Effect of different stocking density on growth, survival and production of endangered native fish climbing perch (Anabas testudineus, Bloch) fingerlings in nursery ponds.Introduction
The climbing perch Anabas testudineus (Bloch 1792) is a teleost belonging to the family Anabantidae and order Perciformes. This species is naturally distributed in Bangladesh, India, Pakistan, Ceylon, Burma, Sri Lanka, Thailand, Cochin-China, Tongking, southern China, The Philippines, Polynesia, and Malaysia [2,27,58,55,60,35,61,41]. Over their native range, climbing perch occur mainly in low lying swamps, marsh lands, lakes, canals, ponds, paddy fields, pools, small pits, and estuaries [27,31,60]. They are hardy and can tolerate extremely unfavourable water conditions . They are renowned for their ability to migrate between ponds over land. Migration is most common at night and after rain storms [58,28,59]. Climbing perch possess a special accessory air breathing organ (ABO), situated just above the gills in a large extension on the upper part of each gill chamber, which facilitates the utilization of atmospheric air . The species is a plankton feeder in its larval and fry stages but soon becomes omnivorous, feeding mainly on insects, invertebrates, fish and plants [57,51]. They are visual feeders, and feeding primarily during daytime .
Climbing perch mature at approximately 70-100 mm. Unlike other anabantids, they do not build bubble nests or care for their eggs, which float at the surface[54,2]. A. testudineus breeds in paddy fields and seasonal ponds with at least 10-25 cm depth. The fecundity of the fish varies from 4,588 to 34,993 in the size range of 7.3 to 18.2 cm.
The species is considered as a valuable food fish species and recommended as diet for the sick and convalescents. Climbing perch flesh contains high amounts of physiologically available iron and copper, essentially for haemoglobin synthesis . In addition, it also contains easily digestible poly-unsaturated fats and many essential amino acids . Due to its flavour, the fish is highly popular with consumers as a protein source of their diets. Unfortunately, in recent years, the fish has become gradually been endangered as the natural habitats and breeding grounds of this fish has been severely degraded due to environmental changes and man-made perturbations in aquatic ecosystems, including destructive fishing practices, reduction of water bodies, application of pesticides in rice cultivation, release of chemical effluents from industrial plants and hydrological changes due to construction of flood control infrastructure[31,26,24,44]. To protect this valuable fish from extinction and enhance stocks for aquaculture and fisheries, it is essential to develop appropriate breeding, nursing and fry/fingerlings rearing techniques under controlled captive conditions. Although Kohinoor et al.  developed a viable induced breeding technique for A. testudineus, and showed that its culture could be highly profitable no detailed data on other important aspects of climbing perch culture are available[57,51,3,4]. Stocking density influences survival, growth, behaviour, health, water quality, feeding and production. Both positive and negative relationships between stocking density and growth have been reported and the pattern of this interaction appears to be species specific[62,11,29,10,13]. The present experiment has been conducted to establish optimal fry stocking density as part of the development of practical and economically viable seed production methodology for A. testudineus.
Materials and methods
The present experiment was carried out for 8 weeks from 30 April to 25 June 2007 in 9 earthen nursery ponds at the Freshwater Station, Bangladesh Fisheries Research Institute, Mymensingh, Bangladesh. The ponds were rectangular in shape and the surface area of each pond was 1.0 decimal (0.004 ha) with an average depth of 0.8 meter. The ponds were drained, freed from aquatic vegetation and well-exposed to sunlight. After drying, quicklime (CaO, 250 kg/ha) was spread over the pond bottom to eradicate harmful insects and pathogens. Three days after liming, all the ponds were filled with ground water to a depth of about 0.8 meter. Five days after liming, the ponds were fertilized with cattle dung at the rate of 2,500 kg/ha. Seven days after manuring, the pond water was sprayed with dipterex (1.0 ppm) to eradicate harmful insects and predatory zooplankton such as copepods and cladocerans. All the nursery ponds were surrounded by fine-meshed nylon nets fixed with locally available bamboo poles to protect the fish from escaping as well as to prevent predators (such as frogs, snakes etc) to enter the ponds.
