| The essence of light is an electromagnetic wave,which has an important impact on fishes that rely on vision for feeding at all stages from embryonic development to sexual maturity.Ambient light conditions consisting of photoperiod,spectrum and light intensity have an important impact on the cultivation effect of largemouth bass(Micropterus salmoides)seedlings in the industrial recirculating systems.At present,there are few reports on the effects of different photoperiod and spectral conditions on largemouth bass larvae.In this paper,the effects of different photoperiods and spectrums on the seedlings cultivation effect of largemouth bass in industrial recirculating systems were discussed from the aspects of growth performance,individual differences within groups,antioxidant capacity,and stress level,in order to provide a theoretical basis for the optimization of light conditions in seedlings cultivation of largemouth bass in industrial recirculating systems.1.The automatic feeding equipment of ArtemiaIn this study,according to the requirements of industrial automation control,an automatic feeding equipment of Artemia was formed,which has the functions of storage,aeration and feeding of Artemia,it can realize automatic feeding of Artemia stably for a long time in the breeding process.In the stability test of the equipment,it was found that the three forms of fluid selected as clear water,Artemia,Artemia+feed mixture did not have significant influence on its working stability,but the form of the fluid and the discharge speed have a certain correlation,the specific performance is that the fluid density is negatively correlated with the discharge speed.The 4 bait outlets integrated in the equipment can better complete the automatic feeding of Artemia in the cultivation of Largemouth bass seedlings in industrial recirculating systems.In the 28-day feeding experiment,there was no significant difference in the final body length(FBL),survival rate(SR)and specific growth rate(SGR)between the automatic feeding group and the manual feeding group,indicating that the equipment can better replace the manual feeding of Artemia,and lay a foundation for the success of subsequent experiments.2.Effects of different photoperiods on the cultivation of largemouth bass seedlings in industrial recirculating aquaculture systemsIn this study,the automatic feeding of Artemia and the control of different photoperiods were completed based on the automatic feeding equipment of Artemia.In the experiment,the photoperiod was divided into 8 periods according to the feeding times,and the photoperiod environment of larvae was adjusted by controlling the light and dark time within 3h interval.The experimental settings were 6L:18D,12L:12D,18L:6D,24L:0D 4 experimental groups(L:Light,D:Dark;numbers represent duration,unit:h),the light intensity is 6001x and the lighting time of the four groups within 180min is 45min,90min,135min,180min for 28d breeding experiments.The results showed that the 24L:0D group had the largest final body length and body weight,and the 6L:18D group was the smallest.With the extension of the lighting time from 6h to 24h,SGR,WGR,and individual differences within the group showed a gradually increasing trend.Different photoperiod treatments had no significant effect on the SR of larvae.The total antioxidant capacity(TAOC)of the 6L:18D and 24L:0D groups was significantly higher than that of the other two groups(P<0.05).The lysozyme(LZM)activity of larvae under different photoperiods was not significantly affected,but the 18L:6D group showed a higher trend.The activities of malondialdehyde(MDA)and alkaline phosphatase(AKP)showed an opposite trend,and the activity levels were the highest in 6L:18D,24L:0D group and 12L:12D,18L:6D group respectively,and the activity in 18L:6D group was significantly higher than other experimental groups(P<0.05).The relative mRNA expression levels of growth hormone(gh),insulin-like growth factor 1(igf-1),and thyrotropin(tsh)were consistent with the phenotype.Melatonin receptor(mt1,mt2,mt3),heat shock protein 70(hsp70),corticotropin-releasing factor(crf),the relative mRNA expression level of caspase 3 in 6L:18D and 24L:0D groups significantly higher than that of the experimental groups with 12h and 18h of illumination times(P<0.05),and the 18L:6D group showed a lower trend.The study concluded that the cyclic light strategy of extending the light time to 135min after feeding was beneficial to the cultivation of largemouth bass seedlings.3.Effects of different spectrums on the cultivation of largemouth bass seedlings in industrial recirculating aquaculture systemsIn this study,the automatic feeding of Artemia and the control of different spectrum LED lights were completed based on the automatic feeding equipment of Artemia and the optimal photoperiod.Using the illumination strategy of 135min within 180min,the light intensity is 600lx,setup 4 experimental groups:full spectrum group(300-780nm),red light group(660nm),green light group(520nm),blue light group(460nm),and carried out 28d breeding experiments.The results showed that,compared with the experimental groups of other spectral treatments,the red light group had the smallest final body length and body weight,and the individual differences between the red light group and the blue light group were small,but the growth performance was poor.The SGR and WGR of the red light group were significantly lower than other experimental groups(P<0.05).The SR of larvae in the full spectrum group was significantly higher than other experimental groups(P<0.05),and showed better cluster phototaxis behavior.The activities of superoxide dismutase(SOD),catalase(CAT),glutathione(GSH),and MDA content in the red light group were significantly higher than other groups(P<0.05).The activities of LZM and AKP in the red light group were significantly lower than those in other experimental groups(P<0.05),and the full spectrum group and the green light group were higher than blue light group.The relative mRNA expression levels of gh,igf-1,tsh were consistent with the phenotype;the relative mRNA expression levels of mt1,mt2,mt3,hsp70,crf,and caspase3 in red light group and blue light group were significantly higher than full spectrum group and green light group(P<0.05).The study concluded that the full-spectrum light environment is conducive to the cultivation of largemouth bass seedlings.The results of this study show that the cyclic illumination strategy of extending the post-feeding illumination time to 135 min under the condition of full spectrum as an artificial light source is helpful for the seedlings cultivation of largemouth bass in industrial recirculating systems. |
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