Effect of human chorionic gonadotropin on sexual maturation, sex steroids and thyroid hormone levels in Caspian lamprey (Caspiomyzon wagneri Kessler, ۱۸۷۰).

The objective of this study was to determine the effect of human chorionic gonadotropin (hCG) on sexual maturation, plasma sex steroids (۱۷β-estradiol, E۲ and ۱۷α-hydroxy progesterone (۱۷α OHP)) and thyroid hormones (triiodothyronine, T۳ and thyroxin, T۴) levels in upstream - migrating Caspian lamprey. During the experiment, ۳۶ fish (۲۴ females and ۱۲ males) in  spring ۲۰۱۳ and ۳۶ fish (۲۴ females and ۱۲ males) in  fall ۲۰۱۳ were collected from the Shirud River estuary in Mazandaran Province, the Southern Caspian Sea during their upstream migration to the freshwater. All fish were injected with hCG at the doses of ۱۰۰۰, ۱۵۰۰ and ۲۰۰۰ IU.kg BW-۱. The injection was a two - step process (۵۰% of hormone in each step) by ۱۲ h interval. After the first injection, fish were retained in the cages in the river beds and ۲۴ hours after the second injection, fish were checked for egg and sperm release after mild abdomen pressure. Blood samples were taken for determining sex steroid levels. Results showed that hCG hormone injections caused increase in migration of germinal vesicle in the oocyte of female and sperm release in males. Significant differences were found in the serum E۲ and ۱۷α-OHP levels in hCG - injected fish compared to the control. However, no significant differences were found in serum T۳ and T۴ levels in the hCG - injected fish. According to the results, the appropriate hCG dosage to induce the reproduction acceleration in Caspian lamprey is ۱۵۰۰-۲۰۰۰ IU.kg BW-۱.

Keywords:

Lamprey , Caspian Sea , Induced reproduction , Hormonal changes