The digestive function in developing fishm larvae and fry. From molecular gene expression to enzymatic activity

Abstract

There is a large amount of scientific literature on digestive enzymes activity during fish larval development. Nevertheless, most of this information refers to descriptive aspects of the ontogeny of hydrolyzing capacities, and only few studies looked into functional aspects and its relation with feeds and feeding activity. A comparison of published data normalized by days-degrees reveals at least three groups of species (precocious, medium and late) in relation to the time required for reaching maximum activity of digestive enzymes capacities, irrespective of the taxonomic group. Recent progress has allowed enlarging our knowledge on fish larvae digestive function. Such progress is partially based on new methodologies, but also on extended experimental designs and sampling protocols. On one side, the molecular basis of the onset of the digestive functionality has been examined in several species, cloning the mRNAs codifying the precursors of the main digestive enzymes and determining the gene expression profiles. On the other side, the daily rhythms coupling feeding and digestive enzyme production activities started to be investigated, giving a new dimension to our understanding of the digestive capacity during these early stages. Comparison between molecular expression and actual activity of the different enzymes is providing new insights on the regulation mechanisms. The connection between feeding behavior and digestive response both at genomic and biochemical levels is a required step towards the rationalization of feeding protocols with both live and inert diets, as a way to increase the nutrients utilization and the developmental performance at these early stages.