Introduction to Inland Fisheries and Aquaculture Systems
Capture versus culture
Odisha's inland sector runs on two systems. Capture fisheries take naturally recruited stocks from rivers such as the Mahanadi, Brahmani, Baitarani and Subarnarekha, from reservoirs such as Hirakud, Rengali, Balimela and Upper Kolab, and from the Chilika lagoon, a brackish-water Ramsar site. The fisher removes fish but cannot control recruitment. In culture fisheries the farmer stocks, feeds and manages the pond and owns the crop. A question usually describes a situation and asks you to name the system and justify it.
Intensity classes
- Extensive: little or no stocking, no feed, roughly 500-1500 kg/ha/yr.
- Semi-intensive: stocking plus manuring and supplementary feed of rice bran and oil cake, 3000-6000 kg/ha/yr. This is the typical Odisha composite-carp pond.
- Intensive: formulated feed, aeration, high density, 8-15 t/ha/yr.
- Special systems: cage and pen culture in reservoirs, biofloc (microbial floc with heavy aeration and minimal water exchange), recirculating aquaculture systems, aquaponics where fish water fertilises plants, and integrated farming such as paddy-cum-fish, duck-cum-fish and pig-cum-fish.
Composite fish culture
The standard practice stocks three Indian major carps so that each depth zone is used: catla on the surface, rohu in the column and mrigal at the bottom. The usual three-species ratio is 3:4:3 by number; a six-species mix adds silver carp, grass carp and common carp at roughly 1.5:2.5:1.5:2:1.5:1.0 per ten fingerlings.
Worked example
A 0.4 ha pond is stocked at 6000 fingerlings/ha using a 3:4:3 ratio. Total fingerlings = 6000 x 0.4 = 2400. The ratio sums to 10 parts, so one part = 240 fish. Catla = 3 x 240 = 720, rohu = 4 x 240 = 960, mrigal = 3 x 240 = 720; the three add back to 2400, which confirms the arithmetic.
Traps that cost marks
- Quoting a stocking ratio by weight instead of by number.
- Treating Chilika as a freshwater system.
- Confusing biofloc with hydroponics or with a RAS.