Cod juvenile production: Research and commercial developments

Atlantic cod (Gadus morhua) has been a new candidate for aquaculture for some decades in countries around the North Atlantic Ocean. Greatest interest in developing a cod farming industry is found in Norway, Canada and the United Kingdom as well as in Iceland and the USA (north east). Modern hatchery methods for cod using cultivated plankton such as rotifers and Artemia were first described in 1984, but it took more than 15 years of dedicated research and development before these efforts now are being translated into up scaled hatchery protocols. Protocols for keeping reproductive stocks of Atlantic cod under different photoperiods have been established resulting in year around production of fertilised eggs. Hatcheries commonly keep 3–5 different stocks to achieve this. The relationship between brood stock nutrition, external cues and reproductive performance is largely unknown and should be studied further. Cod larvae have a very high growth potential (> 20% day− 1), they are aggressive feeders and can be cannibalistic if food availability is sub optimal. Both temperature and light are found to influence growth in larval cod. Research has addressed cod larval nutrition, both qualitative and quantitative requirements. Also, development of feeds and feeding strategies that would allow early weaning onto inert diets has been a primary objective in cod juvenile production research. Using a diet designed to support larval requirements, weaning can start from 15–20 days post hatch. This strategy has resulted in satisfactory growth and survival without use of Artemia, thus reducing the dependency on live feeds. Huge variation in survival and a high incidence of deformities have been reported in hatchery-reared cod juveniles. These observations have been ascribed partly to unfavourable environmental conditions (gas super-saturation) and the problem has to a large extent been solved. Methods to produce large numbers of cod juveniles have been implemented in several Atlantic countries in recent years, and present hatchery capacities can support an annual production of several hundred thousand tons of farmed cod. Common practices in cod hatcheries are presented and future perspectives on cod juvenile production are discussed.