| In the process of selecting and developing freshwater aquaculture species,yellow catfish(Pelteobagrus fulvidraco)has received widespread attention from Chinese farmers and fishery scientist and technologists.Achieving full artificial breeding of yellow catfish would help improve the quantity and quality of fingerlings supplied for large-scale production of this species.Temperature and dissolved oxygen are the most important abiotic factors affecting the efficiency of aquatic organism breeding.In this study,the synergistic effects of temperature and dissolved oxygen on fertilization rate(FR),hatching rate(HR)and larval growth of hybrid yellow catfish were studied by central composite design(CCD)and response surface methodology(RSM).A quadratic regression model for the effects of temperature and dissolved oxygen on FR,HR and deformity rate(DR)were established,and the combination of temperature and dissolved oxygen was optimized.The first and second order effects of temperature and dissolved oxygen on FR and HR were significant under the conditions of this experiment(P<0.05).The first and second order effects of temperature on DR were significant(P<0.05).However,there was no significant effect of dissolved oxygen on DR(P>0.05).Temperature and dissolved oxygen had significant interaction effects on FR(P<0.05).High temperature and high dissolved oxygen environments reduced FR and HR of yellow catfish eggs and increased DR of the newly hatched larvae.The optimal combination of temperature and dissolved oxygen was 26.0℃ and 8.3 mg/L,respectively.Maximum FR and HR coincided with minimal DR,whose predicted values were 87.2%,89.1%and 2.7%respectively,with reliability of 0.979.Maintaining temperature and dissolved oxygen in the best combination will help to improve breeding efficiency and ensure production of the highest quantity and quality of fingerlings.Water temperature and dissolved oxygen are important environmental factors that affect the early development of fish.There is no relevant report on the optimal condition of water temperature and dissolved oxygen for the seedlings stage of yellow catfish.The effects of water temperature(19-33℃)and dissolved oxygen level(2.0-12.0mg/L)on the growth and antioxidant enzyme activities of newly hatched larvae of hybrid yellow catfish were studied based on the design of the central composite experiment.In addition,we use the response surface method to optimize the response values in order to promote growth and reduce oxidative stress.The experimental period is 50d.The results showed that the water temperature had significant effects on the specific growth rate(SGR),liver malondialdehyde content(MDA),superoxide dismutase(SOD)and catalase(CAT)activities of the newly hatched larvae(P<0.05).The dissolved oxygen level had significant effects on the SGR,survival(S),MDA,SOD and CAT(P<0.05).It was found for the first time that the secondary effects of temperature and dissolved oxygen had significant effects on the SGR,SR and SOD and CAT activities(P<0.05).Increasing dissolved oxygen in water at low temperatures can stimulate the SOD and CAT activities and alleviate oxidative damage in fish.The adjusted R2 for the quadratic regression models of SGR,SR,CAT,SOD and MDA are 0.734,0.937,0.916,0.894 and 0.826,respectively.When the combination of water temperature and dissolved oxygen were 26.8℃ and 7.3 mg/L,the simultaneous optimation of SGR,SR and hepatic CAT,SOD and MDA content/activities were 1.23%/d,88.57%,69.30U/(mg prot),3.47U/(mg prot)and 0.23mmol/mg,respectively.The results showed that suitable conditions of water temperature and dissolved oxygen during the culture of yellow catfish seedlings has a great importance for farming purposes. |
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