Pseudopleuronectes Americanus Walbaum Research Articles

Winter flounder (Pseudopleuronectes americanus Walbaum) burial in estuaries: Acoustic telemetry triumph and tribulation

Measuring the reliance of adult spawning winter flounder (Pseudopleuronectes americanus Walbaum) on estuarine habitat is problematic and may require acoustic telemetry. Efforts in various estuaries over several years have been hampered by sporadic results in detection of telemetered fish, possibly due to burial. After confirming that captive winter flounder in ambient temperature flow-through enclosures buried often and sometimes deeply, especially during low temperatures, we analyzed the effect of burial on tag signal (76.8kHz, 5s repeat rate) during periodic visitation of a grid of listening stations, vessel-towed and autonomous underwater vehicle (AUV) searches, and continuous 3-D tracking through a synchronized multiple-hydrophone positioning array. Controlled tests of tag burial in situ resulted in complete signal loss with burial at all of the tested depths. The difference between tag detection and decoding was demonstrated to be very important. Water column depth during mobile telemetry positively affected reception of tags lying on the sediment surface. Signal strength of tags on fish at liberty as recorded by an AUV-mounted hydrophone was similar during daytime and subsequent nighttime transects, as were mean counts of decoded signals per tag. However, variance was highly skewed with some tags being heard much more often at night, an expected consequence of nighttime emergence from burial, despite windier (noisier conditions) at night. Meter-scale tracking by multi-hydrophone trilateration over periods of days to weeks determined burial by timeline disruption for individual fish. The use of Markov Models, reference tags, and environmental conditions presents an opportunity to correct for biases in tag detection rates due to burial post facto. In addition, telemetry should consider nighttime efforts during the spawning season and continuous mobile (e.g. towed transect) or more frequent listening stations in search grids and closer moored hydrophone spacing than suggested by reference tags. These approaches may be relevant to other flatfishes and other fishes that bury or use benthic shelters.

Determining an optimal release site for juvenile winter flounder Pseudopleuronectes americanus (Walbaum) in the Great Bay Estuary, NH, USA

One of the main elements in developing an optimal release strategy for an enhancement effort is to evaluate and select release sites that will support growth and survival of newly released, cultured fish. Three potential release sites (New Castle (NC), Broad Cove (BC) and Oyster River (OR)) in the Great Bay Estuary, NH, USA were evaluated for pilot-scale releases of winter flounder (Pseudopleuronectes americanus Walbaum). Cultured juvenile flounder were placed in cages at each of the three sites. Sites were evaluated based on growth and survival of the fish in relation to water temperature, prey availability and sediment composition. Fish grew faster in the two upper estuarine sites BC (0.54 mm day(-1)) and OR (0.56 mm day(-1)) than at the site at the mouth of the estuary (NC = 0.37 mm day(-1)). Fish survival (44-53%) and water temperature (17.8-19.7 degrees C) did not vary between sites. Benthic samples showed that prey was available to, and eaten by, the flounder. Sediment composition was the main difference between the three sites, with one site (NC) characterized by gravel whereas the other two sites were sandy. These results corroborate other studies showing the importance of sediment quality for the distribution of flatfish populations. From these results, we can confidently eliminate NC as a potential release area and recommend that sandy sites are better for stocking cultured juvenile winter flounder than gravely sites.

Predatory impact of the green crab ( Carcinus maenas Linnaeus) on post-settlement winter flounder ( Pseudopleuronectes americanus Walbaum) as revealed by immunological dietary analysis

