Mrigal is cultured mainly as a component of carp polyculture systems in the ponds of India and Bangladesh, the major producing countries. The Lao People's Democratic Republics, Thailand, Vietnam, Pakistan, Myanmar and Nepal also use mrigal as one of the principal components in carp polyculture systems. Mrigal is normally cultured along with the other two Indian major carps - catla (
Catla catla) and rohu (
Labeo rohita). It is also cultured in composite carp culture systems that include the three Indian major carps as well as two Chinese carps - silver carp (
Hypophthalmichthys molitrix) and grass carp (
Ctenopharyngodon idella) - and common carp (
Cyprinus carpio). Being a bottom feeder, mrigal is usually stocked at 20-30 percent of the total species stocked in three-species culture, while in six-species culture mrigal constitutes only about 15-20 percent. In India, carp is cultured in about 900 000-1 000 000 ha of ponds and 'tanks' (water bodies that are usually larger than a pond but less than 10 ha) that are privately or community owned. In Bangladesh, however, carp farming is carried out mostly in small traditional ponds, of which only about 16 percent are semi-intensive.
Seed supply
Mass scale seed production of mrigal in hatcheries through induced breeding now supplies almost the entire seed requirement in all the producing countries, although riverine collection still forms the source of seed in certain small areas. As mrigal does not breed in confined waters, injections of pituitary extract and other synthetic commercial formulations of purified salmon gonadotropin and dopamine antagonists such as Ovaprim, Ovatide and Wova-FH have also been successfully used in recent years. When pituitary extract is used, females are injected with a stimulating dose of 2-3 mg/kg BW followed by a second dose of 5 to 8 mg/kg after a lapse of 6 hours; males are given a single dose of 2-3 mg/kg at the time of second injection of the female. When synthetic formulations are used, a single dose of 0.4-0.5 ml/kg BW (females) or 0.2-0.3 ml/kg (males) is administered. The spawn recovery of mrigal usually ranges from 100 000 to 150 000/kg. The Chinese circular hatchery is the most common system used. In this system, broodstock are kept at 3-5 kg /m
3, with a 1:1 female:male stocking ratio by weight (1:2 by number). Fertilized eggs are obtained after 6-8 hours and are transferred to the hatching tank, optimally stocked at 700 000-800 000/m
3. Water circulation is continuous and the eggs are retained until 72 hours, during which the embryos develop into hatchlings of about 6 mm.
Rearing fingerlings
Nursery phase
Three-day old hatchlings are reared in a nursery system for a period of 15-20 days till they become fry of 20-25 mm. Small earthen ponds of 0.02-0.1 ha are normally employed, though brick-lined or cement tanks are used in certain areas. The stocking density usually ranges from 3-10 million/ha in earthen ponds and 10-20 million/ha in brick or cement tanks. Though monoculture is advocated for nursery rearing, farmers often raise mrigal along with the other two Indian major carps. In these cases, the growth and survival of mrigal is higher than the other two. The other management measures include organic manuring and fertilization, and the provision of a mixture of rice bran and oil cake (1:1 w/w) as a supplementary feed. Survival normally ranges from 30-50 percent. Good pre-stocking nursery pond preparation includes control over predatory and weed fish, and insects. Farmers often neglect such procedures, resulting in low fry production. Another limiting factor is the non-availability of commercial feed, which forces farmers to resort to the conventional bran-oilcake mixture.
Fingerling production
The fry from the nursery system are further raised to fingerling size (80-100 mm; 5-10 g). Earthen ponds ranging from 0.05 to 0.2 ha are commonly used. Although monoculture is advocated in the nursery phase, in fingerling rearing mrigal are stocked at about 30 percent and cultured along with other carp species at a combined density of about 200 000-300 000/ha. Feeding and fertilization regimes are similar to the nursery phase but vary according to the intensity of culture and the natural productivity. Overall survival in the fingerling rearing stage ranges from 60 to 70 percent; generally, mrigal has a higher survival level than catla and rohu. Fish are reared in this phase for 2-3 months, after which they are transferred to grow-out production systems.
Ongrowing techniques
The grow-out culture of mrigal in polyculture systems is confined to earthen ponds and normal management practice includes predatory and weed fish control with chemicals or plant derivatives; stocking of fingerlings at a combined density of 4 000-10 000 fingerlings/ha; fertilization with organic manures like cattle dung or poultry droppings and inorganic fertilizers; supplementary feeding with a mixture of rice bran/wheat bran and oil cake; and fish health monitoring and environmental management. The grow-out period is usually one year, during which mrigal grows to about 600-700 g. Production is normally 3-5 tonnes/ha/yr, with mrigal contributing about 20-25 percent.
The lack of fingerlings of suitable size in adequate quantities is the most important limiting factor, compelling farmers to stock ponds with fry instead of fingerlings. High prices for commercial feeds and feed ingredients often restrain farmers from feeding at the proper level, thus limiting production.
Mrigal also forms one of the important components in the sewage-fed carp culture system practiced in an area totalling over 4000 ha in West Bengal, India. In this form of culture, which includes multiple stocking and multiple harvesting of fish larger than 300 g, primary treated sewage is provided to the fish ponds as the main input. Even without the provision of supplementary feed, this system produces 2-3 tonnes/ha/yr. With supplementary feeding, this can be increased to 4-5 tonnes/ha/yr.
Harvesting techniques
The bottom dwelling habit of mrigal hinders its effective harvesting by dragnet, the most common gear used in carp culture. Complete harvesting is possible only through draining. These harvesting difficulties make mrigal the least preferred species among the three Indian major carps for farmers. Cast nets are often used for partial harvesting in small and backyard ponds.
