This site presents facts from scientific research to show that fish feel pain, and expose the cruelty involved in angling: http://www.fishpain.com/
“‘Catch and release’ anglers kill the fish inadvertently at a later time. The fish may die from damage from hooks, stress or be attacked by predators while they are helplessly hooked. While “humane slaughter” for other animals killed for their flesh is a marketing myth, there is not even this pretence when fish are killed. They instead struggle and gasp while they slowly suffocate to death. Just because fish die in silence, does not mean that they do not suffer.
Not only can fish detect and perceive painful events, but they also show disturbed behaviour.
Russian scientists found that loach made sounds with their swim bladders immediately after being wounded.
Fish pain expert, Dr Lynn Sneddon, experimented with trout, where she injected painful bee venom or vinegar into their lips. Disturbingly, they showed their suffering by breathing twice as quickly, swimming less, ceasing to feed, rocking backwards and forwards, and rubbing their lips on the ground and tank walls. These are signs of pain that we can empathise with.
Most anglers are deluded into believing that the fish that they release swim away unaffected by their encounter. This is not the case. Many fish will suffer and die, sometimes several hours later, once the culprit has left the scene. Studies have found that a third, half, or even more fish can die at a site.
Fish caught at tournaments are at the greatest risk of dying, as they are often repeatedly caught in the same day. Damage by hooks, exhaustion, and sometimes excessive pressure when the fish is brought to the surface, all contribute to loss of life. However, the mere trauma of capture, even for short periods, can herald death.”