Body size, functional form and environmental correlates of maximum longevity in marine-occurring fishes.

Maximum longevity varies widely among marine-occurring fishes, but the form of its relationship with body size and the contribution of broad environmental gradients remain uncertain. We analysed 757 species, using maximum length as the primary size metric and completed mass only in sensitivity analyses. A quadratic length model improved fit over a linear comparator and captured broad attenuation in the size-longevity association. Maximum depth was positively associated with log10 maximum longevity after accounting for this curvature (estimate per 1000 m = 0.0692, 95% CI 0.0312 to 0.1072, p < 0.001). Latitude estimates varied among range-based metrics and model specifications, and the latitude term performed less consistently when entire families and orders were withheld. None of the group or continuous-interaction contrasts met the defined FDR threshold of q < 0.05. FishTree matched 605 species but excluded every elasmobranch in the canonical dataset; branch-length phylogenetic generalized least squares (PGLS) therefore provides a matched-subset sensitivity rather than full phylogenetic coverage. Linear contrasts from 5000 species-level bootstrap resamples and nonlinear quantile sensitivities did not indicate broad upper-tail steepening. Teleostei-only, broad-Class-adjusted and Family-clustered analyses retained a positive maximum-depth coefficient, whereas latitude was less stable under clustered uncertainty. Body size and maximum depth thus provide the most consistent macroecological associations with maximum longevity. Latitude remains exploratory, and the data do not identify causal mechanisms.