Predation on flatfish during the early juvenile stage is an important factor regulating year-class strength and recruitment. In this study, immunological dietary analysis was performed on green crabs ( Carcinus maenas) collected from the Niantic River, Connecticut, in an effort to evaluate the predatory impact of this species on post-settlement winter flounder ( Pseudopleuronectes americanus). Through the use of species-specific antiserum, winter flounder proteins were identified in 4.8% of the green crab stomachs analyzed ( n = 313, size range = 14–74 mm carapace width, CW), revealing that crabs ≥ 29 mm CW are predators of post-settlement winter flounder in natural populations. The most significant factor underlying the predator–prey interaction was the relative size relationship between species, such that the incidence of winter flounder remains in the stomach contents of green crabs was positively correlated with predator-to-prey size ratio. Results from dietary analysis were incorporated into a deterministic model to estimate the average daily instantaneous mortality and cumulative mortality of winter flounder owing to green crab predation. Accordingly, green crabs may account for 0.4% to 7.7% (mean = 2.2%) of the daily mortality of winter flounder and consume 1.1% to 32.3% (mean = 10.2%) of the flounder year-class. Model simulations further indicate that variations in green crab abundance and size-structure account for the greatest variability in winter flounder mortality. Relative to other macro-crustacean predators, however, predation by green crabs has a minimal effect on winter flounder survival, due in large part to the low densities of these crabs in temperate estuaries.

Comparison of stress responses in wild and captive winter flounder (Pseudopleuronectes americanus Walbaum) broodstock

Chronic stress is responsible for many problems occurring in fish holding facilities, such as increased susceptibility to disease, reduced growth rate and suppression of the immune response. The goal of this study was to verify if wild winter flounder (Pseudopleuronectes americanus Walbaum) suffer from chronic stress when kept several months in captivity. We hypothesized that winter flounder not subjected to chronic stress in captivity would have similar or higher condition indices and similar stress response compared to fish from the wild. Our results showed that the condition index of winter flounder kept in captivity was higher (1.50) than those from the wild (1.33) even after one year of captivity. The intensity of the acute stress response following short-term exposure to air was similar between wild and captive fish (no significant interaction between the factors ‘stress’ and ‘origin of the fish’). Body water content (an indicator of energy reserves) was lower (76.1%) compared to wild fish (79.8%) after one year of captivity, suggesting that the winter fast had been less energetically demanding in captive fish. These results indicate that no chronic stress was present in captive fish. On the other hand, the mortality during captivity was around 30%, which is high for the aquaculture industry. Further work to address this problem is required.

An Assessment of the Feeding Success of Young-of-the-Year Winter Flounder (Pseudopleuronectes americanus) near a Municipal Pier in the Hudson River Estuary, U. S. A.

We examined feeding success of young-of-the-year winter flounder (Pseudopleuronectes americanus Walbaum) (20–50 mm TL) around a large, municipal pier in the Hudson River estuary, USA. Replicate, 3-h feeding experiments were conducted using benthic cages (0.64 m2) deployed under, at the edge, and outside of the pier during late spring and early summer in 1998 and 1999. Significantly more winter flounder caged under piers had empty stomachs ( $$\bar x$$ =71.9%) than at the edge or in open water ( $$\bar x$$ =29.2% and 14.4%, respectively). Feeding intensity was significantly higher outside of the pier ( $$\bar x$$ =0.40%) than the edge or under the pier ( $$\bar x$$ =0.19% and 0.03%, respectively). Simultaneous with feeding experiments, benthic core samples were collected adjacent to cages. Variability was high, but abundances of prey were consistently higher under the pier ( $$\bar x$$ =200.14±113.3 SD in 1998; 335±290.2 in 1999) than at the edge ( $$\bar x$$ =126.6±50.2 in 1998; 70.8±68.5 in 1999) or in open water ( $$\bar x$$ =53.4±16.1 in 1998; 123.8±193.9 in 1999). No significant differences in prey biomass were determined, suggesting that small, numerous prey were available under the pier and fewer, larger taxa were present at the edge and outside. Data indicate that feeding is suppressed among young-of-the-year winter flounder caged under piers in spite of sufficient prey available. Based on these and other experiments we submit that areas under piers are not suitable long-term habitats for juvenile fish because they interfere with normal feeding activities.

