Orth claims that whenever someone uses fish for any reason, they need to ask certain questions: How might these actions influence fish? Do fish feel pain? Do fish suffer? Are fish aware of their actions? Do fish in captivity have what they want? Is the fish healthy? How can humans balance fish welfare with the benefits they get from fish? This chapter presents the factual evidence and philosophical views and practices related to minimizing pain and suffering in fish.

In this review, Lambert et al. have sought to (1) catalog the extent to which fish sentience has featured over the past 31 years in the scientific literature and (2) discuss the importance of fish sentience in relation to their commercial uses. They searched a journal database using 42 keywords that describe traits or elements of sentience to find articles that were referring to or exploring fish sentience. Their review returned 470 results for fish sentience in 142 different species and subspecies of fish, and featured 19 different sentience keywords. The top four keywords were; “stress” (psychological), “anxiety,” “fear,” and “pain.” Their findings highlight an abundance of evidence for fish sentience in the published scientific literature. Lambert et al. conclude that legislation governing the treatment of fish and attitudes towards their welfare require scrutiny so that their welfare can be safeguarded across the globe.

This article discusses the ongoing debate about whether fish feel pain or merely respond to nociception (tissue damage). The authors review concepts of consciousness and identify “red herring” measures they argue should not be used to infer sentience because these are also present in non-sentient organisms. They suggest that more valid indicators might include working memory, operant conditioning, and higher-order cognition. Due to the lack of definitive evidence, the debate remains unresolved. The authors call for precautionary principles to protect fish welfare while acknowledging the high evidential standards required to prove fish sentience.

Contemporary studies over the last ten years have demonstrated that bony fish possess nociceptors, the simple detection of potentially painful stimuli usually accompanied by a reflex withdrawal response; that these are similar to those in mammals; that they demonstrate pain-related changes in physiology and behavior that are reduced by painkillers; that they exhibit higher brain activity when painfully stimulated; and that pain is more important than showing fear or anti-predator behavior in bony fish. This review will assess the field of pain perception in aquatic species, focusing on fish and selected invertebrate groups to interpret how research findings can inform human understanding of the physiology and evolution of pain. Further, if one accepts that these animals may be capable of experiencing the negative experience of pain, then the wider implications of human use of these animals should be considered.

Bshary and Brown present two reasons why fishes are a particularly interesting group of vertebrates to study cognition. First, they occupy a key position in the vertebrate phylogenetic tree, thus sharing key genetic features that code for the body structure (e.g., the vertebrate brain). The second reason to study fish cognition is that fish have had their own independent evolution/radiation since they split from tetrapods. Bony fishes are by far the most species-rich vertebrate group and thus provide the best options for a comparative approach that aims to link the evolution of cognition to a species’ ecology. Bshary and Brown provide some examples of fish cognition research and highlight two major areas in which fish have made a substantial contribution to human understanding of the evolution of cognition: social cognition and spatial learning.

Brown reviews the current state of knowledge of fish cognition starting with their sensory perception and moving on to cognition. The review reveals that fish perception and cognitive abilities often match or exceed other vertebrates. A review of the evidence for pain perception strongly suggests that fish experience pain in a manner similar to the rest of the vertebrates. Although scientists cannot provide a definitive answer on the level of consciousness for any non-human vertebrate, the extensive evidence of fish behavioral and cognitive sophistication and pain perception suggests that best practice would be to lend fish the same level of protection as any other vertebrate.