Winter Flounder Research Articles

Molecular cloning and characterization of two putative appetite regulators in winter flounder ( Pleuronectes americanus): Preprothyrotropin-releasing hormone (TRH) and preproorexin (OX)

cDNAs encoding for preproTRH and preproorexin were cloned in winter flounder, a species that undergoes a period of natural fasting during the winter. For both peptides, the deduced amino acid structure of the hormone precursor shows 30–70% similarities with their homologs in other fish species. RT-PCR studies show that these peptides are present not only in the brain, but also in several peripheral tissues, including gastrointestinal tract and testes. Fasting induced increases in both preproorexin and preproTRH expressions in the hypothalamus, but did not affect their expression levels in the telencephalon/preoptic area. In addition, the mRNA expressions of both preproorexin and preproTRH were higher in the winter than in the summer in both hypothalamus and telencephalon/preoptic area. Our results suggest that orexin and thyrotropin-releasing hormone (TRH) might have a role in the seasonal regulation of food intake in winter flounder.

Piscine PTHrP regulation of calcium and phosphate transport in winter flounder renal proximal tubule primary cultures

Multiple factors control calcium (Ca(2+)) and inorganic phosphate (P(i)) transport in the fish nephron, and the recently discovered members of the piscine parathyroid hormone-like protein family are likely participants in such regulatory mechanisms. The effects of an NH(2)-terminal peptide (amino acids 1-34) of Takifugu rubripes parathyroid hormone-related protein, (1-34)PTHrP, on Ca(2+) and P(i) transport were investigated in winter flounder (Pseudopleuronectes americanus) proximal tubule cells in primary culture (fPTCs). RT-PCR performed on RNA extracted from fPTCs and from intact kidney tissue indicated that expression of PTHrP and types 1 and 3 PTH/PTHrP receptors occurred both in vivo and in vitro and that circulating levels of PTHrP measured by specific radioimmunoassay averaged 2.5 +/- 0.13 ng/ml. fPTC monolayers were mounted in Ussing chambers, and under neutral electrochemical conditions, addition of 10 nM (1-34)PTHrP to the basolateral side induced a slight increase in Ca(2+) transport rate from luminal to peritubular side, significantly stimulating net Ca(2+) reabsorption. (1-34)PTHrP also significantly increased the P(i) secretory flux, and slightly reduced P(i) reabsorption, evoking a significant increase in P(i) net secretion. This stimulatory effect was partially inhibited by bisindolylmaleimide, an inhibitor of protein kinase C. Incubation of ex vivo flounder renal tubules with (1-34)PTHrP resulted in apparent reduction of Na(+)-P(i) cotransporter type II (NaP(i)-II) protein in tubule membranes. PTHrP seems therefore to participate in the modulation of Ca(2+) and P(i) homeostasis by fish kidney.

Brominated flame retardants and organochlorine contaminants in winter flounder, harp and hooded seals, and North Atlantic right whales from the Northwest Atlantic Ocean

Various brominated flame retardants (BFRs), including polybrominated diphenyl ethers (PBDEs) and current-use, non-PBDE BFRs, as well as organochlorine (OC) pesticides and polychlorinated biphenyls (PCBs), were measured in winter flounder, harp and hooded seals, and North Atlantic right whales from the Eastern United States and Canada. The concentrations of PBDEs in winter flounder and right whales were similar in magnitude to the levels of PCBs, which was unlike the pattern observed in seals. In these marine mammals, the levels of PBDEs were orders of magnitude lower than the levels of OCs and PCBs detected. Evidence existed for the accumulation of methoxylated (MeO)-PBDEs of natural origin in seals and right whales. Current-use, non-PBDE BFRs (including hexabromocyclododecane, pentabromoethylbenzene, hexabromobenzene, and pentabromotoluene) were detected in winter flounder and marine mammals. Future research should focus on monitoring PBDEs, current-use, non-PBDE BFRs, and MeO-BDEs of natural origin in marine organisms from Massachusetts and Cape Cod Bays.

