Environmental constraints shape growth plasticity, early maturation, and longevity in an endangered freshwater fish

Abstract The interaction between organisms and their environment strongly influence growth, longevity, and fitness, yet the roles of resource availability and predation remain poorly resolved for threatened freshwater fishes. This study investigates how environmental conditions shape growth, survival, and life-history traits in two spatially isolated populations of the endangered Macquarie perch ( Macquaria australasica ) inhabiting contrasting lotic and lentic habitats in south-eastern Australia. Age, growth, fecundity, and mortality were estimated from otolith and gonadal analyses; predation pressure was assessed through stomach content analysis of Maccullochella spp.; and compensatory growth was tested using a 12-month pond grow-out experiment. Fish from Cataract Dam exhibited markedly reduced growth and longevity (maximum length 174 mm TL and age 6 years) compared with conspecifics from an adjacent predator-free stream (241 mm FL, 11 years) and populations elsewhere across the species’ range. Reservoir mortality was high (46% annually), largely attributable to piscivory by Maccullochella species. Under food-rich conditions, individuals more than doubled in length and increased 13-fold in mass within 1 year, demonstrating strong growth plasticity. These findings highlight how resource limitation and predation regulate growth, maturation, and survival, while demonstrating that life-history plasticity enables rapid phenotypic responses critical to persistence under ecologically constrained conditions.