No description available.

Little information has been published regarding the American plaice, Hippoglossoides platessoides platessoides (Fabricius), a subarctic species which is distributed from Cape Cod to Labrador. In recent years plaice has risen rapidy in commercial importance in eastern Canada. In 1940 only 3 million lb were landed compared to a total of more than 74 million lb in 1960. American plaice in 1961 made up 64 per cent by weight of the total Canadian flounder landings, excluding halibut. [...]

No description available.

No description available.

The study of larvae, their behaviour & physiology has gathered momentum in recent years due to the development of improved techniques of rearing during the past decade. Many marine larvae have been successfully reared in the laboratory (Shelbourne, 1964; Schumann, 1967; Blaxter, 1968,1969; Houde & Palko, 1970; Futch & Detwyler, 1970; Lasker, Feder, Theilacker & May, 1970). Fish larvae, in particular those of most marine species form an important tool for research in that at hatching they only possess the rudiments of most organs. Thus they are ideal material for ontogenetical studies. Although the respiratory mechanisms of adult fish have been the subject of a great deal of investigation from the point of view of gas exchange (see Randall 1970) gill structure (Hughes, 1966; Hughes & Grimstone, 1965; Newstead, 1967; to name a few) and dimensions (see Muir, 1969) gill ventilation and perfusion (see Shelton, 1970) circulatory systems (see Randall, 1970) bioenergetics, (see Brett, 1970) the respiratory systems of larvae have not been investigated in any great detail. Apart from a few studies on oxygen uptake (see Blaxter, 1969) and Harder (1954) on the development of branchial elements, no detailed study of the development of respiratory mechanisms have been made in marine fish larvae. The purpose of this study was to investigate the development of respiration in two species of marine larvae viz. the herring (Clupea harengus L.) and the plaice (Pleuronectes plates sa L.) These two species are well separated taxonomically and both adults and young have very different life histories. Herring lay demersal eggs, the plaice pelagic ones. The yolk-sac larvae of both species are planktonic, later feeding on diatoms and copepod nauplii and much later copepods. Adult herring are pelagic, living in mid water as juveniles and moving into deeper water with age, ranging from offshore to about 200m. They perform migrations partly caused by the distribution and density of food organisms. In contrast to this plaice at metamorphosis show an interesting asymmetry in that one eye migrates over the head and comes to lie against its opposite number. At this stage pelagic life ceases and the young fish assumes a bottom-living existence. Other features associated with asymmetry are secondary to the migration of the eye and follow on from the adoption of the benthic mode of life. They range from the shoreline when young to lOOOm feeding on bottom living organisms. During development the mechanism of respiration changes from a cutaneous one to gill respiration typical of the adult form. There is apparently no respiratory pigment in the early stages but the blood becomes pink at metamorphosis. The problem was approached from a morphological and a physiological viewpoint. The main parts of the study are as follows. (1) The survival times in water of low oxygen concentrations. (2) The oxygen uptake at normal oxygen concentrations. (3) The oxygen uptake at low oxygen concentrations. (4) Measurement of the body surface area as well as the gill area available for respiration. (5) The appearance of haemoglobin and its quantitative measurement.

Thesis (M. Sc.), Memorial University of Newfoundland, 1998. / Bibliography: leaves p. 71-84.

Thesis (M.Sc. )--Memorial University of Newfoundland, 1997. / Bibliography: leaves 137-145.