Structures and ice-binding faces of the alanine-rich type I antifreeze proteinsThis paper is one of a selection of papers published in this special issue entitled “Canadian Society of Biochemistry, Molecular & Cellular Biology 52nd Annual Meeting — Protein Folding: Principles and Diseases” and has undergone the Journal's usual peer review process.

Antifreeze proteins (AFPs) protect cold-blooded organisms from the damage caused by freezing through their ability to inhibit ice growth. The type I AFP family, found in several fish species, contains proteins that have a high alanine content (>60% of the sequence) and structures that are almost all alpha-helical. We examine the structure of the type I AFP isoforms HPLC6 from winter flounder, shorthorn sculpin 3, and the winter flounder hyperactive type I AFP. The HPLC6 isoform structure consists of a single alpha-helix that is 37 residues long, whereas the shorthorn sculpin 3 isoform consists of two helical regions separated by a kink. The high-resolution structure of the hyperactive type I AFP has yet to be determined, but circular dichroism data and analytical ultracentrifugation suggest that the 195 residue protein is a side-by-side dimer of two alpha-helices. The alanine-rich ice-binding faces of HPLC6 and hyperactive type I AFP are discussed, and we propose that the ice-binding face of the shorthorn sculpin 3 AFP contains Ala14, Ala19, and Ala25. We also propose that the denaturation of hyperactive type I AFP at room temperature is explained by the stabilization of the dimerization interface through hydrogen bonds.

Impacts of Climate Change on Narragansett Bay

Abstract The objective of this paper is to examine the impacts of global climate change on Rhode Island's coastal ecosystems. Average annual air temperature in Rhode Island has increased by 1.7 °C since 1880, water temperatures of Narragansett Bay have increased by 1.2 °C since 1950, precipitation increased 27% between 1895 and 1999, and sea level rose 0.13 m between 1931 and 2007. We can already see the effects of these climatic changes on the Narragansett Bay ecosystem, including ecological changes in the Bay's food web from phytoplankton and Zooplankton to fish, e.g., changes in phenology of seasonal phytoplankton blooms and dominant fish species (e.g., Pseudopleuronectes americanus [Winter Flounder]). These climatic changes have increased freshwater inputs and the concomitant pollutant loads into the Bay. Rising sea level has contributed to ongoing erosion of the coast and has put waterfront homes at increased risk. It is imperative to continue monitoring these effects.

Assessment of paternal effect and physiological cost of metamorphosis on growth of young winter flounder Pseudopleuronectes americanus juveniles in a cold environment

This study assessed the paternal effects on the growth of early juvenile winter flounder Pseudopleuronectes americanus and examined the energy allocation strategy employed during this critical stage. Males from three different locations (Passamaquoddy Bay, Baie‐des‐Chaleurs and the St Lawrence Estuary) were crossed with females from the Baie‐des‐Chaleurs, and the growth characteristics of hybrids from settlement to 45 days post‐settlement were monitored under similar culture conditions. Young juveniles displayed good growth rates (0·09 ± 0·02 mm day−1), with no differences related to sire origin, in terms of growth indicators (length, width, RNA:DNA and triacylglycerol:sterol ratios), condition indices (Fulton's K, pigmentation and fin erosion) and biochemical components (nucleic acids, proteins and lipid classes). These results suggest the absence of a paternal contribution to the growth strategy during the early juvenile stage of P. americanus. The results also highlight the high energetic cost associated with metamorphosis: young juveniles mobilized most of their triacylglycerol reserves during the growth period following settlement.

Stable carbon and oxygen isotope ratios of otoliths differentiate juvenile winter flounder (Pseudopleuronectes americanus) habitats

The use of natural tags for identifying the source locations of individuals recruited to fish populations has become an important area of research in fisheries science. We used stable carbon (δ13C) and oxygen (δ18O) isotope ratios in otoliths to differentiate juvenile winter flounder (Pseudopleuronectes americanus) collected from locations along the coast of Rhode Island, USA. Sagittal otoliths from the flounder were analysed for δ13C and δ18O using isotope ratio mass spectrometry. Plots of δ13C v. δ18O and discriminant function analysis (DFA) indicated differences among samples from Narragansett Bay, the coastal ponds and the Narrow River. Separations were observed among fish from the upper, middle and lower portions of Narragansett Bay and along the salinity gradient in Narrow River. Otoliths from sites grouped on the basis of low, medium and high salinities also showed differences according to DFA. Correlation analysis indicated a significant negative relationship (r = –0.60, P = 0.009) between seawater temperature and δ18O, and a significant positive relationship (r = 0.93, P < 0.001) between salinity and δ18O for the combined dataset. These results indicate that δ13C and δ18O values of juvenile winter flounder otoliths may prove useful for differentiating individuals from various juvenile habitats.

