Accumulation of neurotoxic organochlorines and trace elements in brain of female European eel (Anguilla anguilla).

Xenobiotics such as organochlorine compounds (OCs) and metals have been suggested to play a significant role in the collapse of European eel stocks in the last decades. Several of these pollutants could affect functioning of the nervous system. Still, no information is so far available on levels of potentially neurotoxic pollutants in eel brain. In present study, carried out on female eels caught in Belgian rivers and canals, we analyzed brain levels of potentially-neurotoxic trace elements (Ag, Al, As, Cd, Co, Cr, Cu, Fe, Hg, MeHg, Mn, Ni, Pb, Sn, Sb, Zn) and OCs (Polychlorinated biphenyls, PCBs; Hexachlorocyclohexanes, HCHs; Dichlorodiphenyltrichloroethane and its metabolites, DDTs). Data were compared to levels in liver and muscle tissues. Eel brain contained very high amounts of OCs, superior to those found in the two other tissues. Interestingly, the relative abundance of PCB congeners markedly differed between tissues. In brain, a predominance of low chlorinated PCBs was noted, whereas highly chlorinated congeners prevailed in muscle and liver. HCHs were particularly abundant in brain, which contains the highest amounts of ß-HCH and ϒ-HCH. p,p'-DDTs concentration was similar between brain and muscle (i.e., about twice that of liver). A higher proportion of p,p'-DDT was noticed in brain. Except for Cr and inorganic Hg, all potentially neurotoxic metals accumulated in brain to levels equal to or lower than hepatic levels. Altogether, results indicate that eel brain is an important target for organic and, to a lesser extent, for inorganic neurotoxic pollutants.

High hydrostatic pressure improves the swimming efficiency of European migrating silver eel.

To reproduce, European eels must undergo a long migration without feeding. During this migration they have to cope with many environmental factor changes, one of them being hydrostatic pressure. We focus on the effects of hydrostatic pressure on swimming energetics: does the pressure exposure modify swimming efficiency? By using a specially designed Blazka type swimming tunnel able to work under pressure, we have measured oxygen consumption of migrating male silver eels at different swimming speeds (from 0.2 to 1.0 BL/s) first at atmospheric pressure then at 101 ATA hydrostatic pressure. The results show that pressure increases the energetic swimming efficiency by decreasing oxygen consumption for a given swimming speed. Such a pressure effect could represent a remarkable adaptation enabling eels to spare their energy stores and swim for a long time.

Pressure and temperature interactions on aerobic metabolism of migrating European silver eel.

During their migration for reproduction, European eels have to cope with many environmental factors changes. The main changes concern hydrostatic pressure and temperature that are important environmental and physiological factors when considering life in the deep sea. We focus on the consequences of pressure (from 0.1 to 12.1MPa by 1MPa steps) and temperature (9, 15, 22 degrees C) shifts on the oxygen consumption (MO(2)) at the whole animal level. Because of their morphological differences, we are also interested in males and females to evaluate the best conditions for migration. Firstly, whatever temperature, males present higher aerobic capacities than females at atmospheric pressure. Secondly, an increase in temperature increases the pressure effects in males (synergy) but decreases them in females (opposite effects). We raise the hypothesis that two different migration strategies could be used in the water column in order to reach the breeding area: males could tend to privilege pressure and cold waters (deep water) and females, on the other hand, could opt for warmer temperature surface waters.

Pressure and temperature interactions on aerobic metabolism in migrating silver eels: results in vitro.

The European eel (Anguilla anguilla) migrates (6000 km) from European coast towards the supposed spawning area: the Sargasso Sea. This intensive and sustained swimming activity is performed without feeding and by using essentially red muscle i.e. aerobic metabolism. Temperature and hydrostatic pressure vary during migration and have known effects on energy metabolism, mainly on mitochondrial functioning. We raise the question about the existence of a pressure-temperature combination that optimizes energy metabolism. We have measured the maximal oxygen consumption (MO2) of red muscle fibres of silver eel (migrating stage) in a temperature range (5 to 25 degrees C) covering what can be reasonably expected during the migration. We have combined (random order) three temperatures (5, 15, 25 degrees C) with 5 different pressures steps from 0.1 to 10.1 MPa (corresponding to depths from surface to 1000 m). The results show that when an adequate temperature is chosen as a reference, pressure effects and pressure sensitivity depend on the temperature. Based on the fact that energy budget is limited in migrating eels, we consider that the best conditions are low temperature and high pressure.