Underwater noise impairs reproduction in zebrafish by disrupting the hypothalamic-pituitary-gonadal axis

Abstract

Anthropogenic underwater noise is a growing threat to fish and has been shown to interfere with social behavior and reproductive outcomes. Yet very few studies have addressed the molecular mechanisms behind it. Here, female and male zebrafish (Danio rerio) were exposed to noise (100–1000 Hz, 130 dB) for 14 days. Reproductive behavior and fecundity were evaluated, and underlying mechanisms were analyzed by examining gonad histopathology, sex hormone, and transcriptional profiles in hypothalamic-pituitary-gonadal (HPG) axis. Males exposed to noise showed a significantly decreased frequency of courtship behavior, including chasing and touching behavior and visits to the spawning area. The spawning capacity was significantly reduced in noise-exposed fish. In males, the concentration of androgen (11-ketotestosterone, 11-KT) was significantly decreased in noise-exposed fish probably by down-regulating expressions of genes in the HPG axis, which contributed to depressed spermatogenesis and courtship behavior. In females, 11-KT was significantly elevated by noise likely due to down-regulated estrogen-converting genes and up-regulated androgen-converting genes, further affecting the gonadal maturation and spawning, which was corroborated in histopathological observation. Overall, noise depressed courtship behavior and disturbed sex hormonal balance and gametogenesis by changing expressions of key genes in the HPG axis, thus inhibiting spawning. This study suggests that noise adversely affects the reproductive outcome by disturbing the endocrine system in fish and could pose a potential threat to fish populations inhabiting noisy waters.