Ling Wang

Effects of organic acids and essential oils blend on growth, gut microbiota, immune response and disease resistance of Pacific white shrimp (Litopenaeus vannamei) against Vibrio parahaemolyticus

ABSTRACT An 8‐week feeding trial was undertaken to evaluate supplemental effects of AviPlus® (AP), a blend of organic acids [citric acid, 25%; sorbic acid, 16.7%] and essential oils [thymol, 1.7%; vanillin, 1.0%], on growth, gut microbiota, innate immunity and disease resistance of Pacific white shrimp (Litopenaeus vannamei) against Vibrio parahaemolyticus. A basal experimental diet was formulated and supplemented with 0, 0.3, 0.6, 0.9 and 1.2 g kg−1 AP to produce five test diets (Con, AP0.3, AP0.6, AP0.9 and AP1.2). Each diet was fed to triplicate groups of shrimp (0.2 ± 0.01 g, mean ± SE) to apparent satiation three times daily. Growth performance and survival rate were not significantly influenced by AP supplementation (P > 0.05). Significantly (P < 0.05) higher serum total protein was found in groups fed ≥ 0.6 g kg−1 AP compared to control. Serum alkaline phosphatase and phenoloxidase activities were significantly increased in AP0.9 and AP1.2 groups. Also, the group received AP0.6 diet showed significantly higher glutathione peroxidase activity than control. Expression of gut pro‐inflammatory genes including TNF‐&agr;, LITAF and RAB6A were down‐regulated by AP administration. Gut microbiota analysis showed the significant enhancement of the operational taxonomic unit (OTU) diversity and richness indices by AP application. AP supplementation led to increased abundance of Firmicutes and a reduction in abundance of Proteobacteria. Also, dietary inclusion of 1.2 g kg−1 AP led to a significant increase in the abundance of Lactobacillus in shrimp gut. The group offered AP0.3 diet showed significantly higher disease resistance than control group. Furthermore, AP application significantly enhanced relative expression of immune related genes including lysozyme, penaeidin and catalase at 48 h post challenge. In conclusion, these findings show that the tested organic acids and essential oils mixture beneficially affects intestinal microflora and improves immune response and disease resistance of L. vannamei. HighlightsA blend of organic acids and essential oils (AP) was tested in shrimp feed.AP application improved serum phenoloxidase and glutathione peroxidase activities.AP enhanced abundance of Lactobacillus and reduced pathogenic bacteria in shrimp gut.Dietary supplementation of 0.3% AP significantly improved shrimp disease resistance.AP application enhanced expression of immune related genes at 48 h post challenge.

Chitooligosaccharide supplementation in low-fish meal diets for Pacific white shrimp ( Litopenaeus vannamei ): Effects on growth, innate immunity, gut histology, and immune-related genes expression

&NA; This study evaluated the effects of supplementing chitooligosaccharide (COS) in low fish meal (FM) diets on growth, immune response, intestine and hepatopancrease histology, and expression of inflammatory and immune‐related genes in Pacific white shrimp (Litopenaeus vannamei). A basal diet was formulated using FM and soybean meal (SM) as primary protein sources and considered as a high FM (HFM) diet, then a low FM (LFM) diet was prepared by substituting 50% of FM with SM and supplemented with 0, 0.3, 0.6, 0.9, 1.2 or 1.5 g COS kg−1 diet (LFM, COS3, COS6, COS9, COS12 and COS15 diets). Each diet was fed to quadruplicate groups of shrimp (0.9 g) to apparent satiation three times daily for eight weeks. At the end of the experiment no significant changes in growth and survival rate were observed among treatments (P > 0.05). FM replacement led to significant (P < 0.05) reduction of serum lysozyme activity and significant improvements were obtained by adding 0.3 or 0.6 g kg−1 COS to the LFM diet. A significant decrease in nitric oxide synthase activity was found in LFM group and no beneficial effects could be achieved by COS application. LFM group showed higher hepatopancrease superoxide dismutase and glutathione peroxidase activities than HFM group and further enhancements were obtained by COS application. Hepatopancrease total antioxidant capacity and alkaline phosphatase activity decreased in LFM group and COS supplementation improved their values. Expression of lysozyme, crustin, Pen3 and proPo genes were significantly up‐regulated in hepatopancrease of groups received 0.3–0.9 g COS kg−1 diet. FM substitution enhanced the expression of HSP70 and inflammatory genes such as AIF and TNF in hepatopancrease and intestine, and COS administration at a moderate level down‐regulated their expression level. Remarkable enhancement in intestinal fold height was obtained by inclusion of 0.3 or 0.6 g COS kg−1 diet compared to the group received LFM diet. Shrimps fed HFM and COS containing diets exhibited higher number of E‐cells within their hepatopancrease tubules than the LFM group. The findings in this study clearly demonstrated that COS could enhance non‐specific immune response and antioxidant activity, and ameliorate the negative impacts of high SM diets on gut and hepatopancrease health in pacific white shrimp. The optimum inclusion level of COS seems to be 0.3–0.6 g kg−1 of diet. HighlightsChitooligosaccharide (COS) inclusion was evaluated in low‐fish meal diets for shrimp.Non‐specific immune response of shrimp was augmented by COS application.COS supplementation enhanced the antioxidant enzymes activity in hepatopancrease.Expression of immune related genes was up‐regulated by COS addition.COS beneficially affected the gut and hepatopancrease health.

