Abstract:
The industrial development of yellow catfish (
Tachysurus fulvidraco) is limited by the shortage of female broodstocks. The aquaculture yield of female yellow catfish is significantly reduced due to the successful promotion of all-male and hybrid new varieties. Meanwhile, wild germplasm resources are not possible to be used as broodstock because of the vigorous implementation of resource conservation policy. It is urgently needed to establish a large-scale producing system of the all-female population, and the key is to efficiently induce fertile XX pseudo-males. In this study, different percentages of masculinization 4.0%, 25.0% and 62.5% were induced by different doses of levonorgestrel (LNG) immersion treatments, 1, 0.1 and 0.01 μg/L, respectively, starting from 12 days post-hatching (DPH) to 60 DPH. Complete-testis-type XX pseudo-males were induced in the 1 and 0.1 μg/L groups, while complete-testis-type (20.8%) and partial-testis-type pseudo-males (41.7%) were both found in the 0.01 μg/L group. A quantity of sperm and intercommunicating seminiferous tubules were observed in XX males at 122 DPH individuals, indicating that induced XX pseudo-male fish have the normal reproductive ability. Reduced oocyte numbers at 62 DPH and gonadosomatic index at 122 DPH of un-masculinized XX individuals after LNG immersion indicate negative effects of LNG on ovarian development. Growth and mortality were not significantly affected by LNG treatments. Our results suggested that LNG-induced masculinization in yellow catfish had the advantages of low treatment dosage, high efficiency on masculinization, and promoting the testis development of the XX pseudo-males. The present work provides new ideas for the optimization of inducing functional XX pseudo-males, and establishes an important foundation for sustainable aquaculture development and high-efficient breeding of yellow catfish. The establishment of the all-female production system will strongly increase the efficiency of genetic breeding in yellow catfish. The roles of progesterone in fish sex differentiation deserve further investigation.