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 a study conducted in three different phases to investigate the effects of a mix of 17 amino acids obtained from extensive hydrolysis of poultry keratin, on plasma protein (PP), oxyhemocyanin (OxyHc), minute till surgical anesthesia for low salinity and dissolved oxygen stress test and their PP and OxyHc at surgical anesthesia, growth performance (GP), size variation (SV), feed conversion ratio (FCR), molting frequency (MF), survival rate (SR), ions and chitin in cuticle and cuticular structure of L . vannamei .
To understand the specific consumed period of MFAA supplementary feed with 38.5% protein to sufficiently maintenance for L. vannamei physiology in terms of PP and OxyHc, shrimp were fed three feeds ( control; two concentrations of MFAA as 5g/kg of feed (MFAA 0.5%) and 10g/kg of feed (MFAA 1% ) for 16 days with three replications. The healthy L.vannamei juvenile with 14.12±0.35 g and 11.67±0.22 cm in size were held in 15 ppt medium at 100 ind/m2 using 250L rectangular plastic tanks for 16 days. They were fed 4 times daily with 5% body wet weight . Exp I: Experimental shrimp at Do molt stage w ere collected the hemolymph for examining OxyHc and PP of day 4, 8, 12, 16. Exp II: It was operated as same at Exp I until 16 days of feeding prior to apply stress test with low dissolved oxygen (LO) and freshwater (FW ). Both test checking the minute till surgical anesthesia (MA) the hemolymph of individual anesthetized shrimp for determination of OxyHc and PP was suddenly collected then transferred to 15 ppt aquaria with well oxygenation to recover and record the number of survivors. Exp III: The two feeds as control and MFAA 1% supplementary feed were operated. Specifications of experimental shrimp and tank including culturing methodology were identical to Exp. I with five replications for 60 days t o determined GP, FCR, SR, MF and SV. After termination, shrimp carapace at Do molt stage was individually sampled for examining ions, cuticular thickness (CT) and number of layers (NL) and chitin content using Electron Microscopy and Energy Dispersive System.
The results of Exp I found that shrimp raised with MFAA supplementary feed with both dosages for 16 days showed significant increase of OxyHc and PP. The results of Exp II for low dissolved oxygen stress test showed the significant longest period for shrimp fed with MFAA 1% supplementation (p<0.05) until the beginning time to surgical anesthesia (BTSA) (58.3 min) with the significant lowest concentration of OxyHc (1.93 mg/l) (p <0.05) versus with control (2.61 mg/l). In the same manner, PP values of M FAA 1.0% group (330.8 mg/ml) was significantly (p <0.05) lower than that of control (347.5 mg/ml) . For freshwater stress test, shrimp fed on MFAA 1% feed showed the significant (p<0.05) longest period at BTSA (86.5 min) with the significant lowest (p<0.05) PP values (342.9 mg/ml) while OxyHc values among groups were not significantly different (p>0.05) .
The results of Exp III showed higher significant % of weight gain, average daily gain and specific growth rate gain of MF AA 1% group (p <0.05) than those of control and FCR of MFAA 1% group was significantly lower (p <0.05) than that of control. % SR , MF, % CV of length and weight w ere not significantly (p<0.05 ) different between groups.
Interestingly, t he CT and NL of Do cuticle of M FAA 1% group w as significantly higher than those of control (p<0.05) . The cuticle architecture of M FAA 1% and control are shown in Fig 1. The endocuticle layer structure of MFAA 1% group was magnified.
The percentages of Ca and Mg of Do cuticle of M FAA 1% group w ere significantly higher than those of control (p< 0.05) versus %Na and %Cl of control were significantly higher those of M FAA 1% (p<0.05). The chitin content of MFAA 1% group showed higher rate (p< 0.05) than that of control.(+19.4%).
This study underlined some particularly interesting effects of MFAA when applied on juvenile whiteleg shrimp, Litopenaeus vannamei . Firstly, regarding growth parameters with positive effects on biomass and feed utilization. Interestingly, we underlined strong influence of MFAA on hemolymph composition in term of oxyhemocyanin and plasma protein after the 16 days of feeding supplementation inducing better resistance to low dissolved oxygen and freshwater stress conditions . Monitoring of oxyhemocyanin and plasma protein in hemolymph at surgical anesthesia also disclosed the interest of MFAA as direct source of energy to balance the osmoregulation during freshwater stress and maintain life under shortage of oxygen. After 60 days of feeding period, the cuticule thickness and structure was also magnified in relation with higher examined concentrations of chitin, but also of calcium (Ca) and magnesium (Mg) linked with Ca and Mg carbonate crystals to construct the cuticle and positively influence the molting. These results confirm the interest of MFAA as a sustainable protein source converted into an efficient functional ingredient for shrimp nutrition.
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
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.