Rev Food Sci Nutr, 1996, 36: 87-121.

[6.] Kraus L Refrigerated sea water treatment of herring and mackerel mackerel, common name for members of the family Scombridae, 60 species of open-sea fishes, including the albacore, bonito, and tuna. They are characterized by deeply forked tails that narrow greatly where they join the body; small finlets behind both the dorsal and  for human consumption. In: J Burt, R Hardy and K Whittle (Eds.), Pelagic pelagic

living in the middle or near the surface of large bodies of water such as lakes or oceans.
 Fish. The resource and its exploitation. Aberdeen, UK: Fishing News Books. 1992; pp 73-81.

[7.] Huss HH (Ed.) 1995. Quality and Quality Changes in Fresh Fish. FAO Fish. Tech. Pap. 1995; 348, FAO, Rome.

[8.] Fisheries Department Fisheries Act 1991-Basic Regulations, 1991 Revision. Nairobi, Fisheries Department, 1991.

[9.] AOAC Official Methods of Analysis, 17th edn. Association of Official Analytical Chemists. Washington, D.C. 2000; pp 1-50.

[10.] Martinsdottir E, Sveinsdottir K, Luten J, Schelvis-Smit R and G Hyldig Sensory evaluation of fish freshness. Reference manual for the fish sector. QIM-Eurofish. 2001; pp 1-50.

[11.] Goulas AE and MG Kontominas Effect of salting and smoking method on the keeping quality of chub Chub, in the Bible
Chub (kŭb), in the Bible, an African people. This may be a textual error for Lub (i.e., Lubim).
chub, in zoology
chub: see minnow.
 mackerel (Scomber japonicus): biochemical and sensory attributes. Food Chem. 2005, 93: 511 - 520.

[12.] AACC Official Methods of Analysis, 10th edn. American Association of Cereal Chemists, Washington, D.C. 2004; pp 1-43.

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[14.] Chomnawang C, Nantachai K, Yongsawatdigul J, Thawornchinsombut S and S Tungkawachara Chemical and biochemical changes biochemical changes (bī·ō·keˈmik·  of hybrid catfish fillet fillet /fil·let/ (fil´et)
1. a loop, as of cord or tape, for making traction on the fetus.

2. in the nervous system, a long band of nerve fibers.


fil·let
n.
1.
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Oceanic trout species (Salmo salar), a highly prized game fish. It averages about 12 lbs (5.5 kg) and is marked with round or cross-shaped spots. Found on both sides of the Atlantic Ocean, it enters streams in the fall to spawn.
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[19.] Pacheco-Aguilar R, Lugo-Sanchez ME and MR Robles-Burgueno Postmortem postmortem /post·mor·tem/ (post-mort´im) performed or occurring after death.

post·mor·tem
adj.
Relating to or occurring during the period after death.

n.
See autopsy.
 biochemical characteristic of Monterey sardine sardine: see herring.
sardine

Any of certain species of small (6–12 in., or 15–30 cm, long) food fishes of the herring family (Clupeidae), especially in the genera Sardina, Sardinops, and Sardinella.
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[20.] Karungi C, Byaruhanga YB and JH Muyonga Effect of pre-icing duration on quality deteroriation of iced Nile perch (Lates niloticus). Food Chem. 2004, 85: 13-17.

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Species (Oncorhynchus mykiss) of fish in the salmon family (Salmonidae) noted for spectacular leaps and hard fighting when hooked. It has been introduced from western North America to many other countries.
. Food Microb. 2004, 21: 157-165.

[22.] Benjakul S, Visessanguan W and J Turksuban Changes in physico-chemical properties and gel-forming ability of lizardfish (Saurida tumbil) during post-mortem storage in ice. Food Chem. 2003, 80: 535-544.

