Assessment of habitat quality for juvenile California halibut (Paralichthys californicus) in a seasonally arid estuary

We evaluated habitat quality for juvenile California halibut (Paralichthys californicus) in a Pacific Coast estuary lacking in strong salinity gradients by examining density, recent otolith growth rates, and gut fullness levels of wild-caught and caged juveniles for one year. Juveniles <200 mm standard length were caught consistently in the inner, central, and outer sections of the estuary. The density of juveniles was two times higher in the inner estuary during most of the year, consistent with active habitat selection by part of the population. A generalized linear model indicated temperature, sampling time, and the interaction between salinity and temperature were significantly related to density. However, the model explained only 21% of the variance. Gut fullness levels of wild-caught juveniles were highest during the summer, but recent otolith growth rates were not related to temperature. The proportion of individuals feeding successfully indicated that seasonal differences in food availability are more important than spatial variation in prey abundance in driving feeding success. Feeding success of caged fishes was limited, precluding the use of growth rates as indicators of local habitat quality. However, marginal increment widths were reliable indicators of somatic growth at low growth rates over two-week periods. The relatively high growth rates and abundance of small wild-caught juveniles found throughout the estuary indicates that the entire estuary system has the potential for serving as nursery habitat.

Diferenciación sexual del lenguado de California Paralichthys californicus y control de la proporción sexual mediante la utilización de la hormona 17β-estradiol

El lenguado de California Paralichthys californicus es una especie con alto valor comercial debido a su gran tamaño y calidad de su carne. Esta especie presenta dimorfismo sexual en el crecimiento donde las hembras crecen más rápido que los machos, por lo tanto el cultivo monosexual de hembras resulta favorable para la producción. En el presente estudio se registró el proceso de diferenciación sexual mediante cortes histológicos de las larvas y gónadas del lenguado de California asimismo se probó el efecto de diferentes concentraciones de 17β-estradiol (E2) (2.5, 5 y 10 mg/kg) a través de la dieta para incrementar la proporción de hembras en el cultivo. A los 25 días después de la eclosión (DDE) se observó el primordio gonadal en ejemplares con una longitud total promedio de 6.96 ± 0.92 mm, hasta el día 75 DDE (37.58 ± 6.58 mm) se observó una gónada indiferenciada evidenciada por la presencia de células germinales primordiales. La primera evidencia de diferenciación se registró a los 115 DDE (55.93 ± 14.67 mm) donde se observó la cavidad ovárica y posteriormente a los 180 DDE (115.70 ± 17.02 mm) se evidencian ovarios con ovocitos en crecimiento y testículos con espermátidas. Por lo tanto, el periodo lábil para la diferenciación sexual se encuentra entre los días 75 y 115 después de la eclosión. Por otro lado, el suministro de E2 a través de la dieta a concentraciones de 2.5, 5 y 10 mg/kg incrementó el porcentaje de hembras de 26.67% (control, no adición de E2) a un 100% en todos los tratamientos. Se encontraron diferencias en la proporción de los tipos celulares (ovogonias, ovocitos primarios en fase I y II) entre el control y los tratamientos mientras que no se registraron alteraciones histológicas como atrofia gonadal en ninguno de los casos.

Development of polymorphic microsatellite markers suitable for genetic linkage mapping of olive flounder Paralichthys olivaceus

Microsatellite markers are important for gene mapping and for marker-assisted selection. Sixty-five polymorphic microsatellite markers were developed with an enriched partial genomic library from olive flounder Paralichthys olivaceus an important commercial fish species in Korea. The variability of these markers was tested in 30 individuals collected from the East Sea (Korea). The number of alleles for each locus ranged from 2 to 33 (mean, 17.1). Observed and expected heterozygosity as well as polymorphism information content varied from 0.313 to 1.000 (mean, 0.788), from 0.323 to 0.977 (mean, 0.820), and from 0.277 to 0.960 (mean, 0.787), respectively. Nine loci showed significant deviation from the Hardy-Weinberg equilibrium after sequential Bonferroni correction. Analysis with MICROCHECKER suggested the presence of null alleles at five of these loci with estimated null allele frequencies of 0.126-0.285. These new microsatellite markers from genomic libraries will be useful for constructing a P. olivaceus linkage map.

