Myoxocephalus Scorpius Research Articles

Ontogenetic changes in the critical swimming speed of Gadus morhua (Atlantic cod) and Myoxocephalus scorpius (shorthorn sculpin) larvae and the role of temperature

Most studies on behavioural contributions to dispersal and recruitment during early life history stages of fishes have focused on coral reef species. For cold ocean environments, high variation in seasonal temperature and development times suggest that parallel studies on active behaviour are needed for cold-water species. Thus, we examined the critical swimming speed (U crit) of marine fish larvae from 2 contrasting species: Gadus morhua (Atlantic cod) and Myoxocephalus scorpius (shorthorn sculpin), a pelagic and bottom spawner respectively. Within-species comparisons showed that sculpin reared at 6 °C had lower initial U crit values, but a faster U crit increase through development compared with 3 °C conspecifics, ultimately resulting in faster critical swimming speeds at metamorphosis (10.5 vs. 9.1 cm·s − 1 ). In contrast, although cod larvae reared at 10 °C were faster swimmers at first feeding than 6 °C fish, temperature differences were absent after the first week. These results show that temperature influences the trajectory of larval critical swimming speed development, but that the relationship is species-specific. Although 6 °C sculpin and cod of similar length had equivalent U crit values, the smaller size of cod at hatch (5.3 vs. 10.8 mm for sculpin) resulted in much lower age-specific U crit values for cod. These data have significant implications for how swimming activity of the two species might affect dispersal, particularly in the first few weeks post-hatch. Overall, our data suggest that temperature during larval development influences the swimming capacity of cold-water marine fishes, and has important ramifications for biophysical models of dispersal.

Comparative analysis of the karyotype of the sculpin Myoxocephalus ochotensis (Pisces: Cottidae) from the Odyan Bay of the Sea of Okhotsk

The karyotype of the endemic Okhotsk Sea sculpin Myoxocephalus ochotensis Schmidt (Cottidae) from Odyan Bay was studied. The number and morphology of chromosomes were determined, 2n = 42 (2 metacentric, 20 subtelocentric, and 20 acrocentric chromosomes), NF = 44. Variability of chromosome number was not revealed; no difference between male and female karyotypes was found. The karyotype of the Okhotsk sculpin M. ochotensis was compared with karyotypes of the Far East Steller’s M. stelleri (Tilesius), snow M. brandti (Steindachner), and plain M. jaok (Cuvier) sculpins, and to the European shorthorn sculpin M. scorpius (Linnaeus) from White Sea. Their similarities and distinctions were shown.

RUSSIAN–AMERICAN LONG-TERM CENSUS OF THE ARCTIC: BENTHIC FISHES TRAWLED IN THE CHUKCHI SEA AND BERING STRAIT, AUGUST 2004

Bottom trawl nets towed at 17 stations from Bering Strait to the northwestern Chukchi Sea during the 1st cruise of the Russian–American Long-term Census of the Arctic (RUSALCA) in August 2004 caught 33 or more species of fishes distributed among 10 families. The families with the most species were Cottidae (8), Zoarcidae (6 or 7), and Agonidae (4). The 4 most abundant fishes were Gymnocanthus tricuspis (Cottidae), Myoxocephalus scorpius groenlandicus (Cottidae), Hippoglossoides robustus (Pleuronectidae), and Boreogadus saida (Gadidae), collectively accounting for 79% of the catch by numbers. Theragra chalcogramma, H. robustus, and M. polyacanthocephalus occurred farther north than previously recorded. We found the 2nd and 3rd records of occurrence of Liparis fabricii for the Chukchi Sea and a new maximum size for that species; and the 2nd record of Pallasina barbata for the Chukchi Sea. New studies of fresh and archived material clarified historical distributions and enabled more accurate identification of species such as M. scorpius, Hexagrammos stelleri, Hemilepidotus (Melletes) papilio, Podothecus veternus, Lycodes mucosus, and L. polaris. Some fishes, notably Gymnelus, could not be readily identified. Color photographs of fresh specimens should assist in field identifications of species that are difficult to identify or are often misidentified.

