Insulin-like growth factors (IGFs) are hormones that primarily stimulate and regulate animal physiological processes. In this study, we cloned and identified the open reading frame (ORF) cDNA sequences of IGF family genes: the insulin-like growth factor 1 (IGF1), insulin-like growth factor 2 (IGF2), and insulin-like growth factor 3 (IGF3). We found that IGF1, IGF2, and IGF3 have a total length of 558, 648, and 585 base pairs (bp), which encoded a predicted protein with 185, 215, and 194 amino acids (aa), respectively. Multiple sequences and phylogenetic tree analysis showed that the mature golden pompano IGFs had been conserved and showed high similarities with other teleosts. The tissue distribution experiment showed that IGF1 and IGF2 mRNA levels were highly expressed in the liver of female and male fish. In contrast, IGF3 was highly expressed in the gonads and livers of male and female fish, suggesting a high influence on fish reproduction. The effect of fasting showed that IGF1 and mRNA expression had no significant difference in the liver but significantly decreased after long-term (7 days) fasting in the muscles and started to recover after refeeding. IGF2 mRNA expression showed no significant difference in the liver but had a significant difference in muscles for short-term (2 days) and long-term fasting, which started to recover after refeeding, suggesting muscles are more susceptible to both short-term and long-term fasting. In vitro incubation of 17β-estradiol (E₂) was observed to decrease the IGF1 and IGF3 mRNA expression level in a dose- (0.1, 1, and 10 μM) and time- (3, 6, and 12 h) dependent manner. In addition, E₂ had no effect on IGF2 mRNA expression levels in a time- and dose-dependent manner. The effect of 17α-methyltestosterone (MT) in vitro incubation was observed to significantly increase the IGF3 mRNA expression level in a time- and dose-dependent manner. MT had no effect on IGF2 mRNA but was observed to decrease the IGF1 mRNA expression in the liver. Taken together, these data indicate that E₂ and MT may either increase or decrease IGF expression in fish; this study provides basic knowledge and understanding of the expression and regulation of IGF family genes in relation to the nutritional status, somatic growth, and reproductive endocrinology of golden pompano for aquaculture development.

Aromatase inhibitor letrozole (LZ) and 17α-methyltestosterone (MT) are commonly used for sex control breeding to induce female-to-male sex reversal in aquaculture. However, studies on the molecular regulatory mechanisms of LZ and MT are still limited. Here, a comparative transcriptome analysis was conducted on the hypothalamus, the gonad, and the liver of golden pompano (Trachinotus ovatus) after 30 days of LZ and MT treatment, which demonstrated significant sexual size dimorphism. Following LZ treatment, the transcriptome data identified 156, 890, and 1286 different expression genes (DEGs) in the hypothalamus, the liver, and the gonad, respectively. After MT treatment, the transcriptome data identified 114, 876, and 950 DEGs in the hypothalamus, the liver, and the gonad, respectively. Functional enrichment analysis revealed that DEGs were involved in oocyte meiosis and steroid-hormone synthesis following LZ treatment. Similarly, the analysis indicated that DEGs were associated with cysteine and methionine metabolism and steroid-hormone synthesis after MT treatment. Further analysis showed that LZ treatment can promote the first meiotic division but inhibit the second meiotic division of the oocyte. MT treatment promotes polyamine synthesis to induce oocyte apoptosis, both of which affect the trajectory of ovarian differentiation in golden pompano. However, LZ and MT have converse effects in sex hormone synthesis. LZ inhibits estrogen metabolism but promotes cholesterol synthesis by regulating sqle, cyp3a40, ugt1a1, and ugt2a1, while MT promotes estrogen metabolism but inhibits the conversion of cholesterol to pregnenolone by regulating cyp19a1, cyp1a, and hsd17b7. This study reveals that both LZ and MT may inhibit the ovarian differentiation and induce masculinization through different regulatory mechanisms, which provides a fundamental insight into the sex control breeding in aquaculture.