The unanswered question of high anaerobic capabilities of carp white muscle

Organ damage and hepatic lipid accumulation in carp (Cyprinus carpio L.) after feed-borne exposure to the mycotoxin, deoxynivalenol (DON)

Deoxynivalenol (DON) frequently contaminates animal feed, including fish feed used in aquaculture. This study intends to further investigate the effects of DON on carp (Cyprinus carpio L.) at concentrations representative for commercial fish feeds. Experimental feeding with 352, 619 or 953 μg DON kg⁻¹ feed resulted in unaltered growth performance of fish during six weeks of experimentation, but increased lipid peroxidation was observed in liver, head kidney and spleen after feeding of fish with the highest DON concentration. These effects of DON were mostly reversible by two weeks of feeding the uncontaminated control diet. Histopathological scoring revealed increased liver damage in DON-treated fish, which persisted even after the recovery phase. At the highest DON concentration, significantly more fat, and consequently, increased energy content, was found in whole fish body homogenates. This suggests that DON affects nutrient metabolism in carp. Changes of lactate dehydrogenase (LDH) activity in kidneys and muscle and high lactate levels in serum indicate an effect of DON on anaerobic metabolism. Serum albumin was reduced by feeding the medium and a high dosage of DON, probably due to the ribotoxic action of DON. Thus, the present study provides evidence of the effects of DON on liver function and metabolism.

Metabolism, nitrogen excretion, and heat shock proteins in the central mudminnow (Umbra limi), a facultative air-breathing fish living in a variable environment

The central mudminnow ( Umbra limi (Kirtland, 1841)) is a continuous, facultative air-breathing freshwater fish found in swamps of central Canada and northeastern USA. The first goal of this field and laboratory-based study was to characterize the physicochemical conditions of mudminnow habitat during the summer. Our second goal was to determine the metabolic, stress response, and nitrogen excretion strategies of this fish following variations in water temperature, dissolved oxygen, external ammonia, and short-term periods of air exposure. We report profound diurnal fluctuations in water temperature (13–31 °C), dissolved oxygen (2%–159% air saturation), and ammonia levels (10–240 μmol·L−1) in habitat of central mudminnow measured on three dates at six different sites over 24 h. The central mudminnow does not induce urea synthesis as a mechanism of ammonia detoxification, either in response to emersion (6 or 20 h) or elevated external ammonia (10 mmol·L–1). Acute exposure to high temperature (~31 °C), aquatic hypoxia, or air resulted in significant increases in blood glucose and liver heat shock protein (Hsp) 70 and hypoxia also caused an increased reliance on anaerobic metabolism. This is the first description of the heat shock response in a facultative air-breathing fish following either hypoxia or air exposure. These metabolic and molecular responses are part of a strategy that allows the mudminnow to thrive in extremely variable freshwater environments.

Cardiorespiratory responses of the common carp (Cyprinus carpio) to severe hypoxia at three acclimation temperatures

In vivo measurements of the cardiovascular responses of anoxia-tolerant teleosts to severe prolonged hypoxia are limited. Here, we report the first direct measurements of cardiac output (Q), heart rate (fH) and stroke volume during prolonged severe hypoxia (<0.3 mg O2 l–1) in common carp (Cyprinus carpio L.) that had been acclimated to 6, 10 and 15°C. While routine Q and fH values varied with temperature under normoxic conditions (Q10 values of 1.7 and 2.6, respectively), severe hypoxic exposure significantly depressed fH and Q to similar minimum values that were largely independent of acclimation temperature (Q10 values of 1.2). In contrast, the duration of cardiac depression and the subsequent time period during which carp could tolerate severe hypoxia were inversely related to acclimation temperature (24 h at 6°C, 6 h at 10°C, and 2.5 h at 6°C). Likewise, respiration rate during hypoxia showed a temperature dependence. An unusual finding was that cardiorespiratory status partially recovered during the latter stages of severe hypoxic exposure. We conclude that the cardiorespiratory responses to severe prolonged hypoxia in common carp involved a mixture of temperature-independent, temperature-dependent and time domain phases.