Ontogeny of predator-sensitive foraging and routine metabolism in larval shorthorn sculpin, Myoxocephalus scorpius

Most animals will reduce foraging activity in the presence of a predatory threat. However, little is known about the onset of this decision-making ability during the early life stages of fishes, and how the trade-off between foraging and predator-avoidance may be affected by changes in metabolic demand during ontogeny. To examine these issues, the foraging behaviour of larval shorthorn sculpin Myoxocephalus scorpius was monitored during visual exposure to a predatory threat (juvenile Atlantic cod, Gadus morhua) throughout development at 3°C (March–April, 2004). Larvae did not respond to predatory exposure during the first week post-hatch, but thereafter showed drastic reductions in foraging activity when exposed to predators. During early development, the mass-specific routine metabolism of shorthorn sculpin larvae displayed a triphasic ontogeny and peaked during metamorphosis. This high mass-specific metabolic demand could make reduced foraging under predation threat very costly during this stage of development. To further investigate this possibility, additional experiments were performed (March–April, 2005) where larvae were reared with visual exposure to predators for 6 h day−1 during the feeding period. At 7-week post-hatch, larvae exposed to predators were smaller (wet mass and SL), showed decreased levels of whole-body lipids and certain fatty acids, and experienced higher rates of mortality as compared to control larvae. In environments where abundant predators cause larval fish to reduce their foraging rate, growth and survival of larvae may be negatively affected.

Temporal trends of mercury in marine biota of west and northwest Greenland

Temporal trends in mercury concentrations ([Hg]) during the last two to three decades were determined in liver of shorthorn sculpin, ringed seal and Atlantic walrus from northwest Greenland (NWG, 77° N) and in liver of shorthorn sculpin and ringed seal from central west Greenland (CWG, 69° N) during the last decade. Stable-nitrogen (δ 15N) and carbon (δ 13C) isotope values were determined in muscle of ringed seals to provide insight into potential trophic level changes through time. Log-linear regressions on annual median [Hg] did not reveal any temporal trend in shorthorn sculpin from CWG and NWG and walrus from NWG. In ringed seals from NWG, an increase in [Hg] of 7.8% per year was observed. When based on δ 15N-adjusted [Hg] this rate increased to 8.5% but was still non-significant. In ringed seal from CWG no trend was found in [Hg] during the period 1994–2004. However, during the last part of the period (1999–2004) the [Hg] increased significantly. Including tissue δ 15N values as a covariate had a marked effect on these results. The annual changes in δ 15N-adjusted [Hg] was estimated to −5.0% for the whole period and 2.2% during the last 5 years compared to −1.3% and 12.4%, respectively, for the non-adjusted [Hg].

The impact of hypoxia on in vivo glucose uptake in a hypoglycemic fish,Myoxocephalus scorpius

The mechanisms controlling carbohydrate utilization in teleost fish are poorly understood, particularly in the heart. Tissue glucose uptake and cardiovascular characteristics were measured in the short-horned sculpin, Myoxocephalus scorpius, a species exhibiting low blood glucose levels, during normoxia and hypoxia to assess the role of adenosine receptors in the control of glucose uptake and anaerobic metabolism. As expected, hypoxia exposure (300 min at 2 mg/l dissolved oxygen) resulted in a bradycardia and plasma lactate accumulation, but glucose uptake rates did not change in heart, brain, gill, spleen, and white muscle. Plasma glucose-to-intracellular glucose ratios indicated that glucose uptake was the rate-limiting step in glucose utilization. The majority of intracellular glucose was unphosphorylated, however, suggesting that hexokinase is also important in controlling the tissue glucose gradient. During hypoxia, the cholinergic blocker atropine resulted in tachycardia but did not significantly change tissue glucose uptake rates or heart and brain adenosine levels. In contrast, the combined treatment of atropine and an adenosine receptor blocker [8-(p-sulfophenyl)theophylline] during hypoxia increased heart glucose uptake to levels fivefold higher than normoxic fish, with no additive effects on cardiovascular parameters. Significant tissue lactate accumulation was observed in this group of fish, signifying that adenosine receptors may depress anaerobic metabolism, even though tissue adenosine accumulation was absent during hypoxia. White muscle accumulated glucose during normoxia, suggesting the presence of gluconeogenic pathways or active uptake mechanisms not previously described in this tissue.

