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Improved spawning of Clarius batrachus (Linnafus) in fish farms.

INTRODUCTION

The walking cat fishes Clarius batrachurs and Clarias macrocephalurs are very popular species for aquaculture in South East Asia (Bardach et al 1972). The species of clarias are widely distributed, being found in all freshwater areas, even in almost dry pools, as they have accessory organs to breath atmospheric air (Smith, 1945). The Asian Catfish is a popular aquaculture species as it can tolerate anoxia, can live in brackish water, has wide-ranging food habits and gives extremely high yields, (Tongasanga et al 1963).

Clarias species are iteroparous. Lehri (1968) established that the reproductive cycle of C.batrachers is divided into five phases; a resting phase (January-February); an early maturing phase (March-April); an advanced maturing phases (May-June); a mature phase (July-September) and a spent phase (October--December).

This gives rise to the hypothesis that the duration of the mature phase of C. batrachus is influenced by the annual temperature cycle. Literature from India, Bangladesh, Thailand, Philippines and Indonesia suggest a negative coorelation between the height of the yearly temperature amplitude and the length of the mature phase of the brood fish, (Zonneveld et al 1988). A decreasing availability of C.batrachus in South--Asian Countries may be a result of habitat deteriotion and ever increasing fishing pressure.

The present technique similar to that of Areerat, (1987), describes a method of spawning catfish by alternating the water levels, whereby a constant supply of seed can be assured year round.

DESIGN AND TECHNIQUE OF SPAWNING

Clarias species exhibit sexual dimorphism and identified when fish reach a length of 20cm, (Sidthimunka, 1972). The anal papilla of the male is pointed while that off the female is oral in shape and reddish in colour at the time of maturity, (Fig.1). The ratio of males and females is always 1:1.

The earthen ponds measuring 20mx10mx1.5m were divided into two equal halves, each pond had a bund on either side, on which the nests were made using circular cement rings of height of 0.30m and diameter 0-80m, (Fig.2). The spawning pond sides were sloped upto the nest opening as and the slopes of the ponds were packed tight for structural support. The sides of the ponds were fenced with bamboo to discourage the females from making nests in the mud to spawn, (Sidthimunka, 1972).

Each circular cement nest was filted with a tube of length 0.20m and diameter 0.15m. This tube, 0.10m from the base of the Cement nest was arranged so that when the pond water level was raised, the male and female fish could go through the tube to spawn on the nesting material inside, (Fig.3).

Initially the ponds are maintained at a level of 0.55m of water. Brood fish aclimetized in ponds for 2-3 weeks. To stimulate spawning, an amount of water equivalent to 0.6m was pumped in so that the water level rises to 1.15m. Water level was raised by 50% once every two weeks and the water level was raised by 50% once every two weeks and the water level was maintained for 4-7 days, until the fish spawn, (Fig.2): Table-1.

To ensure that spawning had taken place, the nests are checked by gently passing the handover the nesting material and netting, the sticking eggs if present are very slimy to touch.

The brood fish can be fed by pelleted feed or depending on availability ground trash fish twice a day. However, feeding is stopped at the time of water raising. The same brood fish can be used year round following the technique of alternating water levels with an interval of 7 days between water raisings.

CONDITIONING OF BROOD FISH

After one year of continous spawning, the same technique of alternating water levels may be continued the following year to condition the spent brood fish. It takes about 5-7 months before the fish are ready to spawn again; depending on feeding and type of feed.

TWO STRATEGIES CAN BE FOLLOWED FOR HATCHING THE EGGS

Generally spawning takes place in the early hours before day break.

STRATEGY I: After each spawning, the nesting materials bearing the sticky eggs are removed and soaked in a 1.0% solution of Sodium Sulfite ([Na.sup.2][SO.sup.3]), (Dorman, 1986). This is done to dissolve the sticky matrix tissue which holds the eggs. The procedure facilitates handling and counting of eggs and increased circulation to individual eggs reducing fungal infection which often occur on the matrix. The eggs are gently rinsed atleast twice or thrice before they are placed in an aquarium with gentle aeration. The eggs hatch within 18-20 hours, The larval rearing technique followed was similar to that decreased by Knud-Hansen et al 1990.

