Lymphocystis disease in the winter flounder, Pseudopleuronectes americanus.

Nodular lesions on the fins of winter flounder, Pseudopleuronemphocystis disease. Hypertrophied, encapsulated connective tissue cells contained cytoplasmic inclusions composed of icosahedral virus particles. The winter flounder is a new host for lymphocystis disease and is the second flatfish in the western North Atlantic to have the disease.     

Experimental infection of American winter flounder (Pseudopleuronectes americanus) with Glugea stephani (Microsporida)

Young-of-the-year Pseudopleuronectes americanus were captured in Sandy Hook Bay, New Jersey and maintained in aquaria at 16–19° C for 115 days in 1982 and 127 days in 1983. Half of them were experimentally exposed to Glugea stephani and the others were sham exposed. During the course of these experiments fish from both groups died as a result of G. stephani infection, demonstrating Glwgea -induced mortality in this species. Infections were found in both control and experimentally exposed fish. Mortality of Glwgea -infected fish in the exposed group was 63% while that in the controls was 28.5%.     

Feeding behavior of newly settled winter flounder (Pseudopleuronectes americanus) on calanoid copepods

Field and laboratory investigations were conducted to examine feeding by newly settled winter flounder (Pseudopleuronectes americanus) on two co-occurring calanoid copepods, Eurytemora affinis and Acartia hudsonica. During the spring, these prey are present when winter flounder initiate their demersal lifestyle in estuaries of the northeastern United States. Epibenthic zooplankton were collected concurrently with winter flounder in the Navesink River estuary, NJ, in May 1998 and 1999. Although both calanoid species were in the estuary during the 2-year survey, E. affinis was consumed nearly to the exclusion of A. hudsonica by newly settled winter flounder. Annually, E. affinis and A. hudsonica had similar size distributions in field collections, indicating that species choice was not size selective. However, when preying on E. affinis, winter flounder preferred the larger sized organisms. In single species laboratory experiments, E. affinis and A. hudsonica were consumed equally by newly settled winter flounder (19-23 mm TL), but there were more strikes made toward E. affinis. Despite the lower catch efficiency, E. affinis was selected over A. hudsonica when the prey species were offered together in equal numbers. The selection for E. affinis over A. hudsonica by newly settled winter flounder may be the result of behavioral and/or morphological differences in the prey species.     

Photoperiod and temperature effects on gametogenesis in winter flounder Pseudopleuronectes americanus

The winter flounder is an in‐shore flatfish living in shallow waters on the east coast of North America from Labrador to Georgia. In the St Lawrence estuary, the reproductive season is May and June. Our objective was to test the effects of winter‐spring photoperiod and temperature conditions on the timing of sexual maturation in both males and females. Groups (16 animals each) of winter flounder breeders were maintained from mid‐January to mid‐May under five different experimental conditions: (1) natural photoperiod and temperature conditions; (2) natural photoperiod, 6° C; (3) 15L : 9D, natural temperature conditions; (4) 15L : 9D, 6° C; (5) accelerated photoperiod increase from winter to spring conditions, 6° C. Natural photoperiod and temperature conditions correspond to a gradual increase in light period from 8L : 16D (January) to 15L : 9D (May) and in temperature from −1° C (January to April) to 6° C (May). GSI and condition factor did not differ among the treatments ( P  > 0·05). In males, milt production occurred simultaneously in the different treatments and histological examination did not indicate any significant effect of either photoperiod or temperature on testes development. In females, seven stages of oocyte development were observed. Both the number of oocytes at the cortical alveoli stage and number of atretic oocytes increased at 6° C (warm temperature conditions). Overall, neither photoperiod nor temperature modified the reproductive period. Warm winter‐spring temperature conditions, however, may decrease egg numbers and egg quality.     

Structural studies on the freezing-point-depressing protein of the winter flounder Pseudopleuronectes americanus

The freezing-point-depressing protein from the winter flounder, $\text{Pseudopleuronectes americanus}$ has been shown from circular dichroism measurements to possess a large proportion (～85%) of the α-helical conformation in aqueous solution (pH 8.0) at ?1°C. The helical content decreases as the temperature is raised. Viscosity data at ?1°C indicate an asymmetric shape for the protein molecule compatible with its high helical content. Thus, the secondary and tertiary structure of this freezing-point-depressing protein as well as its primary structure (reported elsewhere), are found to be different from its counterpart glycoproteins isolated from the Antarctic fish.     

