Are fish early growth and condition patterns related to life-history strategies?

Life-history studies provide a global framework for comparison of fish species responses and trade-offs facing ecological and environmental constrains. A broad comparison among fishes' early growth and condition traits is performed in order to determine ecological patterns of early development regarding latitudinal distribution, habitat use and life-history strategies. Based on Winemiller and Rose (1992) classification of life-history strategies, data on early growth and condition indices of 46 fish species worldwide was analysed. Available information on fishes' early features, namely first year length percentage (relative to species maximum theoretical length), age at maturation and Fulton's condition index (K), provided a good segregation of species by latitudinal distribution and habitat use, and evidenced the categories of the three-endpoint model. Higher larvae and juvenile growth rates and condition indices (K, mean RNA-DNA ratios and protein contents) were associated with tropical and temperate fish species that occur in complex or variable habitats (respectively coral reefs and estuaries). These species selected for the opportunistic and periodic strategies, investing highly in rapid growth in order to increase survival probability to counter high mortality rates during early stages or unstable habitat conditions. Later age at maturation, slower larvae and juvenile growth as well as lower mean condition indices were consistent with fish species from more stable or predictable environments, as polar regions and freshwater habitats, which selected for the equilibrium strategy. Nonetheless, differences in energy allocation strategies during early stages were not observed, evidencing the scarcity of available data regarding condition indices and/or the importance of integrating life-history intermediate strategies. Future research into condition indices and other physiological processes, for a broader set of species and for a wider latitudinal and habitat range including seasonal variability (particularly for species from tropical and polar regions), is essential to better understand or test current theories of species ecological patterns. The use of direct quantitative measures of young fishes' metabolic investment and fitness constitutes a new approach for life-history studies, and should be fundamental for predicting species' responses to acute environmental or human constrains, especially in a global climate change scenario that is expected to affect distribution and abundance of fish species worldwide.