Polar cod, Boreogadus saida (Gadidae), show an intermediate stress response between Antarctic and temperate fishes

To examine whether the attenuated stress response observed in Antarctic notothenioid fishes is a specialism for life in sub-zero waters, the polar cod, Boreogadus saida, and the temperate shorthorned sculpin, Myoxocephalus scorpius, were subjected to various stress treatments. Activity stress in both species had no effect on plasma catecholamine and cortisol levels, splenic mass, and on the haematological variables in B. saida. In contrast, heat stress caused a significant rise in circulating noradrenaline and adrenaline levels in B. saida, accompanied by a significant increase in haematocrit and haemoglobin concentrations, at constant plasma cortisol levels, red blood cell count and splenic mass. A concomitant rise in blood lactate concentrations indicated that heat-stressed B. saida were hypoxaemic. The capacity to synthesise catecholamines in B. saida was 38% of the value in M. scorpius, but similar to the values for Antarctic notothenioids. The lack of any adrenergic response to activity stress suggests that dominance of cholinergic control of the cardiovascular system may not be restricted to Antarctic notothenioids. Rather, the stress response in B. saida appears to be intermediate between Antarctic and temperate teleosts, in keeping with their relatively recent occupation of cold Arctic waters.

Feeding ecology of sympatric European shags Phalacrocorax aristotelis and great cormorants P. carbo in Iceland

The feeding ecology of the European shag (Phalacrocorax aristotelis) and the great cormorant (P. carbo) in Iceland was studied. These bird species may affect their marine environment, for instance, by predating on several commercially important fish species in coastal waters. The shag and cormorant diets were studied throughout the year in the period 1996–2000 by analysing the content of about 300 stomachs from each species. The shag relies heavily on sandeel (Ammodytes marinus) in the breeding season, whereas bull-rout (Myoxocephalus scorpius) and gadoids (Gadidae) become increasingly important in autumn and winter. The main food of the cormorant in all areas and seasons is the bull-rout. Depending on location and season, secondary food consists mainly of butterfish (Pholis gunnellus), gadoids and flatfishes (Pleuronectiformes). Similarity in diets of these two co-existing bird species was least in the breeding season when overlap in the birds’ distribution was greatest. The results suggest that predation by shags and cormorants could sometimes affect the stocks of the commercially important saithe (Pollachius virens) and plaice (Pleuronectes platessa) in Iceland.

Endothelin receptors in teleost fishes: cardiovascular effects and branchial distribution

By observing gill blood flow using epi-illuminating microscopy, in parallel with cardiovascular recordings and immunohistochemistry, we have tried to identify the receptor mediating endothelin (ET) type 1 (ET1)-induced pillar cell contraction in the lamellae of the Atlantic cod (Gadus morhua). Intra-arterial injection of the specific ET(B) receptor agonist BQ-3020 induced dose-dependent increases in ventral aortic blood pressure, gill vascular resistance, and pillar cell area (indicating contraction). The specific ET(A) receptor antagonist BQ-610 did not prevent either pillar cell contraction or increased gill vascular resistance induced by ET-1 injection. The cardiovascular responses were corroborated by the detection of ET(B) receptor-like immunoreactivity (IR) associated with pillar cells in the lamellar region and in neuroendocrine cells. ET(B) receptor-like IR was also found lining the muscle layer of lamellar arterioles and filament arteries. In contrast, strong ET(A) receptor-like IR was found on branchial nerves throughout the filaments. In addition, ET-like IR was concentrated in neuroendocrine cells in the filament and lamellae. We also present data suggesting that ET-mediated pillar cell contraction is widespread among teleost fish, including Atlantic cod, rainbow trout (Oncorhynchus mykiss), sculpin (Myoxocephalus scorpius), and mackerel (Scomber scombrus). Taken together, our results suggest that an ET(B)-like receptor mediates pillar cell contraction in fishes, whereas ET(A)-like receptors may serve another function in the gill, inasmuch as ET(A) receptor-like IR is found on branchial nerves.

