Modifying Atlantic salmon behaviour with light or feed stimuli may improve parasite control techniques

Abstract

The aquaculture of Atlantic salmon Salmo salar faces severe health, environmental and economic concerns caused by the parasitic sea lice Lepeophtheirus salmonis and Caligus spp. An experimental delousing method exists whereby the surface jumping behaviours of salmon are combined with a floating, oil-infused chemical therapeutant, resulting in the fish dousing themselves passively. We tested whether a light stimulus or feed event, or a combination of both, during submergence (denial of surface access for the fish) increased the surface-oriented behaviours of salmon. Groups of 10 salmon were submerged in a sea-cage for 19 h and exposed to a light stimulus, feed event, or both. Control treatments involved submergence only. For a 2 h period after surface access was reinstated, light and feed treatments induced a higher proportion of individuals to exhibit surface behaviours. On average, 84 and 82% of salmon in the light and feed treatments jumped, respectively, which was 1.6 times higher than fish in the control group (50%). Salmon exposed to light or feed jumped an average of 1.7 and 1.5 times after exposure to light or feed treatments, respectively, compared to 0.92 jumps fish -1 for the control. The combined light and feed treatment did not produce a synergistic effect. The average time until first jump was 31 to 50 min, with no difference in times among treatments. The elevated surface-oriented behaviours effectively crowded the majority of the fish in the surface waters within a short period of time. This increased surface activity may be used for a range of salmon farming applications, including improving the efficacy of sea-lice treatment techniques.

Behaviour in the toolbox to outsmart parasites and improve fish welfare in aquaculture

“…When access to the surface is removed for a short period (submergence) and reinstated, an increase in jumping and rolling behaviours is observed (Dempster et al 2008). Therefore, these behaviours could be encouraged through temporary submergence, ultimately reducing the attachment of parasites (Dempster et al 2011;Bui et al 2013).…”

Salmonid Jumping and Playing: Potential Cultural and Welfare Implications

“…are parasitic crustaceans (Siphonostomata: Caligidae). They represent a challenge to the net pen culture of Atlantic salmon [ 4 , 17 , 18 , 19 ]. An ingenious control scheme for this parasite [ 4 ] exploits the natural tendency of Atlantic salmon to jump out of the water.…”

“…194–195), [ 7 ] (p. 175), [ 8 ] (p. 136), [ 9 ] (p. 143)). It is important in practical fish culture and management, especially in the control of sea lice [ 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ] and in fishway design [ 20 , 21 , 22 , 23 , 24 ].…”

Behaviour in Atlantic salmon confers protection against an ectoparasite

“…All fish were tagged adjacent to the dorsal fin with an anchor tag (11 cm, Hallprint Ltd, Australia) with unique colour combinations (e.g. Bui et al ., ). Fish in the sedated treatment ( N = 29) were then injected into the dorso‐posterior lateral muscle with a volume containing a 40 mg kg −1 dose of ketamine hydrochloride (in solution at 10 mg ketamine base millilitre; Ketalar ™ ), calculated specifically for each individual according to their weight.…”