Winter flounder 4

This study explored whether winter flounder, a benthic species, are potentially exposed to contaminants such as heavy metals released from the sediment of the Bay of Fundy/Gulf of Maine, both critical habitats identified to have increases in heavy metal levels. Experimentally in fish, exposure to certain heavy metals resulted in reduced weight for length and structural abnormalities, but it is unknown if this occurs in wild fish. Winter flounder (n = 72), harvested between 2015 and 2018 from the aforementioned western Atlantic region of Canada/USA, had detectable levels of most heavy metals, with some exhibiting levels of concern (arsenic, cadmium, lead, selenium, zinc) in muscle, liver, and kidney. A 1.4% incidence of structural abnormalities was noted. When compared to 1980 regionally matched flounder data, the 2018 flounder had significantly reduced weight for length, exacerbated with age. Clearly winter flounder are affected by worsening heavy metal contaminant levels in this geographic area.

The factors determining the renal handling of 2,4-dichlorophenoxyacetic acid (2,4-D) were examined in winter flounder, Pseudopleuronectes americanus, using isolated tubules and clearance techniques. In vitro, extensive energy-dependent uptake was seen with tissue/medium ratios of 30-fold at 1 micronM 2,4-D. The velocity of uptake was concentration-dependent with apparent Km and Vmax v,lues of 70 micronM and 3.6 micronmol/g of tubules per hr, respectively. Uptake was inhibited by other organic acids and 2,4-D competitively inhibited p-aminohippurate uptake. 2,4-D did not inhibit organic cation transport by the tubules. In vivo, 2,4-D was actively secreted with clearances of nearly 500 times the glomerular filtration rate at 1 micronM 2,4-D in plasma. At higher plasma concentrations (10-60 micronM) a transport maximum of 0.85 micronmol/g of kidney per hr was observed. Secretion was inhibited by other organic acids. 2,4-D also inhibited p-aminohippurate secretion in vivo. Little metabolism was noted; approximately 10% was excreted as the taurine conjugate. Plasma binding was 70%. Examination of the effects of added proteins on in vitro uptake showed that protein binding could limit 2,4-D transport but that flounder plasma (low in albumin) was far less effective than bovine serum albumin in binding and inhibition of transport. The roles of plasma binding, intracellular binding and metabolism in determining the rate of 2,4-D elimination by the kidney are discussed.

This study evaluated the relative importance of the N arragansett Bay estuary (RI and MA, USA), and associated tidal rivers and coastal lagoons, as nurseries for juvenile winter flounder, Pseudopleuronectes americanus, and summer flounder, Paralichthys dentatus. Winter flounder (WF) and summer flounder (SF) abundance and growth were measured from May to October (2009-2013) and served as indicators for the use and quality of shallow-water habitats (water depth < 1.5-3.0 m). These bioindicators were then analyzed with respect to physiochemical conditions to determine the mechanisms underlying intra-specific habitat selection. WF and SF abundances were greatest in late May and June (maximum monthly mean = 4.9 and 0.55 flounder/m2 for WF and SF, respectively), and were significantly higher in the tidal rivers relative to the bay and lagoons. Habitat-related patterns in WF and SF abundance were primarily governed by their preferences for oligohaline (0.1-5 ppt) and mesohaline (6-18 ppt) waters, but also their respective avoidance of hypoxic conditions (< 4 mg DO/L) and warm water temperatures (> 25 °C). Flounder habitat usage was also positively related to sediment organic content, which may be due to these substrates having sufficiently high prey densities. WF growth rates (mean = 0.25 ± 0.14 mm/d) were negatively correlated with the abundance of conspecifics, whereas SF growth (mean = 1.39 ± 0.46 mm/d) was positively related to temperature and salinity. Also, contrary to expectations, flounder occupied habitats that offered no ostensible advantage in intra-specific growth rates. WF and SF exposed to low salinities in certain rivers likely experienced increased osmoregulatory costs, thereby reducing energy for somatic growth. Low-salinity habitats, however, may benefit flounder by providing refugia from predation or reduced competition with other estuarine fishes and macro-invertebrates. Examining WF and SF abundance and growth across each species' broader geographic distribution revealed that southern New England habitats may constitute functionally significant nurseries. These results also indicated that juvenile SF have a geographic range extending further north than previously recognized.