Warm water treatment increased mortality risk in salmon

Area of Science:

• Aquaculture
• Fish Health
• Animal Welfare

Background:

• Sea lice infestations pose a significant challenge to Atlantic salmon farming.
• Thermal treatments are a controversial method used to control sea lice.
• Evidence on the welfare and physiological impacts of thermal treatments on salmon is growing.

Purpose of the Study:

• To assess the impact of thermal treatments on salmon welfare, behavior, physiology, and health.
• To provide data to inform the use of thermal treatments in aquaculture.

Main Methods:

• Atlantic salmon were subjected to two thermal treatments (30s at 27°C, 30°C, or 33°C) four weeks apart.
• Control groups included procedural (14°C) and negative (no treatment) controls.
• Evaluated parameters included behavior, eye damage, growth, condition factor, blood plasma, organ health, long-term coping ability, and mortality.

Main Results:

• Fish exhibited clear behavioral responses to warm water treatments, even with moderate temperature differences.
• Increased prevalence of eye damage was observed in fish exposed to warm water.
• Mortality rates significantly increased with higher treatment temperatures (up to 18.9% at 33°C).
• Growth, condition factor, blood parameters, organ health, and long-term coping ability showed minimal differences between groups.

Conclusions:

• Thermal treatments, while potentially addressing sea lice, lead to significant increases in salmon mortality.
• The observed eye damage and behavioral changes indicate welfare compromises.
• Further research is needed to balance sea lice control with maintaining optimal fish health and welfare in aquaculture.