[23.] Nayak J, Nair PJV PJV Porgera Joint Venture (Papua New Guinea) , Ammu K and S Mathew Lipase lipase (lī`pās), any enzyme capable of degrading lipid molecules. The bulk of dietary lipids are a class called triacylglycerols and are attacked by lipases to yield simple fatty acids and glycerol, molecules which can permeate the membranes  activity in different tissues of four species of fish: rohu (Labeo rohita Hamilton), oil sardine (Sardinella longiceps Linnaeus), mullet (Liza subviridis Valenciennes) and Indian mackerel (Rastrelliger kanagurta Cuvier). J Sci Food and Agric. 2003, 83: 1139-1142.

[24.] Losada V, Pineiro C, Barros-velazquez J and SP Aubourg Inhibition of chemical changes related to freshness loss during storage of horse mackerel (Trachurus trachurus) in slurry ice. Food Chem. 2005, 93: 619-625.

[25.] Sikorski Z and A Kolakowska Changes in protein in frozen stored fish. In: Z Sikorski, BS Pan and F Shahidi (Eds.), Seafood proteins. New York New York, state, United States
New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of
: Chapman and Hall Chapman and Hall was a British publishing house, founded in the first half of the 19th century by Edward Chapman and William Hall. Upon Hall's death in 1847, Chapman's cousin Frederic Chapman became partner in the company, of which he became sole manager upon the retirement of . 1994; pp 99-112.

Okeyo GO (1), Lokuruka MNI See Merom New Instructions.  (2) * and JW Matofari (3)

(1) Master of Science (Food Science) Candidate, Department of Dairy and Food Science and Technology, Egerton University, P.O. Box 536-20115, Egerton, Kenya. E-mail: markokeyo@yahoo.com

(2) Senior Lecturer in Food Science, Department of Dairy and Food Science and Technology, Egerton University, P.O. Box 536-20115, Egerton, Kenya.

(3) Lecturer and Food Microbiologist, Department of Dairy and Food Science and Technology, Egerton university, P.O. Box 536-20115, Egerton, Kenya. E-mail: matofari@yahoo.com

* Corresponding author email: lokuruka@hotmail.com
Table 1: The QIM scheme developed for the Nile perch (Lates niloticus)
stored in ice.

Parameters          Attributes                           Demerit points

Appearance
Skin                Very bright, pearl shiny                      0
                    Bright                                        1
                    Dull                                          2
Slime               Clear- transparent                            0
                    Slightly cloudy/milky                         1
                    Cloudy                                        2

Eyes
Clarity             Clear-translucent                             0
                    Slightly opaque                               1
                    Opaque                                        2
Shape               Convex                                        0
                    Flat                                          1
                    Concave/sunken                                2

Texture
Elasticity          Elastic (finger mark disappears               0
                      immediately)
                    Slightly marked by pressure                   1
                    Clearly marked by pressure                    2
Belly               Intact                                        0
                    Slightly intact                               1
                    Soft                                          2
                    Very soft                                     3

Gills
Colour              Bright/dark red                               0
                    Brownish red                                  1
                    Discolored/brown                              2
Odor                Fresh, seaweedy                               0
                    Neutral                                       1
                    Fishy/sour                                    2
                    Off-odour/rotten                              3
Slime               Clear-translucent                             0
                    Slightly cloudy                               1
                    Cloudy                                        2

                    Total demerit points                         20

Table 2: A scheme for the evaluation of cooked Nile perch fillet.

