Stock and parental effects on embryonic and early larval development of winter flounder Pseudopleuronectes americanus (Walbaum)

A hierarchical breeding design was used to determine if winter flounder Pseudopleuronectes americanus embryos and yolk-sac larvae sired by Georges Bank males developed and grew larger than fish sired by Passamaquoddy Bay males, and to examine parental contributions to variations in fertilization success, time to 50% hatch, hatch success and larval morphological development. Significant stock effects were detected for time to hatch and larval development. Eggs fertilized by Passamaquoddy Bay males reached 50% hatch significantly earlier than eggs fertilized by Georges Bank males. Larvae sired by Georges Bank males were significantly larger during larval development for four of the six traits measured at 12 days post-hatch: head depth, jaw length, myotome height and body area. Embryo and larval development were strongly influenced by maternal contributions; there were significant maternal variance components for the majority of the variables measured. Paternal variance components were significant for fertilization success, time to hatch, larval jaw length and larval head depth, however, they acted principally through parental interactions. This information has important implications for the long-term sustainable development of winter flounder for aquaculture purposes as well as for understanding winter flounder genetic variation in the wild.     

Seasonal changes in the intestinal mucosa of winter flounder, Pseudopleuronectes americanus (Walbaum), from Passamaquoddy Bay, New Brunswick

Winter flounder from Passamaquoddy Bay, N.B. undergo an annual fast from November to May which results in a decrease in the slope of the length-weight relationship (3·17 to 2·54), in the condition factor (9 to 12%), in the liver (75%) and white muscle (24%) lipid contents, and an increase in muscle water content (2·4%). Winter flounder appear to have sufficient lipid reserves to support the winter fast, as muscle water content declined only at the onset of feeding.
The intestine could be divided into pyloric caeca (4), foregut, midgut and hindgut. Mucosal folding was reduced in all sections of the intestine during the fast. Goblet cell number declined, but little change in enterocyte ultrastructure was observed. Intestinal length remained the same, although the caeca shortened. Overall, mucosal mass declined by 57% from May to January, while surface area declined by 50%. This value is less than that in literature reports for a fast of shorter duration in freshwater rainbow trout. We propose that the continued need for salt and water transport for osmoregulation maintains the proximodistal gradient of mass and surface area and ameliorates the effect of starvation on mucosal mass and area.     

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.     

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.     

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.     

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.     

Estuarine and habitat-related differences in growth rates of young-of-the-year winter flounder (Pseudopleuronectes americanus) and tautog (Tautoga onitis) in three northeastern US estuaries

Instantaneous growth rates of young-of-the-year winter flounder Pseudopleuronectes americanus (Walbaum) (12.0-60.4 mm standard length, SL) and tautog Tautoga onitis (Linnaeus) (21.4-73.8 mm total length, TL) from three estuarine systems in New Jersey (Great Bay-Little Egg Harbor and Navesink River) and Connecticut (Hammonasset River) were used in an attempt to assess the relative quality of selected nominal habitats. A series of short-term field caging experiments were conducted during 1994 and 1995 in: macroalgae (primarily, Ulva lactuca), eelgrass (Zostera marina), unvegetated areas adjacent to macroalgae and eelgrass and tidal creeks in Spartina dominated marsh. Growth rates varied with habitat, estuary and year. Comparisons across nominal habitats within and among estuaries did not show any one habitat with consistently higher growth, and growth was relatively independent of whether a habitat was vegetated or adjacent to vegetation. The growth rates of winter flounder and tautog from the Hammonasset River were not different among habitats in either year of the study. In the Great Bay-Little Egg Harbor, both winter flounder and tautog had higher growth rates in macroalgae with growth in eelgrass varying significantly between years. Conversely, in the Navesink River both species had higher growth rates in eelgrass. Environmental changes associated with temperature and dissolved oxygen appeared to influence growth rates. Winter flounder growth rate and survival was depressed in tidal marsh creeks in the three estuaries and in vegetated macroalgae habitats in the Navesink River where dissolved oxygen levels were often very low (<2 mgl(-1)) for extended periods. In summary, the growth rates of the young-of-the-year of these two species varied temporally and were dependent on the interaction of both the specific estuary and habitat in which the experiments took place. Further, habitat quality, as defined by relative growth rate, was difficult to evaluate because it can be variable and nominal habitat designations are often not sufficient to define the boundaries of a species habitat requirements.     

