Fisheries

Fish, fisheries and aquaculture

Fisheries means catching, culturing, processing and marketing fish and other aquatic animals. Capture fisheries take fish from natural waters; culture fisheries (aquaculture) raise fish in ponds, tanks, cages or pens under control. By water type, fisheries are marine (sea), inland freshwater (rivers, ponds, reservoirs) and brackish water (estuaries, coastal lagoons). The rapid rise in fish production is called the Blue Revolution.

General characteristics of fish: aquatic, cold-blooded (body temperature changes with water), streamlined body, breathe by gills, move with fins, body usually covered with scales, a lateral line to sense water movement, two-chambered heart. Bony fishes have a swim bladder for buoyancy.

Types of fish:

• Cartilaginous fish (Chondrichthyes): skeleton of cartilage, no swim bladder, gill slits uncovered: sharks, rays.
• Bony fish (Osteichthyes): bony skeleton, gills covered by an operculum: carps, catfish, sardine, mackerel.
• Prawns, crabs and mussels are cultured too, but they are shellfish, not true fish.

Composite fish culture: six species stocked together so that every feeding zone of the pond is used and they do not compete:

• Catla (surface feeder, zooplankton) and silver carp (surface, phytoplankton)
• Rohu (column feeder) and grass carp (feeds on aquatic weeds and grass)
• Mrigal and common carp (bottom feeders)

Catla, rohu and mrigal are the Indian major carps; silver, grass and common carp are exotic carps.

Pond management: remove predatory and weed fish, apply lime and manure to grow plankton, stock fingerlings, give supplementary feed (rice bran and oilcake), harvest. Induced breeding of carps uses pituitary extract or hormone injection (hypophysation). Important marine fish: Indian oil sardine, mackerel, pomfret, Bombay duck, tuna.

Key points

• Capture vs culture; marine, inland, brackish.
• Blue Revolution = fish production.
• Indian major carps: catla (surface), rohu (column), mrigal (bottom).
• Grass carp eats aquatic weeds.
• Sharks and rays: cartilaginous.

Exam tips

Feeding-zone questions in composite culture are very common. Also learn bony vs cartilaginous differences.

Common mistakes

• Calling prawn a fish.
• Placing rohu at the surface; catla is the surface feeder.