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 yield by 9.3% and a reduction of the viscerosomatic index (VSI) of 19.5% for MFAA1.00 (P<0.05).
Fillet composition analysis underlined significant influence of MFAA on the fillet lipid content (+88% with MFAA0.75). Thirty-seven different fatty acids were exanimated in the muscle tissues of the fish following the different diet treatments. Most of the analysed individual monounsaturated fatty acids (MUFA) such as palmitoleic acid (C16:1), oleic acid (C18:1 n9c), and erucic acid (C22:1 n9), as well as the total amount of MUFA, were found to be higher in the muscle from fish fed any MFAA diet compared to the control group (P<0.05). Interestingly, linoleic acid (C18:2 n6c) and α–linolenic acid (C18:3 n3) levels were higher in the fish fed MFAA0.75 and MFAA1.00 diets (P<0.05).
In relation with these observations, the fillet color measured on ventral and dorsal regions was also significantly influenced with higher value of L, expressing the lightness and white color of the fillet, respectively +13.7% and +7.2% for the L value of the fillet ventral and dorsal regions with MFAA0.75 (P<0.05).
Digestive enzyme activies (amylase, lipase and proteinase) were significantly increased with MFAA0.75 and MFAA1.00 treatments, respectively from 34.9%, 10.4% and +39.9%, in comparison with the negative control (P<0.05).
Discussion
This study underlined some particularly interesting effects of MFAA when applied on Nile tilapia fingerling feed. Firstly, regarding growth parameters with positive effects on biomass and feed utilization. Interestingly, we underline strong improvements of VSI, fillet composition and fillet color. We can hypothesize a relation between these observations and a better assimilation of the feed due to an optimisation of the energy by the digestive system. In addition, we can hypothesize that the more pronounced white color of the fillet is probably in relation with a reduction of fat oxidation.
Interestingly, we noted a reduction of the VSI, potentially linked with a higher amylase activity generating a better utilization of the polysaccharides. This parameter probably induce a lower fat deposition around the viscera and a higher lipid transfer to the fillet. The results also revealed higher contents of important fatty acids such as oleic acid (C18:1 n9c), linoleic acid (C18:2 n6c) and α–linolenic acid (C18:3 n3) in fish fed with MFAA.
The strong effects of MFAA on digestive enzymatic parameters with positive impact on body condition indices and fillet quality open new development possibilities to improve fish feed utilization and farming performances.
This new field of application confirms their interest as a sustainable protein source converted into an efficient functional ingredient for fish nutrition.
Bibliography
[1] Le Reste Guillaume, Kersanté Pierrick, Duperray Joël. 2019. Free Amino-Acids Mix made of Poultry Keratin as a new Functional Ingredient for White Shrimp (Litopeaneus vannamei) feed. Universal Journal of Agricultural Research 7(6): 203-209. https://www.hrpub.org
[2] Kersanté, P., Le reste, G., Diringer, B., Quimi, J., Sergheraert, R., Duperray, J., 2021. Free amino acids mix made of poultry keratin improves survival of whiteleg shrimp post larvae (Litopenaeus vannamei) challenged with acute hepatopancreatic necrosis disease and white spot syndrome virus. Aquaculture International. 29, 879-890. https://doi.org/10.1007/s10499_021-00665-x.
[3] Eakapol Wangkahart, Pierrick Kersanté, Po-Tsang Lee, Onanong Sanbut, Supap Nontasan, Anut Chantiratikul. Effect of Kera-Stim®50, a feed additive containing free amino-acid mix on growth, antioxidant and immune responses, digestive enzymes, and fatty acid composition in Nile tilapia (Oreochromis niloticus). Aquaculture 551 (2022) 737874. https://doi.org/10.1016/j.aquaculture.2021.737874