Effects of Water Temperature on Gonad Development in the Cold-Water Fish, Kumgang Fat Minnow Rhynchocypris kumgangensis

Abstract

Water temperature is one of the most important factors in the survival of aquatic organisms. We investigated the effects of increased water temperature on the physiology of Kumgang fat minnow Rhynchocypris kumgangensis, a small cold-water species of freshwater fish that is endemic to Korea. We examined how organ indices and oocyte histology differed by season and exposure to high water temperatures. Fish were collected from streams in Korea during three different seasons, maintained at the same temperatures at which they were collected for three weeks, and then exposed to either control temperatures reflecting the same conditions from which they were collected (15.0°C, August; 7.8°C, November; and 12.3°C, April) or experimental temperatures that were increased a total of 7°C over seven days (to 22.0°C, August; 14.8°C, November; and 19.3°C, April) and maintained at the final temperature for an additional three days. Among the studied organ indices, the gonadosomatic indexes (GSI) in both sexes differed by season, and were significantly decreased by exposure to increased water temperatures during the germ-cell-developing season. The histological features of oocytes also differed by season, and exposure to increased water temperatures during the relevant season markedly attenuated oocyte development. These findings highlight sensitivity of both GSI and oocyte histology on water temperature change, and the possible negative effects of high water temperature on reproduction in Kumgang fat minnow.