Effect of noxious stimulation upon antipredator responses and dominance status in rainbow trout

Abstract

A potentially painful experience may modify normal behavioural responses. To gauge the importance of pain relative to predation or social status, we presented competing stimuli, a predator cue or an unfamiliar social group, to two groups of noxiously treated rainbow trout, Oncorhynchus mykiss. In the predator cue experiment, fish were classified as bold or shy. Noxiously stimulated fish did not show antipredator responses, suggesting that pain is the imperative. In the social status experiment, noxiously stimulated fish held individually and undisturbed showed an increase in respiration rate and plasma cortisol. As a comparison, we used the dominant or subordinate fish in a group as the noxiously stimulated fish. After the noxious treatment, we returned this test fish to a familiar or unfamiliar social group. Neither dominants nor subordinates showed a negative change in physiology compared to their controls. However, in a familiar group the dominant was much less aggressive, suggesting a behavioural impairment in response to noxious stimulation. In an unfamiliar group, no reduction of aggression was seen, suggesting that maintaining dominance status took priority over showing signs of pain. These findings may reflect an ability to prioritize motivational drivers in fish, and as such provides evidence for central processing of pain rather than merely showing a nociceptive reflex. In animal models of pain, exposure to a new circumstance or a potentially fear-inducing or stressful situation reduces pain reactivity (e.g.

Plasticity of boldness in rainbow trout, Oncorhynchus mykiss: do hunger and predation influence risk-taking behaviour?

“…Whilst this should be considered when interpreting behaviour, alarm pheromone does elicit antipredator responses even in farmed trout (Ashley et al, 2009), though comparisons between wild and farmed individuals could be explored in future studies.…”

“…Predation risk was simulated by using a plastic heron head (Ardea cinerea) mounted on a pole to simulate a predator attack (see Johnsson et al, 2001b;Jönsson et al, 1996). Attacks were made from behind a screen to prevent association with the presence of a human, and consisted of three swift strikes into the water followed by (Smith, 1992) with rainbow trout increasing cover use and decreasing activity and feeding (Ashley et al, 2009;Brown and Smith, 1998). Alarm substance was prepared from dissected skin from non-experimental trout that was then washed with sterile distilled water (SDW) and homogenised in 50 ml Falcon tubes containing 6.25 ml SDW per 1 g skin.…”

Pain in aquatic animals

“…Opercular beat rate (ventilation of the gills) is dramatically increased more than in a stress response in rainbow trout and zebrafish (Danio rerio) when they are injected with noxious chemicals. Additionally, an increase in plasma cortisol has been recorded in rainbow trout (Sneddon, 2003b;Ashley et al, 2009) 2008b; Correia et al, 2011;Roques et al, 2012). Guarding behaviour (such as avoiding using an area in which a painful stimulus has been administered) has been recorded in trout, who avoid eating after a painful injection to the lips for up 3 h (Sneddon, 2003b); sham-handled (anaesthetized only) and saline-injected controls resume feeding after 80 min as do acid-injected fish when treated with a painkiller.…”

Characterisation of chemosensory trigeminal receptors in the rainbow trout,Oncorhynchus mykiss: responses to chemical irritants and carbon dioxide

“…The mixture was then homogenised and centrifuged for 15min at 3500g at 4°C. The supernatant was extracted, filtered to remove debris, placed in a clean 50ml tube and frozen at 20°C (Ashley et al, 2009). Samples were defrosted and allowed to warm to room temperature before use.…”

“…The alarm pheromone was produced from rainbow trout skin using a behaviourally validated method (Ashley et al, 2009). It was extracted by skinning humanely killed trout, rinsing the skin with deionised water and cutting it with a razor to damage the cells.…”