| Summary: | Antarctic teleosts C. aceratus (lack hemoglobin, Hb−) and N. coriiceps (possess hemoglobin, Hb+) are extremely stenothermic and live in the Southern Ocean at temperatures near 0°C. While survival of both species is threatened by anthropogenic activities, it is thought to be more so for Hb− fishes which are less tolerant to temperature elevation than Hb+ animals. To examine behavioral thermoregulation of these fishes, freely swimming in a tank, we studied their responses to acute thermal stress. We found that both Hb+ and Hb− species follow generally similar strategy ‐ avoidance‐ and escape‐like transient bursts of locomotion interleaved by periods of relative motionless (possibly, an energy saving maneuver), with some species‐specific differences in onset, duration and intensity. Survival strategy of both species also includes a repertoire of respiratory modularity behaviors, some of which have been previously attributed to parental care in other species of fish. We also found that thermally triggered escape‐like fast S‐starts and C‐turns in N.coriiceps (but not slow C‐turns and withdrawals in C.aceratus ) are lateralized. At high temperatures, total reversal (followed by a gradual loss) of lateralization was observed, which may indicate the onset of nervous system malfunction. We conclude that both Hb+ and Hb− Antarctic fishes undergo a variety of ambulatory and respiratory behaviors that appear to represent attempts to avoid and/or escape hazardous temperatures (and, possibly, to adapt to elevated temperatures within a limited range), all similarly sensitive and well‐orchestrated by the nervous system to prevent malfunction, that occurs only when rise in temperature is extreme and unescapable. Support or Funding Information Supported by NSF ANT‐1341602. This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .
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