Grow out culture of Magur

Catfishes belong to four families; namely, the Ictaluridae, Claridae, Pangasidae and Siluridae and are widely distributed around the world. The traditional culture of catfishes have been practiced in Southeast and South Asia. Catfishes are considered high value species in certain areas whereas in other areas are considered lower and medium value market species. Catfishes are hardy in nature; they have the ability to stand longer time without water and have an accessory respiratory organ. There is a specialized trade of live fish in some places of Eastern India.

The most important aquaculture species of Catfish is the Asian catfish, Clarias batrachus. It belongs to Claridae family. Another important species is the Clarias macrocephalus which is highly preferred due to its appearance and flesh quality. However, because of unavailability of seeds and poor growth performance, it has attracted least attention.

Clarias species are normally found in freshwater and brackish water with lower dissolved oxygen. They have the ability to grow even in poor environmental condition. They are reared up to market size in earthen ponds, whereas, in Eastern India, it is grown in partially improved swamps.  Clarias batrachus normally called as magur in India has greater value and high demand in India due to its therapeutic value.

Broodstock maintenance

• A healthy brood stock is essential especially in captive condition to produce a healthy fry and attain a greater survival rate.
• The C. batrachus attains maturity in the first year. The brood fishes are reared in an earthen pond with a stocking density of 2 – 3/m².
• Before 2 – 3 months to the spawning season, the brood fishes are transferred to soil based (2 – 3 cm) cement tank for conditioning. In the commercial hatchery, the brood fishes are stocked in hapa in the same ponds for conditioning.
• The brood fishes are fed with a mix of groundnut oil cake and rice bran at about 3 – 5 percent of body weight of fish.
• For better breeding performances, fishes are fed with the mixture of groundnut oilcake, soybean meal, rice bran, vitamin and mineral mixtures at 32 percent of protein concertation during gonadal development.
• 20 – 30 percent of water is exchanged to maintain good quality water in the culture system.
• Additionally, inbreeding should be avoided, because it reduces the survival, growth rate and increases the deformity of fry. It can be averted by exchanging brood fish between the farmers or adding the brood fish from the natural environment.
• The sexes can be identified through secondary sexual characteristics. The female has the round and bulging abdomen with pinkish button shaped anal papilla. The male has a pointed anal papilla.
• Magur normally breeds during June to August. The brood fishes above 100g is preferable, but 100 – 150g is recommended for better breeding performance.
• A female brood fish of 150g size can be expected to spawn 5000 – 6000 eggs.

Artificial propagation

• The spawning can successfully be done by artificial propagation method.
• The synthetic hormone such as the ovaprim, ovatide, WOVA-FH and carp pituitary extract are used to induce the female magur. Except carp pituitary extract, other synthetic hormones are used at about 1.0 – 1.5 ml/kg. The carp pituitary gland extract is used at the rate of 30 – 40 mg/kg body weight of fish.
• Usually, no injection is given for male brooder because they do not ooze the sperm albeit. However, the synthetic hormone at 0.5ml/kg of fish is injected to male brood fish to obtain better milt quality.
• The female is stripped after 17 hrs of injection to get the ovulated eggs.
• The male fishes do not respond, and males are sacrificed to collect the testis. Hence the sperm solution (macerated testis + saline solution (0.9 percent of sodium chloride)) is prepared by using male creamy white testis to get the sperm suspension.
• The eggs are collected in a plastic tray and fertilized with sperm suspension by using feather. A little amount of water is added to activate the eggs.
• After mixing for 2 – 3 minutes, eggs are washed in running water, and it is transferred into incubation plastic container.
• Flow through hatchery system is adopted for fry production of magur.  The plastic container is kept under the tap and has an outlet provision at the height of 4 – 5 cm.
• Generally, 1000 – 1500 fertilized eggs are uniformly accommodated in each plastic container, and feeble water flow is provided to maintain the optimum oxygen level.
• For hatching, it takes about 24 – 27 hrs, at 27 – 30^OC. A newly hatched larvae measures 4 – 6 mm length and 2 – 3 mg weight.

