Forget the Pseudoscience : All Fish Feel Pain
The study of pain in fish
The View Underwater
Kahan, Dan M. and Peters, Ellen and Dawson, Erica Cantrell and Slovic, Paul, Motivated Numeracy and Enlightened Self-Government (September 3, 2013). Yale Law School, Public Law Working Paper No. 307.
Rose, J.D. (2002) The neurobehavioral nature of fishes and the question of awareness and pain. Reviews in Fisheries Science 10, 1–38.
Rose, J.D, Arlinghaus, R., Cooke, S.J., Diggles,B.K., Sawynok, W., Stevens, E.D and Wynne C.D.L. (2012) Can fish really feel pain? Fish and Fisheries, in press. DOI: 10.1111/faf.12010
Shiffman, D., Hammerschlagg N., Fisheries • Vol 39 No 9• September 2014
Sneddon, L.U. (2003b) The evidence for pain in fish. Use of morphine as an anaesthetic. Applied Animal Behaviour Science 83, 153–162.
Weber EP, Weisse C, Schwars T, Innis C, Klide AM Anesthesia, diagnostic imaging, and surgery of fish, Compend Contin Educ Vet. 2009 Feb;31(2): E11.
Every point I made above is supported by rigorous scientific research--I have included some of the most prominent, but it is easy to find more once one begins to research the subject in the literature. Countless studies on fish pain and their welfare have been done.