Fish–macrofauna interactions in a kelp (laminaria hyperborea) forest

predator–prey interactions between fish and macrofauna in kelp (laminaria hyperboea) forest were examined. fish were caught in gill-nets and fish traps at two sites and throughout the diurnal cycle. their stomach contents were analysed. the most abundant fish species, except pollachius virens, were caught in larger numbers at night than during daytime. the examined fish fed throughout the diurnal cycle and kelp-associated fauna were found to be important prey. pollachius virens was caught in the same numbers throughout the diurnal cycle and contained mainly pelagic prey, in larger numbers during the day than at night. small labrids were specialists, feeding mainly on the two numerically dominant kelp-associated gastropods rissoa parva and lacuna vincta. the larger labrus bergylta, gadus morhua and myoxocephalus scorpius were generalists, feeding on a large range of kelp-associated invertebrates. some fish species showed preference for particular vertical levels when feeding in the kelp forest. the most mobile and/or the largest invertebrates were most heavily preyed upon.

Influence of cruising and ambush predators on 3-dimensional habitat use in age 0 juvenile Atlantic cod Gadus morhua

Predators and prey often co-exist at high densities within the same habitat, yet the behavioural and spatial dynamics underlying this co-existence are not well known. To better understand small-scale, predator–prey co-occurrence, the spatial patterns and behaviour of age 0 juvenile cod Gadus morhua 75–88 mm SL and two of their known predators, age 2+ cod and short-horn sculpin Myoxocephalus scorpinus, were examined in two habitats (i.e., sand and eelgrass) using three-dimensional video analysis. Both habitat and predator type interacted to result in unique spatial patterns of prey. Spatial overlap between predators and prey was highest in open habitat in the presence of the cruising predator but lowest in the presence of sculpin in the same habitat. In eelgrass, age 0 cod avoided predators primarily along the vertical axis (i.e., distance off bottom). Age 0 cod stayed above eelgrass in the presence of sculpin but lowered themselves into the eelgrass while in the presence of predator cod. Anti-predator behaviour (i.e., predator–prey distance, prey cohesion and freezing) was significantly reduced over eelgrass compared to sand, suggesting eelgrass has lower ‘inherent risk’ than open habitats. However, predator consumption was similar across all treatments, suggesting that, 1) complex habitat also impairs the visual cues needed for anti-predator behaviour (e.g., schooling) and assessing the location of predators, and 2) predators change their behaviour with habitat to enhance their opportunities for finding and capturing prey.

Biological responses to PCB exposure in shorthorn sculpin from Saglek Bay, Labrador

A local source of polychlorinated biphenyls (PCBs) in Saglek Bay, Labrador, has contaminated marine sediments and the coastal food web. As part of a larger assessment of ecological risks in the Bay, we evaluated biological responses to PCB concentrations in a northern fish species, the shorthorn sculpin ( Myoxocephalus scorpius). Biological endpoints, including ethoxyresorufin- O-deethylase (EROD) activity in liver tissue, fish body condition, lipid content, and relative liver mass were examined in 35 sculpin collected during August–September 1999. Across a wide range of PCB concentrations (5.1–6920 ng/g wet weight (ww) in whole fish excluding liver), sculpin showed significant EROD induction (as much as 25-fold in the most exposed group). Responses varied directly with PCB concentrations but there was also an apparent threshold for induction at about 50 ng/g ww (whole fish excluding liver). A strong relationship between sculpin PCB concentrations and the concentrations of PCBs in the marine sediments of Saglek Bay suggests that concentrations above this threshold can arise from very low concentrations in sediments (2.3 ng/g dry weight). Other biological endpoints did not show significant responses to PCB concentrations, nor were they related to the observed EROD activity. Although PCDF compounds were present in trace amounts (primarily 2,3,4,7,8-PnCDF), mono- ortho and non- ortho substituted (coplanar) PCBs appeared to contribute the majority of the total dioxin toxic equivalent (TEQ) concentrations. Overall, the results indicate that biological responses occur in shorthorn sculpin with relatively low PCB concentrations (∼50 ng/g), which are not unrealistic for even mildly contaminated areas in northern Canada.

