Abstract
Estuaries supply a critical habitat to many ecologically and commercially valuable fish species, providing safety and food availability during the larval and juvenile stages. However, dissolved oxygen is naturally dynamic in these systems, varying from complete anoxia to hyperoxia. In some species, the larval stage may be particularly vulnerable to low‐oxygen stress due to incomplete development of oxygen transport systems, high metabolic cost associated with early feeding and a narrow aerobic scope to support additional activity. Increasing seawater temperatures further increase oxygen demand in poikilothermic species and are amplified in shallow inshore habitats. In teleost fish, estuarine hypoxia and warming may lead to recruitment bottlenecks at the larval stage, which often requires a narrower range of environmental conditions than juveniles or adults. Here, we compared the physiological oxygen supply capacity ( α ) and aerobic scope of late‐larval and early‐juvenile common snook Centropomus undecimalis (Bloch 1792), a coastal marine species found in the Gulf of Mexico, Caribbean and western Atlantic from Florida to Brazil. We hypothesized that larvae would be more hypoxia sensitive than juveniles but instead found that routine and maximum metabolic rates scaled similarly with body mass, resulting in size independence of factorial aerobic scope and critical oxygen partial pressure between life stages. The α value matched maximum demand across the transition from larval to juvenile stages, suggesting that C. undecimalis can effectively regulate the supply of oxygen from the environment to their tissues as early as 17 days post hatching. Additionally, C. undecimalis exhibited a P cmax value of 18.63 kPa, indicating that their full aerobic potential can be met only at oxygen pressures near air saturation. Although this is the expected P cmax based on their previously reported prevalence in surface waters, this may lead to reduced habitat availability as estuarine deoxygenation worsens in the Gulf of Mexico.