Assessment of dietary inclusion of crude or hydrolysed Arthrospira platensis biomass in starter diets for gilthead seabream (Sparus aurata)

This work evaluates the effects of the dietary inclusion of crude or hydrolysed Arthrospira platensis (Cyanobacteria) biomass on growth, muscle composition, digestive functionality and immune activities in gilthead seabream (Sparus aurata) fry (20.32 mg mean body weight). A 40-day feeding trial was conducted, aimed at assessing four experimental diets that included 5 or 10% (w/w) A. platensis, either crude or hydrolysed, plus a microalgae-free diet as control batch. Overall, none of the dietary treatments caused negative impacts on fish growth, body composition, muscle fatty acid profile, or innate immune response. Thus, the dietary inclusion of both crude and hydrolysed A. platensis reduced significantly the oxidation of muscle lipids, especially when using hydrolysed biomass, regardless of the dietary inclusion level. In relation to digestive enzymes, significantly higher levels of trypsin, chymotrypsin and leucine aminopeptidase activities were measured in fish fed on A. platensis-supplemented diets compared to control fish. In addition, within each inclusion level (5 or 10% w/w), those animals fed with diets that included the hydrolysed biomass yielded consistently higher digestive enzyme activities than those receiving the crude biomass. Microalgae dietary inclusion also induced favourable changes in fish gut morphology, according to the increase in microvilli length and diameter observed. This fact might well have contributed to reinforce the role of the intestinal mucosa as a protective barrier against microorganisms, as well as to enhance the absorptive capacity of the intestinal mucosa. Finally, 10% inclusion of microalgae hydrolysate enhanced lysozyme activity in liver, this fact suggesting improved protection against infectious diseases. In conclusion, the positive effects observed in fish fed with the diets including A. platensis up to 10% (not least the hydrolysed biomass) with regard to the different parameters assessed (digestive enzyme activities, intestinal epithelium ultrastructure, muscle lipid oxidation, and lysozyme activity) suggest the benefits of including this product in starter feeds for gilthead seabream fry