A132 マイクロチャネル内水流における氷結晶の成長への不凍タンパク質の影響(OS-1:固液相変化を伴う伝熱現象(III))

We have carried out an experiment on the freezing aqueous solution flow of winter flounder antifreeze protein in a micro-channel of 0.15mm in height, 1.2mm in width and 21mm in length. An electro-osmotic pump was used to create the flow of the solution in the channel. The flow was cooled from the side wall. An ice/solution interface is observed at low magnification in a high-resolution biological microscope. It is found from our experiment that, as the flow rate increases, the growing rate of the ice/solution interface decreases and the interface becomes more serrated. This is because the interaction between the interface and the protein, continuously approaching the interface due to the flow, occurs more frequently with an increase in the flow rate.

Potential of mean force calculation of the free energy of adsorption of Type I winter flounder antifreeze protein on ice

Antifreeze proteins (AFPs) are a unique class of proteins that inhibit ice growth without changing the melting point of ice. In this work, we study the detailed molecular mechanism of interactions between the hydrophobic side of the winter flounder (WF) AFP and two mutants, AAAA and SSSS, in which threonine residues are substituted by serines and alanines, respectively. Umbrella sampling molecular dynamics simulations of the separation of the proteins from the (2 0 1) surface in an explicit water box is carried out to calculate the potential of mean force free energies of adsorption using AMBER10i. We estimate wild-type WF's free energy of adsorption to ice to be about −12.0 kcal/mol. Gas-phase pseudopotential plane-wave calculations of methane adsorption onto select surfaces of ice are also carried out under periodic boundary conditions to address the possible enthalpic role of WF's methyl groups in binding. The contributions of hydrophobic residues to the free energy of adsorption are discussed.

Effects of Diet Composition and Trophic Structure on Mercury Bioaccumulation in Temperate Flatfishes

The summer flounder Paralichthys dentatus and winter flounder Pseudopleuronectes americanus support valuable fisheries along the northeastern United States. The importance of these flatfish as a human dietary resource indicates they are potential sources of mercury (Hg) to fish-consuming citizens. In this study, summer flounder (SF) and winter flounder (WF) were collected from the Narragansett Bay (Rhode Island, USA) and were measured for total Hg burden in whole-body or dorsal muscle tissue. Interspecies differences in Hg contamination were analyzed relative to flounder body size, age, and Hg content of preferred prey. Stable isotope signatures were also used to elucidate the effect of trophic processes on Hg accumulation in the estuarine food web. The mean Hg content of SF exceeded concentrations measured in WF across multiple life-history stages (0.039-0.100 and 0.016-0.029 mg Hg/kg wet weight for SF and WF, respectively), and observed values for both species were lower than the US Environmental Protection Agency regulatory threshold of 0.3 mg Hg/kg wet weight. Total Hg concentrations were also positively correlated with flounder age and length, verifying that both flatfish bioaccumulate Hg. SF accumulate Hg at an accelerated rate, however, owing to this species consuming Hg-enriched prey (teleosts, squid, and macrocrustaceans; mean Hg content = 0.023 mg Hg/kg wet weight), whereas WF feed on prey with low Hg levels (amphipods and polychaetes; mean Hg content = 0.013 mg Hg/kg wet weight). The positive correlation observed between mean biota Hg content and stable nitrogen (delta(15)N) isotope signatures further indicates that Hg is trophically transferred through the food web, and higher trophic level organisms (i.e., enriched delta(15)N) have increased Hg concentrations. Therefore, results from this study suggest that dietary preference and trophic structure are the main factors affecting Hg bioaccumulation in the estuary. Total Hg concentrations of flatfish from the Narragansett Bay, however, do not necessarily reflect coastwide contamination patterns. This reinforces the importance of having research conducted at sufficiently small spatial scales, including the local assessment of Hg contamination for the purpose of issuing state consumption advisories.

