The Well – Mixing skirt and freshwater lens concepts with smart-lighting and -feeding to enhance lice prevention and safeguard fish welfare

Abstract

A commercial scale sea-cage design, combining skirt and freshwater lens concepts with smart lighting and feeding for improved lice prevention and fish welfare, was trialed. Environment, lice levels and fish welfare were assessed. In addition, acoustic tags and echo sounders were used to track fish behaviour. An associated laboratory trial on brackish water salinity effects on host-attached salmon lice was also conducted. We found that within the interval standard skirt and freshwater lens skirt cages were fully-functioning, there was no significant effect on lice levels or fish welfare. Fish behaviour monitoring found variable use of the freshwater lens, though night lighting appeared to increase fish residence in the low salinity space provided. From this work an ultimate conclusion on the effectiveness of this technology cannot be drawn, but it is clear that a less saline brackish water is needed in combination with higher residence time of the fish to have a substantial reducing effect on lice levels on caged salmon. The lab scale trial suggested that to delay host-attached lice development < 12 ppt is required and to kill host-attached copepodids < 4 ppt is needed over durations of 3 hours or more.

The Well – Mixing skirt and freshwater lens concepts with smart-lighting and -feeding to enhance lice prevention and safeguard fish welfare