10                      8                 6                 4
                                   Rejection
                                   Level

                                   ODOUR
Species            Fresh fish,     Slightly fishy     Sour, stale,
Rotten, putrid

Specific           seaweed         Slightly sour      cabbage,
                                                      Sulphidy

                                   TASTE

Meat flavor,       Sweet, reduces  Neutral, slightly  Musty, fishy,
Rotten, putrid

Sweet,             in intensity    fishy              slightly sour
Watery                                                some off-flavor

                                   TEXTURE

Firm, elastic,     Firm, springy,  Less firm, less    Softer, mealy
Slippery,
springy,           juicy           juicy
sloppy,
flaky, juicy
greasy

10                      2                 0

                   ODOUR
Species            Rotten,         spoilt
Rotten, putrid

Specific           strong          ammonia

                   TASTE

Meat flavor,                       Slightly rotten,
Rotten, putrid

Sweet,                             sour, sulphide
Watery

                   TEXTURE

Firm, elastic,                     Very soft
Slippery,
springy,
sloppy,
flaky, juicy
greasy

Adapted from Huss, 1995

Table 3: Demerit points assigned to each parameter during ice storage
of the Lake Victoria Nile perch (Lates niloticus.)

Parameters      Days of sampling

                       3                   6

Skin            0.4 [+ or -] 0.2    0.8 [+ or -] 0.2

Slime           0.3 [+ or -] 0.1    0.7 [+ or -] 0.2

Eyes clarity    0.4 [+ or -] 0.0    0.7 [+ or -] 0.2

Eyes shape      0.2 [+ or -] 0.0    0.4 [+ or -] 0.2

Elasticity      0.3 [+ or -] 0.2    0.5 [+ or -] 0.2

Belly           0.4 [+ or -] 0.2    0.8 [+ or -] 0.3

Gill color      0.4 [+ or -] 0.2    0.8 [+ or -] 0.4

Gill odor       0.3 [+ or -] 0.2    0.6 [+ or -] 0.1

Gill slime      0.4 [+ or -] 0.2    0.8 [+ or -] 0.2

Total demerit   3.3 [+ or -] 0.5    6.2 [+ or -] 0.9
  points

Parameters      Days of sampling
                       10                  14

Skin            0.8 [+ or -] 0.1    1.0 [+ or -] 0.1

Slime           1.1 [+ or -] 0.2    1.5 [+ or -] 0.1

Eyes clarity    1.0 [+ or -] 0.0    1.2 [+ or -] 0.2

Eyes shape      1.0 [+ or -] 0.2    0.9 [+ or -] 0.0

Elasticity      0.9 [+ or -] 0.3    1.5 [+ or -] 0.1

Belly           1.2 [+ or -] 0.3    1.5 [+ or -] 0.1

Gill color      0.9 [+ or -] 0.2    1.3 [+ or -] 0.2

Gill odor       1.0 [+ or -] 0.1    1.6 [+ or -] 0.2

Gill slime      1.0 [+ or -] 0.0    1.5 [+ or -] 0.1

Total demerit   9.1 [+ or -] 0.8    12.0 [+ or -] 0.2
  points

Parameters      Days of sampling
                       18                  22

Skin            1.1 [+ or -] 0.1    1.5 [+ or -] 0.6

Slime           1.8 [+ or -] 0.2    1.9 [+ or -] 0.1

Eyes clarity    1.7 [+ or -] 0.2    1.9 [+ or -] 0.1

Eyes shape      1.7 [+ or -] 0.2    1.9 [+ or -] 0.1

Elasticity      1.7 [+ or -] 0.2    1.9 [+ or -] 0.0

Belly           2.2 [+ or -] 0.3    2.6 [+ or -] 0.4

Gill color      1.4 [+ or -] 0.3    1.7 [+ or -] 0.1

Gill odor       2.0 [+ or -] 0.7    2.6 [+ or -] 0.5

Gill slime      1.9 [+ or -] 0.1    1.9 [+ or -] 0.1

Total demerit   15.6 [+ or -] 1.1   18.1 [+ or -] 0.5
  points

n=9

Table 4: Average scores for the evaluation of cooked Nile perch flesh.

