Ovarian development and changes in the serum vitellogenin levels in the river sculpin, Cottus hangiongensis, during an annual reproductive cycle
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Annual changes in the ovarian development and serum vitellogenin concentration were investigated in the river sculpin, Cottus hangiongensis, sampled monthly from a river in southern Hokkaido, Japan. Ovarian development started advancing from summer and continued during the winter months until March with a maximum mean gonadosomatic index (GSI) of 15.99%. Hepatosomatic index (HSI) was also highest in March with a range of 5.13-5.95%. Spawning season usually occured from April to May. Annual changes in serum vitellogenin level correlated very well with the patterns of GSI and HSI, as well as histological changes of the ovary. However, high serum vitellogenin was maintained in March and April.