Edelman, David B. (2016) Leaving the door open for fish pain: Evolutionary convergence and the utility of ‘just-so stories’. Animal Sentience. 3(36)
Brian Key, Why fish do not feel pain
Key argues that fish do not experience pain because they lack the necessary (but not necessarily sufficient) brain structures and associated functional circuitry to engender such conscious percepts. I propose that fish pain may be dependent on neuroanatomical regions and pathways that are structurally and/or functionally analogous — but not strictly homologous — to well-characterized mammalian substrates of pain. An example is the convergent appearance of the complex, single-compartment eye across invertebrate and vertebrate phylogeny. Structural-functional convergence is ubiquitous in evolution. Comparative inferences and correlative lines of evidence play an important role in building evolutionary arguments. The dismissal of the perception of pain in fish may be premature at best.