The welfare and quality of farmed salmonids at harvest.

Byrne, Hazel

Abstract

Salmonid farming has become a firmly established industry within the UK. To maintain or expand current markets the industry needs to produce high quality fish by humane and environmentally sustainable methods. This study examined the effects of harvesting on the stress response and carcass quality of farmed salmonids with a view to recommending best practice. Current salmonid harvesting techniques were determined via a questionnaire circulated to the industry. Commonly used killing/ stunning methods were tested for their effects on the welfare and quality of rainbow trout, (Oncorhynchus mykiss, Walbaum 1792), and Atlantic salmon, (Salmo salar, Linnaeus 1758). The effect of a 30-40 degree-day fast on rainbow trout quality was investigated. A short-term fast was shown to increase fish freshness in rainbow trout. Killing/ stunning method caused a variable response in both salmonid species, which responded in a similar manner. There was less evidence of muscle activity in fish that were instantly stunned, by electricity (trout) or percussion (both species), compared with those that died naturally, in ice (trout) or air (both species), or had been anaesthetised by carbon dioxide (salmon). A control group of trout anaesthetised with benzocaine showed the least signs of muscle activity. Reduced muscle activity at harvest increased fish freshness. The primary stress response data were more equivocal. Differences were not detected in plasma noradrenaline levels in cither species. The death in ice slurry trout appeared to exhibit the lowest stress response with the least adrenaline and cortisol: it was hypothesised that reduced neural responses due to the low body temperature of these fish caused this effect. Adrenaline levels were high in electrically stunned trout, the carbon dioxide narcosis salmon, and the death in air fish (both species). Percussively stunned salmon had higher plasma cortisol levels than those in the fish left to die in the air. When trout were anaesthetised before stunning/ killing compared with their nonanaesthetised counterparts they exhibited a decline in muscle activity (ice slurry fish) and plasma adrenaline levels (electrically stunned fish). Recommendations to the industry were, in order to improve fish freshness, fish should be fasted before harvest and muscle activity reduced by stunning the fish quickly before killing.

Citation

BYRNE, H. 2002. The welfare and quality of farmed salmonids at harvest. Robert Gordon University, PhD thesis. Hosted on OpenAIR [online]. Available from: https://doi.org/10.48526/rgu-wt-2807315

• Thesis Type: Thesis
• Deposit Date: Jun 13, 2025
• Publicly Available Date: Jun 13, 2025
• DOI: https://doi.org/10.48526/rgu-wt-2807315
• Public URL: https://rgu-repository.worktribe.com/output/2807315
• Award Date: Oct 31, 2002