Type I Antifreeze Proteins: Possible Origins from Chorion and Keratin Genes in Atlantic Snailfish

Type I antifreeze proteins (AFPs) are alanine-rich alpha-helical polypeptides found in some species of right-eye flounders, sculpin, and snailfish. In this study, a shorthorn sculpin skin type I cDNA clone was used to probe an Atlantic snailfish liver cDNA library in order to locate expressed genes corresponding to snailfish plasma AFPs. Clones isolated from the cDNA library had sections with substantial amino acid and nucleotide sequence similarity to snailfish type I AFPs. However, further analysis revealed that the positives were actually three different liver-expressed proteins-two were eggshell proteins, while the third was a type II keratin. We propose that a shift in reading frame could produce alanine-rich candidate AFPs with possible antifreeze activity or ice crystal modification properties. Furthermore, it is plausible that one or more of the liver-expressed proteins represent the progenitors of snailfish type I AFPs.

PCBs in sediments and the coastal food web near a local contaminant source in Saglek Bay, Labrador

Polychlorinated biphenyls (PCBs) were measured in marine sediments and the coastal food web in Saglek Bay, Labrador, to investigate the influence of a local PCB source. Saglek Bay has been the site of a military radar station since the late 1950s and there was PCB-contaminated soil at a beach prior to cleanup in 1997–1999. PCB concentrations in marine sediments during 1997–1999 ranged from 0.24 to 62 000 ng/g (dry weight) and decreased exponentially with distance from the contaminated beach. Given this gradient, spatial trends of PCBs in the food web were examined over four zones, according to distance from the contaminated beach: within 1.5 km — zone one, 1.5–4.5 km — zone two, 4.5–7.5 km — zone three, and greater than 7.5 km — zone four. PCB concentrations in a bottom-feeding fish (shorthorn sculpin, Myoxocephalus scorpius), decreased significantly from zone one to zone two, three, four, and distant Labrador reference sites. PCB concentrations in the eggs of a diving seabird (black guillemot, Cepphus grylle) were as high as 48 000 ng/g during 1997–1999 and average concentrations in zones one and two were 84 and 13 times higher than in zone four. Marine invertebrates closely reflected the concentrations of PCBs in the associated sediment. In contrast to the benthic-based food web, anadromous arctic char ( Salvelinus alpinus) showed no evidence of PCB accumulation from the contaminated sediments. Relatively high PCB concentrations were discovered in some great black-backed gulls ( Larus marinus) and ringed seals ( Phoca hispida) but appear to relate more to their high trophic level than sampling location. Those species that fed on or near the seabed and had limited foraging ranges were strongly influenced by the local contamination. Total PCB concentrations in the benthic-based food web were significantly higher than background levels for a distance of at least 7.5 km from the contaminated beach. This area is small in the context of widely distributed contamination from long-range transport but the area's high concentrations are comparable to levels associated with adverse effects elsewhere. Our findings should be useful to better assess the environmental impacts of PCB contamination at other coastal sites in the Arctic.

Occurrence of leeches (Hirudinea, Piscicolidae) on some marine fishes in Norway

Marine fish from several locations along the west coast of Norway were examined for leeches. Seven leech species were detected, Calliobdella nodulifera (Malm, 1863) from codfish, flatfish and a ray, Calliobdella lophii van Beneden & Hesse, 1863 from Lophius piscatorius L., Platybdella anarrhichae (Diesing, 1859) on Anarhichas lupus L., Platybdella quadrioculata Malm, 1863 on Symphodus melops (L.), Oceanobdella sp. on Zeugopterus punctatus (Bloch), Malmiana brunnea (Johansson, 1896) on Myoxocephalus scorpius (L.) and Malmiana bubali Srivastava, 1966 on Taurulus bubalis (Euphrasen). Calliobdella nodulifera infected unrelated hosts (euryxenic); the others appeared to be host specialists (oio- or stenoxenic). Details on the occurrence of Calliobdella nodulifera on Enchelyopus cimbrius (L.) during 1 year are given, which together with other observations suggest that its life cycle exceeds a year. A brief account on the morphology of “Platybdella” quadrioculata is provided, justifying its transfer to the genus Oceanobdella Caballero, 1956 as O. quadrioculata comb. nov. With the new additions, the Norwegian marine piscicolid fauna contain 12 species. At least ten additional species, known from adjoining areas, also probably occur along the Norwegian coast.

