The influence of dietary constituents on the molecular ontogeny of digestive capability and effects on growth and appetite in Atlantic cod larvae (Gadus morhua)

Development of optimal nutrition feeding protocols is considered a major challenge in intensive marine fish larval rearing. There is a general lack of knowledge on the molecular basis underlying larval digestive capability and endocrine function, and relatively few studies have employed molecular biological techniques to study the ontogeny of digestive capability and effects of nutrients on growth and appetite of marine fish larvae. In this study, Atlantic cod larvae were fed either Acartia tonsa nauplii, rotifers grown on Rhodomonas baltica or a control rotifer diet, before weaning to formulated diet. Larvae were sampled at 5, 8, 16, 29 and 38 days post hatch. Larval dry weight and specific growth rate were measured, and gene expression patterns of trypsin, amylase, bile salt-activated lipase, phospholipase A2, Acyl CoA dehydrogenase, neuropeptide Y, cholecystokinin, growth hormone and thyroid hormone receptors α and β determined by quantitative PCR. We show that transcripts involved in appetite regulation and digestion were differentially expressed after different feeding protocols. Interestingly, several similar transcript profiles for genes coding for digestive enzymes and neural controlling factors were demonstrated. In addition, these relationships were partially reflected in larval specific growth rates, demonstrating for the first time in cod, that the ontogeny of digestive capability and its hormonal components may be tied directly to the type and quality of initial and early dietary constituents.