Production of Butter Catfish

The butter catfish is a non-air breathing freshwater catfish. It is nocturnal, predatory and carnivorous that inhabits the wetland and open water channels connected to lower reaches of rivers. The adult fish thrives on insects and their larvae and other small fishes, while the early fingerling (40 mm) feeds on cladocerans, copepods, rotifers, protozoa and insect larvae and advanced fingerling (>70 mm) feeds on small insects, nematode worms, annelids, small minnows, shrimps and detritus. It grows to a size of 30-40 cm.

The butter catfish attains sexual maturity in the first year. Male become ready to breed by late April, while the female during late May. Its breeding season extends from early June to August with a peak in July. During the breeding season the fish move in shoal and migrate from water-logged area towards the mouth region of the shallow confined water adjoining the river where breeding occurs. The consumer demand for the fish is high due to its unique flavour, soft flesh, shiny appearance, less spine, easy digestibility and high nutritional value. Over the last few decades, its wild population has been declining rapidly due to various anthropological activities.

Seed Production

Broodstock management

The fish weighing not less than 40 g size is procured from farm or wild during January to February, disinfected with 200 ppm formalin dip for 40 seconds and stocked at a density of 10 no./m² in outdoor circular cement cistern of 2-4 m diameter with 1.2 m depth or at a density of 5 no./m² in earthen ponds having about 0.02-0.1 ha area with 0.75-1.5 m water depth. The broodfish is fed twice daily at 5% of the body weight with a mixed diet consisting of clam meat, shrimps, chopped earthworm, trash fish and boiled fish waste. It can be weaned gradually to take a formulated pelletted feed having 35% protein. The pond is provided with floating aquatic weeds like water hyacinth up to 20-25% of surface area, which offers shelter and hiding places and harbours many insects as feed for fish. Ceramic pipe of 5-10 cm diameter is also provided as hideouts.

Selection of brooder

The male and female show sexual dimorphism and are easily identified by the secondary sexual characters developed during the breeding season. In the case of a mature male, the genital papilla is elongated and pointed or somewhat conical in shape. The pectoral fin is thick and serrated with a relatively large spine, and the body is slender, smaller in body size, less pigmented and more translucent. In the case of a mature female, the spine is very feeble. The abdomen is soft, round and bulged and the genital papilla is somewhat fleshy, round, bulged and large in size with reddish vent. The mature female has distinct granular ovaries with orange-yellow colour. When the female becomes ripe, on applying slight pressure on the belly, orange-yellow bulged transparent ova come out through the genital aperture.

Flat abdomen of male And Swollen abdomen of female

Spawning

The mature female and male are selected and induced to spawn by intramuscular injection of synthetic hormones like Wova-FH at 1.5 ml/ kg body weight for female and 0.5 ml/kg body weight for male as a single dose. After a gap of 8-10 hours of hormone injection, natural spawning happens under favourable conditions. Otherwise, the abdomen of the male is cut-open and testis is removed, chopped and macerated to prepare sperm suspension followed by stripping the female fish as explained for the walking catfish. The collected eggs are mixed thoroughly with the sperm suspension using a feather by adding a little amount of freshwater to activate the sperm. The fertilised eggs are then washed with freshwater, cleaned and transferred for incubation. Fecundity is 200-300 no./g body weight.

Incubation

It is almost similar to that explained for the walking catfish. Hatching takes place within 22-24 hours after fertilisation at a temperature of 27-30⁰C and alkalinity of 100-150 ppm. The hatchlings are cylindrical in shape, transparent, devoid of mouth, and have pectoral fins and body pigments. The yolk sac is pale greenish in colour and is absorbed in 3 days.

Rearing of hatchling

Just before the opening of the mouth, usually 2 dph, the larvae are transferred from incubation unit to an indoor nursery rearing unit. The nursery-rearing unit may be cement cistern or FRP tank having 1 t capacity and 40 cm height. At the bottom of the cistern/tank, 5 cm thick layer of soil is provided. Initially, the water depth in the tank is maintained at 10 cm, and it is gradually raised up to 20 cm within a period of one week in accordance with different stages of larval development to minimize stress.

The soft water with less alkalinity and rich organic carbon base is ideal. Hence, water from a disease-free natural pond is used, instead of ground water, which would usually be hard with high alkalinity. The disinfection of water is done by filtration/ UV sterilization in place of chlorination. The ideal water temperature and DO for larval rearing is 28-32⁰C and >5 ppm respectively.

The 2 dph larvae are stocked in the nursery-rearing tank, initially at a density of 15 no./l. As it shows extreme cannibalism from the 2 dph onwards, wherein the healthy larvae eat upon the weaker ones, subsequent size grading is done once in 3-5 days, and the density is further reduced to 5 no./l by thinning and stocking into different tanks. A little amount of live feed is provided from 2 dph onwards. The larvae are fed ad-libitum with live zooplankton up to 7 dph. Later, mixed zooplankton (@ 8-10 cc/ l) along with tubifex and egg custard is given twice daily @ 25% of the body weight up to 15th day.

Daily 50% water is exchanged twice to maintain water quality or provided with the continuous re-circulation system. The unwanted material accumulated at the tank bottom is removed by siphoning twice daily. Water quality parameters are checked once every 3 days.

Rearing of fry

Adequate hiding place is provided for better survival, as the larvae prefer darker places. After 15 dph, the fry is fed 2-3 times daily @ 5% of the body weight with a formulated diet comprising of egg custard, fish meat/meal and silkworm pupae powder. It can also be replaced with chopped or minced fish. The fish seed attains 5-6 cm size within a rearing period of 40-45 days with 80% survival.

Farming in Pond

Selection of pond

Earthen pond of 0.05-0.2 ha size with a water level of 75-100 cm is desirable. The bottom and sides of the pond have to be made free from holes or crevices.

Pond preparation

Pond preparation practices including removal of predatory and unwanted fish, liming, manuring etc are to be followed as explained for the farming of the major carps. The pond is provided with floating aquatic plants like Eichornia up to 25% of the water spread area to simulate their natural habitat.

Stocking

Seeds having an average size of 6 cm (1 g) are stocked at a rate of 6- 8 no./m². Seeds of grass carp may also be stocked @ 500 no./ha.

Feeding

The fish is fed daily twice (early morning and evening) with a formulated pelletted feed having 30-35% protein @ 10% of the body weight initially and gradually reduced to 3% in the final stage.

Harvesting

The fish attains the marketable size of 50-60 g in 8-10 months culture period. Usually, multiple harvesting is practiced by drag netting, followed by complete harvesting by hand picking after dewatering the pond.

Source : Department of Fisheries, Government of Kerala