Fish growth, physiological stress, and tissue condition in response to rate of temperature change during cool or warm diel thermal cycles

The effect of the rate of temperature change on fish was studied by exposing a variety of North American fish species to diel temperature cycles containing rates of change of 0.8, 1.1, 2.2, or 4.4 degrees C.h(-1). During a simulated cool season (3.9-11.7 degrees C), bluntnose minnow (Pimephales notatus), spotfin shiner (Cyprinella spiloptera), and white sucker (Catostomus commersonii), but not smallmouth bass (Micropterus dolomieu), gained mass in response to 0.8, 1.1, or 2.2 degrees C.h(-1) but not constant mean temperature. White sucker did not grow under 4.4 degrees C.h(-1), which was slower than expected based upon bioenergetics models. Physiological indicators of acute stress (day 1 cortisol), chronic stress (day 44 cortisol and triglycerides), and histomorphological measures suggested no effect of treatment. During a simulated warm season (20.0-27.8 degrees C), growth by channel catfish (Ictalurus punctatus), rosyside dace (Clinostomus funduloides), smallmouth bass, and spotfin shiner was not altered by any rate of temperature change; however, walleye (Sander vitreus) and white sucker grew slower than expected under 4.4 degrees C.h(-1). Physiological indicators of acute stress (day 1 cortisol), chronic stress (day 29 cortisol and triglycerides), and histomorphological measures suggested no effect of treatment. Chronic exposure to temperature change of 4.4 degrees C.h(-1) may not induce an acute or chronic stress response but may slightly impair growth for some species.