Nuclear hormone receptors (NHRs) are ligand-activated transcriptions factors which transduce the effects of various hormones as well as nutritional and other environmental signals. They thus function to maintain physiological homeostasis by integrating the tissue expression of specific target genes to regulate a wealth of biological processes including reproduction, development, metabolism and environmental adaptation. Mounting evidence indicates NHRs are the target of endocrine disrupting compounds (EDCs), exogenous chemicals, often of anthropogenic origin, which disrupt NHRs and thus the processes under their control. EDCs can interfere with NHR signalling by activating receptors (agonists), by inhibiting the actions of the receptor (antagonists), or by disrupting endogenous hormone synthesis, secretion, transport or metabolism. Much of the focus to date has been on the risk of EDCs to reproductive functions, via estrogen and androgen NHRs in humans, and also in aquatic organisms. However environmental pollutants also have the potential to interact with other NHRs, particularly in aquatic environments, and cause dysregulation of other critical physiological processes, including energy homeostasis, immune functions and the stress response. To address this possibility a reporter gene assay was developed, allowing the high-throughput screening of pollutants for their interactions with piscine NHRs with critical roles in energy homeostasis, stress reponse and immune functions, namely the peroxisome proliferator-activated receptors (PPARs) and corticosteroid receptors (CRs) from European plaice (Pleuronectes platessa) and European flounder (Platichthys flesus), respectively. Complementary DNA (cDNA) sequences encoding the ligand-binding domains of PPARs and CRs, critical for receptor-ligand interactions and receptor activation, were ligated to the DNA-binding domain (DBD) of the yeast Gal4 transcription activator protein to create experimental expression plasmid constructs. Co-transfection of these expression plasmids into the fathead minnow (FHM) cell line with an upstream-activating sequence (UAS)-firefly luciferase reporter gene plasmid increased luciferase expression in the presence of known PPAR and CR ligands. Several aquatic pollutants including pharmaceuticals, industrial by-products and biocides were tested for their potential to disrupt PPAR and CR functions by interacting with these receptors in an agonistic or antagonistic manner. Several fibrates, a group of pharmaceutical compounds used to treat dyslipidemia in humans by targeting the PPARs, were able to activate plaice Gal4-PPARα and Gal4-PPARβ in the reporter gene assay, indicative of an interaction with PPAR receptors in non-target species. Fibrates which did not activate Gal4-PPARα were able to inhibit the activation of Gal4-PPARα by the PPARα-specific agonist, Wy14643, suggesting differential effects of fibrates on human and flounder PPARs. In addition some metabolites of widespread phthalate ester pollutants were also agonists of the Gal4-PPARα and Gal4-PPARβ constructs. The Gal4-PPARγ construct was unresponsive to almost all the compounds tested, including the mammalian PPARγ agonist, rosiglitazone. The exception to this was the phthalate metabolite monobenzylphthalate, which induced a small increase in firefly luciferase in Gal4-PPARγ transfected cells. All of the above effects required concentrations of at least 10 µM, which are unlikely to be encountered in the aquatic environment. In contrast bis(tributyltin) oxide (TBTO), a notorious environmental pollutant, inhibited Gal4-PPARα and Gal4-CR constructs at concentrations as low as 1 nM and 100 nM, respectively. These concentrations are lower than those reported in aquatic environments, or in fish tissues, making TBTO a candidate endocrine disruptor in fish by inhibiting PPARα and CR signalling. A European flounder cDNA microarray was used to investigate the trasnscriptional responses of flounder hepatocytes to TBTO (10 nM) exposure. Exposure to TBTO and Wy14643, both alone and in combination, indicated a TBTO-driven downregulation of several potential PPARα-target genes with functions in the immune system, the proteasome, and lipid metabolism, although, based on mammalian comparisons, some potential PPARα-target genes were also upregulated, indicating differences in mammalian and fish PPAR-target genes or reflecting the complexity of organisms at a higher organisational level than cell-based assay systems. However, the microarray-based approach was useful in formulating further hypotheses about the effects of TBTO on PPARα signalling. Overall, these results indicate that exogenous chemicals entering the aquatic environment can interfere with NHRs with functions in energy homeostasis, immune functions and stress, in non-target organisms. The cell-based reporter gene assay is a useful tool for identifying potential endocrine disruptors which target PPARs and CRs and would be a useful method in a first tier testing approach, limiting the use of live animal models and enabling investigation into specific receptors which are targets of endocrine disrupting compounds. Although more work is required to confirm the physiological consequences of TBTO inhibition of PPARα, the results presented here indicate that organisms inhabiting TBTO-polluted environments may experience suppression of the immune system, an increase in non-functional or misfolded proteins through suppression of genes involved in the ubiquitin/proteasome system and a disruption in lipid homeostasis.

