| Hybrid grouper(♀Epinephelus fuscoguttatus × ♂E.lanceolatus)may benefit from the use of feed additives such as L-carnitine(LC)to boost immune systems and tolerance to environmental perturbations.Fishmeal(FM)was replaced with corn gluten meal(CGM)/ wheat gluten meal(WGM)and supplemented with LC in an 8-week experiment.The focus of the first research was to assess if replacing FM with CGM supplemented with LC(LC)LC0,LC0.2,LC0.4,LC0.6,LC1.2,LC1.4,LC1.6,with LC levels of 0 for the control group,200,400,600,1200,1400,and 1600mg/kg,respectively,may be a viable option.It‘s impact on juvenile hybrid grouper growth,immunity,gene expression,and disease resistance.Each group in the experiment had three replicates(initial weight = 12.70?±?0.9?g)and were fed their respective diets for eight weeks.When LC0.2 was compared to LC0,it significantly improved growth(P?<?0.05).The treatment groups had no differences in crude protein,moisture,or ash content.Serum acid phosphatase(ACP),alkaline phosphatase(AKP),total antioxidant capacity(TAOC),and glutathione peroxidase(GSHPx)all increased.Fish fed LC0.2 had more steatosis in their hepatocytes in the liver than fish fed LC0;however,the differences were not significant in LC0(P ? 0.05).In the LC0.6,LC1.2,and LC1.4 groups,FAS m RNA levels were significantly downregulated.The expression of PPARA and PPARR was higher in the LC0.2 and LC0.4 groups but not significantly different(P ?0.05)from the LC0.Replacing FM with CGM supplemented with LC0.2(200mg/kg)may meet fish’s nutritional needs.For the second study,LC supplementation in CGM diets positively affected juvenile hybrid grouper growth,immunity,lipid metabolism,and metabolomics.These groups were named control group LC0(FM diets without LC),LC0.2,LC0.4,LC0.6,LC1.2,LC1.4,and LC1.6 respectively with fish average initial weight 13.07±0.09 g.Fish fed LC0.2 diets had higher weight gain(WG)and condition factor(CF)than the control group after a feeding trial for 56 days.However,they were not substantially different from the control group(P < 0.05).Fish fed LC0.2 had the highest values of 368.09% and 1.69(g/cm3)2 for WG,and CF,respectively.With rising dietary LC levels,antioxidant parameters such as GSHPx in the liver substantially increased and then reduced(P <0.05).Superoxide dismutase(SOD),T-AOC,however,was unaffected(P < 0.05).Fish fed the LC0.2 diet had significantly greater PPARα m RNA expression compared to fish fed the basal diet(LC0)in terms of gene expression related to lipid metabolism.Bile secretion,ABC transporters,and glycerophospholipid have been identified as the differential metabolites in the distal gut of fish,with an upregulation occurring after feeding with experimental diets.LC level of 200 mg/kg in CGM diets increases fish growth and immunity and regulates hepatic metabolism.For the third study,Hybrid groupers exposed to heat shock stress were fed diets containing LC at 0,400,600,1200,1400,and 1600 mg/kg,resulting in a low survival rate.A large number of survivors were observed in the treatment group with 400 mg/kg LC supplementation(LC 400),obtaining the highest survival rate.Heat stress decreased(P < 0.05)the activities of alkaline phosphatase and acid phosphatase in the control group but was increased in fish fed the LC 400 diet.In the LC 400 treatment,malondialdehyde content decreased considerably(P < 0.05)compared to LC0.Hybrid grouper exposed to a high temperature of 36 °C for 1 hour without LC(LC0,control group)supplementation showed the most increased Aspartate Aminotransferase(AST)activity(2.04 U L-1).Additionally,the LC 400 group reached the maximal value for the expressions of genes in the PPARs(peroxisome proliferator-activated receptors)signaling pathway,which showed a tendency of downregulation and,subsequently,up-regulation.The gene expression of FAS(fatty acid synthase)was discovered upstream and downstream(P < 0.05).The lowest m RNA level was found in the lowest LC supplementation treatment(200 mg/kg).A CPT-1(carnitine palmitoyltransferase)that controls fatty acid oxidation showed upstream and downstream activity in response to increasing doses of L-carnitine supplementation.L-carnitine400 mg/kg reduces heat stress-related mortality and oxidative damage by enhancing grouper’s survival and enzymes.The fourth research examined the effects of substituting FM with WGM(WGM0,WGM1,WGM2,WGM3,WGM4,and WGM5),with WGM in the diet following W0(0%),W1(10.21%),W2(12.42%),W3(14.65%),W4(16.87%),and W5(19.1%)on growth,economic analysis,biochemical,and antioxidant activities,intestinal histology,gut microbiota,and disease resistance in juvenile hybrid grouper.The initial mean weight was 11.00?±?0.00 g.WGM2 had a significantly higher weight gain rate(498.82±22.50%)than the control group(345.57±24.93%)(P?<?0.05).The survival rates among the treatment groups were not significantly different from those of the control group.Still,they were much lower in the control group(97.78%).WGM1 and WGM2 had a lower feed conversion ratio(FCR)than the control group(WGM0).There were no significant differences among the treatment groups.Compared to the control group,WGM3 and WGM4 had higher levels of Acid phosphatase,Lysozyme,and Glutathione Peroxidase in fish than in the control group.Cholesterol and glucose were not significantly affected after replacing FM with WGM in juvenile hybrid grouper diets.Aspartate aminotransferase activity in fish-fed WGM2 was significantly lower than in the control group(P < 0.05).Malondialdehyde in the fish liver was significantly reduced in fish fed WGM diets.The histopathological analyses in fish gut displayed that villus length and villus width depth were statistically different among the treatment groups(P?< 0.05)and increased in the WGM2 than the control group(WGM0).The 16 S r RNA gene sequencing performed on the gut content samples produced 134,027 high-quality reads.Relative abundance for Bacillus and Photobacterium was more abundant in fish fed WGM2 and WGM3 than WGM0 at the genus level.Replacing FM with WGM at 12.42% may meet all dietary nutritional requirements for fish.Lastly,fish were fed with various LC levels of 0 for the control group,200,400,600,1200,1400,and 1600 mg/kg,at(LC)LC0,LC0.2,LC0.4,LC0.6,LC1.2,LC1.4,LC1.6,respectively with(average initial weight 11.04?±?0.00?g).Supplementation of LC in fish diets significantly enhanced growth including weight gain,SGR,and FCR in fish fed LC0.6.Improved body composition,biochemistry,gut histology,gut microbiota,and disease resistance in juvenile hybrid grouper were observed.The dietary LC significantly reduced the lipid deposition in fish liver and muscle,MDA,CHO,AST,and ALT in fish fed LC4 and LC6 than the control group.Economic models indicate that the calculated diet cost was lower for the LC1.2(7.29￥/kg)than the control group.The histopathological analyses in fish gut displayed that villus length(VL)and VWD were not statistically different among the treatment groups(P > 0.05)but increased in the LC4 and LC1.4 than the LC0.The 16 S r RNA gene sequencing performed on the gut content samples produced 136,973.00 high-quality reads.Proteobacteria,Actinobacteria,Photobacterium,and Firmicutes dominated the fish gut among all the treatment groups.Photobacterium was abundant in fish fed LC diets compared to the control group at the genus level.Fish fed the control diet had higher cumulative mortality than those provided the LC6 and LC1.2 diets after the bacteria challenge test within 14 days(P < 0.05).Replacing fishmeal with plant protein sources and supplementing optimum LC improves growth,economic analysis,immune,microbiota,metabolomics,disease resistance and stress tolerance. |
