Central monoaminergic responses to salinity and temperature rises in common carp

Juvenile common carp, Cyprinus carpio, were exposed to increased levels of salinity (1 % NaCl) at 25 °C and 30 °C. Levels of the monoamine neurotransmitters dopamine (DA) and serotonin (5-HT) and their metabolites dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid were determined in different brain parts. Whereas the elevated temperature only resulted in higher levels of the metabolites, increased salinity caused increased levels of DA and 5-HT as well. Increased levels appeared after the first day of exposure and most effects were further enhanced after 1 week in 1 % NaCl. Increases in DA and 5-HT levels were most pronounced in the hypothalamus, which is the major integrative centre controlling the release of hormones. Thus, one possible role of these changes in neurotransmitter metabolism could be to control the release of prolactin and cortisol, two major hormones involved in the regulation of ion homeostasis in teleosts.

The energy metabolism of common carp (Cyprinus carpio) when exposed to salt stress: an increase in energy expenditure or effects of starvation?

Stenohaline common carp (Cyprinus carpio) were chronically exposed to the two main osmoregulatory ions, Na+ and Cl-, at levels close to their isoosmotic value for 28 d (171 mM NaCl; 324 mosm kg-1; 10 per thousand). The aim of this study was to assess whether or not the disturbed ion and osmoregulation affected the energy demand and the energy stores of the exposed fish. Salt exposure reduced food intake by 70% and had adverse effects on growth and survival. Although food consumption decreased and growth was seriously affected, routine oxygen consumption of the exposed fish did not drop, indicating a reallocation of energy expenditure from growth toward other processes. A stress-induced increase in plasma glucose was observed. As a result of low food intake, lower levels of protein were used for fuel. Protein use itself was probably replaced by the use of carbohydrates. These effects were confirmed by the depletion of both muscle and liver glycogen stores during the experimental period. We conclude that, besides the effects of reduced feeding, stress induced extra energy requirements leading to the depletion of energy stores.

Morphological and metabolic changes in common carp, Cyprinus carpio, during short-term copper exposure: interactions between Cu2+ and plasma cortisol elevation.

The effects of increased endogenous cortisol levels were compared with those of sublethal copper exposure in the freshwater common carp, Cyprinus carpio. Fish were exposed to either increased levels of endogenous cortisol (200 ng/ml) or sublethal copper (1.9 microM) alone or were pretreated by elevating plasma cortisol levels prior to copper exposure to assess whether interactions between both treatments occurred. Effects induced by increased cortisol levels included increased Na+/K(+)-adenosine triphosphate (ATPase) activity and increased plasma Na+ and plasma osmolarity, while copper exposure induced anaerobic metabolism, gill damage, decreasing Na+/K(+)-ATPase activity, decreasing plasma ion levels, and blood thickening. Pretreatment of copper-exposed fish with cortisol partially protected these fish by reducing the copper-induced decrease in Na+/K(+)-ATPase activity. Overall, the results obtained in this study argue against a major role for cortisol as an intermediate for the toxic effects of copper.

Effects of sublethal copper exposure on copper accumulation, food consumption, growth, energy stores, and nucleic acid content in common carp.

Juvenile common carp were exposed for 28 days to three different sublethal copper concentrations (0.20 microM, 0.55 microM, and 0.80 microM). Food consumption was monitored on a daily basis during the exposure period, while growth, copper accumulation, energy stores, and nucleic acid contents were assessed weekly. Copper exposure to 0. 80 microM affected both growth and feeding behavior in common carp. At 0.55 microM, growth was affected despite normal food consumption. Even at the lowest copper concentration (0.20 microM), metabolic demand for the fish increased, challenging the carp with an increased demand for food. Copper accumulation mainly occurred in the liver, reaching an equilibrium between uptake and excretion after 1 month of exposure. Substantial biochemical changes were observed at the two highest copper exposure concentrations, but the correlation between growth rate and RNA:DNA ratio was poor considering the substantial differences in growth rate. The use of the RNA:DNA ratio as a sensitive biomarker is questioned.