Effects of dietary supplementation of Lactobacillus plantarum and Bacillus subtilis on growth performance,survival,immune response,antioxidant capacity and digestive enzyme activity in olive flounder(Paralichthys olivaceus)

In present study,a 10-month feeding trial was carried out to investigate effects of dietary Lactobacillus plantarum and Bacillus subtilis supplementation singly on growth performance,innate immune response,antioxidant capacity and digestive enzyme activity of olive flounder under a commercial production environment.Two experimental groups fed basal diet with supplementation of L.plantarum(5.0×107 CFU/g diet)and B.subtilis(1.0×108 CFU/g diet)respectively,and control group fed with basal diet without probiotics supplement.At harvest,serum immune parameters,liver antioxidant indices and digestive enzyme activities in liver,stomach and intestines were measured.Fish fed with B.subtilis supplemented diet showed the highest growth rate which was significantly higher than L.plantarum supplemented group(P<0.05)which was also significantly higher than control group(P<0.05).Survival rate were significantly elevated by feeding diet with L.plantarum supplementation(P<0.05),while the improvement was not significant for B.subtilis supplemented diet compared to control group.All the studied immune parameters in serum were substantially enhanced in both experimental groups.Similar results were observed for the antioxidant capacity in liver.Besides,the activities of digestive enzymes increased substantially in both experimental groups compared to control group and the detected improvement in dietary B.subtilis supplemented group were all higher than in L.plantarum supplemented group,though not all the improvements were significant.In summary,the separate supplementation of B.subtilis and L.plantarum in diet is more beneficial for growth performance and healthy status respectively.Hence,in olive flounder aquaculture,favorable effects of compounded supplementation of L.plantarum and B.subtilis are expected.

Estimationof genetic parameters for juvenile growth performance traits in oliveflounder(Paralichthys olivaceus)

The aim of this study was to evaluate genetic parameters of growth traits for improving selective breeding in olive flounder(Paralichthys olivaceus).A total of 82 full-sib families from 2 year-classes with complete pedigree information were used to estimate heritabilities and genetic/phenotypic correlations for 4 growth performance traits(body weight BW,total length TL,body height BH and condition factor K)based on uni-trait and multi-trait linear mixed models,respectively.Data were analyzed by the restricted maximum likelihood(REML)method.The heritabilities of BW,TL and BH were 0.81,0.70 and 0.61,which are relatively high,however,heritability for K is low(0.11).For all growth traits,the common full-sib effects(c^(2))were at a low to moderate level(0.14–0.20);the maternal effects(m^(2))of the traits(except K)were also detected(0.15–0.19).The phenotypic and genetic correlations among BW,TL and BH were highly positive(0.70–0.91),however,the correlations between K and the other 3 traits was low or negligible(−0.22–0.26).According to our results,these traits(except K)could be selected and enhanced simultaneously.In addition,direct selection based on TL or BH,which is an easily measurable trait,will be more favorable than selection on BW.Moreover,our results indicated that growth parameters estimated in the juvenile stage could be used as a predictor of growth performance at later growth stages.

Insights into the genetic covariation between harvest survival and growth rate in olive flounder(Paralichthys olivaceus)under commercial production environment

In aquaculture,selective breeding for survival till harvest have become an alternative strategy for improving disease resistance and production.However,knowledge of genetic parameters of harvest survival,e.g.,heritability and genetic correlations between survival and growth rate traits,is still scarce.The aims of this study were to estimate genetic parameters for harvest survival and growth rate traits under commercial farming conditions in olive flounder(Paralichthys olivaceus).Harvest survival was defined as a binary trait;growth traits were measured as average daily gain(ADG),specific growth rate(SGR),daily growth coefficient(DGC)and body weight(BW).Data from a population of 241 full-sib families(involving 39,904 individuals,four generations)were used.Heritabilities of survival were low but significant,which were 0.15±0.04 and 0.22±0.01 on observed and underlying scale,respectively.Heritability estimates for ADG,SGR and DGC were medium to high,which were 0.33±0.06,0.83±0.07,0.58±0.07,respectively.While the heritability of BW is of low magnitude(0.17±0.08).The genetic correlations between harvest survival and three growth rate traits(i.e.,ADG,SGR and DGC)were very strong(ranging from 0.66 to 0.79),which is an exciting result.However,the genetic correlation between harvest survival and BW was much lower(0.17±0.08).These results suggest that selection for harvest survival would consequentially result in concomitant increase of growth rate,and vice versa.Our findings revealed novel insights into the genetic improvement of growth rate and harvest survival through genetic selection in olive flounder.

Estimation of heritabilities of disease resistance to Edwardsiella tarda and genetic correlations between resistance and growth traits in Chinese tongue sole (Cynoglossus semilaevis)

Chinese tongue sole(Cynoglossus semilaevis)is an important marine flatfish which is widely cultured in coastal areas in China.Infectious bacterial diseases such as Edwardsiella tarda imposed serious threats to this species.A potential strategy to prevent this disease is to select resistance strains.The aim of the present work was to estimate the genetic variation of disease resistance to E.tarda and to evaluate the genetic correlations between resistance traits and growth traits.Three types of models were fitted by using different trait definitions(binary,continuous and categorical).After a 9-day challenge test,the overall survival was 75.4%(ranging from 6.4%to 100%in families),and at test day 6,the overall survival was 50.7%.We set test day 6 and 9 as cut-off point times respectively.The heritabilities of survival traits were ranging from 0.10 to 0.36.Considerably higher heritability values were obtained at day 6 than at day 9,regardless of which model or trait definition used(except Trait 2 in LIN).The genetic correlations between disease resistance traits and growth traits(i.e.body weight and total length)were low and not significant from zero(−0.12–0.24).There is a substantial re-ranking of families when defined resistance as categorical and continuous traits compared to binary trait.These results confirm the existence of genetic variation for resistance against E.tarda and weak genetic correlations indicate that joint genetic improvement of E.tarda resistance and growth is scarcely available.

Transcriptome analysis and candidate gene identification reveals insights into the molecular mechanisms of hypermelanosis in Chinese tongue sole(Cynoglossus semilaevis)

Blind-side hypermelanosis has emerged as a major concern in flatfish aquaculture worldwide,including tongue sole(Cynoglossus semilaevis)in China.The causative gene and the molecular basis are still unclear.In this study,comparative transcriptome analyses were performed using different skin tissues of tongue sole:ocular-side normal(pigmented)skin,blind-side normal(non-pigmented)skin and blind-side hypermelanotic(pigmented)skin.Finally,60 key hypermelanosis-related genes were mined,providing potential candidate gene resources involved in blind-side hypermelanosis.These genes were selected based on the log2(FoldChange)and false discovery rate(FDR)values(with corresponding P-Values<0.05),and they were verified in other species to assess if they were directly or indirectly related to melanogenesis.The protein-protein interaction network of these 60 genes and the relationship between tyr and other key hypermelanosis-related genes were illustrated.The qRT-PCR validation of 16 differentially expressed genes(DEGs)showed that the data of qRT-PCR were consistent with those of RNA-seq.Further analyses revealed that the selected DEGs were significantly overrepresented in several pigment metabolic processes and in the melanogenesis pathway.Our results may imply that blind-side hypermelanosis is a pattern of environmental regulation of gene expression and adaptation in flatfish.Membrane transport proteins(such as OCA2 and SLC45A2)may serve as a“switch”for melanogenesis in tongue sole.Overall,this study provided novel insights into the molecular mechanism of hypermelanosis in flatfish species and will facilitate future selective breeding of tongue sole for this market-favoured trait in aquaculture.