Prof Alan Roberts, in giving his opinion on the ability of fish to experience pain ( Can fish feel pain? The jury is still out, Letters, 7 April), neglected to mention the wealth of published scientific evidence outside of behavioural and hormonal responses. I was the first to identify the existence of nociceptors in a fish, the rainbow trout, in 2002. These are specialised receptors for detecting injury-causing stimuli, and their physiology is...