Fish culture

Not every fish species suits commercial culture — a good cultivable fish needs a high growth rate over a short period, must accept supplementary feed, must be hardy against common diseases and parasites, must coexist peacefully with other species in polyculture, and must convert feed into flesh efficiently. Cultivable fish fall into three groups: indigenous freshwater fish (Major carps, Catla, Labeo, Clarias), salt-water fish acclimatised to fresh water (Chanos, Mullet), and exotic fish imported from other countries (Common carp) — among these, major carps are considered best suited to Indian conditions because they feed on zooplankton, phytoplankton, decaying weeds and debris, tolerate turbid water and warmer temperatures, tolerate variation in dissolved oxygen, transport easily between locations, and are both highly nutritive and palatable. External factors such as temperature, light, rainfall, water current, turbidity, pH, hardness, salinity and dissolved oxygen all influence fish culture, with light and temperature particularly important for breeding. Managing a fish farm means running fish through a sequence of specialised ponds: breeding ponds (near natural water sources, using either natural riverine 'bundh breeding' or induced breeding, where fish seed quality is improved either by artificial fertilization — manually stripping eggs and milt from mature fish for external fertilization — or by hypophysation, injecting a gonadotropin-rich pituitary extract to trigger spawning); the resulting fertilized eggs go to hatching pits (small, good-quality-water ponds near the breeding grounds, including net-and-bamboo hatching hapas); the fry that hatch move to nursery ponds to grow into fingerlings, then to long, narrow rearing ponds free of toxicants and predators, and finally to stocking ponds, kept free of weeds and predatory fish and organically/chemically manured to boost yield. Harvesting removes well-grown fish for market (returning undersized fish to the pond) using methods such as stranding, angling, traps, dip-nets, cast nets, gill nets, drag nets and purse nets, with the catch preserved by refrigeration, deep freezing, freeze drying, sun drying, salting, smoking or canning. Stocking several compatible species together — composite fish farming (polyculture), using species such as Catla catla, Labeo rohita and Cirrhinus mrigala — fully uses all available niches in a pond without competition or harm between species, while imported exotic fish such as Cyprinus carpio and Oreochromis mossambicus add further culture options; disease management relies on regularly monitoring water quality, aeration, feeding and mortality, and watching for parasitic or microbial infection. Economically, fish are a rich protein source, with species like sardine, mackerel, tuna and herring particularly high in amino acids such as histidine (responsible for the flesh's meaty flavour) and in omega-3 fatty acids, plus minerals including calcium, magnesium, phosphorus, potassium, iron, manganese, iodine and copper. Fish by-products add …