New research on Atlantic salmon scale growth

Research from Dr Katie Thomas of the Marine Institute has investigated the mechanisms for growth mark formation in scales of Atlantic salmon (Salmo salar Linnaeus) and the cause of variations in scale growth measurements.

Written by: editorial / Marine Institute Ireland

Dr Thomas recently graduated with her PhD entitled ‘Scale Growth Analysis of Atlantic salmon (Salmo salar L) Unlocking Environmental Histories’ from the Galway-Mayo Institute of Technology (GMIT) under the supervision of the Dr Niall Ó Maoiléidigh, Marine Institute, Dr Deirdre Brophy, GMIT and Tom Hansen, Institute of Marine Research Norway. The PhD was funded by the Marine Institute, the Institute of Marine Research Norway and the Loughs Agency, Northern Ireland.

The Atlantic salmon is native to the temperate and sub-Arctic regions of the North Atlantic Ocean, and utilises rivers for spawning and nursery, and the marine environment for adult feeding, development and rapid growth. Direct observation of the salmon’s life is challenging and costly, so scales are widely used to assess and monitor changes in growth.

“The entire life history of an individual fish is recorded on a scale which begins to form during the fry stage of the lifecycle. As the scale develops, it lays down concentric ridges or rings called circuli, which look similar to rings on a tree. The number of circuli on a scale and the distances between each circuli are measured to provide a history of individual and population growth histories. These changes over time can be used to infer the salmons use of the ecosystem, and indicate whether changes in growth are apparent over time and between populations,” Dr Thomas said.


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