Digestive biochemistry as indicator of the nutritional status during early development of the long snouted seahorse (Hippocampus reidi)

Abstract The activities of some of the main digestive enzymes of long snouted seahorse ( Hippocampus reidi ; Ginsburg, 1933) measured during the initial 20 days after birth were used to assess the nutritional response to different enrichment of the Artemia salina used as live food. Some significant differences in the activities of trypsin total protease and esterases were observed among the experimental treatments, changes in the activities of acid and alkaline phosphatases, as well as in the trypsin/estaerase ratio, were linked to the different dietary treatments. This provided information both on some characteristics of the digestion process in newborns and the influence of the diet on the maturation of the intestinal epithelium during their early development. The use of a multivariate analysis combining the information of all the enzyme activities highlighted differences between treatments. Results obtained confirm the interest of using digestive enzymes as valuable indicators of nutritional condition in larvae of this species and may help to optimize feeding protocols required for mass-scale production of seahorses in captivity. Statement of relevance Overexploitation, habitat loss, and incidental bycatch during commercial fishing operations, make seahorses susceptible to decline. The high global demand of seahorses exceeds supply from specimens breeding in captivity, and in this unsustainable situation, the long snouted seahorse, H. reidi , is one of the most frequently commercialized species. Larval rearing remains the bottleneck for successful cultivation of seahorses. In this sense, the design of a suitable feeding regime based on food adapted to the nutritional needs of the species is highly desirable. Due to their key role in nutrient digestion and assimilation, changes in the production patterns of the main digestive enzymes can be used as indicators of the nutritional status helping to assess the adaptation to foods with different content in macronutrients and therefore contributing to optimize feeding strategies for this species. The biochemical parameters proposed as indicators of nutritional status might be good analytic tools, not only to establish the time of change of live prey during the weaning but also to formulate the most digestible biochemical composition of live prey. Phosphatases activities, trypsin/esterase ratio and the clusters of enzyme activities, were consistent in the results and might be considered as good indicators of nutritional status in this species.