Warm and cold temperatures limit the maximum body length of teleost fishes across a latitudinal gradient in Norwegian waters

As the majority of marine organisms are water-breathing ectotherms, temperature and dissolved oxygen are key environmental variables that influence their fitness and geographic distribution. In line with the temperature-size rule (TSR), marine ectotherms in warmer temperatures will grow to a smaller maximum body size, yet the extent to which different species experience this temperature-size response varies. Here, we analysed the maximum body length of ten teleost fish species in line with temperature, dissolved oxygen concentration and geographic location (that encompasses multiple latent variables), across a broad (26°) latitudinal gradient throughout Norwegian waters. Our results showed that the two largest study species, spotted wolffish (Anarhichas minor) and cusk (Brosme brosme), display the strongest negative temperature-size response. We also observed smaller maximum body lengths for multiple species within the coldest extent of their temperature range, as well as parabolic relationships between maximum length and temperature for Atlantic wolffish (Anarhichas lupus) and beaked redfish (Sebastes mentella). The smaller maximum body lengths for high latitude species at both warm and cold temperature extremes of species’ thermal ranges corroborate the temperature-size mechanisms of the gill-oxygen limitation theory (GOLT), whereby spontaneous protein denaturation limits growth at both warm and cold temperatures.