Diet of Winter Flounder in a New Jersey Estuary: Ontogenetic Change and Spatial Variation

Juvenile and adult winter flounder,Pseudopleuronectes americanus Walbaum (Pleuronectidae), from the Navesink River and Sandy Hook Bay, New Jersey, U.S., were examined for ontogenetic, seasonal, and spatial variation in dietary content. Fish (n=1291 non-empty) were placed by cluster analysis of dietary content into three size groups: 15–49, 50–299, and ≥300 mm total length. Clear ontogenetic patterns were revealed, in particular the disappearance of calanoid copepods from the diet as fish grew >50 mm and an increase in number of taxa in the diet with growth. Fish in size group 1 fed upon spionid polychaetes, the calanoid copepodEurytemora affinis, and ampeliscid amphipods. Fish in size group 2 added various species of polychaetes, amphipods, and siphons of the bivalveMya aremaria to their diets. Size group 2 was present during all months of the survey, but only minor seasonal differences in their diet were apparent. One obvious change was the increase in consumption of the shrimpCrangon septemspinosa in summer and fall. Size group 3 fish, collected mainly in fall, ate large volumes ofM. arenaria and glycerid polychaetes. Cluster analysis showed a largescale spatial pattern in diet among fish of size group 1, related to the presence ofE. affinis in winter flounder diets in the river and a marsh cove in the bay. Small-scale spatial differences in diets of fish in size group 2 were possibly related to prey distribution.

Induction and reversal of the non‐reproductive state in winter flounder, Pseudopleuronectes americanus Walbaum, by manipulating food availability

Reversal of the non‐reproductive slate of winter flounders was induced by improved feeding.

A comparison of the effect of captivity on the epidermis of prespawning and postspawned winter flounder, Pseudopleuronectes americanus

The effect of captivity on the epidermis of Pseudopleuronectes americanus Walbaum is influenced by the phase of the reproductive cycle. Towards the end of the prespawning period captive male flounder had a higher GSI than flounder from the wild population, and the seasonal epidermal sexual dimorphism in these captive flounder was more pronounced. Flounder maintained in the laboratory during the postspawning period manifested a thick epidermis and increased mucigenesis in late summer, when these characteristics displayed seasonally low values in the inshore population from which the flounder were sampled. Possible regulatory factors and implications for protocols involving captive fish are discussed.

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.

Monoaminergic substances in the teleost brain: Catecholamine levels in male and female winter flounder,Pseudopleuronectes americanus Walbaum, associated with gonadal recrudescence

High performance liquid chromatography with electrochemical detection (HPLC-EC) was used to quantitate catecholamine (CA) levels in the winter flounder brain following perchloric acid extraction/alumina purification of CNS tissues. Greater concentrations of norepinephrine (NE) and dopamine (DA) were present in the hypothalamus compared with the CA levels in whole brain. A seasonal study of CA brain levels in reproductively active male and female flounder demonstrated that monoamine levels reach their maxima in October in association with the rapid increases in gonadosomatic index. When perchloric acid extracts of the teleost and rat hypothalamus were submitted to direct HPLC-EC analysis, without alumina purification of CA neurotransmitters, similar hypothalamic profiles were obtained indicating the presence of identifiable biogenic amine neurotransmitters substances including NE, DA and serotonin (5-HT).

Seasonal changes in the epidermis of the winter flounder, Pseudopleuronectes americanus

Profound cyclical changes were observed in the epidermal thickness and in the concentrations of goblet cells and epidermal melanophores in an inshore population of winter flounder, Pseudopleuronectes americanus Walbaum. There is sexual dimorphism which is particularly prominent in the thickness of the epidermis during the pre-spawning period in the spring. At this time the male develops a significantly thicker lower epidermis. During and shortly after the spawning period (lower skin), or somewhat earlier (upper skin), there is a significant thinning of the epidermis in both sexes. Significant increases occur in goblet cell frequency, those of females being greater than males, during autumn and early winter and the April/May pre-spawning period. Goblet cell frequencies decrease in mid-winter (January–March) when general activity is low, and in the thin summer epidermis. These observations are compared with data from other teleosts and discussed in relation to hormones possibly affecting the epidermal structure of teleosts and in relation to known hormonal cycles in winter flounder.

