Thermal sensitivity and aerobic scope in paralarvae of Octopus tetricus

Temperature strongly influences metabolic performance and survival during the early life stages of cephalopods, yet the thermal requirements of octopus paralarvae remain poorly defined. This study examined the effects of temperature on metabolic rates and aerobic scope of gloomy octopus (Octopus tetricus) paralarvae to identify an optimal rearing temperature during the first four days post-hatch. Oxygen consumption was quantified using closed-system respirometry at six temperatures (12, 15, 18, 21, 24, and 27 °C) in paralarvae aged 0, 2, and 4 days post-hatch. Standard (SMR), routine (RMR), and maximum metabolic rates (MMR) were measured, and used to calculate aerobic scope (AS). Metabolic rates varied significantly with temperature, with both low and high thermal extremes depressing performance. AS exhibited a clear temperature-dependent parabolic pattern, peaking at 3.34 mg O₂ gDW^-1 h^-1. Quadratic modelling identified an optimal temperature (T_opt) of 18.98 °C. Behavioural observations aligned with physiological trends as paralarvae at cooler temperatures showed reduced activity and delayed exhaustion, whereas elevated temperatures increased metabolic demand and reduced aerobic capacity. Temperature-dependent Q₁₀ analyses revealed exceptionally high thermal sensitivity immediately post-hatch, which moderated rapidly by 4 dph, indicating strong early developmental constraints and a narrowing of physiological vulnerability with age. These findings indicate that rearing O. tetricus paralarvae at ∼19 °C maximizes aerobic performance during a critical developmental window when individuals transition from yolk utilisation to active predation. This study provides the first empirically derived T_opt for any octopus paralarva and establishes a physiological basis for refining aquaculture protocols while informing predictions of early-life sensitivity to ocean warming.