Enzymatically pre-hydrolyzed microalgae biomass as a feesdstock for aquafeed diets

DO NASCIMENTO, M.; GARCÍA MARTÍNEZ L.; BADER, A.; ZANAZZI, N.

Congreso; XVIII Congreso de la Sociedad Argentina de Microbiología General; 2023

Aquaculture contributes to almost 50% of world annual fish production. The growing demand for fishmeal as a source of bulk protein and essential fatty acids for fish diets has become a serious problem with economic and environmental implications, making it necessary to look for more sustainable alternatives.Microalgae have a high protein content (40-60% DW) and a high amount of essential amino acids that make them suitable for protein supplementation. Furthermore, they have a high content of polyunsaturated fatty acids (Ω3 and Ω 6), that are essential for fish growth. However, the presence of complex cell walls act as a barrier, limiting the bioavailability of nutrients because of poor in vivo digestibility. The aim of this work was to evaluate the nutritional quality of produced algal biomass, and the effect of its in vitro hydrolysis on Nile tilapia (Oreochromis niloticus) fish productivity.For this purpose, Ankistrodesmus sp. SP2-15 was cultivated in 80L flat panels photobioreactors with synthetic medium under environmental conditions and CO2 supplementation. Cells were harvested by autoflocculation and sedimentation, and sun dried. Biomass hydrolysis was carried out by using enzymes secreted by Aspergillus niger culture by solid state fermentation on wheat bran. The biomass load was 25% (w/v) and the reaction was initiated by addition of 1/60 (v/v) of the concentrated enzyme and incubation at 55ºC for 24 h.Then, two experimental isoproteic diets were formulated to replaced 30% (p/p) of the fish meal with crude or hydrolyzed biomass. We assessed the impact of these diets on the growth performance and nutritional status of O. niloticus juvenile´s in a 68 days’ feeding trial bioassay.No significant differences in fish growth parameters were observed between experimental treatments indicating that the replacement was very successful. A slight increase in feed conversion efficiency was observed in the group fed with hydrolyzed microalgae. Interestingly, a differential enzymatic activity was observed in stomach and gut samples, with a decrease of acid protease activity in stomach, and alkaline protease in foregut samples. In contrast, an increase of alkaline protease and amylase activity was observed in midgut samples. Results suggest that microalgae based diets can modulate the expression and activity of digestive enzymes. However, under the bioassay’s conditions this was not correlated with any change in fish biomass production.Together these results confirm the potential use of Ankistrodesmus sp. SP2-15 biomass either crude or hydrolyzed to partially substitute fishmeal in aquafeeds for O. niloticus juvenile´s.