Food and Agriculture Organization of the United Nationsfor a world without hunger
Fisheries and Aquaculture Department
Body bilaterally symmetrical and streamlined, its depth about equal to length of head; body with cycloid scales, head without scales; snout blunt, often with pores; mouth broad, transverse; upper lip entire and not continuous with lower lip, lower lip most indistinct; single pair of short rostral barbels; pharyngeal teeth in three rows, 5.4.2/2.4.5 pattern; lower jaw with a small post-symphysial knob or tubercle; origin of dorsal fin nearer to end of snout than base of caudal; dorsal fin as high as body with 12 or 13 branched rays; last unbranched ray of dorsal fin non-osseous and non-serrated; pectoral fins shorter than head; caudal fin deeply forked; anal fin not extending to caudal fin; lateral line with 40-45 scales; lateral transverse scale rows 6-7/5½-6 between lateral line and pelvic fin base; usually dark grey above, silvery beneath; dorsal fin greyish; pectoral, pelvic and anal fins orange-tipped (especially during breeding season).
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, the Lao People's Democratic Republic, Thailand and Nepal. Mrigal has also been introduced into Sri Lanka, Vietnam, China, Mauritius, Japan, Malaysia, Philippines and the former USSR.
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.
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.
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 /m3, 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/m3. Water circulation is continuous and the eggs are retained until 72 hours, during which the embryos develop into hatchlings of about 6 mm.
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.
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.
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.
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.
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.
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.
Suppliers of pathology expertise
The following are examples of locations where expertise can be accessed:
In all the producing countries, almost all farmed mrigal is consumed in the local market. Governmental regulations and controls over the domestic marketing system are almost non-existent in these countries and demand and supply thus influence product value. Being the least preferred among the three Indian major carps, mrigal fetches comparatively low market prices, usually fetching 10-20 percent less than rohu or catla. However, consumer preference makes the prices obtained for these species always higher than those for common carp and Chinese carps.
Several factors have enhanced the status of the farming of the Indian major carps:
Other factors have caused problems. The adoption of intensive farming practices, unregulated use of inputs and lack of scientific know-how among the farmers has led to increased disease incidence. However, continued thrust on health management leading to development of therapeutics has helped the sector to overcome from such situations.
India has already drawn up a strategic plan for doubling freshwater aquaculture production through increases in productivity and area. Since mrigal forms an important component of the carp polyculture system, it can be expected that there will be a two-fold increase in its production in India by 2015. Bangladesh is also expected to enhance farmed mrigal production. The high growth potential of the Indian major carps has attracted the attention of several tropical South-Eastern Asian and Middle-Eastern countries.
Other factors are expected to influence further growth in the farming of Indian major carps, including:
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.
Being a low input-based system, carp culture has not generally been perceived as a threat to the environment. However, increased emphasis on intensification for enhancing production in recent years has resulted in increased use of chemical fertilizers, feeds, therapeutics, drugs, chemicals, etc., which pose some concern. It is therefore necessary that the practicing countries should formulate guidelines and impose strict regulatory measures for the judicious use of these critical inputs. Application of the principles of Article 9 of the FAO Code of Conduct for Responsible Fisheries would be appropriate.
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