Background Opsariichthys bidens is an economic fish species with great potential for development in freshwater aquaculture in China, with delicious meat and strong adaptability, but the efficiency of artificial breeding is limited by the level of ovarian development of parental O. bidens.

Objective The aim of the present study is to investigate the effect of stocking density on the ovarian development of parental O. bidens.

Methods Parental O. bidens of the same specification and healthy physique were selected and randomly divided into four density gradients: a low density group (M₁, 2 kg/m³), a medium density group (M₂, 4 kg/m³), and two high density groups (M₃, 6 kg/m³), and (M₄, 8 kg/m³) for cultivation, and the experimental cycle was 45 d. The ovarian sections of ovaries were observed and counted to calculate the gonadal index (GSI) and the proportion of phases of ovarian development to stage Ⅳ (F); the contents of conventional nutrient fractions such as moisture, crude protein, crude fat, crude ash, phosphorus and calcium of the ovaries were determined; and statistics analysis on the induced spawning rate, hatching rate and fertilization rate were carried out.

Results The results showed that the gonadal index of the medium density group (13.35%±1.97%) was significantly higher than those of the other density groups (P<0.05); and the phase of ovarian development to stage Ⅳ in the medium density group was 46.62%±3.20%, which was significantly different from that of the other groups (P<0.05). Regarding the conventional nutrient composition of the ovaries, the moisture content of the ovaries of the O. bidens in the medium density group was significantly lower (P<0.05) and the crude fat content was significantly higher (P<0.05), while the differences in the contents of crude protein, crude, ash, calcium, and phosphorus were not significant (P>0.05). In terms of fecundity, the medium density group had significantly (P<0.05) higher induced spawning rate (93.30%±3.30%) and hatching rate (81.40%±4.00%) than those of the other density groups, and had the optimum fertilization rate.

Conclusion The above results indicate that reasonable stocking density can improve the level of ovarian development of parental O. bidens to a certain extent.