Document Type

Letter to the Editor

Publication Date



Newby and Stevens’ (2008) paper ‘‘The effects of the acetic acid ‘pain’ test on feeding, swimming, and respiratory responses of rainbow trout (Oncorhynchus mykiss)’’ examines the effects of a noxious stimulus on the behaviour of trout in an attempt to replicate research conducted in my laboratory (Sneddon, 2003a; Sneddon, 2007; Sneddon et al., 2003a,b; Reilly et al., 2008). However, the authors used a different protocol to the one already published and I would like to respond to some of their points of discussion to provide scientific explanations for their results using data from my laboratory. The authors show that swimming behaviour and time to resume feeding are not impaired by administering 2% and 5% acetic acid subcutaneously but the fish do show the classic rise in respiration rate that has already been published. Recent electrophysiological investigations from my group have demonstrated that applying 2% acetic acid topically destroys nociceptor output and the neuron effectively dies (Ashley et al., 2006, 2007). Therefore, the lack of anomalous rubbing behaviours and resumption of feeding in the Newby and Stevens (2008) experiment can be attributed to them injecting such a high concentration of acid. If no nociceptive information is being conducted to the central nervous system then no behavioural changes will be elicited. This demonstrates the importance of following the experimental design of published studies to get comparable results (Sneddon, 2003a; Sneddon, 2007; Sneddon et al., 2003a,b; Reilly et al., 2008).


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