Behavioural and physiological responses of lumpfish (Cyclopterus lumpus) exposed to Atlantic salmon (Salmo salar) sensory cues

Abstract First interaction with carnivorous clients induces stress responses even in the boldest of cleaner fishes observed in nature. This is relevant for the expanding use of lumpfish in aquaculture, where stress could impede the species ability to interact with Atlantic salmon. The study investigated how naive lumpfish (34.3 g, S.D. ± 6.48) responded to different heterospecific cues including (1) exposure to water from a tank with Atlantic salmon (“Olfaction”), (2) salmon lifelike models (“Model”) and (3) Atlantic salmon (“Live”). Experiments were repeated thrice, using duplicate tank replicates on each occasion (n = 36 per treatment). Behaviour was recorded 30 min before and 30 min after the introduction of each treatment. Responses measured included swimming activity, body colour and pigmentation, neurotransmitters, and plasma cortisol. Data demonstrated a significant increase in swimming activity upon introduction of Olfaction and Live salmon, but not from Models. After 30 min of interaction, swimming activity decreased towards levels observed in control groups. Body colour significantly increased in lumpfish exposed to Olfaction while body pigmentation significantly increased in both Olfaction and Model treatments. Neurotransmitters and plasma cortisol measurements did not differ between treatments and control, yet large individual variation was observed. Our findings revealed that lumpfish discriminated salmon cues, whereas Olfaction induced the overall strongest behavioural and physiological responses. The study suggested that acute change in skin colour and pigmentation can be impacted by salmon interaction, yet deployment of naive juvenile lumpfish with small Atlantic salmon is preferable based on the overall mild stress responses.