Hypertrophy and polysaccharide production in the kidney associated with sexual maturation of male small-egged Kajika, Cottus pollux SE
2016
Koya, Yasunori | Fujii, Ryoji | Yambe, Hidenobu | Tahara, Daisuke
Although renal hypertrophy during the reproductive period has been reported previously in species of Cottus, the function of the kidney in reproduction remains unknown. In order to clarify the role of the kidney in reproduction, seasonal changes in gonad and kidney weight, serum androgen levels, kidney histology, and the protein content of urine, were examined in the small-egged Kajika, Cottus pollux SE sensu Yokoyama and Goto (2005). Compared to the non-reproductive period (August), renal hypertrophy of male fish during the reproductive period (December) was equivalent to a twofold increase in kidney-somatic index values. A marked increase in epithelial cell height in the proximal convoluted tubule (PT) was correlated with elevated serum 11-ketotestosterone levels, suggesting that total kidney weight increased from the non-reproductive to the reproductive period. Periodic acid-Schiff (PAS)-positive granules containing polysaccharides were observed in the cytoplasm of PT epithelia during the reproductive period. Urine retained in the urinary bladders of males exhibiting nesting behavior contained glycoproteins and low-molecular-weight substances containing polysaccharides during the reproductive period. We discussed the role of the kidney and kidney secretions in nesting male species of Cottus.
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