Larval abundance of summer flounder (Paralichthys dentatus) as a measure of recruitment and stock status

Summer flounder (Paralichthys dentatus) is one of the most economically and ecologically important estuarine-dependent species in the northeastern United States. The status of the population is currently a topic of controversy. Our goal was to assess the potential of using larval abundance at ingress as another fishery independent measure of spawning stock biomass or recruitment. Weekly long-term ichthyoplankton time series were analyzed from Little Egg Inlet, New Jersey (1989–2006) and Beaufort Inlet, North Carolina (1986–2004). Mean size-at-ingress and stage were similar between sites, whereas timing of ingress and abundance at ingress were not similar. Ingress primarily occurred during the fall at Little Egg Inlet and the winter at Beaufort Inlet. These findings agree with those from earlier studies in which at least two stocks (one north and one south of Cape Hatteras) were identified with different spawning periods. Larval abundance at Little Egg Inlet has increased since the late 1990s and most individuals now enter the estuary earlier during the season of ingress. Abundance at Little Egg Inlet was correlated with an increase in spawning stock biomass, presumably because spawning by larger, more abundant fish during the late 1990s and early 2000s provided increased larval supply, at least in some years. Larval abundance at ingress at Beaufort Inlet was not correlated with spawning stock biomass or with larval abundance at ingress at Little Egg Inlet, further supporting the hypothesis of at least two stocks. Larval abundance at Little Egg Inlet could be used as a fishery-independent index of spawning stock size north of Cape Hatteras in future stock assessments. Larval occurrence at Beaufort Inlet may provide information on the abundance of the stock south of Cape Hatteras, but additional stock assessment work is required.

The effect of temperature on the duration of spawning markers—migratory-nucleus and hydrated oocytes and postovulatory follicles—in the multiple-batch spawner Japanese flounder (Paralichthys olivaceus)

The duration of spawning markers (e.g. signs of previous or imminent spawnings) is essential information for estimating spawning frequency of fish. In this study, the effect of temperature on the duration of spawning markers (i.e., oocytes at early migratory nucleus, late migratory nucleus, and hydrated stages, as well as new postovulatory follicles) of an indeterminate multiple-batch spawner, Japanese f lounder (Paralichthys olivaceus), was evaluated. Cannulation was performed to remove samples of oocytes, eggs, and postovulatory follicles in individual females at 2–4 hour intervals over 27–48 hours. The duration of spawning markers was successfully evaluated in 14 trials ranging between 9.2° and 22.6°C for six females (total length 484–730 mm). The durations of spawning markers decreased exponentially with temperature and were seen to decrease by a factor of 0.16, 0.36, 0.30, and 0.31 as temperature increased by 10°C for oocytes at early migratory nucleus, late migratory nucleus, and hydrated stages, and new postovulatory follicles, respectively. Thus, temperature should be considered when estimating spawning frequency from these spawning markers, especially for those fish that do not spawn synchronously in the population.

The trophic dynamics of summer flounder (Paralichthys dentatus) in Chesapeake Bay

Data on the trophic dynamics of fishes are needed for management of ecosystems such as Chesapeake Bay. Summer flounder (Paralichthys dentatus) are an abundant seasonal resident of the bay and have the potential to impact foodweb dynamics. Analyses of diet data for late juvenile and adult summer flounder collected from 2002−2006 in Chesapeake Bay were conducted to characterize the role of this flatfish in this estuary and to contribute to our understanding of summer flounder trophic dynamics throughout its range. Despite the diversity of prey, nearly half of the diet comprised mysid shrimp (Neomysis spp.) and bay anchovy (Anchoa mitchilli). Ontogenetic differences in diet and an increase in diet diversity with increasing fish size were documented. Temporal (inter- and intra-annual) changes were also detected, as well as trends in diet reflecting peaks in abundance and diversity of prey. The preponderance of fishes in the diet of summer flounder indicates that this species is an important piscivorous predator in Chesapeake Bay.

A Brief Interpretation of Summer Flounder, Paralichthys dentatus, Movements and Stock Structure with New Tagging Data on Juveniles

Summer flounder, Paralichthys dentatus, are managed as a single stock along the Atlantic coast from the U.S.– Canada border to the southern border of North Carolina. Justification of the single-stock approach is based on lack of genetic evidence for multiple stocks and the difficulty presented by managing the species from Cape Hatteras to the U.S.–Canada border. In this review, we present an interpretation of various morphometric, meristic, biochemical, and tagging studies, published and unpublished, that indicate the presence of two, or possibly three, distinct stocks in the management area. In addition, we have included new data from a tagging study that was conducted on juveniles from Virginia that aids in defining the stock(s) north of Cape Hatteras. Summer flounder, overfished for the past two decades, is recovering, and reconsideration of proposed stock structure could have direct implications for management policy decisions.

