Digestive function in Atlantic cod larvae- effects of intensive and extensive rearing systems and correlation with peaks in mortality

High mortality in the early larval stages is one of the main problems resulting in unpredictable production outcome for commercial producers of Atlantic cod. The symptoms prior to the mortality can be observed from 2-3 weeks after hatching and are charac terized by passive larvae followed by a reduced appetite. The gut lumen becomes opaque, distended and filled with fluid. Even though the larvae continue to eat, the digestibility of any ingested preys appears to be very low. As a result, the growth rates and condition factors are reduced, often followed by a peak of mortality 6-8 weeks after hatching. Most of the current research on this problem focus on the bacterial aspects. However, it is unknown if the bacterial infections described are the primary or secondary character of the clinic. The problems are only known from intensive rearing systems and is not known in systems where the fish is reared on natural zooplankton. The proposed project focus on the functionality of the digestive system in larva l Atlantic cod in the critical first three weeks, in order to understand the ontogenetic differences between larvae reared with natural zooplankton and larvae reared in intensive systems. We aim to work with key genes and mechanisms that are critical in 1 ) the proteolytic degradation of ingested nutrients, 2) the absorption of digested feeds and 3) the regulation of digestive function. The project benefits from coordinated studies on the bacterial aspects already established as a research council project at the production site. The synergetic studies aims at improving first feeding rearing protocols for more predictable production of Atlantic cod fry.