Production of Stinging Catfish

The stinging catfish, Heteropneustes fossilis is commonly called as Singhi, is a freshwater air-breathing fish, which survives even in oxygen-depleted waters due to the presence of tubular air sacs as outgrowth of the gill chambers extending as far as the middle of the tail region for aerial respiration. It tolerates low water quality and high concentration of carbon dioxide. The pectoral spine is very sharp and can make a painful wound, if the fish is handled without proper care.

It is an omnivore, which thrives in all kinds of shallow freshwater habitats. It breeds in confined waters during monsoon. It can tolerate overcrowding and is reared at extremely high stocking density. It also tolerates slightly saline water.The fish is mainly caught from weed- infested ponds and paddy fields. During summer months when the seasonal ponds get dried, stinging catfish bury into the soil. The fish fetches high price due to fewer spines in the flesh, less fat, high digestibility and high iron and calcium content. It is believed that the fish is suitable for sick and convalescence persons.

Seed Production

Broodstock management

The fish weighing not less than 100 g is procured from farm or wild prior to 3 months of the breeding season and disinfected. The broodfish is stocked at a density of 3-5 no./m² in outdoor circular cement cistern of 2-4 m diameter and 1.2 m depth and covered with nylon net (2 mm mesh size) leaving a clearance of 60 cm from the water surface. The broodfish is fed twice daily at 2-3% of the body weight with a formulated feed having 30-35% protein containing a mixture of fish meal, groundnut oil cake, soya bean meal and rice bran augmented with the vitamin-mineral mixture. Other aspects of broodstock management are similar to that explained for the walking catfish.

Selection of brooder

The fish at the age of one year (150 g) attains sexual maturity and spawns during June-August. The female is larger than the male and has a soft swollen abdomen with a reddish vent that releases eggs on applying slight pressure on the abdomen. In a male, the genital papilla is conical and pointed, protruding and highly vascularized during the breeding season, but doesn't discharge milt on applying pressure on the abdomen.

Spawning

The mature and healthy female and male in the ratio of 1:1 by body weight are induced for spawning by intramuscular injection of synthetic hormone like Wova-FH as a single dose of 0.6-0.9 ml/kg body weight. The injection is given during evening near the base of dorsal fin above the lateral line at an angle of 30⁰ to the body and to a depth of 2-3 cm using an insulin syringe. Care should be taken such that needle does not touch the vertebral column. The hormone is injected slowly allowing it to disperse properly into the body; otherwise, when the needle is withdrawn, the solution may be ejected out.

After injection, the broodfish is released into an FRP tank of 1 t capacity, where water depth is maintained at 30-45 cm with mild aeration. Adequate quantity of Hydrilla is provided to simulate the natural breeding habitat. The top of the tank is covered with nylon net. A temperature of 25-28°C is most conducive for spawning.

The fish exhibit pre-spawning activities for a period of 6-8 hours and display prolonged and intermittent courtship and spawning behaviour for the next 6 hours. Perforated rubber mat of 5 cm thickness with holes of 3 cm diameter is placed to cover the entire tank bottom facilitating free fall of the egg into the tank bottom, thereby preventing egg damage. Soon after the completion of spawning, the spent parent, aquatic plant and rubber mat are removed from the breeding tank. If the fish doesn't spawn naturally, semi-wet stripping is done for female. In the case of male fish, the testis is collected and macerated, as explained in the case of walking catfish, to fertilise the eggs.

The fertilised eggs are spherical, moderately adhesive, demersal and greenish-blue in colour and tend to settle at the bottom with heavy yolk and have 1.1-1.6 mm diameter. It is disinfected in 5 ppm malachite green for 10 minutes and carefully transferred for incubation. The fecundity is 50-350 no./g bodyweight. The unfertilised egg is whitish in colour and float at the water surface.

Incubation

Fine mesh nylon net is spread horizontally in the incubation tub 10 cm below the water surface, and fertilised eggs are spread evenly in a single layer over the nylon net. The incubation tub is kept under running water for maintaining quality. Hatching takes place within 16-20 hours at 27-30°C.