Preliminary screening of perfluorooctane sulfonate (PFOS) and other fluorochemicals in fish, birds and marine mammals from Greenland and the Faroe Islands

Extensive screening analyses of perfluorooctane sulfonate (PFOS) and related perfluorinated compounds in biota samples from all over the world have identified PFOS as a global pollutant and have shown its bioaccumulation into higher trophic levels in the food chain. Perfluorinated compounds have been found in remote areas as the Arctic. In this study a preliminary screening of PFOS and related compounds has been performed in liver samples of fish, birds and marine mammals from Greenland and the Faroe Islands. PFOS was the predominant fluorochemical in the biota analyzed, followed by perfluorooctane sulfonamide (PFOSA). PFOS was found at concentrations above LOQ (10 ng/g wet weight) in 13 out of 16 samples from Greenland and in all samples from the Faroe Islands. The results from Greenland showed a biomagnification of PFOS along the marine food chain (shorthorn sculpin<ringed seal<polar bear). The greatest concentration of PFOS was found in liver of polar bear from east Greenland (mean: 1285 ng/g wet weight, n=2). The geographical distribution of perfluorinated compounds in Greenland was similar to that of persistent organohalogenated compounds (OHCs), with the highest concentrations in east Greenland, indicating a similar geographical distribution to that of OHCs, with higher concentrations in east Greenland than in west Greenland.

Solution Structure of a Recombinant Type I Sculpin Antifreeze Protein,

We have determined the solution structure of rSS3, a recombinant form of the type I shorthorn sculpin antifreeze protein (AFP), at 278 and 268 K. This AFP contains an unusual sequence of N-terminal residues, together with two of the 11-residue repeats that are characteristic of the type I winter flounder AFP. The solution conformation of the N-terminal region of the sculpin AFP has been assumed to be the critical factor that results in recognition of different ice planes by the sculpin and flounder AFPs. At 278 K, the two repeats units (residues 11-20 and 21-32) in rSS3 form a continuous alpha-helix, with the residues 30-33 in the second repeat somewhat less well defined. Within the N-terminal region, residues 2-6 are well defined and helical and linked to the main helix by a more flexible region comprising residues A7-T11. At 268 K the AFP is overall more helical but retains the apparent hinge region. The helical conformation of the two repeats units is almost identical to the corresponding repeats in the type I winter flounder AFP. We also show that while tetracetylated rSS3 has antifreeze activity comparable to the natural AFP, its overall structure is the same as that of the unacetylated peptide. These data provide some insight into the structural determinants of antifreeze activity and should assist in the development of models that explain the recognition of different ice interfaces by the sculpin and flounder type I AFPs.

Halogenated organic contaminants in marine fish and mussels from southern Greenland—pilot study on relations to trophic levels and local sources

Mussels and marine fish (shorthorn sculpin and Greenland cod) were sampled at three locations with varying human activity. Fish livers and mussels were analysed for polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs) and chlorinated pesticides including chlordane and toxaphene. Levels of chlorinated contaminants in shorthorn sculpins from the background location, [capital Sigma]PCB (217-224 ng g(-1) lw), [capital Sigma]DDT (180 ng g(-1) lw) and hexachlorobenzene (32-44 ng g(-1) lw), were in the same range as previously observed in eastern Greenland but exceeded the levels previously observed in southern and western Greenland. Multivariate analysis showed that pollutant concentrations were mainly explained by trophic levels of the species (cod > sculpins > mussels). A pooled sample of shorthorn sculpins from the harbour of Qaqortoq had significantly higher PCB and PBDE concentrations with a different congener pattern compared to the background site, while other contaminants were comparable. This points towards local pollution sources, possibly accumulated emissions from burning of waste.

