Serotonin plus spiperone induce ovarian maturation, spawning and potential release of ovarian maturation inducing pheromones in the Pacific white shrimp Litopenaeus vannamei (Penaeidae)

In this study, we further investigate the hypothesis that serotonin plus spiperone (Ser+Spi) injection induces ovarian maturation and releases ovarian maturation inducing pheromones into the water, thereby stimulating neighboring untreated females. Litopenaeus vannamei females (b.w. = 40.40 ± 5.84 g; n = 120) and males (b.w. = 34.25 ± 4.68 g; n= 90) were divided into three 18-m 2 maturation tanks. Each tank contained 40 non-ablated females and 30 males with two treatments per tank. In tank 1, 20 females received a low dose of Ser+Spi (Ser at 25 µg g-1 b.w. and Spi at 2.0 µg g-1 b.w.) along with a control vehicle-injection. In tank 2, 20 females received a high dose of Ser+Spi (Ser at 40 µg g-1 b.w. and Spi at 4.0 µg g-1 b.w.) with the same control vehicle-injection applied to tank 1. In tank 3, unilateral eyestalk ablation (ESA) was performed on 20 females, while 20 control females were maintained non-ablated/injected. The experiment spanned 18 weeks and was divided into three phases. Ovarian maturation was observed in both Ser+Spi-treated and control females, with stages III-IV of maturation occurring one week after injections at both tested doses. Statistical analysis revealed that the average ovarian maturation index (OMI) was significantly higher for the control group in tank 2 (OMI = 0.25), compared to the Ser40+Spi4.0 group. Additionally, control females in tank 1 matured similarly to Ser25+Spi2.0 group (p ≤ 0.05). The control group of tank 3 displayed very low maturation activity (OMI = 0.1). Controls from tanks 1 and 2 exhibited a higher number of mated females and spawning events. These results support the potential of Ser+Spi to induce ovarian maturation and spawning and suggest that Ser+Spi-treated females may release a metabolite into the water that acts as an ovarian maturation inducer for neighboring females.