Effect of water temperature and growth variation on the sex ratio of experimentally reared eels

• Published in: Ecology of Freshwater Fish
• Main Author: Holmgren, K.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1996
• Subjects: Ecology; Aquatic Science; Ecology, Evolution, Behavior and Systematics; Anguilla anguilla
• Online Access: http://dx.doi.org/10.1111/j.1600-0633.1996.tb00134.x; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fj.1600-0633.1996.tb00134.x; https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1600-0633.1996.tb00134.x

Abstract In a controlled experiment, elvers ( Anguilla anguilla L.) were reared for 137 weeks at 17, 20 and 26°C. Most eels with macroscopically sexable gonads were males. The proportions of females were 14% of sexable individuals at 26°C and 7–8% at 17 and 20°C. During the first 15 weeks, 20–50% of initial numbers were lost, but this early mortality was not significantly size selective. In spite of a long term experiment, a significant number of the survivors never attained a sexable size. Nongrowers (7–9 cm) were still alive nearly three years after being caught as glass eels. Among the earliest fast growers, 5% females, or less, were found. The proportion of females increased in later grading groups, but the pattern of increase did not indicate that males and females have separated mean ranks in a fixed growth hierarchy. Water temperature influenced observed sex ratios, but probably not through direct influence on the sex differentiation. Some alternative hypotheses, dealing with population density and individual growth status, are discussed.