Effect Of Light Mangement And Feeding Strategy On Food Intake,growth Performance And Innate Immunity Function Of Blunt Snout Bream

Blunt snout bream,Megalobrama amblycephala,is commonly known as wuchang fish.This species is one of the seven conventional freshwater fish specieses which include black garp,grass carp,silver carp,bighead carp,common carp and crucian carp because it takes advantages of unique growth charactertics,excellent flavor and high economic value.In recent years,in order to meet the growing market demand of blunt snout bream by customers,the intensive large-scale pond farming has been expandirtg.This study is aimed to determine the optimum feeding strategy and artificial light condition of blunt snout bream,establishing the scientific feeding technology and appropriate artificial light management.Under the premise of avoiding affecting the healthy growth of blunt snout bream,we plan to maximine the economic benefits of blunt snout bream farming by applying optimum feeding strategy and aquaculture management.This study is mainly composed by the following seven experiments:1 The effect of photoperiod on growth performance,daily varation of plasama melatonin and cortisol,and antioxidative ability of juvenile blunt snout breamJuvenile blunt snout bream Megalobrama amblycephala were reared under three photoperiods,8L:16D,12L:12D and 16L:8D(L:Light,D:Dark).Over the 8-week experiment period,the results showed that growth performance in blunt snout bream was significantly enhanced by long photoperiod.Contrary to feed conversion ratio,final length,final weight,weight gain and feed intake increased significantly as the illumination time increased from 8 hours daily to 16 hours daily.Low size heterogeneity and whole-body lipid content in fish exposed to long photoperiod were observed.Plasma melatonin concentration in blunt snout bream exposed to 12L:12D photoperiod displayed a significant daily variation that fitted a cosinusoid rhythm within a 24-hour period.The lowest values of plasma cortisol in each group were observed at the middle the photophase while the highest values were observed at the transition between the day and night span.The activities of liver catalase and glutathione peroxidase were lowest in fish exposed to 16L:8D photoperiod and significantly lower than that in fish exposed to 8L:16D,however the malonaldehyde activities showed the opposite trend.These results indicate that photoperiod manipulation may not only improve growth performance but also reduce size heterogeneity.The daily variation of plasma melatonin increased in the scotophase and decreased in the photophase.Besides,prolonging periods of day time might cause chronic stress in blunt snout bream since plasma cortisol level was higher in the long photoperiod group,leading to the increasing activities of antioxidant enzymes.2 The effect of light intensity on growth,whole-body composition,skin color and liver function of juvenile blunt snout breamJuvenile blunt snout bream Megalobrama amblycephala were subjected to five levels of light intensities(100,200,400,800 and 1600 lx)for 8 weeks.The result of the present study indicated that light intensity signifaicantly affect the growth performance in blunt snout bream.Contrary to feed conversion ratio,final weight,weight gain,specific growth rate and feed intake significantly increased with light intensity increasing from 100 lx to 400 lx,then decreased with the further increasing light intensity.Light intensity significantly affected whole-body compositon of blunt snout bream.As the light intensity increasing from 100 lx to 800 lx,the lipid content of juvenile blunt snout bream elevated from 7.2%to 7.6%,then decreased to 6.81%at 1600 lx light intensity level.The lightness value of skin kept elevated with the increasing light intensity.Liver aspartic transaminase(AST)and alanine aminotranferase(ALT)level in fish subjected to 400 lx light intensity was significant higher than that in fish subjected to 100 and 1600 lx light intensity.We suggested that the optimum light intensity in juvenile blunt snout bream was around 400 lx.3 Light intensity affects stress,innate immunity and disease resistance of juvenile blunt snout breamLight is necessary for many fish species to develop and grow normally since most fishes are visual feeders.However,too intense light may be stressful or even lethal.Thus,the present study