Effects Of Different Dietary Amino Acid Patterns And Sources On Growth, Survival, Activities Of Digestive Enzymes And Protein Metabolism Of Large Yellow Croaker (Larimichthys Crocea) Larvae

A series of30-day feeding experiment was conducted to study the nutritional physiologyof amino acid for large yellow croaker (Larimichthys crocea) larvae. Each tank (500L) wasstocked initially with5000individuals, and the larvae were manually fed to satiation with theexperimental diets or live copepods five times daily. During the rearing period, watertemperature ranged from22.8to24.5°C, pH from7.8to8.2and salinity from22to26. About200–300%of the water volume was renewed daily; dissolved oxygen was more than6mg L-1.The experiments content and results are as follows:1. This study was conducted to evaluate the effects of dietary amino acids (AA) patterns ongrowth performance, survival, activities of digestive enzymes and aminotransferases of largeyellow croaker larvae. The control diet was produced using intact protein as the only proteinsource. Four isonitrogenous and isolipidic semi-purified diets were formulated withcrystalline-AA replacing approximately40%fish meal protein-bound nitrogen. The AApatterns of these diets were adjusted according to the overall AA pattern of large yellowcroaker egg protein (FEAA), large yellow croaker larvae whole-body protein (LBAA), largeyellow croaker muscle protein (AMAA) and white fishmeal protein (FMAA), respectively.The test diets or live copepods were fed to triplicate groups of larvae (initial body weight3.15±0.15mg) five times (6:00,8:30,12:30,14:30and17:00) daily for30days. The resultsshowed that specific growth rate (SGR) of fish fed the FMAA diet was significantly higherthan FEAA and LBAA diet (P<0.05). At the end of the growth trial, there was no significantdifference in survival rate among larvae fed FEAA, LBAA, FMAA and the control diet(P>0.05), whereas the highest value was recorded in larvae fed the LBAA diet, followed byFMAA, the control, FEAA and AMAA diet, respectively. Whole-body crude protein contentwas significantly higher in larvae fed the FMAA diet compared to the FEAA and LBAA diet(P<0.05). Larvae fed the live copepods had significantly higher whole-body crude proteinand lipid contents than those in larvae fed artificial microdiets (P<0.05). Whole-bodymoisture content was not significantly affected by dietary treatments (P>0.05). Specificactivities of digestive enzymes and the ratio―pancreatic enzyme in intestinalsegment/pancreatic enzyme in pancreatic segment‖were significantly higher in fish fed the FMAA diet than fish fed LBAA and FEAA diet (P<0.05). Specific activities of alanine andaspartate aminotransferases were significantly higher in fish fed the FMAA diet compared tothe other treatments (P<0.05). Results of this study indicated that white fishmeal proteinamino acid pattern was a more suitable amino acid pattern in diets of large yellow croakerlarvae compared to the amino acid pattern of FEAA, LBAA and AMAA.2. This study was conducted to evaluate the influence of various size fractions of fish proteinhydrolysate (FPH) on the growth performance, survival, digestive enzymes andaminotransferases activities of large yellow croaker larvae. FPH was produced byhydrolyzing fish with two protease and size fractionated by ultra-filtration. A diet containingonly intact protein was used as a control (diet FM). Three semi-purified diets wereformulated to be isonitrogenous and isolipidic and to contain the various size-fractionatedFPH (retentate or permeate after ultra-filtration or the untreated hydrolysate) replacingapproximately40%of fish meal protein-bound nitrogen. The test diets were fed to triplicategroups of larvae (3.15±0.15mg) five times (6:00,8:30,12:30,14:30and17:00) a day for30days. Another group of larvae only fed with live prey (copepods) twice a day. The resultsshowed that specific growth rate (SGR) of fish fed the diet containing permeate afterultra-filtration was significantly higher than fish fed the diet containing retentate fromultra-filtration (P<0.05), but was not significantly different from fish fed the other diets orlive prey (P>0.05). At the end of the growth trial, survival rate of fish fed the diet containingpermeate after ultra-filtration was significantly higher compared to fish fed with the dietcontaining untreated hydrolysate (P<0.05), but was not significantly different from fish fedthe control diet (P>0.05). Both whole-body crude protein and lipid contents were notsignificantly affected in larvae fed artificial microdiets (P>0.05). Whole-body moisturecontent was not significantly affected by dietary treatments (P>0.05). Specific activities ofdigestive enzymes and the ratio―pancreatic enzyme in intestinal segment/pancreatic enzymein pancreatic segment were significantly higher in fish fed the diet containing permeate afterultra-filtration compared to fish fed the diet containing retentate from ultra-filtration oruntreated hydrolysate (P<0.05). Specific activities of alanine and aspartate aminotransferaseswere significantly higher in fish fed the diet containing permeate after ultra-filtration than theother diets (P<0.05). Results of this study indicated that various size-fractionated FPHreplacing approximately40%of fish meal protein significantly affected the survival andsome small molecular weight compounds present in the fish hydrolysate are essential foroptimal growth performance in large yellow croaker larvae.3. Cloning the PepT1cDNA from large yellow croaker and the effects of dietary inclusions of size-fractionated peptides and crystalline amino acids (CAA) on PepT1mRNA relativeexpression in larval intestinal segments were conducted. PepT1cDNA was cloned by3’RACE and5’RACE technology. The full length of the large yellow croaker PepT1cDNAwas2923bp including an open reading frame (ORF) of2181bp which specified a putativeprotein of726amino acids with high sequence similarity with other vertebrate homologues.The PTR2family proton/oligopeptide symporters signature1’ and2’ motif,12potentialmembrane spanning domains with a highly conserved cAMP/cGMP-dependent proteinkinase phosphorylation motif close to the putative spanning domain9, which arecharacteristics of PepT1. Effects of dietary inclusions of size-fractionated peptides and CAAon PepT1mRNA relative expression in larval intestinal segments were analyzed by real-timequantitative PCR. The result showed that PepT1mRNA level was significantly higher inlarvae fed the diet containing permeate after ultra-filtration compared to fish fed with the dietcontaining retentate from ultra-filtration (P<0.05) with replacement40%fish meal protein,but was not significantly different from the other treatments. These data suggest that PepT1may be variably recruited in response to changes in the luminal protein source content. ThePepT1mRNA expression was up-regulated by fish hydrolysate rich in di-and tri-peptides inlarge yellow croaker larvae.