Abstract
AbstractNorth American Burbot Lota lota maculosa occupy habitats from deep, cold lakes to prairie streams. Controlled laboratory trials were conducted to evaluate the growth, immune response, and thermal stress physiology of juvenile Burbot subjected to fluctuating, high diel temperatures. Age‐0 Burbot from a captive propagation program associated with population restoration in the Kootenai River, Idaho, were tested in temperature cycles that imitated summer conditions observed in regional stream habitats. The diel temperature cycle for the treatment group varied from 18°C at night to 27°C during the day, whereas the control group was held at a constant temperature of 14°C. We evaluated survival, growth, feed efficiency, heat shock protein 70 (hsp70) levels, hsp70 gene expression, serum lysozyme levels, and proximate body composition in samples taken from fish before, during, and at the completion of the trials. Both treatments had high survival and similar growth rates, but the control group gained significantly more weight and had better feed conversion rates than the treatment group. Mean hsp70 expression and hsp70 abundance were significantly higher in the treatment group but varied between sampling events and between tissue types. Expression of hsp70 in treatment fish was highest on day 15 for muscle tissue (251 times the control value) and on day 30 for liver tissue (1,131 times the control value), with variable abundance of hsp70 at both sampling points. Serum lysozyme levels were not different between treatments. An additional short‐term trial was conducted to evaluate the response of Burbot to upper lethal temperatures, with daily maxima approaching 32°C. Despite being commonly referred to as a coldwater stenotherm, the Burbot displayed resilience to thermal stress, and were able to withstand temperatures exceeding 31°C.Received September 13, 2016; accepted May 12, 2017 Published online July 31, 2017
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