Evaluation of Aloe vera by-product against cereals in feeds for golden mullet (Liza aurata)

Among of the actual challenges for the sustainable aquaculture development are to lower the trophic level of the cultured species, and to increase the use of by-products from the primary sector. The golden mullet (Liza aurata) is a marine low trophic level consumer present in the Mediterranean and in the Canary Islands, where there was a significant consumption in the past. On the other hand, Aloe vera plant, which production in Canary Islands is highly world representative, contains more than 70 biologically active components which have aroused the interest for its use in aquaculture, although the enormous quantity of the generated by-products has no use at all, and has never been tested for aquaculture purposes. The objective of this study was to run the first controlled feeding test with Liza aurata in the Canary Islands, as a target species to promote its cultivation, and to evaluate the use of pure Canarian Aloe vera against different levels of the by-product, to determine the effects in growth, health, and quality parameters. Therefore, 5 diets were formulated to contain 0% of aloe inclusion (diet control), 2% of pure form of aloe (diet P2), and 2, 4 and 6% of aloe by-product (diets BP2, BP4 and BP6). At 91 days of feeding, growth, proximal and fatty acid composition of liver, muscle and whole body, serum lysozyme, serum antibacterial activity, and malonaldheyde content of liver and whole body, were measured. According to obtained results, up to 6% of the aloe by-product could be included in diets for this species, without any rejections in growth or quality parameters, although no improved results compared to the control fish could be observed. Further studies are on the way to determine the sustainability and bioeconomic impact of present results, to gain knowledge on their direct industrial applications.