Trawl hangs, baby fish, and closed areas: a win–win scenario

The frequency and geographic distribution of trawlnet hangs from a fishery-independent survey are evaluated. The hangs data were plotted on a substratum map to confirm that many, but not all, were naturally occurring, high relief substrata. The data were also coupled with the occurrence of juvenile cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) to assess the degree of association between juvenile gadoids and high relief substrata. The average minimal distance from a fish occurrence to a hang ranged from 8.1 to 12.0 km (4.4–6.5 nautical miles), well within the reported daily range of movement for these fish. A similar pattern was detected for the sea raven (Hemitripterus americanus), a predator of juvenile gadoids, confirming the location of these microhabitat foodwebs. On average, closing an area 3.7 km (2 nautical miles) around a hang will enclose 17–30% of the populations of these juvenile fish; a wider buffer (18–28 km; 10–15 nautical miles) will close a linearly increasing portion of the populations. Additionally, closing areas surrounding the hangs, particularly regions of high hang density, will help to minimize losses of or damage to fishing gear. We propose a win–win scenario by establishing or evaluating closed areas in regions with high concentrations of known hangs. This approach is widely applicable for many marine ecosystems and may help to achieve simultaneous conservation and resource management goals, whereby one can both protect pre-recruit fish and enhance the effectiveness of a fishery.

Myoglobin deficiency in the hearts of phylogenetically diverse temperate-zone fish species

Previous studies relying upon spectrophotometric methods reported low levels of myoglobin, an intracellular oxygen-binding protein, in oxidative muscles of some sluggish benthic fishes distributed throughout the North Atlantic Ocean. Using immunochemical techniques we show that myoglobin is not expressed in the heart ventricles of Cyclop terus lumpus (Cyclopteridae), Anarhichas lupus (Anarhichadidae), Macrozoarces americanus (Zoarcidae), and Lophius americanus (Lophiidae). Hemitripterus americanus (Hemitripteridae) expresses myoglobin at 2.3 ± 0.2 mg·g wet mass–1 (mean ± SD). Myoglobin was not detected in oxidative skeletal muscle (pectoral adductor profundus) in either the white-hearted fishes examined or red-hearted H. americanus. Supporting these results, myoglobin messenger RNA was not detected in cardiac muscles of white-hearted fishes by means of either direct Northern blot analysis or by the reverse transcriptase – polymerase chain reaction followed by amplification of cDNA product. The partial cDNA sequence of H. americanus myoglobin was determined and shows 86.9% identity with a known teleost myoglobin cDNA from Chionodraco rastrospinosus. The 3' untranslated region of H. americanus is 255 nucleotides longer than the 3' untranslated region of C. rastrospinosus. Comparisons of the deduced amino acid sequence of H. americanus with those of other teleosts show 66.2% sequence identity with Cyprinus carpio, 74.6% with Scomber japonicus, and 80.3% with Thunnus albacares and C. rastrospinosus.

Metabolic effects of cortisol treatment in a marine teleost, the sea raven

Sea raven (Hemitripterus americanus) given intraperitoneal implants of coconut oil containing cortisol (50 mg kg-1) and sampled 5 days later had plasma cortisol, glucose and urea concentrations higher than in a sham-implanted group. No differences in plasma ammonia, free amino acid or fatty acid concentrations were apparent between the cortisol- and sham-treated groups. There was no change in hepatic glycogen content, whereas glutamine synthetase, allantoicase, arginase, aspartate aminotransferase, tyrosine aminotransferase, alanine aminotransferase, glutamate dehydrogenase, phosphoenolpyruvate carboxykinase and 3-hydroxyacyl-coenzyme A dehydrogenase activities were higher in the cortisol-treated fish liver compared with the sham-implanted fish. On the basis of these general increases in enzyme activities, our results suggest that cortisol stimulates nitrogen metabolism in the sea raven. Amino acid catabolism may be a major source of substrate for gluconeogenesis and/or oxidation, while fatty acid mobilization may provide the fuel for endogenous use by the liver in cortisol-treated sea raven. These results further support the hypothesis that cortisol plays a role in the regulation of glucose production in stressed fish.

