Glass‐Eel‐Stage American Eels Respond to Conspecific Odor as a Function of Concentration

Abstract

The American Eel Anguilla rostrata has experienced staggering population declines in recent decades and is now the focus of restoration efforts. Studies have demonstrated that olfaction is critical to anguillid behavior and that glass eels (the life stage which migrates inland from saltwater to freshwater) are attracted to conspecific washings. We evaluated conspecific cueing as a potential mechanism for American Eel inland migration coordination by assessing (1) the affinity of glass eels to conspecific washings, (2) the concentration–response relationships, and (3) changes in responsiveness to washings during the glass eel‐to‐elver transition. In two‐choice maze assays, glass eels were attracted to glass eel washings over a wide range of concentrations (0.20–0.40 g of glass eels·L−1·h−1), and a logarithmic function provided the best fit to the concentration–response relationship. When given a choice between two conspecific washings of higher and lower concentrations, the glass eels generally preferred the higher concentration. Responses to undiluted glass eel washings did not significantly differ among stage‐3–7 glass eels, although stage‐7 eels were not attracted to the washings, whereas the other stages were. Washing affinity remained similar over the course of several weeks. These results support aspects of the conspecific cueing hypothesis at the glass eel life stage under laboratory conditions, suggesting that conspecific cueing is an important component of migration coordination among juvenile American Eels and warrants additional study. Received September 11, 2015; accepted January 20, 2016 Published online June 15, 2016

American eels produce and release bile acid profiles that vary across life stage

“…This suggests that bile acid concentration differences may be responsible for the observed nontarget differences in washing profile, which may be further complicated by release rate. Since dose‐dependent responses were observed to odourants in previous studies (Briand et al ., ; Pesaro et al ., ; Schmucker et al ., ; Sola & Tosi, ), these results support the hypothesis that concentration is an important factor in determining glass eel response to conspecific odours.…”

“…Since bile acids are common constituents of the attractive glass eel washings used in Schmucker et al . () and attractive elver washings used in Galbraith et al . (), their presence could be potentially responsible for the washing attractiveness.…”

“…Many of the washings evaluated in this study were prepared by Galbraith et al ., and Schmucker et al . (, ) and frozen following preparation for storage until use in this study.…”

“…Anguillids are thought to rely on multiple cues to guide migration, including current, salinity gradient, lunar period, water temperature and, more recently, conspecific chemical cues (Huertas et al ., 2008; Pesaro et al ., 1981). Studies have shown that glass eels are attracted to odours emitted by other glass eels in a dose‐dependent relationship (Briand et al ., ; Pesaro et al ., ; Schmucker et al ., ). Glass eels are also attracted to elver odour and natural river water collected from waterbodies with established anguillid populations (Creutzberg, ; Galbraith et al ., Hain, ).…”

“…. Studies have shown that glass eels are attracted to odours emitted by other glass eels in a dose-dependent relationship (Briand et al, 2002;Pesaro et al, 1981;Schmucker et al, 2016). Glass eels are also attracted to elver odour and natural river water collected from waterbodies with established anguillid populations (Creutzberg, 1961;Galbraith et al, 2017Hain, 1975.…”