Taurine transport by the flounder (Pseudopleuronectes americanus) intestine

Taurine transport by the flounder gut was characterized in isolated strips of intestine mounted between Ringer's solutions. Taurine was transported into the cell, against its concentration gradient, by a sodium-dependent system present in both the mucosal and serosal membranes. This system appears to be specific for beta-amino acids and is regulated by cyclic nucleotides (cGMP and cAMP). Kinetic analyses indicated that under physiological conditions the magnitudes of the bidirectional taurine uptake rates would favor net absorption of taurine from lumen to blood.     

Thermoregulatory behavior and diel activity of yearling winter flounder,Pseudopleuronectes americanus (Walbaum)

Synopsis Sixteen yearling winter flounder, tested individually for 3-day periods in electronic shuttleboxes, voluntarily occupied an 8–27°C range of temperature, with a modal final thermal preferendum of 18.5°C (mean 18.7°C, median 19°C, midpoint 17.5°C, s.d. 1.9°C, S_k + 0.33). The locomotor activity pattern of the yearling fish in the laboratory was markedly nocturnal, with mean hourly nocturnal activity exceeding mean hourly diurnal activity by a factor of 3.4. Maximum activity occurred at 0300 EST, minimum activity at 1400 EST. While activity generally increased with temperature, a local activity minimum occurred at 18.7°C, coinciding with the 24-hour mean final thermal preferendum. Comparison of these laboratory data with previously published field data suggest that behavioral responses to temperature and light play significant roles in determining age- and size-specific differences in seasonal depth stratification and onshore-offshore distributions in this species.     

Individual variability in the epidermis of prespawning inshore winter flounder, Pseudopleuronectes americanus

Prespawning winter flounder, Pseudopleuronectes americanus Walbaum, manifest epidermal thickening as a secondary sexual characteristic, but with considerable individual variability. The correlation between epidermal thickness and fish size in post-spawned flounder is less apparent in prespawning flounders due to factors associated with sexual maturation. Thus, epidermal thickness in individual prespawning flounder displays significant correlation with gonadosomatic index and. in females, with the degree of final maturation of vitellogenic oocytes. However, both epidermal thickness and gonadosomatic index of individual flounders also display significant correlation with condition factor. It is proposed that body size and condition factor represent important primary physiological determinants influencing individual variability in seasonal epidermal thickness, and that factors associated with sexual maturation represent a secondary physiological determinant.     

Mechanisms responsible for the enhanced pumping capacity of the in situ winter flounder heart (Pseudopleuronectes americanus)

In situ Starling and power output curves and in vitro pressure-volume curves were determined for winter flounder hearts, as well as the hearts of two other teleosts (Atlantic salmon and cod). In situ maximum cardiac output was not different between the three species (approximately 62 ml.min(-1).kg(-1)). However, because of the small size of the flounder heart, maximum stroke volume per milliliter per gram ventricle was significantly greater (2.3) compared with cod (1.7) and salmon (1.4) and is the highest reported for teleosts. The maximum power output of the flounder heart (7.6 mW/g) was significantly lower than that measured in the salmon (9.7) and similar to the cod (7.8) but was achieved at a much lower output pressure (4.9 vs. 8.0 and 6.2 kPa, respectively). Although the flounder heart could not perform resting levels of cardiac function at subambient pressures, it was much more sensitive to filling pressure, a finding supported by pressure-volume curves, which showed that the flounder's heart chambers were more compliant. Finally, we report that the flounder's bulbus:ventricle mass ratio (0.59) was significantly higher than in the cod (0.37) and salmon (0.22). These data, which support previous studies suggesting that the flatfish cardiovascular system is a high-volume, low-pressure design, show that vis-à-fronte filling is not important in flatfish, and that some fish can achieve high levels of cardiac output by vis-à-tergo filling alone; and suggest that a large compliant bulbus assists the flounder heart in delivering extremely large stroke volumes at pressures that do not become limiting.     

The effect of androgen treatment on the epidermis of post-spawned winter flounder, Pseudopleuronectes americanus (Walbaum)

The effect of androgen treatment on the thin epidermis of post-spawned winter flounder, Pseudopleuronectes americanus (Walbaum), freshly collected from an inshore population was investigated. Over the duration of the experiment, control flounders displayed epidermal thickening and increased goblet cell frequencies associated with captivity in this species. Treatment of males with 11-ketotestosterone induced significantly more differential thickening of the blindside epidermis. Compared with the controls testosterone treatment did not induce additional thickening of male epidermis, but it did increase differential thickening on the blind side of females.     

Life on the bottom: the chemical and morphological asymmetry of winter flounder (Pseudopleuronectes americanus) sagittae

Environmental Biology of Fishes - We observed that paired winter flounder (Pseudopleuronectes americanus) sagittae are not morphologically or chemically identical. Statistically significant...     