Migratory and within-estuary behaviors of adult Summer Flounder (Paralichthys dentatus) in a lagoon system of the southern mid-Atlantic Bight

We monitored the movements of 45 adult Summer Flounder (Paralichthys dentatus) between June 2007 and July 2008 through the use of passive acoustic telemetry to elucidate migratory and within-estuary behaviors in a lagoon system of the southern mid-Atlantic Bight. Between 8 June and 10 October 2007, fish resided primarily in the deeper (>3 m) regions of the system and exhibited low levels of large-scale (100s of meters) activity. Mean residence time within this estuarine lagoon system was conservatively estimated to be 130 days (range: 18–223 days), which is 1.5 times longer than the residence time previously reported for Summer Flounder in a similar estuarine habitat ~250 km to the north. The majority of fish remained within the lagoon system until mid-October, although some fish dispersed earlier and some of them appeared to disperse temporarily (i.e., exited the system for at least 14 consecutive days before returning). Larger fish were more likely to disperse before mid-October than smaller fish and may have moved to other estuaries or the inner continental shelf. Fish that dispersed after mid-October were more likely to return to the lagoon system the following spring than were fish that dispersed before mid-October. In 2008, fish returned to the system between 7 February and 7 April. Dispersals and returns most closely followed seasonal changes in mean water temperature, but photoperiod and other factors also may have played a role in large-scale movements of Summer Flounder.

Coupling ecology and economy: modeling optimal release scenarios for summer flounder (Paralichthys dentatus) stock enhancement

Increasing interest in the use of stock enhancement as a management tool necessitates a better understanding of the relative costs and benefits of alternative release strategies. We present a relatively simple model coupling ecology and economic costs to make inferences about optimal release scenarios for summer flounder (Paralichthys dentatus), a subject of stock enhancement interest in North Carolina. The model, parameterized from mark-recapture experiments, predicts optimal release scenarios from both survival and economic standpoints for varyious dates-of-release, sizes-at-release, and numbers of fish released. Although most stock enhancement efforts involve the release of relatively small fish, the model suggests that optimal results (maximum survival and minimum costs) will be obtained when relatively large fish (75–80 mm total length) are released early in the nursery season (April). We investigated the sensitivity of model predictions to violations of the assumption of density-independent mortality by including density-mortality relationships based on weak and strong type-2 and type-3 predator functional responses (resulting in depensatory mortality at elevated densities). Depending on postrelease density, density-mortality relationships included in the model considerably affect predicted postrelease survival and economic costs associated with enhancement efforts, but do not alter the release scenario (i.e. combination of release variables) that produces optimal results. Predicted (from model output) declines in flounder over time most closely match declines observed in replicate field sites when mortality in the model is density-independent or governed by a weak type-3 functional response. The model provides an example of a relatively easy-to-develop predictive tool with which to make inferences about the ecological and economic potential of stock enhancement of summer flounder and provides a template for model creation for additional species that are subjects of stock enhancement interest, but for which limited empirical data exist.

Nutrient digestibility coefficients of diets with varying energy to protein ratio for Japanese flounder, Paralichthys olivaceus

A laboratory trial was conducted in a sea water recirculatory system to study the nutrient digestibility coefficients of diets with varying energy to protein ratios in Japanese flounder Paralicthys olivaceus. Six different experimental diets with two protein levels (45 and 55%) having six different energy to protein ratio of 87, 90, 94, 107, 110 and 114 were formulated using white fish meal and casein as protein sources. The results of the study showed that the apparent protein digestibility (APD) value ranged between 90.59 to 91.61% and there were no significant differences (P>0.05) between the APD values of diets 1, 2, 3, 4 and 6. The apparent lipid digestibility (ALD) values of diets ranged between 88.24 to 90.18%. The apparent energy digestibility (AED) values ranged between 80.55 to 87.52% with diet 3 producing significantly the highest AED value. In general, except in diet 1 the ALD and AED values increased with the increase of dietary lipid at both protein levels. The results of the present investigation indicated that Japanese flounder can efficiently digest the dietary nutrients at varying energy to protein ratios.