Spawning of A. testudineus was performed by artificial propagation following the technique of Kohinoor et al., . One day after fertilization, the hatchlings (larvae) were transferred into fine-meshed rearing hapas. Two days after fertilization, when the yolk sacs of larvae were fully absorbed, the hatchlings were fed with boiled egg-yolks for 2 days. One day after poisoning of pond water, four-day-old hatchlings having an average length of 0.44 [+ or -] 0.05 cm and weight of 0.14 [+ or -] 0.05 mg were stocked in the experimental ponds. Three triplicate treatments differing in stocking densities of hatchling viz., 1.0 million/ha (treatment 1, [T.sub.1]), 1.2 million/ha (treatment 2, [T.sub.2]) and 1.4 million/ha (treatment 3, [T.sub.3]) were tested.
Fry were fed twice daily with SABINCO commercial nursery feed (32.06% crude protein) at a rate of 14% of the estimated body weight of fry for the first two weeks, 12% for the second two weeks, 10% for the third two weeks and 8% for the fourth two weeks. The feed was broadcast on the pond water surface. Application of cattle dung (1000 kg/ha) was done at weekly intervals. Fry were sampled weekly by a fine-meshed nursery net for the assessment of growth, health condition and feed adjustment.
Water quality parameters of ponds were monitored weekly between 09.00 and 10.00 h. Temperature ([degrees]C) and dissolved oxygen (mg/l) were determined directly by a digital water quality analyzer (YSI, model 58, USA), pH by a digital pH-meter (Jenway, Model 3020, UK), transparency (cm) by a secchi disc and ammonia nitrogen by a HACH water analysis kit (DR 2000, USA). Total alkalinity was measured following the standard method [1,59].
Quantitative and qualitative estimates of plankton in the experimental ponds were also taken weekly. Plankton samples were collected from the ponds by passing 10 l of depth-integrated water samples through a fine-meshed plankton net (25 [micro]m) to obtain a 50 ml sample. The samples were preserved immediately with 5% buffered formalin in plastic bottles. Plankton density was estimated by using a sub-sampling technique. A Sedgwick-Rafter counting chamber was used under a calibrated compound microscope for plankton counting. Plankton cells in 10 randomly chosen squares were counted for quantitative estimation using the formula proposed by Rahman .
Thirty randomly selected individuals from each experimental pond were sampled weekly for length and weight. Length and weight gain were calculated by deducting the mean initial length and weight values from that of the final. Specific Growth Rager (SGR), the instantaneous change in weight of fish as the percentage increase in body weight per day over any given time interval , was calculated as follows:
SGR (%/day) = In[W.sub.2] - In[W.sub.1]/[T.sub.2] - [T.sub.1] x 100
Where, [W.sub.1] = initial live body weight (g) at time [T.sub.1] (day) and [W.sub.2] = final live body weight (g) at time [T.sub.2] (day).
The Food Conversion Ratio (FCR) was calculated according to the formula proposed by Castell and Tiews as follows:
FCR = Feed fed (dry weight)/Live weight gain
After 8 weeks of rearing, the fingerlings were harvested by repeated netting, followed by drying the ponds. Live fingerlings were counted and weighed individually. Survival rates were estimated on the basis of the number of fish harvested (no. of fish harvested/no. stocked x 100) and production (number/ha) of fingerlings were then estimated and compared among the treatments.
The mean values for growth, survival, production, water quality parameters and plankton abundance of different treatments were tested using one-way analysis of variance (ANOVA). A "Bartlett's test" was used to analyze the homogeneity of variances. When variances were not significantly heterogeneous and no major departures from normality, a one way analysis of variance (ANOVA) was done followed by Duncan's New Multiple Range test. All statistical analyses were performed with the aid of a computerized statistical package, 'Stat View' version 4.0. Standard deviation in each parameter and treatment was calculated and expressed as mean [+ or -] SD. The level for statistical significance was set at 0.05%. A simple cost-benefit analysis was done to estimate the net benefits from each of the three treatments.