The binding of zinc to the soluble proteins of intestinal mucosa in winter flounder (Pseudopleuronectes americanus).

1. The binding of Zn2+ to soluble proteins of intestinal mucosa of winter flounder was examined using an equilibrium dialysis technique. 2. There appeared to be more than one binding system present for Zn2+ in the mucosal cytosol. 3. It required four times the normal endogenous Zn2+ level found in the mucosal cytosol to saturate the highest affinity (K1 = 2.42 x 10(7] binding system. 4. Of 10 metals tested Cu2+ was the only one which interfered with Zn2+ binding to the mucosal cytosol proteins. 5. It is postulated that binding proteins in the mucosal cytosol of winter flounder may play a role in the transport of Zn2+.     

Pharmacokinetics of morphine in fish: winter flounder (Pseudopleuronectes americanus) and seawater-acclimated rainbow trout (Oncorhynchus mykiss)

We made a single intraperitoneal (IP) injection of morphine sulfate (40 mg/kg) into winter flounder and seawater acclimated rainbow trout at 10 degrees C and then followed its disposition by measuring the change in plasma morphine concentration for 100 h using a morphine specific ELISA. Disposition also was followed for 6h after a single IV injection of 7.5mg morphine sulfate in winter flounder. Plasma morphine reached a maximum within an hour post-injection IP and then decreased in a bi-exponential fashion with a rapid distribution phase followed by a slower elimination phase. The disposition was slower in flounder than in trout even though the fish were held at the same temperature. For example, plasma clearance was 76 mL h(-)(1) kg(-)(1) in the flounder but was almost twice as much in the trout (153 mL h(-)(1) kg(-)(1)) and mean residence time was 27.9h in the flounder but was 7.0 h in the trout. The present study is the first comprehensive pharmacokinetic analysis for any analgesic in an ectotherm, and our results show that: 1) significant intra-specific variation exists between fishes: and 2) the disposition of morphine in fish is approximately one order of magnitude slower than it is in mammals. These differences may be due in part to mass specific differences in cardiac output.     

The effect of dissolved oxygen on the growth of young-of-the-year winter flounder,Pseudopleuronectes americanus

Synopsis The effects of constant and diurnally fluctuating levels of dissolved oxygen on the growth of young-of-the-year winter flounder,Pseudopleuronectes americanus, were examined under controlled laboratory conditions. Fish were exposed for either 10 or 11 weeks to constant levels of 6.7 (high) and 2.2 (low) mg l^–1, and a diurnal fluctuation, ranging from 2.5 to 6.4 mg 0₂l^–1. Growth rates, calculated for both standard length and weight, for fish exposed to low and diurnally fluctuating levels were significantly reduced (p < 0.001) as compared to those for fish exposed to the high level. Growth rates of fish exposed to the high level were over twice those of fish held under low oxygen conditions. Under fluctuating conditions, fish grew at intermediate rates. Following these exposures, all fish were subsequently held at 7.2 mg Oz l^–1 for five weeks. Growth rates increased over two and a half times for fish previously exposed to the low oxygen level and were significantly (p < 0.001) higher than for the other two groups.     

Epidermal characteristics of reproductive subsets in an inshore population of winter flounder, Pseudopleuronectes americanus

The winter flounder, Pseudopleuronectes americanus (Walbaum), population off Newfoundland can include a 'non-reproductive post-mature' subset at any time together with 'reproductive' and 'immature' subsets. Skin samples were taken from male and female specimens from each subset in the winter, after reproductive flounder have normally undergone a pre-winter phase of gonadal recrudescence, and also during the spring prespawning period and in the summer following spawning. Results for immature flounder demonstrate that fish size influences epidermal thickness in this species. The epidermis of reproductive flounders is thick, representing a secondary sexual characteristic, during gonadal recrudescence. A thick epidermis is most pronounced on the blind-side, particularly in prespawning males. Although the epidermis of non-reproductive post-mature fish was thinner than in prespawning males and females, it was thicker than in immature flounders. Also, the epidermal thickness of non-reproductive post-mature individuals can still display some seasonal change although gonadal recrudescence has not been sustained. There is also a relationship between condition factor and epidermal thickness which is manifested particularly clearly in immature and non-reproductive post-mature flounder.     

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 °C-acclimated flounder exposed to graded hypoxia, and in 8 °C-acclimated fish exposed to an acute temperature increase to their critical thermal maximum (CTM). The extent of bradycardia in 8 °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 °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 °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 °C (～ 15 mL min^? 1 kg^? 1), and hypoxic bradycardia was surprisingly absent at 15 °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.