Variability in digestive enzyme capacity in early stages of marine fish larvae: Ontogenetic variations, biorhythms, hormonal control and nutrient sensing mechanisms

Abstract

In recent years, no substantial progress has been achieved to significantly improve survival rates of cultured marine fish larvae and make the viability in offspring production more predictable. Improving survival and quality of marine larvae in aquaculture industry beyond the present status requires consideration of nutritional quality of the feed but also an in-depth knowledge of larval physiology to account for biorhythms in digestion capacity, appetite and regulation of food ingestion and endocrine control of digestion processes associated to nutrient sensing and feeding activity. Since gut hormones are most likely stimulated and released in response to specific nutrients it is crucial to study the nutrient sensing mechanisms also in the gastrointestinal tract of fish larvae and the importance of nutrients as they are not only substrates, but active regulators of physiological processes. This chapter focuses on the importance of the daily and circadian rhythms in the digestion capacity in larval stages of fish, emphasising the potential variability of enzyme secretion during the day, addresses the specific role of the gut hormones cholecystokinin and ghrelin on appetite and digestive functions in fish larvae and provides a comprehensive consideration of the food sensing mechanisms in the gastrointestinal tract of fish larvae associated to specific nutrients. Knowledge in these research areas, through larval ontogeny, will be specifically beneficial for the development of stage-specific micro diets and replacement of live feed with formulated feed. Recommendations on future research aspects and approaches within these themes are discussed and suggested in the specific sections.