Effect of rearing density on Siberian sturgeon larval development

Introduction: Given its high market value and conservation status, the Siberian sturgeon (Acipenser baerii) is an important species in aquaculture. Mortality of A. baerii occurs during larval development in particular in the free-embryo stage, during which larvae totally rely on endogenous yolk-sac reserves for energy and growth. The efficiency at which these reserves are utilized for growth is very dependent on environmental factors, such as stocking density. However, little information is available about the effects of rearing density on sturgeon yolk-sac larvae. Therefore, the aim of this study was to evaluate the effect of three stocking densities on larval growth, survival and muscle development in A. baerii . Materials and Methods: A. baerii yolk-sac larvae were subjected to three different stocking densities until complete yolk-sac absorption: 30, 80 and 150 larvae/l. Sampling timepoints were: hatching, schooling and complete yolk sac absorption. Survival was estimated by daily counting of dead larvae. Sacrificed larvae were weighed and measured. Histometrical and immunohistochemical (anti-PCNA) analyses, and scanning electron microscopy (SEM) were performed in order to characterize muscle growth and development. Results: There were no significant differences in survival across densities. Larvae reared at the lowest density showed a higher specific growth rate and were significantly longer than the other two densities (P<0.05). PCNA quantification revealed a significantly lower muscle white fibres proliferation in larvae subjected to the highest density, both at the schooling stage and at the yolk-sac absorption stage (P<0.05). SEM analyses revealed no deformities at any density. Conclusion: Siberian sturgeon commercial hatcheries could take into account to use lower stocking densities in this stage of development. Further studies would be necessary in order to understand the effect of stocking density on the stress status and muscle development mid-long term basis. All husbandry and experimental procedures were approved by the Ethic Committee of the University of Milan (OPBA_22_2017).