Studies On Nutritional Physiology Of Amino Acid And Fatty Acid For Large Yellow Croaker (pseudosciaena Crocea) Larvae

A series of 30-day feeding experiment was conducted to study the nutritional physiology of amino acid and fatty acid for large yellow croaker larvae (13 days after hatch, DAH). Blue plastic tanks (80×60×60 cm, 288L) were placed in an indoor concrete pond (800×400×160 cm) to install experimental system. Each tank was stocked initially with 3000 individuals, and the larvae were fed to satiation each time. During the rearing period, water temperature was 23±1°C; pH was 8.0±0.2; salinity was 23±2‰; dissolved oxygen was more than 6 mg L^-1; and 150-300 % of the water volume was renewed daily. The experiments content and results are as follows:1. A 30-day feeding experiment was conducted to estimate the optimal lysine requirement of large yellow croaker larvae (2.75±0.11mg, initial weight). Six isonitrogenous and isoenergetic micro-diets (MDs) containing graded levels of L-lysine·HCl ranging from 2.48 to 4.10% diet in placement of glycine and glutamic acid were formulated. Mixture of crystalline amino acids (MAA) was supplemented to simulate the amino acid (AA) profiles of whole body of this larva except for lysine. The MAA and supplemented lysine for each diet were coated with tripalmitin. Triplicate groups of 3000 fish were fed to apparent satiation by hand eight times per day. The results showed that specific growth rate (SGR) and survival were first increased (from 2.48 to 3.35% lysine) and then decreased (from 3.72 to 4.10% lysine). The results of SGR and survival were both the highest in 3.35% lysine treatment. The result of crude protein content in larvae body was similar to SGR, with a highest value in 3.35% lysine treatment. Crude lipid content had a contrary tendency with crude protein. There were no significant differences in larvae body moisture content (P>0.05). The results of anlysis of enzyme indicated that pancreatic secretion capacity and development of intestinal epithelial cell were enhanced by appropriate lysine supplementation. The optimal dietary lysine requirements estimated by second-order polynomial model based on SGR and survival were 3.32% (6.45% dietary protein) and 3.30% (6.41% dietary protein) dry diet, respectively. The estimated requirements for the other essential AAs were calculated by A/E ratios of whole body AA profile of this larva based on lysine requirement.2. This experiment was conducted to study the effects of free amino acid (FAA) on the growth, survival and metabolism of amino acid in large yellow croaker larvae (2.75±0.11mg, initial weight), and to compare the effects of coated and non coated EAA. Crystalline amino acids mixture (simulate the amino acid pattern of large yellow croaker larvae body and coated with tripalmitin) were used to substitute 0%, 25%, 50%, 75%, 100% of fish meal (MD; FM, 25%CAA, 50%CAA, 75%CAA and 100%CAA), with a control treatment of non coated EAA at 25% level (N-25%CAA). All the MDs were isonitrogenous and isoenergetic. SGR and survival of larvae first significantly increased (from 0% to 25%, P<0.05) then decreased (from 25% to 100%, P<0.05). SGR and survival of larvae in N-25%CAA group had no significant differences with that of FM and 25%CAA treatments (P>0.05), and the order was 25%CAA>N-25%CAA>FM. The crude protein content was the highest in larvae body fed the diet with 25%CAA, which was significantly higher than that in 50%CAA, 75%CAA and 100%CAA group. There were no significant differences on crude lipid content in larvae body among 50%CAA, 75%CAA and 100%CAA treatments, but any of them was significantly higher than that of FM and 25%CAA group (P<0.05). The results of specific activities of digestive enzymes indicated that 25% EAA level enhanced the pancreatic secretion capacity and development of intestinal epithelial cell. AST/ALT in 25%CAA group was significantly higher than that of other substituted levels (P<0.05), and there was no significant difference between 25%CAA and N-25%CAA group (P>0.05). In conclusion, it is feasible to add tripalmitin coated crystalline amino