De novo assembly and characterization of seabass Lateolabrax japonicus transcriptome and expression of hepatic genes following different dietary phosphorus/calcium levels

Fish farming seriously influences the aquatic environment because most dietary phosphorus (P) is excreted in the effluent. To increase the P utilization in fish, molecular techniques should be explored given the remarkable development of these techniques. Thus, to identify the candidate genes related to P utilization and molecular alterations following administration of a P-deficient diet in seabass Lateolabrax japonicus, we assessed the de novo pituitary, gill, intestine, liver, kidney, scales and vertebra transcriptomes, and we compared the expression of hepatic genes with three diets varying in P and Ca levels: diet I (0.4% P, 0.3% Ca), diet II (0.8% P, 0.3% Ca), and diet III (0.8% P, 3% Ca). In total, we identified 99,392 unigenes, and 37,086 (37.31%) unigenes were annotated. The results showed that 48 unigenes were significantly (P<0.05) up-regulated, while 55 genes were significantly down-regulated in the liver of group I compared with group II. Offering the P-sufficient and high Ca diet, diet III significantly up-regulated 24 unigenes and down-regulated 46 genes in the liver. There were significant differences in the regulation of 8 unigenes (3 up-regulated and 5 down-regulated) between groups II and III. Gene ontology (GO) functional enrichment and KEGG pathway analysis of differently expressed genes were performed for each pair of groups. The GO analysis showed that a large number of biological processes were significantly altered between P-deficient and P-sufficient treatments (I vs II and I vs III). Comparing group I and group II, seven KEGG terms were enriched significantly: glycine, serine and threonine metabolism, one carbon pool by folate, arginine and proline metabolism, the biosynthesis of unsaturated fatty acids, fatty acid elongation, drug metabolism-cytochrome P450, and fatty acid metabolism. There was no significantly enriched KEGG pathway between groups II and III. In conclusion, our study revealed that a P-deficient diet could increase catabolism and decrease anabolism of protein, as highlighted by low protein efficiency in fish fed the P-deficient diet. Furthermore, P-deficiency could motivate the biosynthesis of fatty acids. However, the dietary Ca level had no significant effect on the growth and expression of hepatic genes in L. japonicus.

Effects of acute salinity stress on the serum osmolality,serum ion concentrations,and ATPase activity in gill filaments of Japanese seabass(Lateolabrax japonicus)fed with diets containing different magnesium levels

An acute salinity stress trial was conducted to estimate the effect of dietary magnesium level on serum osmolality,serum ions and ATP enzyme in gill filaments of Japanese seabass Lateolabrax japonicus.Four semi-purified diets were formulated containing 0.413 g(D1),1.042 g(D2),1.577 g(D3),1.991 g(D4)magnesium(as magnesium sulphate)per kilogram diet to feed triplicate groups of fish[initial average weight(30±0.5)g]in freshwater circulation system for 50 days.Then all fish were transferred from freshwater to seawater to collect the serum and gill filaments at 0,1,3,6,12,24 h,respectively.The results showed that dietary magnesium levels significantly affected the levels of serum ions(Na+,Cl-,K+,Mg2+),serum osmolality and the activities of Na+/K+-ATPase(NKA)and Ca2+/Mg2+-ATPase(CMA)in gill filaments at 0 h(P0.05).The serum osmolality,serum Mg2+ and NKA of gill filaments increased with the increase of dietary magnesium levels.The levels of serum Mg2+ and osmolality,NKA and CMA activities in gill filaments of fish fed D4 were significantly higher than those fed the other diets(P0.05),which indicated the Japanese seabass fed D4 was in a state of high intensity osmotic pressure regulating.During the salinity stress periods,the contents of serum Na+ and Cl-increased with the time extension of salinity stress,while the levels of serum osmolality,K+,Ca2+ and Mg2+,NKA and CMA activities fluctuated with stress duration from 0 to 24 h.NKA and CMA activities of fish fed D1 were significantly lower than those of other groups,which indicated it would reduce the sensitivities of NKA and MKA in gill filaments to salinity stimulation for Japanese seabass fed low magnesium level diet for 50 d.The results suggested that in order to reduce energy consumption for higher activities of NKA and CMA in gill,dietary magnesium level should be lower than 1.991 g/kg for Japanese seabass cultured in freshwater,however,high dietary magnesium levels improve NKA and CMA activities in gill,which could be beneficial to quick adaptation high salinity environment for Japanese seabass transferred from low salinity water into high salinity water.