CT_max is repeatable and doesn't reduce growth in zebrafish

Area of Science:

• Physiology
• Ecology
• Animal Behavior

Background:

• Critical thermal maximum (CTmax) is a key metric for upper thermal tolerance limits in ectotherms.
• Understanding the repeatability and physiological costs of CTmax experiments is crucial for reliable data.
• Zebrafish are a common model organism for physiological studies.

Purpose of the Study:

• To assess the repeatability of CTmax measurements within individual zebrafish across multiple trials.
• To determine the physiological impact of repeated CTmax trials on zebrafish growth and survival.
• To investigate the relationship between innate thermal tolerance and acclimation response.

Main Methods:

• Zebrafish were subjected to four repeated CTmax trials.
• Repeatability of CTmax was calculated across trials.
• Effects on growth and survival were monitored after repeated trials.

Main Results:

• Initial CTmax repeatability was 0.22, increasing to 0.45 for trials 2-4 after acclimation.
• CTmax increased from trial 1 to 2 due to thermal acclimation.
• Individual differences in innate tolerance and acclimation capacity were observed.
• Repeated trials showed no significant effect on growth and a high survival rate (99%).

Conclusions:

• CTmax exhibits moderate repeatability in zebrafish, particularly after an initial acclimation phase.
• Repeated CTmax trials are physiologically safe, with no negative impacts on growth or survival.
• The findings support the continued use of CTmax as a valid metric for acute thermal tolerance.
• Zebrafish populations may possess diverse thermal tolerance strategies, including innate tolerance and plasticity.