Growth and Survival of Apache Trout Under Static and Fluctuating Temperature Regimes

Abstract

Increasing stream temperatures have important implications for arid‐region fishes. Little is known about effects of high water temperatures that fluctuate over extended periods on Apache Trout Oncorhynchus gilae apache, a federally threatened species of southwestern USA streams. We compared survival and growth of juvenile Apache Trout held for 30 d in static temperatures (16, 19, 22, 25, and 28°C) and fluctuating diel temperatures (±3°C from 16, 19, 22 and 25°C midpoints and ±6°C from 19°C and 22°C midpoints). Lethal temperature for 50% (LT50) of the Apache Trout under static temperatures (mean [SD] = 22.8 [0.6]°C) was similar to that of ±3°C diel temperature fluctuations (23.1 [0.1]°C). Mean LT50 for the midpoint of the ±6°C fluctuations could not be calculated because survival in the two treatments (19 ± 6°C and 22 ± 6°C) was not below 50%; however, it probably was also between 22°C and 25°C because the upper limb of a ±6°C fluctuation on a 25°C midpoint is above critical thermal maximum for Apache Trout (28.5–30.4°C). Growth decreased as temperatures approached the LT50. Apache Trout can survive short‐term exposure to water temperatures with daily maxima that remain below 25°C and midpoint diel temperatures below 22°C. However, median summer stream temperatures must remain below 19°C for best growth and even lower if daily fluctuations are high (≥12°C). Received June 26, 2013; accepted May 19, 2014

Species‐specific effects of subdaily temperature fluctuations on consumption, growth and stress responses in two physiologically similar fish species

“…A variety of species exhibit increased consumption and growth rates when exposed to diel thermal cycles compared to individuals exposed to the stable mean temperature of the cycle, given that the mean temperature is at or below the optimum temperature for the species and the maximum temperature experienced during the thermal cycle is below the upper lethal temperature Diana 1984;Geist et al 2011). Energetic benefits can be offset when the magnitude of thermal change is excessive or maximum temperatures are greater than a species' optimum (Recsetar et al 2014). The longer rate of temperature change during diel thermal cycles, compared to subdaily fluctuations, allows fishes to physiologically acclimate to even severe (e.g., D 17°C) diel thermal changes (Podrabsky & Somero 2004).…”

A global review of freshwater crayfish temperature tolerance, preference, and optimal growth

“…Aquatic organisms do not normally experience constant water temperatures over long periods of time in wild settings, yet almost no studies of crayfish thermal ecology use fluctuating temperatures to estimate optimal growth or other parameters. Recsetar et al (2014) studied growth of a salmonid under both static and fluctuating temperatures and showed that the fish could survive exposure to higher temperatures if they fluctuated. In a different approach, Simčič et al (2014) estimated temperature tolerance for two species of crayfish using respiratory electron transport system activity.…”

“…Other approaches termed acclimated chronic exposure (ACE) and chronic lethal method (CLM) created a more natural thermal environment, whereby test organisms were exposed to slow changes in water temperature (e.g., 1°C/day). The ACE method is a static method that used a system that acclimated test organisms by raising temperatures at a rate of &1°C/day until a target temperature was reached, and then held at that temperature to observe mortality using LT 50 methods (Selong et al 2001;Recsetar et al 2014). The CLM method is dynamic, whereby temperatures were raised at a defined rate (e.g., 1°C/day) until the experimental endpoint was reached (generally mortality; Beitinger et al 2000).…”

Determination of Habitat Requirements for Apache Trout

“…Most Apache Trout were in waters ranging from 10ºC to 21ºC at the time of capture. The HSC developed for water temperature by a laboratory-based experiment for thermal tolerances of Apache Trout (Recsetar et al 2014) found that mortality increased substantially when temperatures exceed 22°C, and growth is decreased at temperatures above 19°C (30-d exposure method). The maximum temperature in all three study streams never exceeded the critical thermal maximum for Apache Trout (28.5-30.5°C; Lee and Rinne 1980;Recsetar et al 2012); however, the maximum temperature in the WFBR (27°C) did approach the critical thermal maximum.…”