Growth Patterns and Growth-Axis Gene Expressions in Sexual Dimorphism of Silurus asotus Linnaeus, 1758

Abstract

Aquaculture has tremendous economic significance in distinguishing males and females in the juvenile Silurus asotus (Linnaeus, 1758) to obtain a female population with tremendous growth potential. To investigate the potential biological markers between young males and females S. asotus, we analyzed the characteristics of sexual dimorphism by measuring the 14 length traits and 9 weight indicators in an artificial insemination population at 3, 5, and 7 months. In addition, quantitative real-time PCR (qRT-PCR) was performed to determine the sexually dimorphic expression of the growth hormone-1 gene (GH-1), growth hormone receptor gene (GHR), and insulin-like growth factor gene (IGF-1) in the hypothalamus, pituitary, gonad, and liver, at 3, 5, and 7 months. The results showed that in morphology, except for eye diameter and the distance between the pelvic and anal fins in 3-month fish, all other morphological indicators were significantly ( $P<0.05$ ) or very significantly ( $P<0.01$ ) different between juvenile males and females. The visceral weight, eviscerated weight, and intestine weight in females were significantly ( $P<0.05$ ) or very significantly ( $P<0.01$ ) higher than in males at 5 and 7 months. Joint static allometric analyses on 14 length indicators relative to weight showed different sex growth patterns in 3-month, 5-month, and 7-month fish. In gene expression patterns, GH-1, IGF-1, and GHR were highly expressed in the pituitary, with higher levels in females ( $P<0.05$ or $P<0.01$ ). In contrast, the three genes were all more highly expressed in the testis than in the ovary ( $P<0.01$ ), indicating their essential roles in testis development. Our results demonstrate that S. asotus has female-biased sexual dimorphism. The length traits related to head shapes could be the potential phenotype marker to distinguish females and males in 7-month juveniles.