High pressure and glycolytic flux in the freshwater Chinese crab, Eriocheir sinensis

In vitro aerobic and anaerobic muscle capacities in the European eel, Anguilla anguilla: effects of a swimming session

In order to have a general view of metabolic requirements during swimming, in vitro aerobic and anaerobic fluxes were measured in red and white muscles from silver eels and yellow eels which differ in activity levels and nutritional states. These measurements were performed in control eels and after a 4 day swimming session (70% U(crit) in yellow eels, 80% U(crit) in silver eels). A swimming session significantly increases U(crit) from 12% to 18%, depending on the stage, with a significantly higher in vitro energy cost during the yellow stage at the muscle level. In vitro, the swimming session brings about a gain in anaerobic capacities rather than in aerobic ones. Some in vivo hypotheses are proposed.

Glycolytic fluxes in European silver eel, Anguilla anguilla: sex differences and temperature sensitivity

European silver eels migrate 6000 km to their supposed spawning area in the Sargasso sea. As the eel is fasting, this intense swimming activity is realised only with fat stores, involving mainly red muscle i.e. aerobic metabolism. However, eel migration is performed at depth and thus in cold water, both being known to induce changes in muscle energy metabolism. During migration, white and red muscles can operate together or separately in order to counteract the eventual effects of low temperatures and/or high pressures. We have studied the temperature sensitivity (5, 15, and 25 degrees C) of aerobic and anaerobic metabolism in both sexes. At the same temperature, migrating eels have a higher basal glycolytic flux. Moreover, there are temperature and sex effects: anaerobic glycolysis (JB) is more sensitive to cold water whereas aerobic (JA) is more affected by warm. Males, which are less sensitive to cold water, also have higher aerobic fluxes than females. As depth corresponds to low temperature, the possibility that males migrate more deeply than females is discussed. In an ecophysiological context, it is interesting to suppose that males and female eels migrate at different depths in order to optimize their energy utilization by aerobic and / or anaerobic pathways.

Fish at high pressure: a hundred year history

Two main periods can be considered in the history of fish metabolism under pressure. The first period (roughly from 1870 to 1970) was mainly descriptive: survival times and behavior were studied and some authors described an increase in oxygen consumption under pressure; later, the counteracting effects of high temperature on pressure were mentioned. The second period (from 1970 onwards) was more integrative and two major ways were explored. The first was to use shallow-water fish, experimentally exposed to hydrostatic pressure, which can induce a metabolic state resembling histotoxic hypoxia. The second way was to use deep-living fish which have, when compared to surface fish, muscle enzymes with higher structural stability, lower activity (in relationship with habitat depth) and kinetics that are less sensitive to pressure increase. Using this approach, it was also shown that muscle composition and function were somewhat different at depth and that deep fish are well adapted to pressure partly by maintaining membrane fluidity (homeoviscous theory). Since about 1990, the two above-mentioned approaches have still been pursued but by fewer researchers. Studies on deep-living fish are mainly concerned with enzyme kinetics whereas shallow water fish are used mainly for cellular energetic studies. Regarding this topic, it has been shown that yellow freshwater eels are able to acclimate to high-pressure effects, by optimizing membrane fluidity and composition (as achieved by deep-living fish), by improving oxidative phosphorylation (increase of P/O ratio) and the glycolytic pathway.