Elevated mortality is a major selective force shaping life‑history strategies and how metabolic demand scales with body size. Theory predicts that high‑mortality environments favour individuals that grow rapidly, mature early, but sustain higher metabolic costs. Platycephalus bassensis populations across lutruwita/Tasmania experience contrasting recreational fishing pressure, yet it remains unclear whether these regional differences correspond to divergent metabolic phenotypes. We quantified standard and maximum metabolic rates (SMR and MMR) across broad size classes to test whether variation in the metabolic scaling exponent (β) or metabolic level (a) reflects region‑specific allocation strategies.
Forty‑three P. bassensis were sampled from the heavily fished south‑east (N=19) and lightly fished north‑east (N=24). Fish were acclimated for two weeks at 15.5 °C in a benthic RAS and fasted for 72 h before intermittent‑flow respirometry trials. SMR was estimated as the 10th percentile Mo₂ over 19 h, and MMR as the highest Mo₂ following a chase protocol. Hierarchical ANCOVA models with AICc selection evaluated regional differences in metabolic scaling.
State‑wide whole‑animal SMR (log₁₀ mg O₂ h⁻¹) scaled with mass at β = 0.78. Southern fish exhibited significantly higher metabolic level (a) than northern fish (16% increase, p = 0.04). Predicted SMR in northern fish remained stable across variation in Fulton’s K‑condition factor, whereas greater K in southern fish elevated predicted SMR at reference mass, indicating higher maintenance costs in better‑condition southern fish. MMR scaled similarly (~0.78) and significantly dampened with age (Age × Mass = −0.065).
These results provide the first comprehensive metabolic scaling exponent for P. bassensis and show that southern fish use more energy at every size, with body condition a key predictor of metabolic variation. Elevated metabolic demand suggests southern fish may be less tolerant to warming and more susceptible to angling interactions due to higher baseline energetic requirements.