The Effect of Temperature On Somatic Growth of Young American Eels (Anguilla rostrata) Reared Under Controlled Laboratory Conditions

Rising water temperatures have been implicated in the recent decline of the American eel, making it critically important to determine thermal growth requirements of the species. Eels fed ad libitum were reared in two replicate experiments at seven constant temperatures 10^oC-28^oC, a range selected to simulate temperatures in the St. Lawrence River system and encompass midsummer thermal conditions (22-25^oC). Glass eels (means, TL–56.0mm, WT–0.11g) from Atlantic Canada  reared first for 84 days and then (TL–91.5mm, WT–0.85mm) for 112 days grew most rapidly at 28^oC with specific growth rates that were not significantly different (% change/d–weight 3.25 and 3.23; length 0.72 and 0.83, respectively). Rearing confirmed that in the northern part of the species’ range, summer temperatures do not exceed optimum temperature for growth. Glass eels from warmer climes near the source of recruitment reared similarly by others grew somewhat faster but had a similar thermal optimum, which is appreciably higher in the American than in the European eel. With global warming, young eels at northern latitudes will grow faster, while at southern latitudes, closer to the source of recruitment, where summer temperatures (25-35^oC), approach and exceed the optimum, growth and recruitment will be negatively affected.