Increasing Dip Net Mesh Size Results in More Fin Splits in Post-Smolt Atlantic Salmon (Salmo salar)

• Published in: Journal of applied animal welfare science Vol. 27; no. 4; pp. 666 - 678
• Main Authors: Moltumyr, Lene, Stien, Lars Helge, Madaro, Angelico, Nilsson, Jonatan
• Format: Journal Article
• Language: English
• Published: England Taylor & Francis 01.10.2024
• Subjects: Animal Fins - injuries; Animal Welfare; Animals; Aquaculture; dip-netting; external injuries; fin splits; Gear effects; Housing, Animal; Salmo salar - injuries; scale losses; fin splits; Gear effects; dip-netting; external injuries; scale losses
• ISSN: 1088-8705; 1532-7604; 1532-7604
• DOI: 10.1080/10888705.2022.2152689

Dip nets are widely used to retrieve fish from the water but can cause injuries to the fish. The objective of this study was to document the potential effects of dip net mesh size with respect to external injuries, more specifically fin splits and scale losses, in Atlantic salmon (Salmo salar). The study included 273 post-smolt Atlantic salmon from two fish batches referred to as the Tank group ( $$\bar w$$ w ˉ  = 178 ± 36 g, n = 198) and the Cage group ( $$\bar w$$ w ˉ  = 1319 ± 334 g, n = 75). Four identical dip nets with mesh sizes of 5, 10, 15, and 20 mm, respectively, were used to net fish out of their enclosures before the external injuries were assessed by visual inspection. The results showed that the number and severity of fin splits increased with dip net mesh size, but no effect of mesh size on the percentage of scale losses was found. Dip-netting of five fish at a time instead of one with the 20 mm dip net, had no statistically significant effect on the examined injuries. It is concluded that the use of dip nets with smaller mesh sizes can be positive for fish welfare by reducing fin splitting.