| In industrial fish farming,water flow velocity was first introduced to promote pollution collection and to reduce the cleaning pressure of farming systems.In recent years,more and more research has shown that water flow velocity is also an important environmental factor affecting fish growth,and that appropriate flow velocity can improve fish growth.However,most of the studies on the effects of factory farming environment on fish at home and abroad have focused on light,temperature,density,dissolved oxygen concentration,etc.There are relatively few studies on the effects of flow velocity on fish behavior and metabolism in industrial fish farming,which limited support to farming production.In order to investigate the appropriate flow velocity conditions for the growth and welfare of juvenile black rockfish(Sebastes schlegelii)under factory farming conditions,we selected juvenile fish with initial body length of(9.57 ± 0.09)cm,setting up control group and three flow velocity treatment groups in the modified adjustable flow rate culture bucket.The average water flows velocity of these treatments was maintained at 0,0.5,1.5,and 2.5 BL/s,expressed as C,L,M,and H,respectively.The experiment lasted for 43 days and eight behavior indicators were analyzed.Three types of behavioral states are included:movement parameters(average velocity and maximum acceleration),preferred areas(accumulated residence time in analysis area)and activity status(maximum zone alternation times,activity and physical contact).Metabolomic analysis is based on the liquid chromatography and mass spectrometry(LC-MS).The metabolic features juvenile black rockfish under different flow conditions are compared respectively.The key metabolites during the metabolic regulation of the several ingredients are dug out,while the key metabolites as well as metabolic pathways modulated by these compounds are elucidated.The results showed the following:(1)There was no significant difference in growth performance between C and H treatment groups(P>0.05);The final body lengths in M and L were significantly higher than in the treatments C and H(P<0.05);The final weight,specific growth rate and weight gain rate of M were significantly higher than those in C and H(P<0.05),but no significant difference between M and L treatment groups(P>0.05);The feed conversion rate of L treatment was significantly lower than that in H treatment(P<0.05),and there was no significant difference between C and M treatment groups(P>0.05).(2)After 30 days of experiment,the maximum accelerations of M and H were significantly higher than in the C and L treatment groups(P<0.05);The accumulated residence time of the outer-circle area was significantly lower in treatments M and H compared with the C and L treatment groups(P<0.05);The accumulated residence time in the middle-circle area of M and L were significantly higher than in the C and H treatment groups(P<0.05);The accumulated residence time of inner-circle area in H treatment was significantly higher than that in the other treatment groups(P<0.05);The maximum zone alternation times of M treatment was significantly higher than the other three treatments(P<0.05);The activity was significantly higher in the M and C treatment groups were compared with the L and H treatment groups(P<0.05);The physical contact of M and L were significantly higher than C and H(P<0.05);After 36 days of experiment,the average velocity of M treatment was significantly higher than the other treatment groups(P<0.05).(3)The important differential metabolites in the muscle of juvenile black rockfish under different flow velocity were mainly concentrated in lysophosphatidylethanolamine(LPE),glycerophosphate-N-arachidonic acid ethanolamine and lysophosphatidylcholine(LPC),etc.The results of the pathway enrichment analysis showed significant changes in the metabolic pathways associated with growth and development,mainly in the Metabolic pathways,purine metabolism and linoleic acid metabolism.On the one hand,moderate water flow velocity promotes the swimming of the black rockfish and reduces the frequent movement and competitive behavior of the fish,on the other hand,flow velocity stimulation improves its feeding desire and disease resistance,which ultimately improves the growth performance of the black rockfish.The optimal flow velocity occurred at 1.5 BL/s under the present experimental conditions.Flow velocity significantly influenced the behavioral characteristics of juvenile black rockfish.Behavioral characteristics,such as regional preference and activity status,could be used to assess the respond of juvenile black rockfish to various water flow velocities.In addition,flow velocity promoted significant changes in metabolites related to growth,such as lysophosphatidylethanolamine(LPE),glycerophosphate-N-arachidonate ethanolamine and lysophosphatidylcholine(LPC);Metabolites involved in Metabolic pathways,purine metabolism and linoleic acid metabolism play a role in the growth and development of black rockfish. |
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