Different dietary protein levels affect meagre (Argyrosomus regius) larval survival and muscle cellularity

A high frequency of cannibalism and high variability of growth rate within the same larval batch are the main bottlenecks for implementation of meagre culture. In this study the effect of two sodium alginate-encapsulated diets containing 55 (control) and 68% protein was tested in terms of larval composition, survival, growth and muscle cellularity. The results showed that the diet with higher protein content improved larval survival but no differences on larval growth were observed between treatments. Diets did not affect the amino acid and fatty acid profiles of meagre larvae. The differences between larval fatty acid profiles were mainly related to larval age rather than treatments. Meagre larvae fed the high protein diet showed a higher frequency of white muscle fibres with an area smaller than 150μm2 and a lower mean fibre area (214.9±160.6μm2 and 187.88±162.7μm2, for 55 and 68% of protein, respectively). These results suggest that a higher dietary protein increases meagre larval survival and leads to a potential higher contribution of fibre hyperplasia. The main aim of this work was to test two diets containing different protein levels (55 and 68%) and determine its effect on larval survival, growth, larval composition and muscle cellularity. This work was carried because meagre has been thought to have a higher protein requirement compared to seabream and seabass (Amoedo, 2011). Nevertheless, meagre is usually fed on diets formulated specifically for seabream suggesting that meagre protein requirements are not being satisfied and meagre growth might be constrained. Given that meagre is the species with highest potential to be intensively farmed in the Mediterranean region it is important to formulate specific diets for this species. The results obtained in this work showed that although growth was not affected by the diet, there seems to be a higher potential for growth in the long-term as fibre recruitment was higher when larvae were fed a high protein diet. •This study tested two levels of dietary protein (55 and 68%) in meagre larvae.•An increase of protein in the diet improved slightly larval survival.•Amino acid and fatty acid profiles were not affected by the diets.•Growth rate was not affected but muscle cellularity results suggest a high potential for growth in the long-term when larvae are fed the HP diet