Farming cod and halibut: biological and technological advances in two emerging cold-water marine finfish aquaculture species

Both Atlantic cod (Gadus morhua) and Atlantic halibut (Hippoglossus hippoglossus) have been considered new candidates for aquaculture in North Atlantic countries including Norway, Canada, the UK, Iceland, and the USA since the 1980s. Differences in cultivation methods existed between these two species mainly due to the differences in life stages and their requirements of nutrition, tank dynamics, and environmental conditions. Initially, extensive cultivation methods were employed for cod and halibut using wild zooplankton; however, decades of research on intensive culture methods using rotifer and Artemia resulted in development of improved hatchery protocols. Improvements have been made in recent years in broodstock management for both species, which resulted in improved egg quality. Year around production of eggs through photo-manipulation has been achieved for cod and halibut, which is a major boast for the industry. However, a bottleneck still exists regarding broodstock nutrition, which generally contributes to inconsistent quality of eggs and larvae. Breeding programs have already been initiated for cod in Norway, Canada, and Iceland, and Ireland will follow soon. No breeding programs are available for halibut; however, a genomics program has been initiated for halibut in Canada. Research activities in the early 1990s have resulted in improved egg and yolk sac larval survival and quality in halibut. Intensive larval rearing protocols are available for both species; however, consistent production of high-quality juveniles and survival are still elusive. Apart from poor broodstock management, dependence on cultured live feed, especially Artemia often contributed to poor larval and juvenile quality. However, attempts to replace live feed with formulated diets have been partly successful for cod, and currently most hatcheries in Norway are using only rotifers in their feed regime. Further improvements in feeds and feeding strategies are warranted to reduce the dependence on live feed further. Poor husbandry practices during larval stages could also result in major loss as the immune system of the larvae is underdeveloped. The on-growing phase of both species is more stable compared to the larval phase; however, disease outbreaks, both viral and bacterial, could provide major threats. More research should be conducted on developing vaccines for these disease problems. Escapes of cod from grow-out systems have become a major problem and more research is needed on cage technology and fish behaviour to minimize these escapes. Research is also needed to produce all-female stocks and sterile fish to avoid fertilized eggs escaping to the wild. Early maturation has been recognized as the major bottleneck in cod culture and light administration appears to have limited effectiveness in preventing early maturation. Production of sterile fish would be a solution not only for minimizing fish escapees interacting with wild fish but also for minimizing early maturation. Market development need to be addressed with an emphasis on product quality and food safety.