Physiological and biochemical aspects of embryonic and larval development of the winter flounder Pseudopleuronectes americanus

Eggs and larvae of the winter flounder Pseudopleuronectes americanus Walbaum were hatched and raised in the laboratory under controlled conditions. Biochemical composition was measured during development and found to be similar to that of other species: 65 to 80 percent protein, 15 to 30 percent fat, and 0 to 5 percent carbohydrate. Ash content was 7 to 10 percent of dry weight. The chorion comprised more than half of the weight of an egg and the data suggested that it was possibly a source of nutrition to the developing embryo. The sequence of utilization appeared to be carbohydrate and then protein to hatching, lipid, mixed lipid and protein, the predominantly protein until feeding began. Carbohydrate was accumulated at first feeding and depleted when growth began. Protein and lipid were deposited in approximately constant proportions. Respiration rates of eggs were low, 0.002–0.015 μl O2 egg-1 h-1, but rose gradually from fertilization to hatching. Respiration rates of early larvae were from two to eight times that of eggs (0.033–0.131 μl O2 larva-1 h-1). Variation in larval respiration rates indicated a three-fold difference in rate according to level of activity. Eggs excreted ammonia at an increasing rate from fertilization to hatching. Larvae excreted ammonia, primary amines, and other unidentified organic nitrogenous substances. Rates of excretion and proportions of excretory products varied with stage of development. Primary amine excretion was variable and a major component in early stages. Ammonia-N excreted was two to 20 times primary amine N excreted. Unidentified substances were the predominant form of N excretion during early feeding. Ammonia accounted for most of the N excreted in older larvae. Early specific growth rates were 2.1 and 5.5%. Net caloric conversion and net and gross nitrogen efficiencies were low in first feeding larvae compared to adult fishes (32.2, 27.7, and 10.7% respectively).

Steroids in the plasma of the winter flounder ( Pseudopleuronectes americanus walbaum). A seasonal study and investigation of steroid involvement in oocyte maturation

Cortisol was a major steroid identified in the plasma of male and female Pseudopleuronectes americanus. Cortisone, corticosterone, 11-deoxycortisol, 11-deoxycorticosterone and 11-dehydrocorticosterone were identified at lower concentrations. In plasma from male fish testosterone concentrations changed only slightly during the annual cycle but 11-ketotestosterone concentrations rose dramatically near the time of spawning. Testosterone levels were highest prior to spawning in plasma from female fish but the concentrations of 11-ketotestosterone remained extremely low throughout the year. Progesterone, 17α- OH-progesterone and 20β-dihydro, 17α- OH-progesterone were also identified in plasma from female fish. Plasmas in which oocytes were stimulated to undergo meiotic maturation in vitro were found to contain greater concentrations of 17α-OH-Progesterone and 20β-dihydro, 17α- OH-progesterone than those which did not have this biological activity.

Emergency call system

Measuring the reliance of adult spawning winter flounder (Pseudopleuronectes americanus Walbaum) on estuarine habitat is problematic and may require acoustic telemetry. Efforts in various estuaries over several years have been hampered by sporadic results in detection of telemetered fish, possibly due to burial. After confirming that captive winter flounder in ambient temperature flow-through enclosures buried often and sometimes deeply, especially during low temperatures, we analyzed the effect of burial on tag signal (76.8 kHz, 5 s repeat rate) during periodic visitation of a grid of listening stations, vessel-towed and autonomous underwater vehicle (AUV) searches, and continuous 3-D tracking through a synchronized multiple-hydrophone positioning array. Controlled tests of tag burial in situ resulted in complete signal loss with burial at all of the tested depths. The difference between tag detection and decoding was demonstrated to be very important. Water column depth during mobile telemetry positively affected reception of tags lying on the sediment surface. Signal strength of tags on fish at liberty as recorded by an AUV-mounted hydrophone was similar during daytime and subsequent nighttime transects, as were mean counts of decoded signals per tag. However, variance was highly skewed with some tags being heard much more often at night, an expected consequence of nighttime emergence from burial, despite windier (noisier conditions) at night. Meter-scale tracking by multi-hydrophone trilateration over periods of days to weeks determined burial by timeline disruption for individual fish. The use of Markov Models, reference tags, and environmental conditions presents an opportunity to correct for biases in tag detection rates due to burial post facto. In addition, telemetry should consider nighttime efforts during the spawning season and continuous mobile (e.g. towed transect) or more frequent listening stations in search grids and closer moored hydrophone spacing than suggested by reference tags. These approaches may be relevant to other flatfishes and other fishes that bury or use benthic shelters.