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

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.

A review of data collection methods used to monitor the associations of wild species with marine aquaculture sites

“…276 The removal of the adipose fin is also a common differentiation tactic when dealing with salmon. 278 Trace elements, stable isotopes, or microchemistry in scales 274,279 and otoliths, 274,280 as well as otolith thermal marking 281,282 have also been demonstrated to accurately distinguish wild from farmed individuals. These chemical analyses, especially in the case of otoliths which cannot be lost or regrown, potentially resulting in misleading signals, have advantages over fatty acid-based identification because fatty acids (see above)…”

“…Methods based on scale shape 275,276 and growth patterns 270,277 may also be effective to differentiate wild from farmed fish, as has otolith shape 276 . The removal of the adipose fin is also a common differentiation tactic when dealing with salmon 278 . Trace elements, stable isotopes, or microchemistry in scales 274,279 and otoliths, 274,280 as well as otolith thermal marking 281,282 have also been demonstrated to accurately distinguish wild from farmed individuals.…”