Effects of the microalga Scenedesmus almeriensis as fishmeal alternative in diets for gilthead sea bream, Sparus aurata, juveniles

The rising costs of fishmeal worldwide promote great research effort aimed to find alternative and renewable ingredients for aquafeeds. In the last years considerable attention has been paid to the use of algae as a potential ingredient for fish feeds. The objective of this work was to evaluate the effects of the microalgae Scenedesmus almeriensis incorporated to diets intended to feed sea bream (Sparus aurata) juveniles in a 45-day trial. Growth, body composition, and intestinal functionality of fish were studied. Microalgae meal was tested in triplicate at different inclusion levels (0%, 12%, 20%, 25% and 39%). At the end of the trial, individual body weight was recorded for evaluation of growth and nutrient utilization, and biological samples were obtained for proximate analysis, determination of digestive enzyme activities, intestinal histology, and microvilli morphological evaluation. Results indicated that S. almeriensis did not cause negative effects on fish growth or nutrient utilization efficiency. Growth rate and protein utilization in fish fed on a diet with 20% Scenedesmus meal tended to be higher, although not significantly different from those fed on control diet. None of the treatments caused adverse effects on body composition. Fish fed 12% S. almeriensis showed higher trypsin than animals fed on control diet. Leucine-aminopeptidase and alkaline phosphatase activities showed a quadratic response with increasing levels of Scenedesmus biomass. Ultrastructural study revealed that the dietary inclusion of algal biomass, especially at 20% level, significantly increased the absorptive capacity of intestinal mucosa in both the anterior and posterior intestinal regions. This study confirmed the usefulness of S. almeriensis to partially replace fishmeal in practical diets for gilthead sea bream juveniles.