Assam ASSEB Higher Secondary Skill Subject Fishery Sciences key terms

The controlled farming of aquatic organisms such as fish, prawns and molluscs in ponds, tanks or cages, where stocking, feeding and harvesting are managed by people to increase production above natural levels.

Harvesting of wild fish and other aquatic animals from rivers, reservoirs, lakes and seas without managing their breeding or feeding, relying instead on natural stocks and the skill of finding and catching them.

A polyculture practice in which several carp species with different feeding habits are stocked together in one pond so that food available at different depths and types is used fully without competition.

The number of fish or seed released per unit area or volume of water, usually expressed as numbers per hectare or per cubic metre, which controls growth, feed demand and oxygen pressure in the pond.

Microscopic floating plants (phytoplankton) and animals (zooplankton) living in the water column, forming the natural food base of ponds and the main food of filter-feeding carp such as catla and rohu.

Adding organic manure or inorganic nutrients to a pond to encourage plankton growth, thereby producing natural food for stocked fish at low cost and improving pond productivity.

Application of lime, usually calcium carbonate or calcium oxide, to a pond to raise alkalinity and pH, improve the buffering capacity of water and increase the availability of nutrients for plankton.

The amount of oxygen gas present in water, measured in milligrams per litre, which fish absorb through their gills; low levels at dawn or after heavy feeding can cause stress and mass mortality.

Mechanical or physical mixing of pond water with air to increase dissolved oxygen and remove excess gases, commonly done at night or before dawn when oxygen is lowest.

The amount of dissolved oxygen consumed by microorganisms while decomposing organic matter in a water sample over a set period, used as an indicator of organic pollution and pond water quality.

The capacity of pond water to neutralise acid, mainly due to bicarbonate and carbonate ions, expressed as milligrams per litre of calcium carbonate; adequate alkalinity stabilises pH and supports plankton.

A circular white and black disk lowered into water until it disappears from view; the depth at which this happens estimates water transparency and hence plankton density and turbidity.

The respiratory organ of fish, made of filaments and lamellae richly supplied with blood vessels, across which oxygen from water is absorbed and carbon dioxide is released.

A gas-filled sac inside the body cavity of most bony fish that adjusts buoyancy, allowing the fish to stay at a chosen depth without expending energy on swimming.

A row of sensory pores running along the side of a fish that detects water movement, pressure changes and vibrations, helping the fish sense prey, predators and obstacles nearby.

The total number of ripe eggs produced by a female fish in one spawning season, usually estimated by sampling the ovary and used to plan hatchery seed production and brood stock selection.

Sexually mature male and female fish kept in good condition for breeding, selected for health, growth and genetic quality, and fed and managed so that their gonads mature properly.

Technique of injecting hormones or pituitary gland extract into mature fish to trigger spawning at a chosen time, used when natural breeding does not occur in captivity.

Induced breeding by injecting pituitary gland extract, usually from a donor fish such as a major carp, into the brood fish to stimulate maturation and release of eggs and milt.

The process in which a developing embryo breaks out of the egg shell, and in hatchery practice the controlled incubation of fertilised eggs in trays or jars until larvae emerge.

A small, well-prepared pond used to rear very young fish larvae or fry for a few weeks, where food, water depth and predators are carefully managed to ensure high survival.

The standard laboratory analysis of a feed or fish tissue for moisture, crude protein, crude fat, crude fibre and ash, used to judge nutritional quality and compare feed ingredients.

The weight of feed given divided by the weight gain of fish produced; a lower value means feed is used more efficiently and feeding practice is more economical.

Manufactured feed formed into compressed particles of defined size and composition, offering balanced nutrition, less waste and easier control of ration than raw or mashed feed.

High-protein powder made by cooking, pressing and drying fish or fish waste, rich in essential amino acids and used as a major protein ingredient in formulated fish feeds.

The increase in length or weight of a fish over a stated period, calculated from measurements at stocking and harvest, used to judge feed quality, health and pond conditions.

A bacterial infection of freshwater fish caused by Flavobacterium columnare, producing grey-white lesions on skin, fins and gills, often after handling stress or in warm water.

A bacterial condition in which the edges of fins fray and erode, often linked to poor water quality or injury, and which can spread to the body if untreated.

Keeping newly purchased or wild-caught fish apart in separate tanks for a set period to observe them for disease and prevent pathogens from entering the main farm.

A wall of netting hung vertically in water that entangles fish when they try to pass through the mesh, with mesh size chosen to catch particular species and sizes.

Non-target animals such as small fish, juveniles and turtles caught accidentally along with the intended species, often discarded and a major concern for sustainable fishing.

The two parts of a fishing unit: craft are the boats or vessels used, and gear are the nets, lines, traps and hooks; together they determine the fishing method and its selectivity.

Cooling freshly caught fish with crushed ice or chilled water to slow bacterial growth and enzyme action, the simplest and most common method of preserving quality between catch and market.

Processing fish into products such as fillets, smoked fish, pickles, fish balls or fish protein concentrate to raise market price, extend shelf life and reduce waste.

The breakdown of fish quality after death through bacterial action and enzyme activity, producing off-odours, softening and unsafe food if the fish is not chilled or preserved quickly.

A financial comparison of total costs and total returns of a fish farming or processing venture, used to decide whether the enterprise is profitable and worth continuing.