Parameters    Days of sampling

                     3                    6

Odour         8.3 [+ or -] 0.1    8.0 [+ or -] 0.2
Taste         8.3 [+ or -] 0.2    8.0 [+ or -] 0.4
Texture       8.7 [+ or -] 0.5    7.8 [+ or -] 0.6

Parameters    Days of sampling

                     10                  14

Odour         7.7 [+ or -] 0.1    7.5 [+ or -] 0.6
Taste         7.4 [+ or -] 0.5    7.2 [+ or -] 0.5
Texture       7.3 [+ or -] 0.3    6.4 [+ or -] 0.5

Parameters    Days of sampling

                     18                  22

Odour         5.9 [+ or -] 0.3    4.4 [+ or -] 1.2
Taste         6.1 [+ or -] 0.2    4.3 [+ or -] 0.8
Texture       5.2 [+ or -] 0.7    3.6 [+ or -] 0.5

n = 9

Table 5: Summary values of the microbiological and biochemical
parameters analyzed (experimental samples).

Parameters                     Days of sampling

                            3                      6

TVC log cfu/g at           6.6                    6.7
22[degrees]C

                           4.3                    4.6
[H.sub.2]S log cfu/g at
22[degrees]C
pH                         6.85 [+ or -] 0.05     6.85 [+ or -] 0.05

%Moisture                 78.5 [+ or -] 0.36     78.5 [+ or -] 0.35

%Ash                       0.63 [+ or -] 0.05     0.61 [+ or -] 0.02

%Crude Lipid               0.63 [+ or -] 0.05     0.60 [+ or -] 0.01

% Crude protein           19.8 [+ or -] 0.1      19.2 [+ or -] 0.2

%FFA                       1.9 [+ or -] 0.00      1.9 [+ or -] 0.00

TVBN mgN/100 g             8.4 [+ or -] 0.7       9.3 [+ or -] 0.4

Parameters                      Days of sampling

                           10                     14

TVC log cfu/g at           7.4                    7.6
22[degrees]C

                           4.8                    5.2
[H.sub.2]S log cfu/g at
22[degrees]C
pH                         6.94 [+ or -] 0.01     7.01 [+ or -] 0.05

%Moisture                 79.1 [+ or -] 0.37     79.3 [+ or -] 0.49

%Ash                       0.59 [+ or -] 0.02     0.6 [+ or -] 0.02

%Crude Lipid               0.61 [+ or -] 0.01     0.60 [+ or -] 0.02

% Crude protein           18.9 [+ or -] 0.2      18.5 [+ or -] 0.2

%FFA                       2.1 [+ or -] 0.02      2.4 [+ or -] 0.05

TVBN mgN/100 g            12.8 [+ or -] 0.4      16.6 [+ or -] 1.0

Parameters                     Days of sampling

                           18                     22

TVC log cfu/g at           7.9                    8
22[degrees]C

                           6.9                    7.3
[H.sub.2]S log cfu/g at
22[degrees]C
pH                         7.08 [+ or -] 0.01     7.18 [+ or -] 0.04

%Moisture                 79.6 [+ or -] 0.31     79.6 [+ or -] 0.21

%Ash                       0.59 [+ or -] 0.01     0.55 [+ or -] 0.05

%Crude Lipid               0.59 [+ or -] 0.01     0.61 [+ or -] 0.01

% Crude protein           18.1 [+ or -] 0.17     17.7 [+ or -] 0.2

%FFA                       2.5 [+ or -] 0.06      2.7 [+ or -] 0.10

TVBN mgN/100 g            21.9 [+ or -] 1.4      26.0 [+ or -] 0.9

n=9

Table 6: Correlations between the different indices studied.

            TVBN     FFA      Demerit      TVC      [H.sub.2]S
                               points

pH          0.97     0.96       0.97       0.81       0.74
TVBN         -       0.98       0.97       0.82       0.75
FFA          -        -         0.96       0.82       0.69
Demerit      -        -          -         0.84       0.74
  points
TVC          -        -          -          -         0.90

Legend: H2S-hydrogen producing bacterial counts at 22[degrees]C
        TVC-total viable bacterial counts at 22[degrees]C.

