Evaluation of Three External Marking Methods of Farmed Atlantic Salmon for the Future Use of Differentiating it From Wild Atlantic Salmon

Atle Mortensen,Oyvind J Hansen

doi:10.4172/2155-9546.1000451

Abstract

We evaluated different external marking methods for farmed salmon to differentiate it from wild salmon without any special tools. Three marking methods were tested: 1) Adipose fin (AF) removal, 2) Freeze branding (FB) and, 3) Visible Implant Elastomer (VIE). Location of the marking method on the fish, combination of marking methods and degree of AF removal were tested in three experiments. Atlantic salmon parr weighing 20 g were marked either with individual marks or in combination of two. Further all the fish were also PIT tagged. They were kept in freshwater tanks for 4 months and later after smoltification, smolts were transferred to sea cages and kept for another 4 months. At the end of four (freshwater phase) and ten (sea cages) months, growth, survival and mark retention were recorded. All these methods had no significant effects on growth and survival compared to the control (no mark but only PIT tagged). Our results showed that of these methods, only complete removal of the adipose fin met the requirements for mark retention and was the cheapest and easiest method to automate. However, a larger commercial scale long-term testing of the AF clipping is required prior to implementing it. Further development of an automated fin clipping in combination with vaccination and an open discussion with consumers, buyers, and environmental groups are also warranted.

Highlights

Atlantic salmon escaping from sea cages in Norway has been increasing until 2006 and since due to the strict implementation of certification rules by the Norwegian Government; salmon escaping from sea cages has been reduced [1]
To cope with the potential problems caused by escaped salmon suggestions are emerging to mark all the farmed fish using externally visible tags/ marking so that any escaped salmon can be distinguished from wild salmon, and eventually traced back to the farm it has escaped from using genetic markers [5]
Marking method had a significant effect on the weight of the Atlantic salmon smolts in saltwater phase but no significant effects were found on length (p=0.025 and 0.054, respectively; Table 2)

Summary

Introduction

Atlantic salmon escaping from sea cages in Norway has been increasing until 2006 and since due to the strict implementation of certification rules by the Norwegian Government; salmon escaping from sea cages has been reduced [1]. It is suggested that farmed fish selected for trait may outcompete for resources (food, territory etc.) with wild fish [2] and genetic pollution can occur through interbreeding with wild fish [3]. To cope with the potential problems caused by escaped salmon suggestions are emerging to mark all the farmed fish using externally visible tags/ marking so that any escaped salmon can be distinguished from wild salmon, and eventually traced back to the farm it has escaped from using genetic markers [5]. Selection of an appropriate external marking method is largely depending on the purpose of the marking, cost effectiveness, retainability of the mark, effects on fish growth, survival and welfare and logistics such as detectability of the mark and legality of the method

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Results

Discussion

Conclusion