The effects of acute changes in temperature and oxygen availability on cardiac performance in winter flounder (Pseudopleuronectes americanus)

Studies on how flatfish cardiovascular function responds to environmental challenges are limited, and have largely relied upon indirect methodologies (i.e. Fick principle). Thus, we measured dorsal aortic blood pressure (P(DA)) and cardiac function in 8 and 15 degrees C-acclimated flounder exposed to graded hypoxia, and in 8 degrees C-acclimated fish exposed to an acute temperature increase to their critical thermal maximum (CTM). The extent of bradycardia in 8 degrees C-acclimated fish (decrease in heart rate of 41%) was consistent with that observed for other teleosts, as was this species' CTM (25.8+/-0.5 degrees C) and its cardiac response to increasing temperature. However, this study provides further examples of how cardiovascular function is controlled differently in the flounder as compared with other fishes. First, the onset of bradycardia in 8 degrees C-acclimated fish occurred earlier than expected for this inactive and hypoxia-tolerant species (60% water air saturation). Second, resting cardiac output was similar in flounder acclimated to 8 and 15 degrees C (approximately 15 mL min(-1) kg(-1)), and hypoxic bradycardia was surprisingly absent at 15 degrees C. Finally, systemic vascular resistance decreased when flounder were exposed to elevated temperature, and this resulted in a 26% fall in P(DA). These are novel findings, however, the extent to which the flounder's behaviour influenced some of the results is unclear.

Temperature of the solution of winter flounder antifreeze protein near ice surfaces in a narrow space

Experiments have been conducted into the unidirectional freezing of the aqueous solution of winter flounder antifreeze protein in a narrow gap between two cover glasses. A gap of 20 μm, which is narrower than the gaps used by Coger (32 μm) and Furukawa (60 μm), has been adopted. It is confirmed that the local temperature near the ice/solution interface can be measured accurately with a near-infrared spectroscopy. The temperature difference between the front and bottom edges of the serrated interface is found to be proportional to the distance between the front and bottom edges. Generally, as ice grows, the wide, shallow regions of the serrated interface become even wider, while the narrow, deep regions of the serrated interface become even deeper. These changes coexist. It is also observed in the case of the lowest interface velocity that the shallow, narrow region becomes shallower quickly, which does not satisfy the proportional relationship.

Effects of moving acclimation cages before release of cultured fish: alternate release strategies for a juvenile winter flounderPseudopleuronectes americanusstock enhancement effort

Biomass of winter £ounder Pseudopleuronectes americanus, a target species of both recreational and commercial ¢sheries, is at an all-time low (Northeast Fisheries Science Center 2008), and due to new unprecedented regulations, the largest of the three stocks is closed to all ¢shing activities in federal waters (National Oceanic and Atmospheric Activities 2009).Winter £ounder population recovery could be expedited by stock enhancement (Waters 1996; Le Francois, Lemieux & Blier 2002), and experimental stocking studies have been conducted since 1996 in New Hampshire. The goal of past projects has not been to initiate large-scale releases. Instead, ‘responsible approach’ (Blankenship & Leber 1995) has been applied to develop the processes needed to successfully enhance winter £ounder by answering key questions in the event that large-scale stocking efforts occur. Much of the research has focused on optimal release strategies for juvenile winter £ounder. In many stock enhancement programmes, initial survival rates of newly released cultured ¢sh are low (Pitman & Gutreuter 1993; Stottrup & Sparrevohn 2007; Sudo, Kajihara & Fujii 2008). These may be due, in part, to stress responses in hatchery-reared ¢sh causing departures from behavioural norms which result in a higher probability of mortality (Schreck, Olla & Davis1997). Developing release strategies that minimize stress responses and reduce post-release mortality is essential to any enhancement eiort and can be done with a combination of hatchery and ¢eld techniques. One such technique is using acclimation cages in situ. For many ¢sh species, acclimation cages improve post-release survival, growth, and site ¢delity (Koshiishi, Itano & Hirota 1991; Jonssonn, Brannas & Lundqvist1999; Kuwada, Masuda, Shiozawa, Kogane, Imaizumi & Tsukamoto 2000; Brennan, Darcy & Leber 2006; Sparrevohn & Stottrup 2007). For juvenile winter £ounder, predation by green crabs Carcinus maenas is of special concern (Fairchild & Howell 2000;Taylor 2005). Acclimation cages have been used at the release site under the assumption that these cages reduce immediate post-release mortality. Cultured £ounder, stocked into these cages for 48 h, adjust to the release site, hone their burial skills, begin pigment change, recover from the stress of transport to the release site and maintain high site ¢delity post release (Fairchild & Howell 2004; Sulikowski, Fairchild, Rennels, Howell & Tsang 2005, 2006; Fairchild, Rennels & Howell 2009). However, the cages also can be detrimental byattracting predators to the release site. In a recent study, Fairchild, Rennels and Howell (2008) compared green crab density when cages were absent, present but empty Aquaculture Research, 2009, 1^5 doi:10.1111/j.1365-2109.2009.02343.x

