Effects of temperature and feeding frequency on the survival and Metamorphosis of Senegalese sole (Solea senegalensis) Larvae.
Supervisors: Manuel Manchado, Adriana Sardi (IFAPA)
Temperature and prey availability are the key most fundamental factors that influence successful recruitment of early life stages in fish. Hence, a better understanding of how these two factors modulate larval growth and survival is essential for modelling larval dynamics in the nature. In this study, two housing systems (one based on 4 mL multi-well microplates and another based on 80 mL containers) were set-up to cultivate Senegalese sole (Solea senegalensis) larvae. The effects of three rearing temperatures (17, 20 and 23˚ C) and three weekly feeding regimes (T2-fed twice, T4-four times and T6-six times/week) from 12 to 32 days post-hatch (dph) were assessed. Survival, growth, metamorphosis progress and gene expression profiles of six genes related to nutrition (tryp1a and apoA4Aa2, cellular stress (hsp90aa), endocrine regulation (tgb) and muscle development (myf4) were evaluated. Feeding regimes as a source of energy was the main factor greatly influencing growth, survival and metamorphosis onset. Larvae fed T2 had the smallest standard length and survival followed by T4 and T6. These differences in size and survival were more pronounced with age and modulated by temperature. All larvae in T2 delayed the onset of metamorphosis with hardy differences in metamorphosis progress between feeding regimes and varying as function of temperature. Although at a much lower significant difference than feed, temperature also had an effect in all investigated traits and larvae cultivated at 17ºC showed the lowest sizes, delayed the onset and progress of metamorphosis, and had a higher survival than larvae reared at 23ºC, pointing at a clear interaction between temperature and feeding regime. Overall performance was significantly better in containers for all tested traits. Gene expression analyses in metamorphic stages S3 and S4 indicated the highest mRNA levels of apoa4a2 and tryp1a in larvae cultivated at 17ºC and fed T2 showing a gradient across temperatures and feeding regime. Moreover, the tgb transcript amounts were the higher in larvae cultivated at 17ºC than 20 and 23ºC. Expression profile of hsp90aa responded to temperature in S3 (higher expression at 17ºC) and both to temperature and feeding regime in S4 (higher expression at 20ºC and S4). All these data demonstrate that energy provision as determined by prey availability is a key driver controlling growth, development and survival that interact with temperature when metabolic and energy demands cannot be fully attended with detrimental effects on larval survival. In any case, larvae are able to trigger a compensatory genomic adaptive response to efficiently mobilize nutrients from gut and adjust the endocrine and cellular response to support metamorphosis transformation and metabolism. All these data are relevant for understanding larval recruitment in fisheries in a context of climate change.