was conducted to whether the different light intensity levels have effect on growth,immune response,antioxidant capability and disease resistance of juvenile blunt snout bream Megalobrama amblycephala.Fish randomly divided into 5 groups were exposed to a range of light intensities(100,200,400,800 and 16001x)in cultures for 8 weeks.After the feeding trial,fish were challenged by Aeromonas hydrophila and cumulative mortality was recorded for the next 96 hours.The results demonstrated that fish subjected to 400 lx showed the greatest weight gain(125.70 ± 5.29%).Plasma levels of glucose and lactate increased with light intensity rising from 100 lx to 1600 lx while the lowest plasma levels of cortisol was observed at 400 lx group.Post.challenged haemato-immunological parameters(including plasma lysozyme and alternative complement activities,as well as plasma initric oxide level and globulin contents)improved with light intensity increasing from 100 lx to 400 lx,and then decreased with further increasing light intensity.However,antioxidant biomarkers such as liver catalase and malondialdehyde showed an opposite trend with immune response with the lowest values observed at 400 lx groups.The application of light intensity at 1600 lx significantly lowered liver glutathione activity to 76.78± 6.91?mol/g.Within a range of light intensity from 100 to 400 lx,no differences were observed in liver total superoxide dismutase and glutathione peroxidase activities while they were significantly higher at 800 and 1600 lx.After challenge,the lowest mortality was observed in fish exposed to 400 lx.It was significantly lower than that of fish exposed to 100 and 1600 lx.The results of the present study indicated that high light intensities(more than 800 lx)not only produced poor growth,but also led to stress response,as might consequently result in the elevated liver oxidation rates and depress immunity of this species.Although no stress response was observed,fish subjected to low light intensities(lower than 400 lx)also showed oxidative stress,immunosuppression and reduced disease resistance.Taken together,the optimal light intensity to enhance growh and boost immunity of this species at juvenile stage is 400 lx.4 The effect of feeding ration growth performance,intestine enzyme.activity and relative gene expression of juvenile blunt snout breamAn 8-week experiment was aimed to investigate the optimum feeding rate of juvenile blunt snout bream Megalobrama amblycephala.More than 800 fish were randomly distributed into 24 cages(35 fish/cage)and fed at 6 feeding ratesdaily which were 2.0%to 7.0%BW/day.The results showed that weight gain rate,specific growth ratio,protein efficiency ratio as well as nitrogen and energy retention increased significantly as feeding rates increased from 2.0%to 5.0%BW/day,but decreased with the further increasing feeding rates while feed conversion ratio kept significantly increasing with the increasing feeding rates.Feeding rates significantly affected lipid contents of whole-body of juvenile blunt snout bream and the highest values was observed in fish fed at 4.0%BW/day.Additionally,activities of intestinal enzymes,including protease,lipase,Na+,K+-ATPase,alkaline phosphatase(AKP)and creatine kinase(CK)was significantly higher in fish fed at 2.0%-4.0%BW/day compared to the fish subjected to other feeding rates.Furthermore,the mRNA levels of growth hormone(GH)and neuropeptide Y in the brain,as well as insulin like growth factors-I(IGF-I)and growth hormone receptor(GHR)in the liver increased significantly as feeding rates increased from 2.0%to 6.0%BW/day,but significantly decreased with further increasing feeding rates;whereas hepatic mRNA expressions of leptin(LEP)and cholecystokinin(CCK)showed an opposite trend.Based on the broken line regression analysis,the optimum feeding rate of Megalobrama amblycephala at juvenile stage was 4.57%BW.5 Feeding rate affects stress,innate immunity and disease resistance of juvenile blunt snout breamThis study is aimed to investigate whether feeding rates affect juvenile blunt snout bream Megalobrama amblycephala on stress response,innate immunity and hypoxia resistance.Fish were fed at 6 feeding rates(2,3,4,5,6 and 7%of body weight/day).After 60-day feeding trial,fish were subjected to hypoxic conditions.The result that reduced hepatic superoxide dismutase(SOD)and catalase(CAT)activities as well as