Glossary of Hatchery terms

Glossary of Hatchery Feed Terms - G - L

October 9, 2019


Green water culture — The enhancement of natural food chains in ponds or tanks by  nutrient enrichment, as a means of increasing food supply to an aquaculture species.

Growth rate, absolute — The actual increase in size of an individual or stock per unit time under known or specific conditions, expressed e.g. in g/day or kg/month.

Growth rate, instantaneous- (g) — A  measure of the daily weight increase determined from a sample of fish over a short period of time and calculated by the following equation: g = (ln Wt - ln W0)/(t1 - t0) where Wt is the weight of the fish after t1 days, W0 is the initial weight and ln is the natural logarithm.

Growth rate, relative (GRR) — The increase in size (length or weight) of an individual or stock per unit of time in proportion to its initial size; often expressed as equal to [(St - S0)/S0] x 100 where S0 is the initial size and St the size at the end of the period.

Growth rate, specific (G) — An expression of daily increase in weight defined as G=gx100 where g is the instantaneous growth rate.


Hatchery — Place for artificial breeding, hatching and rearing through the early life stages of animals, finfish and shellfish in particular. Generally, in pisciculture, hatchery and nursery are closely associated.

Hatchery constant — A single value derived by combining the factors in the numerator of the feeding rate formula. Hatchery constant = (3 x feed conversion x daily length increase x 100) / length of fish. This value may be used in fish hatcheries to estimate feeding rates (in percent body weight/day) when water temperature, feed conversion and growth rate remain constant.

Hatching stage — For brine shrimp: last developmental stage of the brine shrimp embryo, when the fully developed nauplius ruptures the hatching membrane and hatches, becoming a free-swimming larva.


Juvenile — Young stage of animals, usually up to the time they first become sexually mature. For fish usually between the postlarval stages up to the time they first become sexually mature. They are generally hardy at this stage.

Larva (Plural:Larvae) — An organism from the beginning of exogenous feeding to metamorphosis into juvenile. At the larval stage the animal differs greatly in appearance and behaviour from a juvenile or an adult.

Larva, (echino) pluteus — Planktonic larva of sea urchins (echinoderm Echinidae), which swims very actively to feed on planktonic  organisms. After metamorphosis, settles on a substrate and becomes a juvenile sea urchin.

Larva, D — Developmental stage of mollusc, so called as the shell of the larva resembles a capital "D". Last stage of a planktonic mollusc larva prior to settlement on the sea bottom.

Larva, competent — Larva of mollusc that is ready to metamorphose and attach to a suitable surface.

Larva, eyed — Generally refers to a molluscan larva, which has developed a foot and is ready to settle out of the plankton and become benthic.

Larva, schizopod — Stage in development of decapod crustacean larva when it resembles an adult mysis in having an exopodite and endopodite to all thoracic limbs.

Larviculture — The culture of larvae, usually in hatcheries.