Size-related shifts in the habitat associations of young-of-the-year winter flounder (Pseudopleuronectes americanus): field observations and laboratory experiments with sediments and prey

Field surveys and laboratory studies were used to determine the role of substrata in habitat selection by young-of-the year winter flounder. A synoptic field survey of winter flounder and sediments in the Navesink River-Sandy Hook Bay estuarine system in New Jersey demonstrated that winter flounder distribution was related to sediment grain size. Analysis using a generalized additive model indicated that the probability of capturing 10-49 mm SL winter flounder was high on sediments with a mean grain diameter of /=40 mm SL) preferred coarse-grained sediments. Burying ability increased with size and all flounders avoided sediments that prevented burial. Subsequent laboratory experiments revealed that the presence of live prey (Mya arenaria) can over-ride sediment choice by winter flounder (50-68 mm SL) indicating the complexity of interrelated factors in habitat choice.     

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...     

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.     

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.     

Spatial expression patterns of skin-type antifreeze protein in winter flounder (Pseudopleuronectes americanus) epidermis following metamorphosis

Two isotypes of Type I antifreeze protein (AFP), the liver-type and the skin-type, have been described from adult winter flounder (Pseudopleuronectes americanus). Although the liver-type AFP has been well studied, the skin-type has just begun to be characterized. It appears to have a wide tissue distribution, be expressed constitutively, and the absence of a signal sequence suggests it is active intracellularly. The current study was designed to examine the onset of skin-type AFP expression during the thickening of the epidermis at metamorphosis from both the nucleic acid and protein levels. The epidermis appeared as a thin layer overlying a thickened dermis at metamorphosis and showed a gradual increase in thickness through the first fall and winter. The onset of skin-type antifreeze expression occurred in conjunction with this epidermal thickening. In situ hybridization and immunohistochemistry showed a distribution of mRNA and skin-type AFP specific for the epidermis and epidermal pavement cells. The AFP immunoproduct showed a distribution intimate with the pavement cell membrane and through the interstitial spaces. This distribution suggests that the AFP may be important in slowing ice crystal formation in these interstitial regions and thus reducing cellular damage due to osmotic imbalance.     

Bifurcation of gill filaments in winter flounder (Pleuronectes americanus Walbaum) from Long Island Sound

Morphological and histological examinations of gills excised from adult winter flounder, Pleuronectes americanus Walbaum, collected at clean and contaminated areas of Long Island Sound were undertaken to assess possible biological consequences of contamination. On the basis of previous studies, three collection sites were chosen: Shoreham, New York, a relatively clean, unindustrialized area, and New Haven Harbor, Connecticut and Hempstead Harbor, New York, both industrialized and heavily populated.
Gill samples were taken monthly at all three sites for light and scanning electron microscopy (SEM) examination. Results from both techniques suggest a relationship between contamination of the sediments and the prevalence of bifurcated gill filaments, the condition being most severe at New Haven Harbor. The bifurcations were not consistently associated with any parasitological or pathological conditions when examined by light microscopy.
Gill samples were subsequently taken from juvenile winter flounder caught in New Haven Harbor to determine how early in the life cycle gill bifurcations develop. The data show that the majority of these anomalies begin in juvenile flounder rather than in embryos, larvae, or adults. Gill bifurcations were found in 27% of the 2-year-old flounder, compared to 12% of the 1-year-old fish and 15% of the adults from the same area.     