Water quality and plankton monitoring
Mean values and ranges of water quality parameters over the 8-week nursery rearing of A. testudineus fingerlings are presented in Table 1. The mean water temperatures in [T.sub.1], [T.sub.2] and [T.sub.3] were 29.58, 29.64 and 29.68[degrees]C, respectively. However, no significant (P > 0.05) differences were observed among the treatments. Mean transparency level in [T.sub.1], [T.sub.2] and [T.sub.3] was 33.65, 44.72 and 52.84 cm, respectively. Transparency depth was significantly (P < 0.05) higher in [T.sub.1] followed by [T.sub.2] and [T.sub.3] in that order. Mean dissolved oxygen (DO) levels were significantly (P < 0.05) higher in [T.sub.1] (6.15 mg/l), than those in [T.sub.2] (5.58 mg/l) and [T.sub.3] (5.00 mg/l), respectively. The pH value did not differ significantly (P > 0.05) but decreased from [T.sub.1] to [T.sub.3]. Mean total alkalinity level in [T.sub.1], [T.sub.2] and [T.sub.3] was 134.44, 132.80 and 130.20 mg/l, decreased from [T.sub.1] to [T.sub.3] but did not significantly (P > 0.05) differ. Ammonia-nitrogen contents in [T.sub.1], [T.sub.2] and [T.sub.3] showed increasing trends but the variations among the treatments were not significant (P > 0.05).
The plankton populations recorded from the pond water over the 8-week experimental period are summarized in Table 2. The phytoplankton comprised of 28 genera and comes under four groups viz., Bacillariophyceae, Chlorophyceae, Cyanophyceae and Euglenophyceae. Significantly higher (P < 0.05) abundance of Chlorophyceae, Bacillariophyceae and Euglenophyceae was recorded in [T.sub.1] followed by [T.sub.2] and [T.sub.3] in that order, but the values of Euglenophyceae in [T.sub.2] and [T.sub.3] did not differ significantly (P > 0.05). Among the phytoplankton groups, Chlorophyceae was the most dominant group in all the treatments followed by Bacillariophyceae, Cyanophyceae and Euglenophyceae. The mean total phytoplankton abundance was significantly higher (P < 0.05) in [T.sub.1] than in [T.sub.2] and [T.sub.3]. The zooplankton population consisted of 12 genera including nauplii in two major groups viz., Crustacea and Rotifera. Rotifera were dominant over Crustacea during the entire experimental duration in all the treatments. However, the abundance of Rotifera and Crustacea was significantly higher (P < 0.05) in [T.sub.1] than those in [T.sub.2] and [T.sub.3]. The abundance of total zooplankton was significantly highest (P < 0.05) in [T.sub.1] followed by [T.sub.2] and [T.sub.3] in that order.
Growth, survival and production of fingerlings
Growth in terms of length and weight of fingerlings at weekly intervals is shown in Figs. 1 and 2. The highest increase in length and weight was obtained in [T.sub.1] followed by [T.sub.2] and [T.sub.3]. The growth indices, survival and production parameters of fingerlings under different treatments over the 8-week experiment are summarized in Table 3. Statistically no significant difference was observed in the initial length and weight of hatchlings stocked in all the experimental ponds. The mean final length and weight of fingerlings were significantly higher (P < 0.05) in [T.sub.1] than in [T.sub.2] and [T.sub.3]. Significantly highest weight and length gain were also observed in [T.sub.1] followed by [T.sub.2] and the lowest in [T.sub.3]. Specific growth rate (SGR) was significantly higher (P < 0.05) in [T.sub.1] than those in [T.sub.2] and [T.sub.3]. The best food conversion ratio (FCR) was observed in [T.sub.1] compared to the other treatments. The highest survival rate was also observed in [T.sub.1] followed by [T.sub.2] and the lowest in [T.sub.3] (P < 0.05).
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
Significantly higher number of fingerlings was produced in [T.sub.3] (620,130/ha) than those in [T.sub.2] (604,920/ha) and [T.sub.1] (561,150/ha) (Table 3). On the other hand, total cost of production (Tk./ha) was consistently higher in [T.sub.1] (207,353) than those in [T.sub.2] (200,953) and [T.sub.3] (192,528). Despite this, highest net benefit (Tk./ha) was also obtained in [T.sub.1] (1,476,097) followed by [T.sub.3] (1,047,732) and the lowest in [T.sub.2] (1,008,887) (Table 4).