glutathione(GSH)contents in low feed ration was observed.Low feeding ration also adversely affected immune reponses of blunt snout bream.The alternative complement(ACH50),myeloperoxidase(MPO),transferring and plasma protein profiles were relatively low in fish fed at inadequate feeding ration while high mortality induced by hypoxia challenge was observed.High feed ration did not result in the amendment in antioxidant capability,immune functions and survival after hypoxia challenge.Additionally,after hypoxia challenge,plasma glucose,cortisol and transferrin contents as well as lysozyme activities significantlyelevated whereas plasma MPO and ACH50 activities as well as plasma globulin levels showed an opposite trends.A significant interaction between feeding rate and hypoxia chanllenge was observed in tems of plasma cortisol,glucose and globulin levels.All in all,inadequate feeding ration might lead to reduced antioxidant ability,compromised immune responses and decreased hypoxia resistancewhile over feeding did not result in the improvement for fish health.An optimal feeding rate to boost the innate immunity of juvenile blunt snout bream is 4-5%BW.6 The effect of feeding frequency on growth performance,intestine enzyme activity and GH-IGF-1 axis gene expression of juvenile blunt snout breamAn 8-week experiment was conducted to determine the optimal feeding frequency of juvenile blunt snout bream Megalobrama amblycephala.Fish were randomly assigned to one of six feeding frequencies(1,2,3,4,5 and 6 times daily)and hand-fed at 5%of the biomass throughout the feeding trial.The results showed that maximum final weight(29.75±0.73 g)and weight gain(20.86 ± 0.77 g)was observed in fish fed 3 times daily.Whole-body lipid content increased significantly(P<0.05)as feeding frequency increased from 1 to 5 times daily,whereas moisture content showed an opposite trend.The activities of intestinal ?-amylase and Na+,K+-ATPase increased significantly(p<0.05)as feeding frequency increased from 1 to 3 times daily,but decreased with further increasing feeding frequency.In addition,growth hormone(GH)mRNA expression level in brain of fish fed 1 and 2 times daily significantly higher(P<0.05)than fish fed in other groups.Hepatic insulin-like growth factor-I(IGF-I)expression increased significantly(P<0.05)as feeding frequency increased from 1 to 3 times daily,but decreased significantly with further increasing feeding frequency.In conclusion,both low and high feeding frequency could result in growth retardation,poor feed efficiency,decreased intestinal enzyme activities and low hepatic IGF-I expression of juvenile blunt snout bream.The optimal feeding frequency for this species at the juvenile stage is 3-4 times daily.7 Feeding frequency affects stress,innate immunity and disease resistance of juvenile blunt snout breamAn 8-week experiment was conducted to investigate whether feeding frequency affect juvenile blunt snout bream Megalobrama amblycephala on stress,innate immunity and disease resistance.Fish were fed a commcercial diet at six feeding frequencies(1,2,3,4,5 and 6 times/day)with the same ration size for 8 weeks.After 8-week feeding trial,blunt snout bream were challenged by Aeromonas hydrophila.Cumulative mortality was checked and recorded every hour for the next 10 days.Plasma levels of both cortisol and lactate kept increased at high feeding frequencies.Fish fed 3-4 times daily obtained lower liver catalase,glutathione peroxidase activities and malondialdehyde levels compared with fish subjected to other feeding frequencies.Post-challenged haemato-immunological parameters(including blood leucocyte and erythrocyte counts as well as plasma lysozyme,alternative complement,myeloperoxidase,acid phosphatase activities and nitric oxide level improved with feeding frequency increasing from 1 times daily to 4 times daily,and then decreased with further increasing feeding frequecy.After the challenge by Aeromonas hydrophila,the lowest mortality was observed in juvenile blunt snout bream fed 4 times daily group.It was significantly lower than that of fish fed 1-3 times daily,but showed no difference with fish subjected to other feeding frequencies.All in all,no matter low or high feeding frequencies could cause oxidative stress and disheartened immunity of juvenile blunt snout bream,as might consequently lead to reduced disease resistance to Aeromonas hydrophila infection.