GLUCOSE METABOLISM BY SEA RAVEN (HEMITRIPTERUS AMERICANUS) AND RAINBOW TROUT (ONCORHYNCHUS MYKISS) ERYTHROCYTES

The fate of extracellular glucose in blood isolated from sea raven (Hemitripterus americanus) and rainbow trout (Onchorhynchus mykiss) was determined. In blood from both species incubated in vitro at low physiological pH, the decrease in plasma glucose concentration was more than adequate to support oxygen consumption. Glucose disappearance could not be accounted for by increases in lactate, red blood cell (RBC) glucose or RBC glycogen concentrations. Rates of 14CO2 production from [6-14C]glucose over a 2 h incubation period were less than 1 % of metabolic rate. Only small amounts of label appeared in RBC protein, lipid or glycogen fractions relative to metabolic rates, but label accumulated in the intracellular acid-soluble fraction (presumably free glucose, glycolytic intermediates, amino acids, citric acid cycle intermediates, etc.) at rates consistent with oxygen consumption and glucose disappearance. The simplest explanation for the mismatch between 14CO2 production and the other estimates of metabolic rate is that incubation times were too short for equilibration to occur. A consequence is that studies of this nature cannot use 14CO2 production to elucidate rates of aerobic fuel utilization. By default, the data imply that glucose serves as a primary aerobic metabolic fuel for the RBCs, at least under some conditions.

Hormonal sensitivity and responsiveness in sea raven hepatocytes: changes with fasting and collagenase exposure

Changes in the apparent sensitivity and responsiveness of carbohydrate metabolism to glucagon and insulin were examined in hepatocytes isolated from fed and 6-week-fasted sea ravens (Hemitripterus americanus), with and without collagenase. The fasted group demonstrated higher rates of total glucose production (TGP) and gluconeogenesis from alanine than the fed group. Metabolic sensitivity to glucagon was increased with fasting, while the maximal responsiveness to both hormones was decreased with fasting; this latter effect may result from elevated control rates in the fasted group. Glucagon increased CO2 production from alanine in the fed group and decreased it in the fasted group. Insulin antagonized the effects of glucagon with respect to TGP and CO2 production, while the effects of the two hormones on gluconeogenesis were additive at high insulin concentrations in the fasted group. Hepatocytes isolated without collagenase perfusion had lower TGP, decreased sensitivity to glucagon, and decreased responsiveness to insulin than cells prepared with collagenase. Furthermore, the additive effects of insulin and glucagon on gluconeogenesis were not apparent when cells were isolated in the absence of collagenase. These results indicate that the response of hepatocyte carbohydrate metabolism to glucagon and insulin is affected by nutritional status, and that collagenase preparation significantly affects sea raven hepatocyte metabolism.

Tissue distribution of fish antifreeze protein mRNAs

The presence of fish antifreeze protein (AFP) mRNA was examined in a variety of tissues from the winter flounder (Pseudopleuronectes americanus), sea raven (Hemitripterus americanus), and ocean pout (Macrozoarces americanus), each of which contains one of the three known AFP types. Northern blot analysis indicates that whereas the AFP mRNA is restricted to liver in sea raven (type II AFP), significant amounts of mRNA are present in many other tissues in both winter flounder (type I) and ocean pout (type III). These results indicate that in sea raven, antifreeze protein synthesis only occurs in the liver, whereas in the ocean pout and winter flounder, synthesis occurs in many tissues throughout the body. These investigations are relevant to understanding the mode of action of these polypeptides.

Metabolic Enzyme Activities, Oxygen Consumption and Glucose Utilization in Sea Raven (Hemitripterus Americanus) Erythrocytes

The organization of energy metabolism was assessed in erythrocytes of the sea raven (Hemitripterus americanus). Cell suspensions displayed a potential for aerobic glycolysis, shown by the presence of the glycolytic enzymes phosphofructokinase, aldolase and pyruvate kinase and the mitochondrial markers citrate synthase and malate dehydrogenase. Rates of oxygen uptake (Moo2) and glucose uptake Mglucose (as assessed by the disappearance of glucose) are closely matched in whole blood and resuspended erythrocyte preparations. Lactate does not accumulate under aerobic conditions. The enzymatic potential is well in excess of maximal rates of carbon flux in intact cells. Overall, the data reveal that sea raven erythrocytes have an aerobic metabolism that is fuelled by exogenous glucose. Calculated rates of glucose oxidation from [6-14C]glucose were 1000-fold lower than rates measured directly from glucose disappearance, implying that exogenous glucose is highly diluted or mixed into the intracellular pools prior to entry into the citric acid cycle.