Table 7: Summary values of the microbiological and biochemical
parameters analyzed (controls).

                      Days of sampling
Parameters           3                     6

TVC log cfu/g at     4.4                   4.7
22[degrees]C

H2S log cfu/g at     2.5                   3.1
22[degrees]C

pH                   6.84 [+ or -] 0.05    6.85 [+ or -] 0.05

% Moisture           78.4 [+ or -] 0.36    78.6 [+ or -] 0.05

% Ash                0.62 [+ or -] 0.05    0.60 [+ or -] 0.03

%Crude Lipid         0.64 [+ or -] 0.01    0.63 [+ or -] 0.01

%Crude Protein       19.5 [+ or -] 0.2     19.2 [+ or -] 0.1

%FFA                 1.9 [+ or -] 0.05     1.9 [+ or -] 0.05

TVBN mgN/100 g       8.4 [+ or -] 0.1      8.6 [+ or -] 0.4

                         Days of sampling
Parameters           10                    14

TVC log cfu/g at     5.2                   6.3
22[degrees]C

H2S log cfu/g at     3.94                  4.5
22[degrees]C

pH                   6.91 [+ or -] 0.01    6.95 [+ or -] 0.1

% Moisture           78.2 [+ or -] 0.7     78.7 [+ or -] 0.2

% Ash                0.61 [+ or -] 0.05    0.6 [+ or -] 0.02

%Crude Lipid         0.62 [+ or -] 0.06    0.61 [+ or -] 0.02

%Crude Protein       19.0 [+ or -] 0.1     18.8 [+ or -] 0.2

%FFA                 2.1 [+ or -] 0.05     2.3 [+ or -] 0.05

TVBN mgN/100 g       11.6 [+ or -] 0.4     15.4 [+ or -] 0.4

                         Days of sampling
Parameters           18                    22

TVC log cfu/g at     6.9                   7.3
22[degrees]C

H2S log cfu/g at     5.22                  6.68
22[degrees]C

pH                   6.99 [+ or -] 0.01    7.04 [+ or -] 0.05

% Moisture           78.7 [+ or -] 0.5     79.6 [+ or -] 0.21

% Ash                0.59 [+ or -] 0.02    0.61 [+ or -] 0.07

%Crude Lipid         0.6 [+ or -] 0.01     0.58 [+ or -] 0.44

%Crude Protein       18.4 [+ or -] 0.2     18.1 [+ or -] 0.2

%FFA                 2.4 [+ or -] 0.06     2.5 [+ or -] 0.04

TVBN mgN/100 g       16.6 [+ or -] 0.9     18.0 [+ or -] 0.4

                         Days of sampling
Parameters           26                    28

TVC log cfu/g at     7.5                   7.8
22[degrees]C

H2S log cfu/g at     6.9                   7.16
22[degrees]C

pH                   7.08 [+ or -] 0.03    7.14 [+ or -] 0.05

% Moisture           79.0 [+ or -] 0.2     78.7 [+ or -] 0.4

% Ash                0.60 [+ or -] 0.05    0.61 [+ or -] 0.02

%Crude Lipid         0.57 [+ or -] 0.08    0.60 [+ or -] 0.01

%Crude Protein       17.9 [+ or -] 0.26    17.5 [+ or -] 0.1

%FFA                 2.6 [+ or -] 0.02     2.7 [+ or -] 0.5

TVBN mgN/100 g       21.9 [+ or -] 0.8     26.8 [+ or -] 0.4

n=9

Table 8: Mean demerit points assigned to each parameter during ice
storage of the Lake Victoria Nile perch (Lates niloticus)
(controls).