Predator-prey relations between age-1+ summer flounder (Paralichthys dentatus, Linnaeus) and age-0 winter flounder (Pseudopleuronectes americanus, Walbaum): predator diets, prey selection, and effects of sediments and macrophytes

Laboratory experiments and weekly trammel net surveys in the Navesink River, New Jersey (USA) were used to examine the predator-prey interaction between age-1+ summer flounder (Paralichthys dentatus) and age-0 winter flounder (Pseudopleuronectes americanus). Winter flounder (24-67 mm TL) were the dominant piscine prey of summer flounder (n=95, 252-648 mm TL) collected in trammel nets. We observed a temporal shift in summer flounder diets from sand shrimp (Crangon septemspinosa) and winter flounder, dominant during June and early July, to blue crabs (Callinectes sapidus) and other fishes (primarily Atlantic silversides, Menidia menidia and Atlantic menhaden, Brevortia tyrannus) later in the summer. Variations in prey selection appeared to be related to changes in the spatial distribution of predators and spatio-temporal variation in prey availability. In laboratory experiments, summer flounder (271-345 mm total length, TL) preferred demersal winter flounder to a pelagic fish (Atlantic silversides) and a benthic invertebrate (sand shrimp) prey, and the vulnerability of winter flounder increased with increasing prey body size from 20 to 90 mm TL. Experiments testing habitat effects showed that mortality of winter flounder in three different size classes (20-29, 40-49, 60-69 mm TL) was not influenced by sediment grain sizes permitting differential burial of the prey. However, vegetation enhanced survival, with fish suffering lower mortality in eelgrass (Zostera marina, 15+/-0.04%) than in sea lettuce (Ulva lactuca, 38+/-0.04%) or bare sand (70+/-0.07%) when the macrophytes were planted to produce similar leaf surface areas (5000 cm(2) m(-2)). Prey vulnerability appeared to be related to the role of vision in the predator's attack strategy and prey activity levels.     

Changes in RNA,DNA, protein contents and growth of turbot Scophthalmus maximus larvae and juveniles

The growth potential of turbot Scophthalmus maximus larvae and juveniles was studied using nucleic acid‐based indices and protein variables. The experiment was carried out from 4 to 60 days post hatching (dph). A significant increase in instantaneous growth rate during metamorphosis and retarded growth rate during post‐metamorphic phase were observed. Ontogenetic patterns of DNA, RNA and protein all showed developmental stage‐specific traits. The RNA:DNA ratio decreased up to 12 dph, then increased rapidly till 19 dph and fluctuated until 35 dph followed by a decline to the end. The RNA:DNA ratio was positively correlated with growth rate of juveniles during the post‐metamorphic phase, whereas this ratio was not a sensitive indicator of growth during the pre‐metamorphic phase and metamorphosis. The protein:DNA ratio showed a similar tendency to the RNA:DNA ratio. Changes of DNA content and protein:DNA ratio revealed that growth of S. maximus performed mainly by hyperplasia from 4 to 12 dph and hypertrophy until 21 dph during the pre‐metamorphic larval phase. Growth was dominantly hypertrophical from the early‐ to mid‐metamorphosing phase and hyperplastic thereafter. The results show that the DNA content and protein:DNA ratio can evaluate growth rates of larval and juvenile S. maximus on a cellular level.     

A model to estimate growth in young-of-the-year tautog, Tautoga onitis, based on RNA/DNA ratio and seawater temperature

This study presents an indirect method for estimating growth rates of young-of-the-year (YOY) tautog, Tautoga onitis, based on laboratory calibration experiments and nucleic acid-based indices. Field-collected tautog were held in the laboratory at 3 temperatures over a 17-day period. Four feeding levels were used to produce a range of growth rates. An ultraviolet absorption assay was used to measure nucleic acid concentrations in white muscle tissue. The strength of the relationship between growth rate and three nucleic acid-based parameters (RNA concentration, DNA concentration, RNA/DNA ratio (R/D)) was tested. Correlation results indicated a significant positive relationship between R/D and weight-based instantaneous growth rate (G) (r = 0.68; p < 0.001). Both R/D (r = − 0.55; p < 0.006) and RNA (r = − 0.56; p < 0.005) were highly negatively correlated with temperature (T). Multiple linear regression showed that R/D and temperature explained 61% of the variability in growth, resulting in the model G = 0.01285(R/D) + 0.00057(T) − 0.03205 (p < 0.0001). This R/D-temperature model can be used to evaluate recent growth rates in YOY tautog under field conditions and has applications for aquaculture when comparing growth rates of fish held under different culture conditions.