Effects of redox cycling compounds on DT diaphorase activity in the liver of rainbow trout (Oncorhynchus mykiss)

BackgroundDT diaphorase (DTD; NAD(P)H:quinone oxidoreductase; EC 1.6.99.2) catalyses the two electron reduction of quinones, thus preventing redox cycling and consequently quinone dependent production of reactive oxygen species. In rat and mouse, a wide range of chemicals including polyaromatic hydrocarbons, azo dyes and quinones induces DTD. Bifunctional compounds, such as β-naphthoflavone (β-NF) and benzo(a)pyrene (B(a)P), induce DTD together with CYP1A and phase II enzymes by a mechanism involving the aryl hydrocarbon receptor (AHR). Monofunctional induction of DTD is mediated through the antioxidant response element and does not lead to the induction of AHR dependent enzymes, such as CYP1A. The aim of this study was to investigate the effects of prooxidants (both bifunctional and monofunctional) on the activity of hepatic DTD in rainbow trout (Oncorhynchus mykiss) in order to evaluate DTD suitability as a biomarker. We also investigated the effect of β-NF on hepatic DTD activity in perch (Perca fluviatilis), shorthorn sculpin (Myoxocephalus scorpius), eelpout (Zoarces viviparus), brown trout (Salmo trutta) and carp (Cyprinus carpio). In addition, the effect of short term exposure to prooxidants on catalase activity was investigated.ResultsIn rainbow trout, hepatic DTD activity is induced by the bifunctional AHR agonists β-NF and B(a)P and the monofunctional inducers naphthazarin, menadione and paraquat. Although exposure to both B(a)P and β-NF led to a strong 7-ethoxyresorufin-O-deethylase (EROD) induction, none of the monofunctional compounds affected the rainbow trout EROD activity. DTD was not induced by β-NF in any of the other fish species. Much higher DTD activities were observed in rainbow trout compared to the other fish species. Catalase activity was less responsive to short term exposure to prooxidants compared to DTD.ConclusionSince rainbow trout hepatic DTD activity is inducible by both monofunctional and bifunctional inducers, it is suggested that rainbow trout DTD may be regulated by the same mechanisms, as in mammals. The fact that DTD is inducible in rainbow trout suggests that the enzyme may be suitable as a part of a biomarker battery when rainbow trout is used in environmental studies. It appears as if DTD activity in rainbow trout is higher and inducible compared to the other fish species studied.

Cardiorespiratory and tissue adenosine responses to hypoxia and reoxygenation in the short-horned sculpinMyoxocephalus scorpius

Adenosine is a product of adenylate phosphate breakdown that can exert protective effects on tissues during energy limitation. Accumulation of cardiac adenosine under hypoxia is well documented in mammals but has not been shown in fish. Adenosine content was measured in heart and brain tissue from short-horned sculpin Myoxocephalus scorpius L. exposed to acute hypoxia and to graded hypoxia and reoxygenation at 8 degrees C. Cardiorespiratory parameters were recorded along with plasma lactate, K(+), Ca(2+) and Na(+) levels and their relationship to adenosine levels investigated. Sculpin exhibited a large bradycardia during hypoxia, with a concomitant drop in cardiac output that recovers fully with reoxygenation. Ventilation rate also declined with hypoxia, suggesting a depression of activity. Plasma lactate concentration was significantly elevated after 4 h at 2.0 mg l(-1) dissolved oxygen while K(+) levels increased during acute hypoxia. Adenosine levels were maintained in heart under acute and graded hypoxia. Brain levels fluctuated under hypoxia and showed no change with reoxygenation. It is concluded that a depression of cardiac activity in conjunction with an adequate anaerobic metabolism allow sculpin to avoid excessive adenosine accumulation under conditions of moderate hypoxia. Cardiac adenosine levels decreased and plasma K(+) levels and heart rate increased significantly at reoxygenation.