Fish

We have chosen to keep carp as the primary kind of fish in our ponds. Just made a trip to the fisheries department in Ooty and they advised the same. Lots of holes in our understanding right now and so we decided to read a lot but also to experiment. So presently we have introduced about 3000 carps in pond No 1.   We have introduced all 3 major carps - Mrigal, Rohu and Catla.

Indigenous varieties of fish including many species of carp such as Mirror carp, Scale carp, Leather carp, Trout, Grass carp, Silver carp, Tilapia, Catla, Mrigal and rohu are available in the District.

Mrigal Carp

Mrigal (Cirrhinus mrigala), a carp endemic to Indo-Gangetic riverine systems, is one of the three Indian major carp species cultivated widely in Southeast Asian countries. This species has long been important in polyculture with other native species, mainly in India. However, records of its culture are available only from the early part of the 20th century. The traditional culture of the species was restricted to eastern parts of India until the 1950s. The technology of artificial propagation, which assured seed supply in the 1960s, led to the foundation of scientific carp culture. The initially higher growth rate of mrigal, coupled with its compatibility with other carps, has helped in establishing this species as one of the principal component species in pond culture. The species was transplanted in the peninsular riverine systems of India, where it has established itself. Subsequently it has spread over whole of India. In addition, mrigal has become an important component in the fish culture systems of Bangladesh, Pakistan, Myanmar, Laos, Thailand and Nepal. Mrigal has also been introduced into Sri Lanka, Vietnam, China, Mauritius, Japan, Malaysia, Philippines and the former USSR.

Habitat and biology

Hatchlings of mrigal normally remain in the surface or sub-surface waters, while fry and fingerling tend to move to deeper water. Adults are bottom dwellers.It is an illiophage in its feeding habit and stenophagous; detritus and decayed vegetation form its principal food components, while phytoplankton and zooplankton comprise the rest. Mrigal is eurythermal, appearing to tolerate a minimum temperature of 14 ºC. In culture, the species normally attains 600-700 g in the first year, depending on stocking density and management practices. Among the three Indian major carps, mrigal normally grows more slowly than catla and rohu. The rearing period is usually confined to a maximum of two years, as growth rate reduces thereafter. However, mrigal is reported to survive as long as 12 years in natural waters. Maturity is attained in two years in captivity. As mrigal needs a fluviatile environment for breeding it does not breed in ponds. However, captive breeding in hatcheries has been made possible through induced breeding by hypophysation and the use of synthetic hormones. Mrigal is a highly fecund fish. Fecundity increases with age, and normally ranges from 100 000-150 000 eggs/kg BW. The spawning season depends upon the onset and duration of the south-west monsoon, which in India, Bangladesh and Pakistan extends from May to September. Mrigal usually breeds at 24-31 ºC. 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 4000-10 000 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 t/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 t/ha/yr. With supplementary feeding, this can be increased to 4-5 t/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.

Main issues

Carps are generally cultured in a closed system that involves herbivorous species, in which organic materials are used as the principal input sources, thereby making it a generally environmentally-friendly practice. Furthermore, the compatibility of mrigal in polyculture systems with regard to habitat preference and feeding habits is good. However, the tendency of farmers to increase income per unit area has led to an excessive use of fertilizers, proteinaceous feeds and chemicals that may have detrimental effects on the environment. The compatibility of mrigal in polyculture systems with other carps has already been established. However, being a bottom dweller, the harvesting of this species is a perpetual problem, especially in undrainable ponds.

Carp Culture.

The most successful system of pond fish culture is the polyculture of three Indian major carp species - catla, rohu and mrigal along with three Chinese carps viz. silver carp, grass carp and common carp. In India this is commonly known as composite fish culture. The best results in terms of fish production in this system results not only through a judicious combination of species, but also due to appropriate management techniques including pond fertilization, supplementary feeding and health care. On the basis of growth performance of different species, modifications are often made in stocking density, species ratio, fertilization schedule and supplementary feeding programme in different agroclimatic conditions.

The carp culture system as a whole is operated as a three-tier culture system where the practices are adopted for rearing fish during their different stages till they are harvested. Spawn (post larvae) are reared up to fry (2–3 cm) stage in nursery ponds, fry to fingerlings (8–12 cm) in rearing ponds and finally fingerlings to table-size fish in composite fish culture ponds or stocking ponds. Relatively smaller, seasonal ponds are mainly used for rearing spawn to fry stage and harvested after 2–3 weeks. Several crops (3–4) of fry are usually taken during the season. Pond fertilization by cattle manure and feeding with 1:1 mixture of oil cakes and rice bran is the usual practice. Fry raised in nurseries are reared up to fingerlings in slightly bigger ponds (0.05 – 0.1 ha) of seasonal or perennial in nature. Fingerlings are removed after 3 months and stocked in composite fish culture ponds.

Integrated Fish/Duck Farming.

This is also an efficient integrated system based on the principle of waste recycling. Pond preparation technique is basically the same. A duck house is normally constructed on the pond embankment or on the pond water on a floating platform. When given free range, ducks feed on aquatic organisms such as insect larvae, tadpoles, molluscs, weeds, etc. The duck droppings like pig excreta act as fertilizer. Ponds are prepared and stocked with fingerlings of all the six carp species at 6 000 ha with surface, column, bottom feeder and grass carp in the ratio of 40:20:30:10. Fingerlings of over 10 cm are preferred for stocking. About 75 to 150 ducks are sufficient to adequately fertilize a 1 acre pond. Normally 2–3 months old ducklings are preferred. Although ducks are able to feed upon natural food from the pond, they are also provided with duck feed at the rate of 100 g/bird/day. Ducks start laying after 5–6 months and continue for 2 years. Fish yields ranging from 1 000–3000 kg/acre/yr are generally obtained.

Useful Links on Carps

Water Harvesting and Aquaculture for Rural Development

Another good link for basic info on Mrigal

Link on how to fish for bottom feeders at Maharashtra State Angling Association website.