Research Article
Atle Mortensen, Oyvind J Ha
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.