Ontogeny of digestive enzymatic capacities in juvenile seahorses Hippocampus guttulatus fed on different live diets

AbstractDifferences in survival and growth rates in seahorseHippocampus guttulatus juveniles feeding on Artemiasp.or copepods have been related to specific digestivecapacities of seahorse newborn, which are capableof actively forage on available prey from the firstday of live. Other seahorse species, such asH. abdominalis and H. hippocampus, show high suc-cess feeding on Artemia nauplii suggesting species-specific differences in the digestibility of prey amongseahorses. In this study, the profiles of digestiveenzyme activity during the initial 15 days afterrelease (DAR) were very low for trypsin, chitinaseand a-amylase. In contrast, higher activities towardsany of the assayed substrates for lipase (butyrate,octanoate and oleate) were evident from 0 DARonwards. From 15 DAR onwards, the effect of dietcomposition became evident in juveniles previouslyfed on a mixed diet (Artemia + copepods), whichshowed a clear increase in all the assayed enzymeswhen compared with juveniles fed on Artemia as asole prey. As a practical applicability of this study, afeeding schedule ensuring an adequate digestibility ofthe prey is proposed based on ontogenetic enzymaticactivities of seahorse juveniles fed on different prey.Keywords: enzyme activity, Hippocampus guttul-atus, digestibility, ontogeny, Artemia, copepodsIntroductionSeahorses (Hippocampus spp.) are fish of the FamilySyngnathidae with particular anatomical andphysiological features such as head shape, snoutand mouth morphology, male pregnancy and feed-ing behaviour (Blanco 2014). The increasedknowledge on seahorse biology has permitted sig-nificant advances in rearing techniques for somespecies (Olivotto, Planas, Sim~oes, Holt, Avella C Olivotto, Planas et al. 2011; Blanco 2014).Although the effects of different feeding scheduleshave been studied and higher survival has beenreported in captivity (Blanco 2014), only few stud-ies have evaluated their digestive enzyme activity(Wardley 2006; Alvarez, Blanco, Silva & Planas,2009; Quintas, Planas & Purser 2010). Hence,great differences in survival and growth rates havebeen reported when feeding seahorses on eitherArtemia or copepods, although it seems that thecombination of both types of live prey may resultin a greater rearing success in some seahorse spe-cies (Payne & Rippingale 2000; Woods 2000; Job,Do, Meeuwig & Hall 2002; Sheng, Lin, Chen, Gao,Shen & Lu 2006; Olivotto, Avella, Sampaolesi, Pic-cinetti, Navarro Ruiz & Carnevali 2008; Planas,Quintas, Chamorro & Balcazar 2009). However,feeding and nutrient assimilation still remains as amain factor of mortalities during seahorse ontog-eny (Blanco, Quintas & Planas 2011).Mortality during early stages of development isa main bottleneck in the production of many spe-cies of marine fish (Kim, Divakaran, Brown O Perez-Casanova, Murray, Gallant,