Factors Affecting Mercury and Selenium Levels in New Jersey Flatfish: Low Risk to Human Consumers

Some fish contain high levels of mercury (Hg), which could pose a risk to fish eaters themselves or their children. In making decisions about fish consumption, people must decide whether to eat fish, how much to eat, what species to eat, and what size fish to eat, as well as suitable (or unsuitable) locations, among other factors. Yet to make sound decisions, people need to know the levels of Hg in fish as a function of species, size, and location of capture. Levels of Hg and selenium (Se) were examined in three species of flatfish (fluke or summer flounder [Paralichthys dentatus], winter flounder [Pseudopleuronectes americanus], and windowpane [Scophthalmus aquosus]) from New Jersey as a function of species, fish size, season, and location. Flatfish were postulated to have low levels of Hg because they are low on the food chain and are bottom feeders, and data were generated to provide individuals with information on a species that might be safe to eat regularly. Although there were interspecific differences in Hg levels in the 3 species, total Hg levels averaged 0.18, 0.14, and 0.06 ppm (μg/g, wet weigh) in windowpane, fluke, and winter flounder, and selenium levels averaged 0.36, 0.35, and 0.25 ppm, respectively. For windowpane, 15% had Hg levels above 0.3 ppm, but no individual fish had Hg levels over 0.5 ppm. There were no significant seasonal differences in Hg levels, although Se was significantly higher in fluke in summer compared to spring. There were few geographical differences among New Jersey locations. Correlations between Hg and Se levels were low. Data, based on 464 fish samples, indicate that Hg levels are below various advisory levels and pose little risk to typical New Jersey fish consumers. A 70-kg person eating 1 meal (8 oz or 227 g) per week would not exceed the U.S. Environmental Protection Agency reference dose of 0.1 μg/kg body weight/d of methylmercury (MeHg). However, high-end fish eaters consuming several such meals per week may exceed recommended levels.

Influence of Sediment Contaminated with Untreated Pulp and Paper Mill Effluent on Winter Flounder, Pleuronectes americanus

