Reproductive biology of Hemitripterus villosus in the Bohai Strait, China

To understand the reproductive biology of Hemitripterus villosus in the Bohai Strait, and fill the key knowledge gap in verifying reproductive seasonality and documenting gonadotropin dependent reproductive cycle of this species, a year-round detail study was conducted for the first time. In total, 263 individuals were randomly sampled off the coasts of the Bohai Strait. Results show that and the overall female-to-male ratio (1.35:1) did not differ significantly from the 1:1 sex ratio. The length and weight relationship for females and males were regressed, depicting an isometric growth for both sexes. Four reproductive phases of the complete gonadotropin dependent reproductive cycle in both sexes were identified. The monthly variations in the gonadosomatic and hepatosomatic indexes for both sexes further indicated that this species spawns a single batch of eggs per year and the peak spawning period is from October to December. The average diameter of eggs ranged from 2.10 to 3.57 mm. The length at first sexual maturity was 224.87 mm for females and 241.26 mm for males. Significant positive relationships between absolute fecundity and fish size, and also gonadal weight were observed. H. villosus from the Bohai Strait exhibited smaller body size, smaller egg diameter, lower gonadosomatic index, lower absolute fecundity, and higher population extinction risk than the other populations’ studied previously. Our findings contribute to understanding the status of this isolated westernmost population, and we emphasize that more efficient protection measures for the species and control measures are urgently required to improve the coastal environment in the Bohai Strait.