First link when you google 'do fish feel pain'
http://news.bbc.co.uk/2/hi/science/nature/2983045.stmFish do feel pain, scientists say
By Alex Kirby
BBC News Online environment correspondent
The first conclusive evidence of pain perception in fish is said to have been found by UK scientists.
Rainbow trout BBC
Fish have pain receptors like us
This complements earlier findings that both birds and mammals can feel pain, and challenges assertions that fish are impervious to it.
The scientists found sites in the heads of rainbow trout that responded to damaging stimuli.
They also found the fish showed marked reactions when exposed to harmful substances.
The argument over whether fish feel pain has long been a subject of dispute between anglers and animal rights activists.
The research, by a team from the Roslin Institute and the University of Edinburgh, is published in Proceedings B of the Royal Society, the UK's national academy of science.
The researchers, led by Dr Lynne Sneddon, say the "profound behavioural and physiological changes" shown by the trout after exposure to noxious substances are comparable to those seen in higher mammals.