Rainbow trout welfare: comparing stunning methods in winter and summer

Area of Science:

• Aquaculture
• Animal Welfare
• Fish Physiology

Background:

• Seasonal changes impact fish physiology and stress responses.
• Effective stunning methods are crucial for fish welfare in aquaculture.

Purpose of the Study:

• To evaluate the impact of different stunning methods on rainbow trout stress and metabolism.
• To investigate seasonal variations in trout stress responses.
• To identify optimal stunning protocols for improved fish welfare.

Main Methods:

• Comparison of three stunning methods: thermal shock (TS), electric shock + thermal shock (ES2, ES4).
• Assessment of blood cortisol levels, skin pigmentation, liver glycogen, and lipids.
• Measurement of reactive oxygen species (ROS) and antioxidant enzyme activity (sod, gpx, cat, gst).

Main Results:

• A significant interaction between stunning method and season was observed for cortisol levels.
• Summer conditions led to higher cortisol, darker pigmentation, and reduced energy reserves.
• Electrical stunning combined with thermal shock (ES4) showed the lowest cortisol levels in winter.
• Increased metabolic activity in summer correlated with higher ROS and antioxidant enzyme upregulation.

Conclusions:

• Stunning method significantly influences trout stress response, with combined electrical and thermal stunning being more effective.
• Seasonal factors critically affect fish stress physiology, necessitating adaptive stunning strategies.
• Optimizing stunning practices is vital for fish welfare, particularly considering climate change impacts on aquaculture.