Handling and processing
The species is mostly marketed fresh in local markets. However, long distance transport of mrigal with other carps packed with crushed ice at 1:1 ratio in rectangular plastic crates (60 cm x 40 cm x 23 cm) in insulated vans is often practiced in India. Post-harvest processing and value-addition is almost non-existent at present in any of the producing countries. During recent years a small quantity of Indian major carps is being exported from India to the Middle East, degutted and frozen.
Production costs
In general, carp are low-valued species fetching market prices of less than USD 1/kg at the producers' level; therefore, the use of major inputs such as seed, fertilizers and supplementary feed, besides labour costs, is kept to a minimum. Supplementary feed constitutes over 50 percent of the total input cost in carp polyculture; therefore, judicious feed management is of prime importance for enhancing profits. In extensive systems, with a targeted production level of 2-3 tonnes/ha, the cost of production is about USD 0.30/kg, while the costs increase to USD 0.5-0.6/kg in semi-intensive culture, where the targeted production is 4-8 tonnes/ha.
In some cases antibiotics and other pharmaceuticals have been used in treatment but their inclusion in this table does not imply an FAO recommendation.
Ulcer |
Aeromonas spp.; Pseudomonas spp. |
Bacteria |
Ulcerations; exophthalmia; abdominal distension |
Destroy badly infected fish; disinfect affected ponds with 0.5 ppm solution of KMnO4; add sulphadiazine (100 mg/kg) or terramycin (75-80 mg/kg) to feed for 10-12 days |
Columnaris |
Flavobacterium columnaris |
Bacterium |
Raised white plaques, often with reddish peripheral zone leading to haemorrhagic spots on body |
Dip treatment with 500 ppm KMnO4 |
Dropsy |
Aeromonas sp. |
Bacterium |
Body scales stretch out resembling pine cone; inflammation; ulceration; exophthalmia; abdominal distension |
Disinfect affected ponds with 1 ppm KMnO4; dip treatment of 5 ppm KMnO4 for 2 minutes |
Saprolegniasis |
Saprolegnia parasitica |
Fungus |
Mould grows like cotton wool on body, penetrating into the muscle; morbid muscle rot |
3-4% NaCl bath; 160 mg/litre KMnO4 bath for 5 days; 1-2 mg/litre malachite green bath for 30 minutes to 1 hour; add formalin at 20 ml/litre to affected ponds |
Branchiomyosis (gill rot) |
Branchiomyces demigrans |
Fungus |
Fungus grows out through gill blood vessels and causes necrosis of surrounding tissues; yellow-brown discolouration & disintegration of gill tissues |
Addition of quick lime (50-100 kg/ha) to affected ponds; in case of limited infections, use 3-5% NaCl bath for 5-10 minutes, or 5 ppm KMnO4 bath for 5-10 minutes |
Ichthyophthiriasis |
Ichthyophthirius multifilis |
Parasite(protozoan) |
Skin, fin rays & operculum covered with white spores; sick fish keep rubbing against hard substratum |
Dip in 1:5000 formalin solution for 1 hour for 7-10 days or in 2% NaCl for 7-10 days; affected ponds should be disinfected with quicklime at 200 kg/ha |
Trichodiniasis |
Trichodina reticulata; T. negre |
Parasite(protozoan) |
Invasion of parasites in skin & gill region |
2-3% NaCl or 4 ppm KMnO4 batch for 5-10 minutes; treat affected ponds with 25 ppm formalin |
White gill spot disease |
Thenohanellus catlae;Myxobolus bengalensis; M. catlae; M. hosadurgensis |
Parasites(protozoan) |
Weakness; emaciation; raising of scales along their posterior margins; scale loss; perforation of scales; loss of chromatophores |
Reduce density; add yeast to feed (1 g/kg); 2-3% NaCl bath |
Dactylogyrosis and Gyrodactylosis |
Dactylogyrus spp.; Gyrodactylus spp. |
Parasites(monogenean trematodes) |
Gill, fin & skin affected; excessive mucus secretion |
3-5% NaCl dip treatment for 5-10 minutes; 100 ppm formalin bath; treat affected ponds with 25 ppm formalin or 4 ppm KMnO4 |
Black spot or Diplostomiasis |
Diplostomum pigmentata |
Parasites (digenean trematode |
Black nodules due to metacercarial cysts in the host body; infects eye and causes blindness |
Remove resident molluscan population |
Argulosis |
Argulus sp. |
Parasite (crustacean) |
Parasites visible to naked eye attached to head & fin rays; haemorrhagic spots found in chronic cases |
Drain and dry ponds showing severe Argulus infection; short duration 5 ppm KMnO4 dip; treatment with 'Butox' three times at 35 ml/ha-m at weekly intervals |
Epizootic Ulcerative Syndrome |
Aeromonas hydrophila; A. sorbia; Aphanomyces invadans |
Bacteria and fungus |
Large red or grey shallow ulcers with necrotic areas on skin; fungus extends deep into the musculature; lesions of acute dermatitis and ulcers |
200 kg/ha quicklime or 0.1 ppm CIFAX (a CIFA, India formulation) |
Suppliers of pathology expertise
The following are examples of locations where expertise can be accessed:
- Central Institute of Freshwater Aquaculture, India.
- Central Institute of Fisheries Education, Mumbai, India.
- College of Fisheries, Mangalore, India.