Victor Øiestad

Mass Production of Atlantic Cod Juveniles Gadus morhua in a Norwegian Saltwater Pond

Abstract In March-April 1983, 2.5 × 106 yolk-sac Atlantic cod larvae were released in a dammed estuarine pond. One month later, more than half a million metamorphosed. The larvae and metamorphosed juveniles depleted the natural food supply by mid-May, but the fish accepted small pellets containing 30% krill meal dispensed from automatic feeders. From mid-June, young Atlantic cod primarily ate the pellets, supplemented with minor amounts of wild calanoid and harpacticoid copepods. The population declined during summer probably due to cannibalism and predation from birds. No outbreaks of disease were observed, and infestation with parasites (nematodes) was less than 20%. Altogether, 75,000 juvenile Atlantic cod were captured alive from late May to October. By October, about 20,000 15-cm-long juveniles were tagged and released in the Austevoll region in a first attempt to augment the fishery for Atlantic cod.

Automatic Feeding and Harvesting of Juvenile Atlantic Cod (Gadus Morhua L.) in a Pond

Abstract Large scale production of juvenile Atlantic cod has been carried out since 1980 in a saltwater pond. A break-through was obtained in 1983 with high survival rates of cod larvae to metamorphosis, in 1985 we made progress within two fields: reduced cannibalism and automatic harvesting. Juvenile cod formed large schools while fed dry pellets in the currents set up by five propellers. An underwater loudspeaker was programmed to give sound pulses just before feeding. During harvesting dry pellets were released inside a fish trap while giving the sound signals the cod juveniles were conditioned to. The cod readily entered the trap and a computer-controlled fish pump transported the fish from the fish trap into a storing tank and grading grids. The trap gradually emptied the pond for fish and more than 80% or 100.000 juvenile cods were captured with the automatic harvesting system.