Risk assessment of marking and tracing methods with regards to the welfare of farmed salmonids. Opinion of the Panel on Animal Health and Welfare.

The Norwegian Food Safety Authority (NFSA) asked the Norwegian Scientific Committee for Food Safety (VKM) for an opinion of risks of reduced welfare implications associated with the different marking and tracing methods, and combinations thereof, for farmed salmonid fish, restricted to Atlantic salmon (Salmo salar) and Rainbow trout (Oncorhynchus mykiss) in Norway. A working group was established comprising members from the Panel on Animal Health and Welfare and external experts from the Institute of Marine Research, the Norwegian Institute of Nature Research, and VKM staff. The Panel on Animal Health and Welfare has reviewed and revised the draft prepared by the working group and has approved the opinion.

There are environmental concerns of escaped farmed salmon interbreeding with wild fish, potentially threatening genetic integrity, and transmission of diseases. The Norwegian government intends to prevent or reduce escapes of farmed salmonids from occurring, and wishes to have those farmed fish that have escaped removed from the environment. In order to facilitate these actions, it is essential to be able to identify escaped fish. In addition, reliable methods for tracing the origin of the escaped fish are also crucial. Mandatory marking of all farmed fish in Norwegian aquaculture has therefore been suggested. On this basis, this VKM report will be used by the NFSA to evaluate which marking methods are most suitable, from both short- and long-term perspectives, in relation to the Animal Welfare Act.

In order to fulfil the requirements, the marking must enable visual identification of escaped fish and also enable an individual fish to be traced back to its origin. There is no single marking system that fulfils both these criteria.

A variety of marking and tracing methods are available for mass marking of farmed fish. These methods differ with regard to their suitability for actually distinguishing wild from farmed (escaped) fish in the field. External marks may be lost or fade over time. Morphology will often differ between wild and farmed fish. However, the differences are often small if the fish has escaped early in the production cycle. Reliable determination of origin, based on morphological variation, requires experience and handling of the fish. Adipose fin removal is the only definitely visible and 100 % permanent marking method, as the adipose fin does not regenerate.

Marking is commonly done by attaching a tag, either externally on the surface of the fish, in tissue, or internally in the body. All marking procedures involve handling fish; this is stressful to the fish, and/or may induce pain. All marking will therefore have an impact on fish welfare. With most marking methods, the risk of reduced fish welfare decreases with time.

Tracing methods differ with regard to their suitability for being used to trace the marked fish back to its origin, either on an individual level (a mark that identifies each fish) or the farm level (a mark that identifies each farm).

In order to visually identify escaped fish and enable tracing back to the farm of origin, a combination of both marking and a tracing method, with sufficient number of available codes, is necessary. Visible marking methods, such as adipose fin removal, VIA tags, VIE tags, freeze branding, or injection of pigments may be used for identifying the fish. These can be combined with tracing using natural marks or the use of CW tags or PIT tags that, with varying reliability, may enable both identification of a fish on an individual level or batch level and from where it originated. Chemical marking along with all types of natural marks (i.e. scales, otoliths, biochemical or genetic composition in tissue) was evaluated as representing the lowest risk of reduced fish welfare. However, these marks require analysis after catch and sampling, in order to determine whether the fish is wild or farmed. All other marking methods presented in this report represent a high risk of reduced fish welfare during or shortly after marking. This risk is reduced to moderate for most of the methods on a long-term scale. Spraying of pigments and most externally attached tags remain a high risk of reduced welfare, on both short-term and long-term scales.

VKM concluded that there are no combinations of marking and tracing methods that are feasible without an increased risk of reduced animal welfare.

VKM also recognizes a number of uncertainties and data gaps related to how and to what extent the different marking methods affect may fish welfare. For example, the functional role of the adipose fin is still unclear, making evaluation difficult concerning how fin clipping affects fish long term. It must also be emphasized that, regardless of the method used to tag fish, there will always be higher risks of reduced fish welfare associated with large-scale marking as opposed to small-scale marking. VKM therefore highlights the need for more scientific documentation and suggests that marking methods should be tested in large-scale trials.