Introduction: Fishes in a warming and deoxygenating world

Abstract

This account serves as the introduction to a Special Issue of the journal Environmental Biology of Fishes. It includes 18 contributions, 12 of which deal predominantly with warming, four explicitly with deoxygenation, one providing the framework, and one addressing how warming and deoxygenation—which all contributions view, implicitly or explicitly, as leading to “oxythermic” stress—are used as a pretext to cover up overfishing. The “Mean Temperature of the Catch” (MTC) concept of Cheung et al. (2013, Nature 497:365–368) inspired five of the studies involving mainly temperature, including its first applications to fresh water and to the past, i.e., to the past 130, 7–8 thousand, and 2 million years. Four contributions, jointly representing 4200 + populations and 1100 + species, deal with the effect of temperature on the maximum and/or the asymptotic length of fish behaving as predicted by the Gill-Oxygen Limitation Theory (GOLT). This theory is also evoked in one of these studies to explain how cold denaturation causes fish to grow to a smaller size when temperatures decline below 4 °C. These contributions, which are here summarized and whose conceptual affinities are also presented in graphic form as a tree-like structure, provide a basis for understanding the changes in fish community composition and size structure resulting from marine or freshwater warming. Jointly, they explain some of the changes in fish behavior and position in the water column resulting from the deoxygenation of their habitats.