Environmental parameters exert a significant influence on the maintenance of a healthy aquatic environment and production of natural food organisms. Feed efficiency, feed consumption and growth of fish are normally influenced by a few environmental factors[7,19]. The range of temperature in the experimental ponds is within the acceptable range for nursing of fingerlings of A. testudineus that agree well with the earlier findings of Haylor and Mollah [22,39,46]. The average values of transparency in the present study showed weekly variations and such variations may be caused by a number of factors, e.g., viewer, time of the day, season, weather etc. Highest transparency depth was recorded in [T.sub.3], which might be due to the reduction of the plankton population density by higher stocking biomass of fish [49,21,46]. Dissolved oxygen level was low in ponds stocked with a higher density of fish compared to ponds with low stocking density, might be due to the higher consumption rate of oxygen by the higher density of fish and other aquatic organisms . However, the DO level was within the acceptable range for fish culture [39,43]. The pH values agree well with the findings of Mollah and Hossain , Rahman and Rahman [47,45] and Rahman et al.  and are within the range of good water quality for rearing of fry/fingerlings in nursery ponds. Natural waters, which contain 40 mg/L or more total alkalinity, are considered as hard water for biological purposes. Hard waters are generally more productive than soft waters. Total alkalinity levels in the present study indicate productivity of the ponds was medium to high . Higher total alkalinity values might be due to higher amount of lime doses during pond preparation and frequent liming during the experimental period [6,28,43]. The level of ammonia-nitrogen recorded from the experimental ponds is lower than that was reported by Dewan et al. . However, the present level of ammonia-nitrogen content in the experimental ponds is not lethal to the fishes [32,34].
The higher abundance of plankton in [T.sub.1] might be due to the lower density of fish than those in [T.sub.2] and [T.sub.3]. It seems likely that in the ponds where stocking density was high, consumption of plankton by the fishes was also high. It was also found in all the ponds that zooplankton abundance was higher than phytoplankton, which might be due to heavy manuring with organic fertilizer (cattle dung), excess uneaten feed  and a high rate of supplementary feeding [40,56,25,9]. Similar results were also reported in various carp and barb nursery ponds [53,21,35,45,47,43].
Growth in terms of final length, length gain, final weight, weight gain and specific growth rate of fingerlings of A. testudineus was significantly higher in [T.sub.1] where the stocking density of hatchlings (1.0 million/ha) was low compared to those of [T.sub.2] (1.2 million/ha) and [T.sub.3] (1.4 million/ha) although same food was applied at an equal ratio in all the treatments. The causes might include competition for food and habitat due to higher number of fish. The results of the present experiment coincides with the findings of Haque et al. , Mollah and Hossain , Islam , Rahman and Rahman [45,47] and Rahman et al. . High density of fry in combination with abundant food in the rearing system might produce a stressful situation if not from the build-up of metabolites than from competitive interaction [21,23,43]. Significantly lower FCR values were in [T.sub.1] than those in [T.sub.2] and [T.sub.3], respectively. The FCR of the present study are lower than the FCR values reported by many workers [50,14,25]. The causes might be smaller ration size, higher digestibility and proper utilization of feed. Reddy and Katro  and Das and Ray  observed increasing trends of FCR values with increasing ration size in the growth trials of air- breathing catfish (Heteropneustes fossilis) and Indian major carp (Labeo rohita). De Silva and Davy  stated that digestibility plays an important role in lowering the FCR value by efficient utilization of food. However, the lower FCR value in the present study indicates better food utilization efficiency, despite the values increased with increasing stocking densities. Significantly higher survival rate of fingerlings was obtained in [T.sub.1], where the stocking density was low compared to higher densities stocked in [T.sub.2] and [T.sub.3]. The reasons for reduced survival rates in these treatments were accounted for by higher stocking density of hatchlings as well as competition for food and space in the experimental ponds. Similar findings were reported by Haque et al. , Kohinoor et al . , Mollah and Hossain , Rahman and Rahman [45,47] and Rahman et al.  during fry/fingerlings rearing experiments of various carp, barb and catfish species.
