Concurrent levels of 11-ketotestosterone in fish surface mucus, muscle tissue and blood

Abstract

Summary A rapid, reproducible method is described for extracting and comparing levels of the ether-soluble fish androgen 11-ketotestosterone (11-KT) in blood serum, muscle tissue and surface mucus. Because widely different volumes of extract were recovered after centrifugation from the three sources, it was important to express androgen levels as pg 11-KT/mg of total soluble protein (TSP). For six male and four female sexually-staged freshwater Koi (Cyprinus carpio), the method yielded similar pg 11-KT/mg TSP ratios in blood serum and extracts of muscle tissue and surface mucus, with the strongest correlation between blood serum and surface mucus. While male Koi were distinguishable from females based on the magnitude of 11-KT levels, reproductive stage and gonadosomatic index levels were not correlated with the 11-KT levels of either sex. Similar pg 11-KT/mg TSP ratios were also found for autologous muscle tissue and surface mucus extracts of 37 captured and sexed wild marine fishes representing seven genera. However, high 11-KT levels were not restricted to mature males. Collectively, results suggest that surface mucus collection (followed by 11-KT assay) is a useful alternative to more invasive methods of determining systemic hormone levels in fish. Without knowledge of seasonal variation in levels of this and other sex hormones, however, reliance on 11-KT levels alone may lead to spurious identification of gender, let alone reproductive stage.