Induction of ovulation in endemic pearl mullet ( Chalcalburnus tarichi), living in the highly alkaline Lake Van, using GnRHa ([ d-Ser( tBu) 6,Pro 9-Net]-GnRH) combined with haloperidol

Abstract

Pearl mullet ( Chalcalburnus tarichi) (Cyprinidae) is an endemic fish species of the Lake Van (Turkey), the largest soda lake (pH 9.8) on earth. During April–June, the spawning period of the fish, the mullet migrate from Lake Van to freshwater rivers around the lake and after spawning they return to the lake. This fish gives hope for improving the fishery in the alkaline environment deprived of other commercial fish species. The objective of this study was to find an optimal method for inducing ovulation of pearl mullet. Mammalian GnRH analogue (GnRHa at 60 μg/kg); dopamine antagonist, haloperidol (HAL at 1.5 mg/kg) and a combination of GnRHa and haloperidol (GnRHa+HAL) at low (20 μg/kg GnRHa and 0.5 mg/kg HAL) and high (60 μg/kg GnRHa and 1.5 mg/kg HAL) doses were tested for this purpose. Saline (0.7% NaCl) injected fish were used as a control group and no ovulation occurred in this group. Based on spawning ratio (the proportion of fish that spawned in each group), spawning index (the weight of eggs as a percentage of female body weight) and fertilization rate, the GnRHa+HAL combination at the high (60 μg/kg GnRHa and 1.5 mg/kg HAL) doses were found to be more efficient (7/7, 16.0±2.4, 86.0±10 respectively) than the low (20 μg/kg GnRHa and 0.5 mg/kg HAL) doses of GnRHa+HAL (3/7, 12.4±2.1, 54.5±6.5 respectively). No females ovulated in the treatment group receiving HAL at 1.5 mg/kg and GnRHa alone at 60 μg/kg. It is concluded that GnRHa+HAL (60 μg/kg+1.5 mg/kg) treatment is effective and reliable for induction of ovulation in pearl mullet broodstocks. Haloperidol improved the GnRHa effect on ovulation. GnRHa alone is not sufficient for spawning induction in the pearl mullet. The results indicate that in pearl mullet, similar to other cyprinids, there is a strong dopamine inhibitory tone on GtH secretion. In addition, the ovulation index and fertilization rates of eggs were influenced by the dosages of the applied GnRHa+HAL combination.