Durch die Zunahme von Offshorewindparks wird der anthropogene Lärmpegel im Meer weiter ansteigen. Deshalb ist es notwendig, mögliche negative Effekte von Windturbinenschall auf Fische zu erkennen und zu minimieren. Um mögliche Effekte des Turbinenschalls auf Kabeljau (Gadus morhua) und Scholle (Pleuronectes platessa) zu untersuchen, wurden die Fische in Laborversuchen verschiedenen tiefen Frequenzen und Schallstärken, wie sie von Windturbinen emittiert werden ausgesetzt. Ein ringförmiges Betonversuchsbecken mit 10 Metern Durchmesser wurde mit Schallisolationwänden in verbundene Viertel unterteilt, wodurch im Becken eine Schalldruckdifferenz von 32-52 dB, abhängig von Frequenz und produziertem Schalldruckpegel erzeugt wurde. Die Fische, die sich frei im Becken bewegen und so, wenn sie wollten, den höchsten Schalldruckpegeln ausweichen konnten, wurden monofrequenten Tönen im Frequenzbereich zwischen 25 und 250 Hz in Schalldruckpegeln von 130 und 140 dB re 1 µPa ausgesetzt. Die Position der Fische im Becken wurde in den 24-Stunden-Phasen vor, während und nach Beschallung verglichen und zeigte in den meisten Versuchen während Beschallung signifikant weniger Kabeljau in der Nähe der Schallquelle, als in den Phasen vor und nach Beschallung. Scholle zeigte uneinheitliche Reaktionen, die teilweise auf Meideverhalten, in anderen Versuchen auf Attraktion durch den Schall hindeuteten. Die Ergebnisse lassen wenigstens kurzzeitige, durch Schall verursachte Verteilungsänderungen von Kabeljau in Offshorewindparks erwarten. / The growing number of offshore wind farms will lead to an increase of anthropogenic noise in the sea. Research is therefore necessary to identify and minimize any potentially negative effects of offshore wind turbine noise on fish. To examine the potential impact of offshore wind farm noise emissions on cod (Gadus morhua) and plaice (Pleuronectes platessa), tank experiments were carried out exposing the fishes to different low frequencies at sound levels as emitted by wind turbines An annular concrete tank of 10 m in diameter was divided in connected quarters by sound barriers, so that sound pressure differences of 32 to 52 dB were achieved, depending on frequency and produced sound levels. Pure tones in the frequency range between 25 and 250 Hz were artificially emitted in sound levels of 130 and 140 dB re 1µPa. The experimental fish were free to move around in the tank and therefore could avoid the highest sound levels if they chose to. The location of fish in the 24 hour periods before, during and after sound production were compared and showed significantly lower numbers of cod in the vicinity of the sound source during sound presentation in the majority of the experiments. Reactions of plaice were ambiguous, suggesting both avoidance of, or attraction to the sound. From the results at least short-term changes in distribution of cod related to sound in the vicinity of offshore wind farms could be expected.

Effects of man made pollutants on an ecosystem are initiated at the cellular level where a prime determinant for survival of an organism is its ability to metabolise and excrete toxic chemicals or their metabolites, thereby preventing cellular toxicity or damage to germ cell DNA. Cytochrome P450 (CYP) enzymes are responsible (in concert with the remainder of the Ah battery enzymes) for the metabolism of numerous xenobiotics and endogenous compounds, including the metabolic activation of most environmental toxic chemicals and carcinogens. Genetic polymorphisms which affect performance of these enzymatic detoxification systems may alter tolerance to pollutants and thus survival in polluted environments. Alterations in the susceptibility of individuals and the development of resistant populations has arisen by forced selection of populations with variant genes, resulting in increased detoxification capacity. There is evidence for such scenarios of variations in activities of pollutant biotransforming enzymes of fish contributing to survival in polluted estuarine environments and several chemically resistant populations have been identified in the USA and Europe. In fish it has been demonstrated that CYP1A enzyme activity is required to activate some carcinogenic xenobiotics to a metabolic state in which they can form DNA adducts. The mechanism of reduced CYP1A expression in highly contaminated populations may therefore represent resistance to chemical stressors. European flounder (Platichthys flesus) from some waterways which have a long history of severe sedimentary contamination do not show elevated levels of CYP1A. The aim of the current study was to investigate whether any heritable differences were apparent between offspring from parents inhabiting long-term polluted and pristine areas. Flounder were obtained from a highly polluted estuary in the UK and crossed with fish from a relatively pristine environment. Offspring were raised in communal tanks in order to standardise environmental conditions, and allow investigations into the genetic variation of CYP1A. To allow identification of offspring to parental fish, polymorphic microsatellite loci were isolated and characterised for the flounder. Novel cDNA probes to transcription factors in the detoxification pathway (AhR2 and ARNT2) were cloned for flounder, and RT-PCR / Southern blot methods were developed for quantitation of gene transcript levels. A novel method of CYP1A quantification using real-time PCR was developed. PAH and PCB exposure trials were carried out on mixed batch offspring, and CYP1A gene transcript levels assessed using Northern blot and real-time PCR techniques. Offspring were genotyped to their parents using the microsatellites obtained, and CYP1A transcript levels were correlated with clean and polluted areas. CYP1A was further correlated to transcription factor expression, and data are presented. Following exposure to the commercial PCB mixture, Aroclor 1254, CYP1A transcript levels were found to be significantly lower in families whose parents originated from a polluted area. This observation indicates that there is a possible genetic component to variation in CYP1A levels, and that these fish may have acquired a heritable tolerance to polluted areas. The lack of induction, or correlation with CYP1A levels, of AhR2 and ARNT2 expression indicates a possible AhR independent pathway for the metabolism of PCBs in the flounder. © Tom Dixon 2003 http://www.tomdixon.org