In the present study, significantly higher numbers of fingerlings were produced in ponds stocked with 1.4 million hatchling/ha ([T.sub.3]) than the ponds with 1.2 million/ha ([T.sub.2]) and 1.0 million/ha ([T.sub.1]), respectively. Despite this, consistently higher net benefits were obtained from [T.sub.1] than those from [T.sub.2] and [T.sub.3]. The higher market price of the larger fingerlings produced in ponds with 1.0 million hatchling/ha, substantially increased the net benefits compared to those obtained from the smaller fingerlings produced at higher stocking densities. Rahman et al.  also found similar results while conducting nursing experiments with critically endangered mahseer (7 or putitora) in earthen nursery ponds where higher net benefits were obtained from ponds stocked with 0.6 million hatchlings/ha than those from 1.0 million/ha and 0.8 million/ha stocking densities, respectively. Overall, highest growth, survival, production and benefits of fingerlings were obtained at a density of 1.0 million hatchling/ha. Physico-chemical parameters of pond water during the study were within the acceptable levels. Growth of fingerlings to a greater extent was depended on the quality and quantity of food. However, availability of natural foods (plankton) varied among the treatments, being more abundant in ponds where lower densities of hatchlings were reared. In the present experiment, the amount of supplementary feeds given in different ponds was based on the number of hatchlings stocked and the amount of feed provided per fry was kept at the same level. Therefore, the observed low growth at higher stocking densities could be due to less availability of natural food and some changes in environmental parameters [35,33,48,43].
The present study revealed that the growth, survival, production and net benefits of A. testudineus fingerlings were inversely related to the stocking densities of hatchlings. In all respects, a stocking density of 1.0 million hatchling/ha performed better than those obtained at higher stocking densities. Therefore, the nursery operators may use a stocking density of 1.0 million hatchling/ha for rearing of A. testudineus fingerlings for 8 weeks in single-stage rearing system.
Spawning and feeding grounds of the climbing perch fishery have been severely degraded. Under the prevailing situation, production of quality seeds through application of our present findings might have important implications for the protection of A. testudineus from extinction as well as for its conservation, stock enhancement and rehabilitation.
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(1) M. Aminur Rahman and (2) K. Marimuthu
(1) Bangladesh Fisheries Research Institute, Freshwater Station, Mymensingh-2201, Bangladesh
(2) Department of Biotechnology, Faculty of Applied Sciences, AIMST University, Kedah Darul Aman, Malaysia
M. Aminur Rahman and K. Marimuthu; Effect of different stocking density on growth, survival and production of endangered native fish climbing perch (Anabas testudineus, Bloch) fingerlings in nursery ponds: Adv. Environ. Biol., C(): CC-CC, 2010
K. Marimuthu, Department of Biotechnology, Faculty of Applied Sciences, AIMST University, Kedah Darul Aman, Malaysia