This study was conducted to ascertain the influence of sediment contaminated with pulp and paper mill effluent in a fjord on winter flounder, Pleuronectes americanus, based on a laboratory study. Flounder, captured from a pristine site, were exposed in a flow-through system for 16 weeks to sediment collected at 2, 5, 7, and 10 km from the outfall. A group of controls was placed in uncontaminated sediment. Mortality occurred almost exclusively in fish exposed to sediment taken from 2 km than from more distant sites. Additionally, the condition factor was lower, the liver was enlarged, and toxicopathic lesions in the liver and spleen were significantly greater in fish submerged in the sediment than in fish from the more distant locations or the controls. Two ectoparasites including a ciliate, Trichodina jadranica, and a monogenean, Gyrodactylus pleuronecti, were observed only in the control group, while a digenean in the digestive tract, Steringophorus furciger, was more abundant in fish exposed to sediment from sites more distant from the outfall and the controls than at 2 km. Comparison of these results with data from a previous gradient field study on biological variables in winter flounder, captured at 2, 5, 7, and 10 km down-current from the outfall, revealed an enlarged liver that was associated with elevated levels of detoxification of hepatic enzymes and prevalence of toxicopathic lesions in both the liver and the spleen; these were significantly greater in samples taken nearest to the outfall from the mill than at more distant sites. Moreover, two metazoan parasites, S. furciger (Digenea) and Echinorhynchus gadi (Acanthocephala), in the digestive were more abundant in samples taken at farther locations and also from the reference sites. These results, based on a laboratory study, are in agreement with previous observations that winter flounder exposed to sediment at the site nearest to the outfall, where high concentrations of toxic contaminants persisted, was greater than in the fish from the other locations.

Anesthetic effects of lidocaine-hydrochloride on water parameters in simulated transport experiment of juvenile winter flounder, Pleuronectes americanus

Simulated transportation of winter flounder, Pleuronectes americanus fingerlings was carried out to study the effects of lidocaine-hydrochloride on water parameters. Dissolved oxygen, ventilation rate, ammonia nitrogen and pH of control group, sham control group and lidocaine-hydrochloride treated groups of 5 ppm, 10 ppm, 20 ppm were tested at 1 h, 2 h, 3 h, 4 h and 5 h treatment duration. Lidocaine-hydrochloride treated groups, followed by sham control and control, were most effective in decreasing oxygen consumption and excretion of ammonia by fish. Lidocaine-hydrochloride dose-related decrease in oxygen consumption and excretion of ammonia were also established. pH declines in lidocaine-hydrochloride and sham control groups were more rapid compared to the control group. The results of this study reveal that lidocaine-hydrochloride is an effective sedative as a transportation mixture for winter flounder.

Seasonal patterns of winter flounder Pseudopleuronectes americanus abundance and reproductive condition on the New York Bight continental shelf

To resolve varied and sometimes conflicting accounts of spawning and habitat characteristics for winter flounder Pseudopleuronectes americanus, seasonal patterns in abundance and reproductive condition were investigated in the New York Bight, near the southern edge of their current reproductive range. Fish were collected from trawl surveys on the inner continental shelf from October 2006 to October 2007. Pseudopleuronectes americanus were most abundant during January and April surveys, were rarely collected in August, with intermediate abundances in June and October. Measurements of fish condition [hepato-somatic index (I(H)), condition factor (K) and the per cent dry mass of muscle tissue (%M(D))] and reproductive condition [gonado-somatic index (I(G))] were determined to evaluate seasonal changes in energy accumulation and depletion and reproduction. Males and females had similar patterns in body and reproductive condition, although the magnitude of change was greater for females. I(H) values were highest during spring and early summer, suggesting increased feeding following spawning. K and %M(D) increased through spring and summer then declined in the autumn and winter concurrent with gonadal development. Gonads began developing in the autumn, and in January, I(G) values approached spawning levels, with many spent individuals collected in spring. Within these general patterns, however, there was a large degree of variability among individuals, and a few mature non-reproductive ('skipped spawning') females were observed. In the period after spawning, increased energy intake, indicated by increased I(H), may influence reproductive output since this energy is gradually transferred to the muscle and used for gonadal development in the forthcoming year. The occurrence of ripening individuals on the inner continental shelf in January suggests that these fish either rapidly move into estuaries to spawn by February-March or they remain on the inner shelf to spawn, or some combination of these. Future studies should evaluate these possibilities, as both estuarine and inner shelf habitats are potentially affected by activities such as dredging, sand dredging and wind energy development.

