Sexual dimorphism is common across the animal kingdom. Knowledge of the mechanisms of sexual size dimorphism is limited although it is important in biology and aquaculture. Tilapia is the common name for ~ 100 species of cichlid fish. Some are important aquaculture species and males outgrow females. To gain novel insights into the mechanisms underlying sexual size dimorphism, we analyzed the differences of brain transcriptomes between males and females in Mozambique tilapia and studied the function of the pro-opiomelanocortin (Pomc) gene in tilapia and zebrafish. The transcriptome analysis identified 123, 55, and 2706 sex-biased genes at 5, 30, and 90 dph (days post-hatch), respectively, indicating sexual dimorphism of gene expressions in the brain. The expression of Pomc in the tilapia brain was a female-biased at 30, 90, and 120 dph. An analysis of the DNA sequence located upstream of the tilapia Pomc transcriptional start site identified two estrogenic response elements. In vitro luciferase assay of the two elements revealed that β-estradiol significantly enhanced the expression of luciferase activity, suggesting that the expression of Pomc is mediated by estrogen. We knocked out Pomc in zebrafish using Crispr/Cas-9. The Pomc-knockout zebrafish showed faster growth and higher sensitivity to feeding as compared to the wild-type fish. Taken together, our results indicate that Pomc contributes to sexual size dimorphism and suggest that the high estrogen level in females promotes the expression of Pomc and suppresses feeding in female tilapias, which leads to the slower growth of female tilapias.

性二态性在整个动物界都很常见。尽管在生物学和水产养殖中很重要，但对性别大小二态性机制的了解是有限的。罗非鱼是大约 100 种慈鲷鱼的通用名称。有些是重要的水产养殖品种，雄性超过雌性。为了获得对性别大小二态性机制的新见解，我们分析了莫桑比克罗非鱼雄性和雌性大脑转录组的差异，并研究了促阿黑皮素( Pomc )基因的功能在罗非鱼和斑马鱼中。转录组分析分别在 5、30 和 90 dph（孵化后天数）鉴定了 123、55 和 2706 个性别偏见基因，表明大脑中基因表达的性别二态性。Pomc在罗非鱼脑中的表达在30、90和 120 dph 时偏向女性。对位于罗非鱼Pomc转录起始位点上游的 DNA 序列的分析确定了两个雌激素反应元件。两种元素的体外荧光素酶测定显示β-雌二醇显着增强荧光素酶活性的表达，表明Pomc的表达是由雌激素介​​导的。我们淘汰了POMC使用CRISPR / CAS-9在斑马鱼。该POMC与野生型鱼相比，敲除斑马鱼表现出更快的生长速度和更高的摄食敏感性。总之，我们的结果表明Pomc有助于性别大小二态性，并表明雌性体内的高雌激素水平促进了Pomc的表达并抑制了雌性罗非鱼的摄食，从而导致雌性罗非鱼生长缓慢。