Microalgae are considered as a source of healthful natural products in human and animal nutrition. Because of their unsustainability, fishmeal and fish oil must be reduced in aquafeed, and some microalgae strains have interesting compositions in terms of proteins and lipids both quantitatively and qualitatively owing to their amino acid or fatty acid profiles. In addition, their pigment composition and antioxidant activity make them an ingredient of choice for aquafeed. For crustaceans, their polyunsaturated fatty acids, such as EPA and DHA, and carotenoid pigments are of particular interest for broodstock feeding to improve fertility and egg quality.
To improve microalgae incorporation in aquafeeds, studies are necessary to determine their suitability in terms of nutritional composition, palatability, digestibility, growth performance, health and post-harvested quality product. The digestibility of an ingredient is one of the most important factors to consider in feed formulation. A highly digestible feed can lower production costs, reduce feed waste, and reduce the risk of eutrophication. The intrinsic characteristics of microalgae, the biomass pretreatments, and the feed preparation methods contribute to the microalgae nutrient and energy digestibility in shrimp feeding. In particular, the composition of the microalgae cell wall is known to affect its digestibility.
The aim of this study is to evaluate in vivo the digestibility of two tropical microalgae isolated, selected and produced in New-Caledonia, a Prymnesiophyceae (Sp.1) and a Chlorodendrophyceae (Sp.2), as potential feed ingredients for the blue shrimps Penaeus stylirostris. No significant impact on shrimp survival and growth is noticed at 10 and 30% incorporation in feed. These two microalgae species have very different nutrient composition. The first one is rich in proteins and lipids and shows a significant capacity for assimilation by shrimps while the second one is less digestible by shrimps, probably due to a lower accessibility of its nutrients linked to the rigidity of its cell wall. The application of a microwave treatment on this second strain apparently improves the availability of lipids, but reduce their assimilation (Fig. 1).