Effect of human chorionic gonadotrophin (HCG) and luteinizing hormone releasing hormone A3 (LHRH-A3) on reproduction and development of brood pouch in Hippocampus erectus

Syngnathid fishes (seahorses and pipefish) are unique in reproduction, with males becoming pregnant and giving birth. The brood pouch provides osmoregulation, gas exchange, waste transport, immunoprotection and nutrition supply. However, the function of hormone trafficking is rarely studied. By injecting the mixture liquor of human chorionic gonadotrophin (HCG, 2 IU/g) and luteinizing hormone-releasing hormone A3 (LHRH-A3, 5 ng/ g) into the brood pouch of Hippocampus erectus, we found the reproductive interactions accelerated dramatically, and 4 pairs were successfully mated. After 24 h, the inner epithelium was highly folded and the loose connective tissue layer was highly distended. In the inner tissue layer of the brood pouch, fibroblasts secreted vigorously, blood vessels multiplied and expanded, indicating the physiological structure of the brood pouch modified hastily from the unpregnant stage to the progravid phase. Correspondingly, transcriptome results revealed the gene expression of circadian, epitheliogenesis, angiogenesis, lipid transfer, and spermiogenesis were significantly up-regulated. We innovatively found that macromolecule exogenous hormone (HCG) can be not only efficiently transported from brood pouch to body, but also promote mating and the physiological changes of the brood pouch.

Automated summary

Syngnathid fishes have a unique reproductive system, and injecting a mixture of HCG and LHRH-A3 into the brood pouch can accelerate reproductive interactions, promote physiological changes, and up-regulate gene expression.