Effects Of High Temperature And Levonorgestrel On Masculinization Of XX Genotypic Yellow Catfish Pelteobagrus Fulvidraco

The industrial development of yellow catfish Tachysurus fulvidraco is limited by the shortage of female broodstocks,while the current methods of producing all-female broodstocks are inefficient and costly.It is urgent to establish an efficient breeding technology system for all-female yellow catfish and the key is fficient production of functional XX pseudo-males.In the present work,taking XX genotypic yellow catfish as the experimental object,we treated sex undifferentiated larvae using high temperature(33.5±0.5℃)and levonorgestrel(LNG).The effects of high temperature and LNG on the masculinization of yellow catfish were analyzed from the perspectives of sex ratio,thermal sensitivity differences,sex differentiation,gonadal development,growth,and mortality.The main research findings are as follows:(1)Under the same high temperature treatment regime(12-35 days post-hatching,DPH),the masculinization rate in four populations was 2.7%,17.6%,22.7%,and 39.1%,respectively,indicating that there was a difference in heat sensitivity of sex reversal among populations.Two different populations underwent three different high-temperature duration treatments,and both showed the highest degree of masculinization(4.4% and 31.3%)in the group of 12-45 DPH of high-temperature treatment.High temperature-induced masculinization of yellow catfish was characterized by delayed gonadal development in XX pseudo-male and high mortality rate in yellow catfish.The above results indicate that in the study of high-temperature induced masculinization of yellow catfish,there are differences in population sensitivity,high mortality rate,and delayed gonadal development in XX pseudo-males fish.(2)In the three LNG treatment groups of 1 μg/L,0.1 μg/L and 0.01 μg/L,the masculinization rates were 4.0 %,25.0 % and 62.5 %,respectively,indicating that LNG immersion treatment can successfully induce masculinization of juvenile yellow catfish,and there is a negative correlation with the concentration.The gonad histological results showed that the gonads of XX pseudo-male in 0.01 μg/L treatment group included complete-testis-type XX pseudo-males(20.8%)and partial-testis-type XX pseudo-male(41.7%).A quantity of sperm and intercommunicating seminiferous tubules could be observed in 122 days post-hatching XX pseudo-male juvenile fish.The number of oocytes at 62 DPH and gonadosomatic index at 122 DPH analysis showed that the degree of inhibition was positively correlated with the processing concentration of LNG.Moreover,all treatments had no significant effect on growth performance and mortality rate compared to the control group by LNG treatments on yellow catfish.Our results indicated that LNGinduced masculinization of yellow catfish,it has had the advantages of high efficiency on masculinization,low dosage,high safety and promoting the testis maturation of the XX pseudo-male.This study shows that LNG,as a progestin,can be used as the drug of choice for high efficiency and high quality production of functional XX pseudo-male.The present work provides new ideas for the optimization of inducing functional XX pseudo-male,and establishes an important foundation for sustainable aquaculture development and highefficient breeding of yellow catfish.The roles of progesterone in fish sex differentiation deserve further investigation.