Introduction
The goal of sustainable aquaculture is to provide a continued supply of farmed aquatic food for human and animal consumption without compromising ecosystems. In the last twenty years soy was a valid alternative protein sources with positive results on growth and health of several aquatic species, including European sea bass. Depside that, plant ingredients may pose contrasts in sustainability and for this reason, in last years, was necessary to find other ingredients more sustainable, well represented by fishery and aquaculture by-product and microalgae as alternative protein sources. Microalgae are widely use in fish nutrition, especially for the high quantities EPA and DHA but are also extremely rich in protein content. Moreover, they can grow on different substrates, such as wastewater, making them the valid sustainable candidates as soy replacement. This study highlighted the possibility to total replace wild FM and FO and soy using by-product from fisheries and aquaculture and with microalgae as alternative protein source without affecting growth, digestibility, enzymatic activities and nutritional performance.
Materials and Method
Five experimental diets (C, 50FMFO, 50FMFO-50MIC, 0FMFO-50MIC, 0FMFO-100MIC) were formulated to totally replace wild fishmeal (FM), wild fish oil (FO) and soy protein using fisheries and aquaculture by-product and microalgae. Fifty fish per tank (initial body weight 46.66 ± 0.04 g), were reared in recirculated aquaculture system for 88 days. At the end of the trial, growth, feed intake (FI), proximate composition, nutritional index, apparent digestibility, somatometric indexes, blood plasma biochemistry were detected. The activity of major digestive enzymes as total alkaline protease (TAP), trypsin, chymotrypsin (CT), alkaline phosphatase (AP) and leucine aminopeptidase (LAP), was detected spectrophotometrically. The assessment of gut microbiota (GM) was made by Next-generation sequencing.
Results
No statistical differences were evaluated for FI and growth parameters. TAP, trypsin and LAP activity did not show any statistical difference among treatments. Results of AP and CT are shown in Figure 1. The activity of AP in proximal intestine increased, reaching highest value in animals fed with 0FMFO-50MIC, then decreased in 0FMFO-100MIC diet. Even in distal segment, the activity of AP presented the highest value in diet with partial replacement of microalgae, 0FMFO-50MIC. The activity of Chymotrypsin was similar in proximal and distal part of juvenile’s intestine. The values increased up to the highest value in 50FMFO-50MIC diet, then gradually decreased. Proteins body content presented lower value in diet 50FMFO-50MIC than in diet 50FMFO and 0FMFO-100MIC. Lipids body content were significantly higher in diet 50FMFO, 50FMFO-50MIC and 0FMFO-50MIC compared to control diet. No statistical differences were detected for apparent digestibility and all nutritional indexes considered. Considering plasma parameters, Creatinine, CHOL, HDL, TP and Fe values were statistically higher in diet C than in other treatments, while lower values were presented in diet with the higher percentage of replacement, 0FMFO-100MIC. On the other side ALP, Na and Cl values were lower in C diets and higher in 0FMFO-100MIC diet.
Discussion
This study highlighted the possibility to total replace wild FM and FO using by-product from fisheries and aquaculture without affecting growth, digestibility and nutritional performance of European sea bass juveniles. The enzymatic activities show the possibility to replace 100% of wild-caught FM and FO with fishery and aquaculture by-product and replace 50% of soy protein with microalgae, with positive effect on intestinal activity. These results make it possible to use by-products and microalgae as an alternative protein source, avoiding the use of soy and making aquaculture more sustainable.
Acknowledgement
This research was undertaken under the NewTechAqua (New technologies Tools and Strategies for a Sustainable, Resilient and Innovative European Aquaculture) which has received funding from the European Union’s Horizon 2020 Programme under grant agreement No 862658, in collaboration within another Horizon 2020 European project, SABANA (Sustainable Algae Biorefinery for Agriculture and Aquaculture).