Ultrasonic imaging-assisted artificial reproduction of critically endangered Sichuan taimen (Hucho bleekeri Kimura)

The critically endangered Sichuan taimen ( Hucho bleekeri Kimura), one of the largest salmonids in the world, has been found in most of the tributaries of the Upper Yangtze River in China. In this study, ultrasonography was used to assist the artificial reproduction of Sichuan taimen. A Treason T3000 portable ultrasonography with a model 12L5 (12-5 MHz) transducer was used to determine the sex of Sichuan taimen before spawning and after hormone induction and spawning. Two scanning areas with two central points were located to easily distinguish between the ultrasound images of females and males before and after spawning. The ultrasound images showed the maturation of the ovary after hormone induction, which is a key for determining the right time for sampling oocytes or sperm and adjusting the dose of the hormone. The transverse ultrasound images of the ovary can also be used to evaluate reproductive characteristics such as potential breeding fertility and relative gonadosomatic index. Thus, ultrasonography may be helpful in dynamically understanding the artificial reproduction of Sichuan taimen and observing the response of the ovary to exogenous hormones, which will benefit the artificial reproduction and conservation of endangered fish species.