acids (CAAs) in the MD, and large yellow croaker larvae could effectively utilized this form of CAA. The substitution level of FM by CAA should be less than 25% in MD of large yellow croaker larvae, and the optimal substitution level needs further study.3. This experiment was conducted to study the effects of free amino acid (FAA), peptide and protein on the growth, specific activity of enzymes and amino acid metabolism in large yellow croaker larvae (2.75±0.11mg, initial weight). The intact protein-based diet was used as the control (FM), and crystalline amino acids mixture (CAA), hydrolyzed fish meal (HFM) and the mixture of CAA and HFM (CAA&HFM) were used to substitute 25% fish meal protein to formulate other 3 experimental diets, respectively. SGR, survival and crude protein of larvae in FM group were significantly lower than those in other treatments (P<0.05). The crude lipid content of larvae in FM and HFM groups were significantly lower than that in CAA group (P<0.05), and there were no significant differences among FM, HFM and CAA&HFM treatments (P>0.05). The specific activities of leucine-aminopeptidase (LA) and alkaline-phosphatase (AP) in FM group were significant lower than those in others (P<0.05). AST/ALT in FM group was significantly lower than that in CAA group (P<0.05), and there were no significant differences among FM, HFM and CAA&HFM treatments (P>0.05). In this experiment, the results indicated that the supplementation of CAA or/and HFM is beneficial for the growth and survival of large yellow croaker larvae, but the appropriate supplemented level need further study.4. A 30-day feeding experiment was conducted to estimate the optimal dietary arachidonic acid (ARA) requirement of large yellow croaker larvae (4.08±0.10mg, initial weight). Six graded levels (0.00%, 0.15%, 0.30%, 0.60%, 1.20% and 2.40%) of ARA were supplemented to formulate six isonitrogenous and isoenergetic artificial MDs. The results showed that the specific growth rate and survival rate significantly increased with increasing dietary ARA from 0.00% to 0.60%, and significantly decreased with increasing dietary ARA from 0.60% to 2.40% (P<0.05). The result of stress resistance was similar to SGR and survival. Though there were no significant differences in body protein, lipid and moisture content among dietary treatments, the fatty acid profiles of the fish larvae were positively correlated with the diets. A significant positive correlation was found between ARA in the diet and the ARA in the larvae (y = 5.1641x + 2.1348, R² = 0.973, P<0.001). However, the EPA content in larvae was negatively correlated with dietary ARA (y = -0.7298x + 5.2963, R² = 0.9714,P<0.001). Based on the survival and SGR, ARA optimal requirement of large yellow croaker larvae were estimated to be 0.87% and 0.93%, respectively.5. This experiment was conducted to study the effects of lipid sources on growth, survival, body composition and specific activities of digestive enzymes of large yellow croaker larvae (4.08±0.1mg, initial weight). Four isonitrogenous and isoenergetic MDs containing different lipid sources (fish oil, FO; linseed oil, LO; soybean oil, SO; oil mixture, fish oil: linseed oil: soybean oil= 1:1:1, MO) were formulated. Larvae fed the diets with FO and MO had better SGR, survival compared with soybean oil (P<0.05). Crude protein of larvae in FO treatment was significantly higher than that in SO group (P<0.05). Crude lipid of larvae in SO treatment was significantly higher than that in other groups (P<0.05). Correlation analysis showed that the larvae body fatty acid composition significantly reflects the fatty acid composition of diet, such as C18:2n-6, C18:3n-3, EPA, DHA,∑n-3PUFA and∑n-6PUFA (R² was 0.986, 0.9911, 0.8877, 0.9878, 0.7723 and 0.9894, respectively.) The results of specific activities of digestive enzymes indicated that LO and SO impaired the pancreatic secretion capacity and development of intestinal epithelial cell. Based on the results of SGR and survival, LO is better than SO for this larvae, MO can replace 2/3 FO, and the optimal substituted level need further study.