Freshwater aquaculture

Unit 4 - Cultivable fish and their culture methods

4.2.1. Culture of Magur (Clarias batrachus)
This is the most popular catfish owing to its good taste and texture. Being an air breathing fish, it can survive in poor water quality conditions. This fish can be cultured at very high stocking densities. The fish can be sold live and hence fetches higher price than carps.
The techniques for breeding, seed production and grow out of magur have been standardized. A few farmers have already adopted these techniques in different parts of the country.

Larval rearing
The aerial respiration in the larvae starts 10-12 days post hatch. They are obligate air breathers and hence need atmospheric oxygen irrespective of dissolved oxygen. Since they lie at the bottom and have to make vertical trips to surface for breathing air the water depth is an important factor to be considered.
Initially, a water depth of 8-10 cm is kept in the larval tank to avoid loss of energy spent for making vertical trips. The depth in gradually increased with the increase in rearing period.
The Hatchlings are stocked @ 2000 – 3000 / m2 in well aerated rearing tanks. They subsist on yolk for about 3 days. Subsequently they are fed with live plankton or Artemianauplii. 50% of the water is exchanged on alternate days. They are reared for 12-14 days when they reach a size of 10-12mm size (30-40mm). They are harvested and transferred to outdoor rearing tanks and stocked @ 200-300 Nos./m2 . The tanks are fertilized in a similar manner as carp rearing tanks. Floating weeds such as water hyacinth or duck weeds are provided as shelter. The fry are fed formulated crumbled feed pellets of 35% protein or a mixture of finally mined trash fish/molluscan meat and rice bran @ 1:1 ratio, @ 5-10% of the biomass. The fry grow to a fingerling size of 3-4 cm (0.8-1g) in about 30 days. They are harvested by draining the tanks.

Grow–out culture
Grow out culture is carried out in earthen or stone pitched ponds. Since magur may migrate out during rainy season, fencing is provided around the ponds. They are stocked @ 50,000 – 70,000 finger lings/ha. The ponds are fertilized in a similar manner as carp ponds.

The fish are fed mixtures of groundnut oil cake, rice bran, fish meal/trash fish. They are fed @ 3-5% biomass in the form of dough placed in baskets or in pellet form at different places in the pond. The feed should contain 30-35% protein. The tanks should be covered with nets to protect them from predation by birds. Broken pipes or tiles are provided as shelters to reduce cannibalism. Water loss through evaporation should be compensated periodically by letting the water in.
Magur attains marketable size of 100-120g in 7-8 months. Harvesting by netting is difficult, hence ponds needs to be drained and fish handpicked. Average production of magur from this system is 3-4 tones/ha/7-8 months.