Effects of acute hypoxia exposure and acclimation on the thermal tolerance of an imperiled Canadian minnow.

Elevated water temperatures and low dissolved oxygen (hypoxia) are pervasive stressors in aquatic systems that can be exacerbated by climate change and anthropogenic activities, and there is growing interest in their interactive effects. To explore this interaction, we quantified the effects of acute and long-term hypoxia exposure on the critical thermal maximum (CT) of Redside Dace (Clinostomus elongatus), a small-bodied freshwater minnow with sparse populations in the Great Lakes Basin of Canada and designated as Endangered under Canada's Species at Risk Act. Fish were held at 18°C and acclimated to four levels of dissolved oxygen (>90%, 60%, 40%, and 20% air saturation).

Estimating maximum oxygen uptake of fishes during swimming and following exhaustive chase - different results, biological bases and applications.

The maximum rate at which animals take up oxygen from their environment (ṀO2,max) is a crucial aspect of their physiology and ecology. In fishes, ṀO2,max is commonly quantified by measuring oxygen uptake either during incremental swimming tests or during recovery from an exhaustive chase. In this Commentary, we compile recent studies that apply both techniques to the same fish and show that the two methods typically yield different mean estimates of ṀO2,max for a group of individuals.

Interindividual variation in maximum aerobic metabolism varies with gill morphology and myocardial bioenergetics in Gulf killifish.

This study asked whether interindividual variation in maximum and standard aerobic metabolic rates of the Gulf killifish, Fundulus grandis, correlates with gill morphology and cardiac mitochondrial bioenergetics, traits reflecting critical steps in the O2 transport cascade from the environment to the tissues. Maximum metabolic rate (MMR) was positively related to body mass, total gill filament length and myocardial oxygen consumption during maximum oxidative phosphorylation (multiple R2=0.836).

Plasticity, repeatability and phenotypic correlations of aerobic metabolic traits in a small estuarine fish.

Standard metabolic rate (SMR), maximum metabolic rate (MMR), absolute aerobic scope (AAS) and critical oxygen tension () were determined for the Gulf killifish, , an ecologically dominant estuarine fish, acclimated to lowered salinity, elevated temperature and lowered oxygen concentration. Acclimation to low salinity resulted in a small, but significant, elevation of (suggesting lower tolerance of hypoxia); acclimation to elevated temperature increased SMR, MMR, AAS and ; acclimation to low oxygen led to a small increase in SMR, but substantial decreases in MMR, AAS and Variation in these metabolic traits among individuals was consistent and repeatable when measured during multiple control exposures over 7 months. Trait repeatability was unaffected by acclimation condition, suggesting that repeatability of these traits is not context dependent.

Standardizing the determination and interpretation of in fishes.

The critical oxygen tension () for fishes is the oxygen level below which the rate of oxygen consumption ( ) becomes dependent upon ambient oxygen partial pressure ( ). We compare multiple curve-fitting approaches to estimate of the Gulf killifish, , during closed and intermittent-flow respirometry. Fitting two line segments of  versus  produced high and variable estimates of , as did nonlinear regression using a hyperbolic (Michaelis-Menten) function.

Independent and Interactive Effects of Long-Term Exposure to Hypoxia and Elevated Water Temperature on Behavior and Thermal Tolerance of an Equatorial Cichlid.

Hypoxia and climate warming are pervasive stressors in aquatic systems that may have interactive effects on fishes because both affect aerobic metabolism. We explored independent and interactive effects of dissolved oxygen (DO) and temperature on thermal tolerance, behavior, and fitness-related traits of juvenile F offspring of the African cichlid Pseudocrenilabrus multicolor. Fish were reared in a split-brood design with four treatments (low or high DO, cool or hot temperature); thermal tolerance, growth, and condition were measured after 1 mo in the rearing treatments, following which behavioral traits were measured over 3.

Effects of passive integrated transponder tagging on cortisol release, aerobic metabolism and growth of the Gulf killifish Fundulus grandis.

The effects of passive integrated transponder (PIT) tagging on cortisol release, standard metabolic rate (SMR) and daily specific growth rate (G ) were evaluated in the Gulf killifish, Fundulus grandis, a small estuarine fish native to the Gulf of Mexico. Cortisol release by individual fish was measured non-invasively prior to PIT tagging, immediately after tagging and once per week for 1 month following tagging. Within the first 2 h of tagging, cortisol release rates were significantly elevated compared with values measured prior to tagging and significantly higher than that of fish handled identically except not implanted with PIT tags.