Cloning, distribution and effects of season and nutritional status on the expression of neuropeptide Y (NPY), cocaine and amphetamine regulated transcript (CART) and cholecystokinin (CCK) in winter flounder (Pseudopleuronectes americanus)

cDNAs encoding for neuropeptide Y (NPY), cocaine and amphetamine regulated transcript (CART) and cholecystokinin (CCK) were cloned in winter flounder, a species that undergoes a period of natural fasting during the winter. Tissue distribution studies show that these peptides are present in several peripheral tissues, including gut and gonads, as well as within the brain. We assessed the effects of season and fasting on the expression of these peptides. Our results show that NPY and CCK, but not CART, show seasonal differences in expression with higher hypothalamic NPY and lower gut CCK expression levels in the winter. In the summer, fasting induced an increase in hypothalamic NPY expression levels and a decrease in gut CCK levels, but did not affect hypothalamic CART expression levels. None of the peptides examined was affected by fasting in the winter. Our results suggest that NPY and CCK, but maybe not CART, might have a major role in the regulation of feeding in winter flounder and might contribute to the seasonal fluctuations in appetite in this species.

Nervous and humoral control of cardiac performance in the winter flounder(Pleuronectes americanus)

Previous studies have suggested that flatfish lack adrenergic cardiac innervation and have a limited humoral adrenergic stress response. However, data on neurohormonal control of flatfish cardiac function is scarce, and has never been directly studied in vivo. Hence, we (1) injected neural and humoral antagonists into flounder (Pleuronectes americanus) in vivo to determine the contribution of autonomic innervation and circulating catecholamines to the control of resting cardiac function; (2) measured pre- and post-stress (90 s chase) catecholamine levels in this species; and (3) constructed in vivo catecholamine dose-response curves for cardiovascular function based on the results of the second experiment. In addition, we quantified the density (B(max)) and ligand-binding affinity (Kd) of flounder ventricular cell-surface beta-adrenoreceptors, and established whether they were of beta1 or beta2 subtype using pharmacological antagonists. The cholinergic contribution to resting flounder heart rate was comparable to other teleosts (cholinergic tonus 26%). Interestingly, however, bretylium increased heart rate, resulting in a negative resting adrenergic tonus (-11.9%), and we were unable to demonstrate that catecholamines supported cardiac function at rest or at circulating concentrations approximating those following an exhaustive chase (adrenaline, 21 nmol l(-1); noradrenaline, 14 nmol l(-1)). Myocardial B(max) was very high in the flounder (252.8 fmol mg(-1) protein), and it appears that flounder ventricular beta-adrenoreceptors are predominantly of the beta2 subtype [based on the inability of atenolol to displace [3H]CGP from the beta-adrenoreceptors, and the IC(50) value for ICI 118551 (1.91 x 10(-6) mol l(-1))]. However, the extremely low affinity (Kd 1.02 nmol l(-1)) for these receptors raises the possibility that the flounder heart is also populated by beta3-adrenoreceptors.

The Effects of Latitudinal Origin and Paternal Contribution on Larval Growth of Winter Flounder in a Northern Environment

AbstractThree stocks of winter flounder Pseudopleuronectes americanus are currently defined in the northwest Atlantic region: One south of Cape Cod, Massachusetts, one north of it, and a third on Georges Bank. Our objectives were to determine whether the different populations along this latitudinal gradient have similar larval development characteristics in a coldwater environment and to test the paternal contribution to larval development. We crossed breeders that had been captured on their natural spawning sites in Passamaquoddy Bay, New Brunswick, and Baie des Chaleurs and the St. Lawrence estuary, Quebec, to produce pure‐strain families (year 1) and hybrids (year 2). Larvae were reared under the salinity and temperature conditions of the St. Lawrence estuary, the northernmost site in our study. Total length and maximum width were measured from hatching to settlement. In the wild population from the St. Lawrence estuary, males were shorter and in better condition and females produced smaller eggs than those from the two more southern wild populations. The time lapse between fertilization and hatch was shorter for embryos from the Baie des Chaleurs. In both the pure and hybrid cross experiments, the different cross‐types showed similar fertilization and hatching success, size at hatch and settlement, and time until settlement but differed in larval growth rate. Larval growth was slower in families sired by St. Lawrence estuary males. When females from the Baie des Chaleurs were crossed with males from the different origins, the results were similar to those obtained in families sired by St. Lawrence estuary males. These results strongly suggest a paternal component to larval growth. Settlement, however, which appeared to be size dependent, was governed more by environmental factors than by parental ones.