Table 1: Mean values ([+ or -] SD) and ranges of water quality parameters of weekly samples over the 8-week experiment Parameters Treatments [T.sub.1] (0.6 million/ha) Water temperature 29.58 [+ or -] 1.42 (a) ([degree]C) (27.60-30.80) Transparency(cm) 33.65 [+ or -] 4.78 (c) (28.60-45.10) Dissolved oxygen 6.15 [+ or -] 0.68 (a) (mg/L) (5.20-7.20) pH 7.89 [+ or -] 0.38 (a) (7.60-8.50) Total alkalinity 134.44 [+ or -] 26.85 (a) (mg/L) (88.50-171.50) Ammonia-nitrogen 0.29 [+ or -] 0.18 (a) (mg/L) (0.01-0.80) Parameters Treatments [T.sub.2] (0.8 million/ha) Water temperature 29.64 [+ or -] 1.46 (a) ([degree]C) (27.70-30.90) Transparency(cm) 44.72 [+ or -] 4.99 (b) (37.70-48.40) Dissolved oxygen 5.58 [+ or -] 0.72 (b) (mg/L) (4.70-6.60) pH 7.82 [+ or -] 0.34 (a) (7.50-8.40) Total alkalinity 132.80 [+ or -] 25.80 (a) (mg/L) (86.50-166.50) Ammonia-nitrogen 0.31 [+ or -] 0.21 (a) (mg/L) (0.01-0.90) Parameters Treatments [T.sub.3] (1.0 million/ha) Water temperature 29.68 [+ or -] 1.48 (a) ([degree]C) (27.80-31.00) Transparency(cm) 52.84 [+ or -] 4.42 (a) (46.50-59.70) Dissolved oxygen 5.01 [+ or -] 0.68 (c) (mg/L) (4.30-6.00) pH 7.77 [+ or -] 0.32 (a) (7.40-8.30) Total alkalinity 130.20 [+ or -] 26.66 (a) (mg/L) (82.50-164.50) Ammonia-nitrogen 0.33 [+ or -] 0.22 (a) (mg/L) (0.01-1.00) Values in the same row having the similar superscript are not significantly different (P > 0.05). Table 2: Mean values ([+ or -] SD) and ranges of plankton abundance (cells/l) of pond water of weekly samples over the 8-week experiment Plankton group Treatment-1 Treatment-2 Phytoplankton 3765 [+ or -] 512 (a) 3412 [+ or -] 218 (b) Bacillariophyceae (3550-4100) (3200-3725) Chlorophyceae 4560 [+ or -] 452 (a) 4122 [+ or -] 385 (b) (4350-4925) (3750-4475) Cyanophyceae 3150 [+ or -] 284 (a) 2775 [+ or -] 277 (b) (2875-3475) (2375-3125) Euglenophyceae 2692 [+ or -] 276 (a) 2389 [+ or -] 248 (b) (2450-3050) (2050-2775) Total 14167 [+ or -] 809 (a) 12698 [+ or -] 760 (b) (13225-15550) (11375-14100) Zooplankton 7928 [+ or -] 486 (a) 6621 [+ or -] 512 (b) Crustacea (7525-8775) (6050-7675) Rotifera 9750 [+ or -] 518 (a) 8605 [+ or -] 506 (b) (9150-10675) (7900-9375) Total 17678 [+ or -] 1288 (a) 15226 [+ or -] 1403 (b) (16675-19450) (13950-17050) Plankton group Treatment-3 Phytoplankton 2870 [+ or -] 242 (c) Bacillariophyceae (2550-3125) Chlorophyceae 3388 [+ or -] 372 (c) (3075-3975) Cyanophyceae 2282 [+ or -] 288 (c) (1975-2775) Euglenophyceae 2178 [+ or -] 275 (b) (1875-2575) Total 10178 [+ or -] 562 (c) (9475-12450) Zooplankton 5318 [+ or -] 456 (c) Crustacea (4525-6375) Rotifera 6978 [+ or -] 535 (c) (6175-7750) Total 12296 [+ or -] 1174 (c) (10700-14125) Values in the same row having the similar superscript are not significantly different (P > 0.05). Table 3: Growth performance, survival, feed utilization and production of A. testudineus fingerlings after 8 weeks of rearing; mean [+ or -] SD with ranges in parentheses Parameters Treatments [T.sub.1] (0.6 million/ha) Initial length (cm) 0.44 [+ or -] 0.05 (a) (0.40-0.50) Final length (cm) 5.78 [+ or -] 0.15 (a) (5.50-6.10) Initial weight (mg) 0.14 [+ or -] 0.05 (a) (0.10-0.20) Final weight (g) 3.78 [+ or -] 0.15 (a) (3.62-4.10) Weight gain (g) 3.80 [+ or -] 0.12 (a) (3.69-3.93) Length gain (cm) 5.34 [+ or -] 0.15 (a) (5.06-5.66) Specific growth rate 18.25 [+ or -] 0.04 (a) (SGR) (%/day) (18.20-18.30) Food conversion 2.94 [+ or -] 0.13 (a) ratio (FCR) (2.86-3.04) Survival (%) 56.12 [+ or -] 2.74 (a) (54.18-58.05) Production of 561,150 [+ or -] 27,365 (c) fingerlings (541,800-580,500) (No. [ha.sup.