| Summary: | 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 2
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.
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