Temperature acclimation of mitochondria function from the hearts of a temperate wrasse (Notolabrus celidotus).

Understanding how mitochondrial function alters with acclimation may provide insight to the limits these organelles place on temperate fish hearts facing seasonal temperature fluctuations. This investigation determined if compromised cardiac mitochondrial function contributed to heart failure (HF) in the New Zealand wrasse Notolabrus celidotus acclimated at their mean summer and winter ocean temperatures. To test this hypothesis, fish were acclimated to cold (CA, 15°C) and warm (WA, 21°C) temperatures. The temperature of HF was determined by Doppler sonography and mitochondrial function in permeabilised cardiac fibres was tested using high resolution respirometry. Heat stress mediated HF occurred at a THF of 26.7±0.4°C for CA fish, and at 28.2±0.6°C for WA fish. Biochemical analyses also revealed that WA fish had elevated resting plasma lactate indicating an increased dependence on anaerobic pathways. When cardiac fibres were tested with increasing temperatures, apparent breakpoints in the respiratory control ratio (RCR-I) with substrates supporting complex I (CI) oxygen flux occurred below the THF for both acclimated groups. While WA cardiac mitochondria were less sensitive to increasing temperature for respirational flux supported by CI, Complex II, and chemically uncoupled flux, CA fish maintained higher RCRs at higher temperatures. We conclude that while acclimation to summer temperatures does alter cardiac mitochondrial function in N. celidotus, these changes need not be beneficial in terms of oxidative phosphorylation efficiency and may come at an energetic cost, which would be detrimental in the face of further habitat warming.

Ionoregulatory physiology of two species of African lungfishes Protopterus dolloi and Protopterus annectens.

Basic ionoregulatory physiology was characterized in two species of African lungfish, slender African lungfish Protopterus dolloi and West African lungfish Protopterus annectens, largely under aquatic conditions. There were no substantive differences between the two species. Plasma [Na], [Cl] and [Ca] were only 60-80% of those typical of freshwater teleosts, and plasma Ca activity was particularly low. Unidirectional Na and Cl influx rates from water were also very low, only c. 10% of teleost values, whereas unidirectional Ca influx rates were comparable with teleost rates. Protopterus spp. were fed a 3% ration of bloodworms every 48 h. The bloodworm diet provided similar amounts of Na and Ca as uptake from water, but almost no Cl. Efflux rates of Na and Cl through the urine were greater than via the faeces, whereas the opposite was true for Ca. Net ion flux measurements and ionic balance sheet calculations indicated that (1) both water and dietary uptake routes are important for Na and Ca acquisition; (2) the waterborne route predominates for Cl uptake; (3) unidirectional ion effluxes across the body surface (gills and skin) rather than urine and faeces are the major routes of loss for Na, Cl and Ca. Tissues (muscle, liver, lung, kidney, intestine and heart) and plasma ions were also examined in P. dolloi'terrestrialized' in air for up to 5 months, during which plasma ion concentrations (Na, Cl, Ca and Mg) did not change and there were only a few alterations in tissue ions, that is, increased [Na] in intestine, decreased [Cl] in kidney and increased [Ca] in liver and kidney.

Thermal plasticity of skeletal muscle mitochondrial activity and whole animal respiration in a common intertidal triplefin fish, Forsterygion lapillum (Family: Tripterygiidae).

Oxygen demand generally increases in ectotherms as temperature rises in order to sustain oxidative phosphorylation by mitochondria. The thermal plasticity of ectotherm metabolism, such as that of fishes, dictates a species survival and is of importance to understand within an era of warming climates. Within this study the whole animal O2 consumption rate of a common New Zealand intertidal triplefin fish, Forsterygion lapillum, was investigated at different acclimation temperatures (15, 18, 21, 24 or 25 °C) as a commonly used indicator of metabolic performance. In addition, the mitochondria within permeabilised skeletal muscle fibres of fish acclimated to a moderate temperature (18 °C Cool acclimation group-CA) and a warm temperature (24 °C. Warm acclimation group-WA) were also tested at 18, 24 and 25 °C in different states of coupling and with different substrates. These two levels of analysis were carried out to test whether any peak in whole animal metabolism reflected the respiratory performance of mitochondria from skeletal muscle representing the bulk of metabolic tissue. While standard metabolic rate (SMR- an indicator of total maintenance metabolism) and maximal metabolic rate ([Formula: see text]O2 max) both generally increased with temperature, aerobic metabolic scope (AMS) was maximal at 24 °C, giving the impression that whole animal (metabolic) performance was optimised at a surprisingly high temperature. Mitochondrial oxygen flux also increased with increasing assay temperature but WA fish showed a lowered response to temperature in high flux states, such as those of oxidative phosphorylation and in chemically uncoupled states of respiration. The thermal stability of mitochondria from WA fish was also noticeably greater than CA fish at 25 °C. However, the predicted contribution of respirational flux to ATP synthesis remained the same in both groups and WA fish showed higher anaerobic activity as a result of high muscle lactate loads in both rested and exhausted states. CA fish had a comparably lower level of resting lactate and took 30 % longer to fatigue than WA fish. Despite some apparent acclimation capacity of skeletal muscle mitochondria, the ATP synthesis capacity of this species is constrained at high temperatures, and that a greater fraction of metabolism in skeletal muscle appears to be supported anaerobically at higher temperatures. The AMS peak at 24 °C does not therefore represent utilisation efficiency of oxygen but, rather, the temperature where scope for oxygen flow is greatest.