Parameters               Days of sampling
                        3                   6

Skin             0.7 [+ or -] 0.3    0.8 [+ or -] 0.3
Slime            0.3 [+ or -] 0.1    0.4 [+ or -] 0.1
Eyes Clarity     0.5 [+ or -] 0.1    0.5 [+ or -] 0.1
Eyes shape       0.2 [+ or -] 0.0    0.6 [+ or -] 0.0
Elasticity       0.2 [+ or -] 0.1    0.3 [+ or -] 0.1
Belly            1.3 [+ or -] 0.0    1.5 [+ or -] 0.3
Gill Colour      0.5 [+ or -] 0.3    0.5 [+ or -] 0.2
Gill Odour       0.2 [+ or -] 0.1    0.5 [+ or -] 0.1
Gill Slime       0.3 [+ or -] 0.1    0.4 [+ or -] 0.2
Total demerit    3.4 [+ or -] 0.8    4.5 [+ or -] 0.8
Points (QI
score)

Parameters               Days of sampling
                        10                  14

Skin             1.0 [+ or -] 0.1    1.0 [+ or -] 0.1
Slime            1.0 [+ or -] 0.1    1.0 [+ or -] 0.1
Eyes Clarity     1.0 [+ or -] 0.0    1.3 [+ or -] 0.1
Eyes shape       1.3 [+ or -] 0.1    1.3 [+ or -] 0.2
Elasticity       0.8 [+ or -] 0.1    1.0 [+ or -] 0.1
Belly            1.6 [+ or -] 0.3    1.7 [+ or -] 0.1
Gill Colour      1.1 [+ or -] 0.1    1.1 [+ or -] 0.2
Gill Odour       1.2 [+ or -] 0.2    1.3 [+ or -] 0.2
Gill Slime       1.0 [+ or -] 0.1    1.2 [+ or -] 0.2
Total demerit    9.3 [+ or -] 0.4    10.5 [+ or -] 0.2
Points (QI
score)

Parameters                Days of sampling
                        18                  22

Skin             1.2 [+ or -] 0.3    1.4 [+ or -] 0.1
Slime            1.3 [+ or -] 0.2    1.6 [+ or -] 0.1
Eyes Clarity     1.3 [+ or -] 0.1    1.6 [+ or -] 0.1
Eyes shape       1.4 [+ or -] 0.1    1.5 [+ or -] 0.1
Elasticity       1.3 [+ or -] 0.1    1.4 [+ or -] 0.0
Belly            1.9 [+ or -] 0.1    1.9 [+ or -] 0.10
Gill Colour      1.3 [+ or -] 0.2    1.5 [+ or -] 0.1
Gill Odour       1.5 [+ or -] 0.2    1.7 [+ or -] 0.4
Gill Slime       1.3 [+ or -] 0.1    1.7 [+ or -] 0.2
Total demerit   12.1 [+ or -] 0.9   14.3 [+ or -] 0.7
Points (QI
score)

Parameters                 Days of sampling
                        26                  28

Skin             1.7 [+ or -] 0.0    2.0 [+ or -] 0.0
Slime            1.9 [+ or -] 0.1    2.0 [+ or -] 0.0
Eyes Clarity     1.8 [+ or -] 0.0    2.0 [+ or -] 0.0
Eyes shape       1.8 [+ or -] 0.0    2.0 [+ or -] 0.0
Elasticity       1.9 [+ or -] 0.2    2.0 [+ or -] 0.0
Belly            2.1 [+ or -] 0.1    2.2 [+ or -] 0.3
Gill Colour      1.8 [+ or -] 0.3    2.1 [+ or -] 0.2
Gill Odour       2.1 [+ or -] 0.3    2.9 [+ or -] 0.1
Gill Slime       1.9 [+ or -] 0.1    2.0 [+ or -] 0.0
Total demerit   16.6 [+ or -] 0.3   19.0 [+ or -] 0.1
Points (QI
score)

n=9
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Author:Okeyo, G.O.; Lokuruka, M.N.I.; Matofari, J.W.
Publication:African Journal of Food, Agriculture, Nutrition and Development
Article Type:Report
Geographic Code:6KENY
Date:May 1, 2009
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