From form to function: Morphology as a proxy for life history and population performance in fish

Life history strategies emerge from trade-offs between growth, survival and reproduction and are key predictors of how populations respond to environmental disturbances. However, estimating these strategies typically requires detailed demographic data, which are unavailable for many species. Because morphological traits govern whole-organism performance, selection on ecological performance can link morphology with life history strategies. Morphological traits can thus be practical proxies for life history strategies, offering a scalable approach for data-deficient populations.

To test the hypothesis that morphological traits predict major life-history axes—and, by extension, population performance and resilience—via shared performance trade-offs, we parameterised dynamic energy budget integral projection models for 290 marine and freshwater fish species to quantify life history strategies and measured eight morphological traits from lateral-view photographs for each species. We used phylogenetically corrected principal component analysis to summarise life history strategies and morphological traits, and tested whether morphology predicts life history strategies, and whether either predicts population growth rate or demographic resilience.

Lateral size morphology, comprising body elongation, relative eye size and oral gape position predicted generation turnover depending on water column position, and predicted reproductive output depending on clade. Generation turnover, reproductive output and lateral size morphology predicted population growth rate and resilience, but population growth rate and resilience were not directly aligned, challenging common assumptions in fisheries management that treat them as interchangeable.

Our results support the hypothesis that morphologies linked to ecological performance scale up to shape demographic strategies, providing proof of concept that morphology can predict life-history strategies. They also highlight the potential to develop performance-based trait proxies for rapid, low-cost estimations of demographic vulnerability and recovery potential across data-poor fish populations—expanding the scope of life-history frameworks for fisheries management and conservation under increasing pressures from overfishing, habitat loss and climate change.