Fin damage in juvenile Atlantic salmon: Farm and experimental, causes and consequences

Abstract

Fin damage in farmed salmonids is an important topic from both a welfare and economic perspective. Fin damage is perceived as a welfare issue as fish fins are living tissue and any damage can potentially be a source of pain and route for infections. The onset and prevalence of fin damage is complex and multifactorial and controlling fin damage is extremely challenging as triggering factors are difficult to identify. The aims of this thesis were to investigate food withdrawal as a major risk factor associated with the development of fin damage and strategies to reduce on-farm fin damage, including reducing industry-standard food withdrawal periods and providing environmental enrichment. The potential consequences of reducing fin damage is an improvement in farm productivity, fish health and welfare. Chapter 1 outlines our current understanding of fish welfare and fin damage. Chapter 2 details a study on the effect of food withdrawal on fin damage. Chapter 3 compares invasive and non-invasive methodologies used to assess fin damage. Chapters 4 and 5 detail a study carried out on a commercial Atlantic salmon farm to investigate the effect of enrichment at the farm-level. Chapter 6 details a novel, on-farm fish welfare assessment method. Chapter 7 summarises the findings of the thesis and directions for future fin damage related research and potential management strategies. The results of this thesis show that food withdrawal is a major risk factor in the development of fin damage. Results also indicated that environmental enrichment reduced the occurrence of fin damage and stress levels, improved growth in the early developmental stages and fish were more spatially distributed, suggesting an overall improvement in general welfare. The significance of the effect of food withdrawal on fin damage has not previously been reported and this is the first report of enrichment effects at the farm-level.