Responses to prolonged hypoxia by rainbow trout (Salmo gairdneri) I. Free amino acids and proteins in plasma, liver and white muscle

In order to estimate the mobilization of nitrogen compounds for energetic purposes in trout under hypoxic conditions, commercial-size rainbow trout, acclimated to 15°C, were maintained for 10 weeks at an oxygen level of 5.3 ± 0.5 mg/l ('hypoxic' group) or 8.4 ± 0.4 mg/I (control group), and the changes in tissue concentrations of free amino acids and proteins studied. In animals subjected to hypoxia, there was a decrease in plasma free amino acids involved in gluconeogenesis, liver alanine and aspartic acid, plasma and liver protein concentrations, and muscle free histidine. These results suggest a trend of rainbow trout metabolic activity towards energy production at the expense of anabolism when oxygen availability in water is limited over a long period of time.

Activities of enzymes associated with phosphoenolpyruvate metabolism in the mudskippers, Boleophthalmus boddaerti and Periophthalmodon schlosseri

1. PK and LDH activities in the muscle of Periophthalmodon schlosseri and Boleophthalmus boddaerti were at least 100-fold higher than their respective activities in the liver. 2. The ratio of PK:PEPCK in liver of B. boddaerti was smaller than that of P. schlosseri. 3. PK:PEPCK ratios in both fishes were intermediate between those of aerobic and anaerobic organisms. 4. MDH activity was higher than other enzymes assayed in the liver of both fishes. 5. The ratios of LDH:MDH in the liver of both mudskippers were comparable to those of anaerobic organisms. 6. AST was at least eight times more active than ALT in the liver of both fishes. 7. In the muscle of these mudskippers, the aspartate content was significantly less than that of alanine. 8. Exposure of these fishes to various experimental conditions led to changes in specific activities of PEPCK, LDH, AST and ALT.

Comparison of in vivo energy metabolism in the brain of rainbow trout, Salmo gairdneri and bullhead catfish, Ictalurus nebulosus during anoxia

1. Rainbow trout and bullhead catfish (Ictalurus nebulosus) were exposed to anoxic water inside a plastic tube until death (12 min for trout; 62 min for catfish). Immediately upon death, the brain was removed and analyzed for metabolites, high energy phosphate compounds, and metabolic fuel while the blood was analyzed for metabolites. 2. Control bullhead brains had higher concentrations of glycogen, ATP, creatine phosphate (CrP), and glucose than control trout. 3. After anoxia bullheads showed a significant decrease in ATP, CrP, and glycogen while lactate more than doubled in concentration. 4. After anoxia trout showed a doubling in brain lactate and a decline in glycogen, but no decline in ATP or CrP. There were no changes in brain glucose, ketone bodies, or alternative anaerobic end-products in either species although an elevation in blood isobutyrate was noted. 5. Brain death in the catfish may be due to depletion of fuel for anaerobiosis and a subsequent loss of ATP. In the trout there may be other causes such as a greater permeability of its neuronal membranes and alterations in intracellular free calcium stores.

Lactate dehydrogenase activity and lactate/pyruvate ratio in muscle of thermally acclimated goldfish

1. Some glycolytic metabolites were determined for red muscle (RM) and white muscle (WM) of goldfish acclimated to 10 and 25 degrees C. 2. Lactate/pyruvate (L/P) was higher in RM than in WM. 3. Lactate dehydrogenase (LDH) of RM was slightly more susceptible to inhibition by lactate than WM-LDH. At L/P found in vivo under resting conditions, RM-LDH was about three times as inhibited as WM-LDH. 4. When 25 degrees C-fish were forced to swim at 25 degrees C, the increase of L/P in WM was mainly due to increased lactate level and that in RM was ascribed to decreased pyruvate level. These changes were obscure in 10 degrees C-fish.