Subcellular localization and inductive expression of the dsRNA-dependent protein kinase PKR from Japanese flounder, Paralichthys olivaceus

The double-stranded RNA (dsRNA)-dependent protein kinase (PKR) belongs to the eIF2 alpha kinase family and plays a critical role in interferon (IFN)-mediated antiviral response. Recently, in Japanese flounder (Paralichthys olivaceus), a PKR gene has been identified. In this study, we showed that PoPKR localized to the cytoplasm, and the dsRNA-binding motifs (dsRBMs) played a determinative role in protein localization. In cultured FEC cells, PoPKR was detected at a low level of constitutive expression but was highly induced after treatment with UV-inactivated grass carp hemorrhagic virus, active SMRV and Poly I:C although with different expression kinetics. In flounder, PoPKR was ubiquitously distributed in all tested tissues, and SMRV infection resulted in significant upregulation at mRNA and protein levels. In order to reveal the role of PoPKR in host antiviral response, its expression upon exposure to various inducers was characterized and further compared with that of PoHRI, which is another eIF2 alpha kinase of flounder. Interestingly, expression comparison revealed that all inducers stimulated upregulation of PoHRI in cultured flounder embryonic cells and fish, with a similar kinetics to PoPKR but to a less extent. These results suggest that, during antiviral immune response, both flounder eIF2 alpha kinases might play similar roles and that PoPKR is the predominant kinase. (C) 2009 National Natural Science Foundation of China and Chinese Academy of Sciences. Published by Elsevier Limited and Science in China Press. All rights reserved.

Expressional induction of Paralichthys olivaceus cathepsin B gene in response to virus, poly I:C and lipopolysaccharide

Cathepsin B is a lysosomal cysteine protease of the papain-like enzyme family with multiple biological functions. In this study, Paralichthys olivaceus cathepsin B (PoCatB) cDNA was isolated from flounder embryonic cells (FEC) treated with UV-inactivated grass carp hemorrhage virus (GCHV) and subsequently identified as a vitally induced gene. The full length cDNA of PoCatB is 1801 bp encoding 330-amino acids. The deduced protein has high homology to all known cathepsin B proteins, containing an N-terminal signal peptide, cysteine protease active sites, the occluding loop segment and a glycosylation site, all of which are conserved in the cathepsin B family. PoCatB transcription of FEC cells could be induced by turbot (Scophthalmus maximus) rhabdovirus (SMRV), UV-inactivated SMRV, UV-inactivated GCHV, poly I:C or lipopolysaccharide (LPS), and SMRV or poly I:C was revealed to be most effective among the five inducers. In normal flounder, PoCatB mRNA was detectable in all examined tissues. Moreover, SMRV infection could result in significant upregulation of PoCatB mRNA, predominantly in spleen, head kidney, posterior kidney, intestine, gill and muscle with 18.2,10.9, 24.7,12, 31.5 and 18 fold increases at 72 h post-infection respectively. These results provided the first evidence for the transcriptional induction of cathepsin B in fish by virus and LPS, indicating existence of a novel function in viral defense. (C) 2008 Elsevier Ltd. All rights reserved.

Functional domains and the antiviral effect of the double-stranded RNA-dependent protein kinase PKR from Paralichthys olivaceus

The double-stranded RNA (dsRNA)-dependent protein kinase PKR is thought to mediate a conserved antiviral pathway by inhibiting viral protein synthesis via the phosphorylation of the alpha subunit of eukaryotic initiation factor 2 (eIF2 alpha). However, little is known about the data related to the lower vertebrates, including fish. Recently, the identification of PKR-like, or PKZ, has addressed the question of whether there is an orthologous PKR in fish. Here, we identify the first fish PKR gene from the Japanese flounder Paralichthys olivaceus (PoPKR). PoPKR encodes a protein that shows a conserved structure that is characteristic of mammalian PKRs, having both the N-terminal region for dsRNA binding and the C-terminal region for the inhibition of protein translation. The catalytic activity of PoPKR is further evidence that it is required for protein translation inhibition in vitro. PoPKR is constitutively transcribed at low levels and is highly induced after virus infection. Strikingly, PoPKR overexpression increases eIF2 alpha phosphorylation and inhibits the replication of Scophthalmus maximus rhabdovirus (SMRV) in flounder embryonic cells, whereas phosphorylation and antiviral effects are impaired in transfected cells expressing the catalytically inactive PKR-K421R variant, indicating that PoPKR inhibits virus replication by phosphorylating substrate eIF2 alpha. The interaction between PoPKR and eIF2 alpha is demonstrated by coimmunoprecipitation assays, and the transfection of PoPKR-specific short interfering RNA further reveals that the enhanced eIF2 alpha phosphorylation is catalyzed by PoPKR during SMRV infection. The current data provide significant evidence for the existence of a PKR-mediated antiviral pathway in fish and reveal considerable conservation in the functional domains and the antiviral effect of PKR proteins between fish and mammals.