The newly hatched larvae move to the bottom of the container through the meshes, leaving the eggshell over the nylon net. It is transparent and faintly brown in colour and measures about 2.5-3 mm in length with a large yolk sac, which gets absorbed in 72-96 hours. The unfertilised and dead eggs and eggshells should be removed immediately by lifting the mesh to avoid fouling of water.

Rearing of hatchling

The larvae are about 2.7 mm having a large yolk sac. After 48 hours, the healthy ones will swim towards the comer of the tank and remain in a group. The yolk sac is completely absorbed within 3-4 dph and the larvae are transferred from the incubation unit to an indoor nursery rearing unit. In the nursery-rearing unit, the larvae are stocked in FRP tank (lt capacity with 40 cm height) with 15-20 cm water depth at a density of 4-6 no./l. The hatchlings are fed 4-6 times daily with minute rotifers, ciliates, Artemia nauplii and boiled egg yolk till 12 dph. From 13 dph onwards, the larvae are fed with chopped molluscan meat in addition to zooplankton. The feed size varies from 10-20 qm upto 8 dph and which can be increased to 40-50 qm thereafter.

The larvae absorb DO from the water up to 10-12 dph. Hence, mild aeration and water quality management is done similar to that explained for the walking catfish. The larvae start the vertical movement by 10-12 dph and come to the water surface for taking atmospheric oxygen. Subsequently, aeration is stopped and the height of the water column in the tank is reduced to 10 cm in the next two days. After 19-20 days, larva transforms into fry.

Rearing of fry

The fry can be reared in an earthen pond (200-400 m²) or outdoor cement tank of 40-80 m² size provided with 2-3 cm thick layer of soil on the bottom. A water depth of 30 cm is maintained initially in the pond/tank and gradually enhanced to 60 cm. The pond/tank is kept in the shade allowing partial exposure to sunlight. The nursery pond preparation and manuring for live feed production is similar to that prescribed for the major carps. The pond/tank should have a freeboard of 60 cm. Plankton collected from ponds is inoculated into these tanks at periodic intervals. The fry is stocked at a density of 150-500 no./m² and fed ad libitum daily during dark hours with finely ground trash fish, prawn meat, chopped clam meat, tubifex and rice bran, which can be replaced with egg custard and minced meat, or crumbled formulated catfish feed. The fish seed grows to 4-5 cm size by 30-40 dph.

Harvesting

The method is similar to that explained for the murrels.

Farming in Pond

The stinging catfish can be effectively cultured in low lying areas such as unutilized swamp, marshy land, wetland and other derelict water bodies.

Selection of pond

The pond having 0.05-0.2 ha size and 75-100 cm depth is ideal. Pond having mud upto 15 cm thickness at the bottom is better; but this may lead to difficulty in the harvest. Culture in a shallow pond helps to reduce the energy consumption for the vertical movements of fish for respiration. Optimum pH is 6.5-8.5.

Pond preparation

It is similar to that of the major carps. The inner side of the bund should be firm and fenced with bamboo, cane or wire screen to a height of 60 cm to prevent the escape of fish.

Stocking

Seed with a size of 5 cm can be selected for stocking. Uniform sized seeds are selected for stocking to reduce cannibalism during early stages. Stocking density of 6 no./m² is usually practised. A dip in 200 ppm formalin for 40 seconds before stocking helps to avoid infection.

Feeding

The fish is fed ad libitum with a formulated pelletted feed with a protein content ranging from 28-35%. It can also be fed witha mixture of rice bran, groundnut oil cake and animal protein in the ratio of 1:1:1.

Care and monitoring

It is done similar to that explained for the walking catfish.

Harvesting

The fish attains a marketable size of 160-170 g in 10 months. Other aspects of harvesting are same as that of the murrels.

Source : Department of Fisheries, Government of Kerala