-1]) * Parameters Treatments [T.sub.2] (0.8 million/ha) Initial length (cm) 0.44 [+ or -] 0.05 (a) (0.40-0.50) Final length (cm) 5.43 [+ or -] 0.19 (b) (5.10-5.70) Initial weight (mg) 0.14 [+ or -] 0.05 (a) (0.10-0.20) Final weight (g) 3.13 [+ or -] 0.12 (b) (2.85-3.30) Weight gain (g) 3.13 [+ or -] 0.12 (b) (2.85-3.30) Length gain (cm) 4.99 [+ or -] 0.18 (b) (4.66-5.26) Specific growth rate 17.88 [+ or -] 0.05 (b) (SGR) (%/day) (17.85-17.96) Food conversion 3.11 [+ or -] 0.20 (b) ratio (FCR) (2.96-3.24) Survival (%) 50.41 [+ or -] 3.58 (b) (47.88-52.94) Production of 604,920 [+ or -] 42,936 (b) fingerlings (574,560-635,280) (No. [ha.sup.-1]) * Parameters Treatments [T.sub.3] (1.0 million/ha) Initial length (cm) 0.44 [+ or -] 0.05 (a) (0.40-0.50) Final length (cm) 5.19 [+ or -] 0.18 (c) (4.90-5.60) Initial weight (mg) 0.14 [+ or -] 0.05 (a) (0.10-0.20) Final weight (g) 2.70 [+ or -] 0.13 (c) (2.45-2.95) Weight gain (g) 2.70 [+ or -] 0.13 (c) (2.45-2.95) Length gain (cm) 4.75 [+ or -] 0.17 (c) (4.46-5.16) Specific growth rate 17.52 [+ or -] 0.06 (c) (SGR) (%/day) (17.44-17.57) Food conversion 3.29 [+ or -] 0.28 (c) ratio (FCR) (3.05-3.46) Survival (%) 44.30 [+ or -] 3.80 (c) (41.61-46.98) Production of 620,130 [+ or -] 53,160 (a) fingerlings (582,540-657,720) (No. [ha.sup.-1]) * Values in the same row having the similar superscript are not significantly different (P > 0.05). * Total number of fingerlings that produced after a nursing period of 8 weeks. Table 4: Costs and benefits from the nursing of A. testudineus fingerlings in 1 ha earthen ponds for a rearing period of 8 weeks Items Treatments [T.sub.1] [T.sub.2] (Tk.) * (Tk.) A. Cost Pond lease (Tk. 30000.00 [ha.sup.-1] 4,615 4,615 [yr.sup.-1]) Lime (Tk. 6.00 [kg.sup.-1]) 1,500 1,500 Cowdung (Tk. 0.35 [kg.sup.-1]) 2,975 2,975 Dipterex (Tk. 800.00 [kg.sup.-1]) 6,848 6,848 Bamboo and fine-meshed nylon net 10,000 10,000 Hatchlings (Tk. 16,000.00/[million.sup.-1]) 16,000 19,200 SABINCO Nursery Feed (Tk. 25.00/kg) 156,075 146,475 Labor (Tk. 70.00 [day.sup.-1]) 7,840 7,840 Miscellaneous 1,500 1,500 Total costs 207,353 200,953 B. Gross benefit Fingerlings ** 1,683,450 1,209,840 Net benefits (B-A) 1,476,097 1,008,887 Items Treatments [T.sub.3] (Tk.) A. Cost Pond lease (Tk. 30000.00 [ha.sup.-1] 4,615 [yr.sup.-1]) Lime (Tk. 6.00 [kg.sup.-1]) 1,500 Cowdung (Tk. 0.35 [kg.sup.-1]) 2,975 Dipterex (Tk. 800.00 [kg.sup.-1]) 6,848 Bamboo and fine-meshed nylon net 10,000 Hatchlings (Tk. 16,000.00/[million.sup.-1]) 22,400 SABINCO Nursery Feed (Tk. 25.00/kg) 134,850 Labor (Tk. 70.00 [day.sup.-1]) 7,840 Miscellaneous 1,500 Total costs 192,528 B. Gross benefit Fingerlings ** 1,240,260 Net benefits (B-A) 1,047,732 * 1 US$ = Tk. 65.00. ** Price of fingerlings fixed by the Institute was Tk. 3.00/piece (T1) and Tk. 2.00/piece (T2 and T3).