Production, fasting and delousing of triploid and diploid salmon in Northern Norway — Report for the 2021- and 2022-generations

Abstract

This report is an investigation into the 2021- and 2022-generations of triploid Atlantic salmon (Salmo salar L.) in Northern Norway and their diploid counterparts. The trajectory of 22 fish groups comprising around 11 million fish is described throughout their production cycles. The commercially cultivated fish vary in origin and rearing environment, and experience different disease and treatment events. As such, although the dataset provides a unique overview of the salmon production cycle, it cannot be considered experimental in its nature as numerous factors were not controlled for. The data, do however, provide insight into all the complex assessment and trade-offs fish farmers and fish health personnel do to optimise the health and welfare of their fish. The data show that both movement of fish between farms and applying delousing treatments increases mortality in the weeks after the operation compared to before, regardless of ploidy. Mortality especially increased after thermal and mechanical treatments even though these were preferentially applied to fish perceived to be stronger. From the most meaningful comparisons in fish transferred to sea between April and August (e.g. Spring transfer), triploids developed a significant increase in winter ulcers during the first winter at sea, had a significantly higher loss at harvest (median, 12 versus 16%), a non-significant 8% reduction in harvest weight (median, 4.8 versus 4.4kg), and significantly fewer “superior” graded fish (medians, 95 versus 82%) compared to diploids. However, there was no ploidy effect on the feed conversion ratio. Therefore, despite some improvements compared to the 2020-generation, the 2021/22 triploid groups were still inferior to the diploid reference groups based on most of the economic and welfare indicators.

Production, fasting and delousing of triploid and diploid salmon in Northern Norway — Report for the 2021- and 2022-generations

Produksjon, fasting og avlusing av triploid og diploid laks i Nord-Norge - Rapport for 2021- og 2022-generasjonene