Fry rearing

Tank preparation

A small cement cistern size of 10 – 20m² is recommended for better management. The bottom of the tank is to be filled with about 2 – 3 cm soil and the water level is to be 0.25 to 0.30 m. The fertilizer (100g single super phosphate and 2 kg cow dung) are provided for nourishment of plankton growth. The tanks have to be prepared about a week before stocking of fry.

Feeding

A newly hatched larva consumes the yolk sac up to 3 dph (days of post-hatchling). After yolk sac absorption, the larvae are fed with mixed zooplankton such as the copepods, daphnia, artemia, tubifex, custard egg, etc. After 8 days the larvae are fed with starter M (a product of CIFA) to obtain better survival and growth.

Stocking density and others

The recommended stocking density is about 1000 – 1500/m². Regular cleaning of uneaten feed and debris, adequate supply of aeration, and water management have to be taken care. It is advised to replenish 50 – 60 percent of water twice daily. Aerial respiration commences after 10 – 11 days. Larvae growth measures about 10 – 20 mm length, 30 – 40 mg weight during 15 – 20 days of rearing.

Fingerling rearing

The better growth and survival are obtained with fry stocking size of 1 g (40 – 45 days) with a density of 50 – 100 m² in fingerling production. Feeding has to be adjusted according to the weight of the fish couple of times in a month. The fry is fed twice a day at 6 – 8 percent of body weight with 30 – 32 percent of protein. Shooting behaviour is normally found at this stage. To avoid this, the larger sized fishes have to be segregated at regular interval to get the enhanced survival rate. It reaches about 4 – 5 g during 60 – 70 days.

Grow out culture

Pond preparation

For grow out of C. batrachus, small ponds of size 0.02 – 0.1 ha is preferred. The water depth is to be maintained at  0.50 – 1.0 m. The pond should have a suitable slope of 1:2 – 1:3, and height of the dyke should be above 100 cm from the water level. C. batrachus moves from one pond to another pond especially during the rainy season. So, the pond has to be constructed in such a way to prevent this migration. The pond is prepared similar to carp grow out pond. The unwanted or predatory fishes and their eggs are eradicated by using the mahua oil cake @ 2500kg/ha/m or bleaching power @ 350 kg/ha. The agricultural lime @ 200 – 250 kg is added when the soil pH is above 6.

Stocking density

Commercially, most of the farmers stock about 200 fingerlings/m², although the recommended stocking density rate is less than half of it (50 – 70/m²).

Feeding

An improved growth and survival is obtained with a size of 3 – 5 g of C. batrachus. Feeding is adjusted according to the weight of the fish twice in a month. Fishmeal based compound feed with 30 – 32 percent is preferred for C. batrachus. The fingerlings are fed two rations at 3 – 5 percent of body weight. It attains marketable size about 100 to 150g in 10 – 12 months. Harvest is done by hand picking method after complete dewatering of the pond. An average production is 2 – 3 tons/ha in 10 – 12 months.

Health management

Mortality due to the bacterial and fungal pathogens are often associated with environmental stress. The CIFAX, potassium permanganate and Oxytetracycline (OTC) are used to manage the infections.

References

1. Jeyasankar, P., Pillai, B.R., Sundaray, J.K., Mohapatra, B.C., Ferosekhan, S., Ananthraja, K., and Kamble, S.P., 2016. Training manual on freshwater aquaculture as a livelihood option. Central Institute of Freshwater Aquaculture, Bhubaneswar, India, pp: 1 – 137.
2. Pillay, T. V. R. and Kutty M. N. 2005. Aquaculture: Principles and Practices, 2nd Edition. Wiley-Blackwell.
3. Sahoo, S.K., Ferosekhan, S., Giri, S.S. and Swain, S.K., 2016. Recent Trends in Breeding and Seed Production of Magur in India. World Aquaculture, p.59.
4. Sahoo, S.K., Ferosekhan, S., Giri, S.S. 2016. Breeding and Seed Production of Magur. ICAR-CIFA Extension series – 19 (English)
5. Sahoo, S.K., Ferosekhan, S., Giri, S.S. 2016. Grow-out of Magur, Clarias batrachus. ICAR-CIFA Extension series – 23 (English).