Introduction
Mixes of free amino acids (MFAA) obtained from extensive hydrolysis of full protein chains are interesting candidates for aquaculture feeds. In addition to their specific amino acids profile, their low molecular weight ensure a fast and high level of assimilation with synergetic effects during the first development stages. Previous investigations on shrimp (L.vannamei) underline MFAA positive effects on zootechnical performances (Le Reste et al., 2019) and survival in case of bacteriological and viral challenges (Kersanté et al., 2021). The results presented here have been obtained from an eight-week study conducted to investigate the effects of a mix of 17 amino acids obtained from extensive hydrolysis of poultry keratin, on the growth performances, biochemical parameters, innate immune response, muscle composition, digestive enzyme activity and muscle fatty acid composition of Nile tilapia (Oreochromis niloticus) (Wangkahart et al., 2022).
Protocol
450 healthy juvenile Tilapia (O. niloticus), 4.76 ± 0.05g initial weight (IW) were purchased from Maha Sarakham province, Thailand. The fish were acclimatized to laboratory conditions in circular fiberglass tanks for 2 weeks, in the aquarium of the Division of Fisheries, Mahasarakham University. During this period, fish were fed with a commercial diet containing 32% of protein and 4% of fat (Charoen Pokphand Foods, CP, Thailand). After acclimatization, fish were allocated in 15 floating cages (2*1.5*1.5m3) in five triplicates groups at a stocking density of 30 fish per cage, in an open circulatory freshwater system.
In order to meet or exceed the nutritional requirements of tilapia established by the National Research Council (2011), we formulated five isonitrogenous (32% crude protein) and isolipidic (4.2% crude lipid) diets, supplemented with MFAA.
Four different concentrations of MFAA were tested: 2.5 g/kg of feed, 0.25%, 5 g/kg of feed 0.50%, 7.5 g/kg of feed, 0.75% and 10 g/kg of feed, 1.00%, respectively MFAA0.25, MFAA0.50, MFAA0.75 and MFAA1.00. The MFAA was included into the pellet mix, before pelletizing.
Fish were fed twice a day (8am, 4pm). A daily feeding rate of 5% of the biomass was applied. It was adjusted every 2 weeks, according to fish growth. The experimentation was conducted during 8 weeks.
Results
The data underline interesting improvements of growth parameters with MFAA supplementation. A dose effect could be seen with best performances achieved for animals fed with MFAA1.00 treatment, generating significant gains on biomass evolution with final weight (FW) improved by 28.9%, weight gain (WG) by 31.5%, specific growth rate (SGR) by 8.9% and a feed conversion ratio (FCR) reduction of 24% after 8 weeks (P<0.05).
Interestingly, growth performances are also correlated with modifications in body composition indices and feed utilisation. These parameters clearly underlined better performances for all MFAA treatments (P<0.05), with significant gains, related to a dosage effect of MFAA, on protein efficiency ratio (PER) improved by 29.2%, carcass