STRATEGY II:Instead of removing the eggs from the nesting material, they are allowed to incubate in the nests itself. The fry are harvested after four or five days with a fine scoop net and placed in a prepared shallow nursery pond with 6 to 7 inches of water depth. The nursery ponds could be 200 [m.sup.2] ponds or even smaller depending upon the management. Ponds are prepared by drying and filling with clean water upto 6 or 7 inches.

Organic manure is added and the water is allowed to stand for a few days till phytoplankton builds up and the water turns green. This is done about three to four days before stocking of fry. Once fry are stocked in the nursery ponds they are fed from the second day with rice bran which is sprinkled on the water surface.

The difference between strategy 1 and strategy II is that in the former it is time consuming and eggs handled with extreme care and survival of eggs is probably better. However, more studies need to be undertaken to compare the two larval rearing strategies.

REFERENCES

(1.) Areerat, S., 1987. Clarias Culture in Thailand. Aquaculture 63: 355-362

(2.) Bardach, J.E., Ryther , J.H. & Larnex , W.O. Mc. 1972 (Eds.) .Aquaculture: The Farming and Husbandry of fresh water and Marine Organisms. New York, J.Wiley and Sons, Inc., 868p.

(3.) Dorman, L. 1986. Spawning jars for hatching catfish. Arkansas Aqua Farming, 4(1): 1-2

(4.) Knud--Hansen, C.F. , Batterson , T.R. ,C.D.Mc. Nabb (east lansing, M1, USA), Hadiroseyani,Y., Dana ,D. and H.Muhammed Eidman (Bogor, Indonesia, 1990). Aquaculture, Vol.89. No.1 : 9-19.

(5.) Lehri, G.K. 1968 . Cyclical changes in the ovary of the Catfish, Clarias batrachus (L). Acta. Anta., 69: 105-124.

(6.) Sidthimunka, A. 1972. The culture of Pla Duk (Clarias Spp.) Inland Fisheries Division, Department of Fisheries, Bangkok, Thailand, No : 12, p. 1-17.

(7.) Smith, H.M. 1945. The Fresh Water Fishes of Siam. Bull. U.S.Nat. Mus. (188) : 6221.

(8.) Tongasanga et al., 1963. Cited in Sidthimunka, A. (1972). The Culture of Pla Duk (Clarias Spp.) Inland Fisheries Division, Department of Fisheries, Bangkok, Thailand, N: 12, p. 1-17.

(9.) Zonnevelol, N. , Rustid W.1.A.R.,Viveen & Wayan Mudana .1988. Aquaculture, 74: 4147.

K.V. Srinivasa Rao Department of Zoology, Andhra University, Visakhapatnam--530 003, AP, India
Table 1 : SUMMARY OF SPAWNING / CONDITIONING TECHNIQUE

S.No. ACTIVITY DURATION

1 Aclimatization of brood fish fed pellets 2-3 weeks.
 or ground trash fish

2 Raise pond water by 50% No feed given Maintained for 4-7
 days
3 Spawning Between day following
 pond raising to 4th
 or 5th day.

4 Egg/Fry Collection (a) Strategy I. Egg
 Collection One to one
 and half hour after
 (b) Strategy II Fry Collection spawning
 Collect on 4th or 5th
 day after spawning.

5 Lower pond water by 50% Fed pellets or Leave for 7 days
 ground trash fish

6 Repeat activity No.2 to No.5 For one year

7 Conditioning spent fish Repeat 5-7 months
 activity No.2 and No.5 for the year
 following.
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Author:Rao, K.V. Srinivasa
Publication:Bio Science Research Bulletin -Biological Sciences
Date:Jul 1, 2006
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