The Norwegian Food Safety Authority (NFSA) asked VKM for an opinion of risks of reduced welfare implications associated with different marking and tracing methods, and combinations thereof, for farmed salmonid fish in Norway.

A variety of methods

A variety of different methods are available for marking and tracing of farmed fish. Marking is commonly done by attaching a tag, either externally on the surface of the skin, in tissue, or internally in the body. Visible marking methods, such as adipose fin removal, freeze branding, or injection of pigments may be used for rapidly identifying fish. Other marking methods such as “snout tags” and PIT tags (Passive Integrated Transponder) require a detector for distinguishing farmed from wild fish. Naturally occurring markers, such as scales, may also be used to trace and determine the origin of fish found in nature.

The methods differ with regard to the suitability of actually distinguishing wild from farmed (escaped) fish in the field. External marks may be lost or fade over time. Adipose fin removal is the only definitely visible and 100 percent permanent marking method, as the adipose fin will not regenerate.

Conclusions

All marking procedures involve handling of fish. This is stressful to the fish, and/or may induce pain. All external 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.
VKM concluded that there are no combinations of marking and tracing methods that are feasible without an increased risk of reduced animal welfare.

Data gaps

VKM also recognizes a number of uncertainties and data gaps related to how and to what extent the different marking methods may affect fish welfare.

VKMs panel on Animal Health and Welfare is responsible for the risk assessment.