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.     

The frequency, distribution, and pathology of three diseases of demersal fishes in the Bering Sea

During September and October, 1975, bottom-dwelling fish from the Bering Sea were examined for diseases. The three most commonly observed diseases and their frequency of occurrence were epidermal papillomas of rock sole ( Lepidopsetta bilineata Ayres), 1-0%; lymphocystis of yellowfln sole ( Limanda aspera Pallas), 2-1 %; and epidermal tumours of the pseudobranch of adult Pacific cod ( Gadus macrocephalus Tilesius), 7-4%. Both the appearance and the histological characteristics of epidermal papillomas on rock sole resembled those found on several species of flatfish in Puget Sound. The frequency of tumour-bearing rock sole ranged from 0-23%, with the highest occurrence at sampling stations around the periphery of the Bering Sea in water depths of 20-30 fathoms (36-54 m). The virus-caused lymphocystis lesions were usually on the 'blind' side fins and skin surfaces of yellowfin sole, the largest lesions being found on the operculum, and the most common site of infection was the pectoral fin. The frequency of lymphocystis was 0-15 %, with a gradual increase of prevalence from the northern to southern sampling stations. The Pacific cod tumours were always bilateral, and contained remnants of normal-appearing pseudobranchial tissue on the surface or deep inside the tumours. Portions of some tumours were necrotic and liquefied. Tumour-bearing cod were most commonly found in the south and south-eastern Bering Sea and the frequency of affected cod ranged from 0-100%.     

Assessment of some innate immune responses in dab (Limanda limanda L.) from the North Sea as part of an integrated biological effects monitoring

The marine flatfish dab (Limanda limanda), which lives in direct contact with contaminated sediments, is frequently used as a sentinel species in international monitoring programmes on the biological effects of contaminants. In this study, immune responses were recorded as indicators of sublethal chronic effects of contaminants, in addition to measurement of the induction of mono-oxygenase ethoxyresorufin O-deethylase (EROD) in liver cells, the inhibition of acetylcholin esterase (AChE) in muscle and a quantification of grossly visible diseases and parasites. In total, 336 dab were analysed from five sampling areas in the North Sea, including the German Bight, the Dogger Bank, the Firth of Forth, and two locations close to oil and gas platforms (Ekofisk and Danfield). When considering plasma lysozyme levels, pinocytosis and respiratory burst activity of head kidney leucocytes, a clear gradient could be observed with decreased levels in individuals collected from the Firth of Forth and locations near the oil or gas platforms compared with dab from the Dogger Bank or the German Bight. Individuals with induced EROD activity displayed reduced lysozyme and respiratory burst activities. Lysozyme levels were also reduced in dab with lymphocystis or with nematodes. The data obtained indicate that the assessment of innate immune parameters in a monitoring programme provides supplementary information about immunomodulatory effects associated with the exposure of fish to contaminants. In particular, concentrations of plasma lysozyme, which can be analysed in an easy and inexpensive assay, are considered to be an appropriate parameter for use in a battery of other bioindicators. Communicated by H. von Westernhagen and A. Diamant     

“Right” or “wrong”? insights into the ecology of sidedness in european flounder,Platichthys flesus

Sidedness polymorphism in flatfish has been linked to ecological selection between morphs. However, the alternate hypothesis that morphological differences between right‐ and left‐sided forms may be due to errors during development, as a consequence of disturbed homeostasis, which still remains largely unexplored. Here, we examined the case of Platichthys flesus (flounder), a polymorphic flatfish exhibiting large and clinal variation in the frequency of the left‐sided morph, which is the reversed condition in this generally right‐sided species. An integrated approach consisting of the analyses of shape variation, stomach contents, and skeletal anomalies was used. Morphological differences were observed between morphs, which are in agreement with previous findings in a congeneric species (Platichthys stellatus). In parallel, significant differences in feeding choices were detected, suggesting a coherent association between subtle morphological differences between morphs and their use of trophic resources. Skeletal anomalies and meristic counts did not corroborate the hypothesis that morphometric divergence in reversed individuals may be caused or reinforced by developmental instability. J. Morphol. 2012. © 2011 Wiley Periodicals, Inc.     

Convergent signs of degradation in both the capacity and the quality of an essential fish habitat: state of the Seine estuary (France) flatfish nurseries

The Bay of Seine is a potentially important nursery ground, especially for flatfish. This area, however, is also strongly anthropogenically influenced. A composite approach was chosen to compare the flatfish nursery function of the Seine estuary with other coastal and estuarine areas and to determine the impact of anthropogenic disturbances. It emerges that alteration of the nursery function in the Seine estuary is related to the loss of nursery habitat and to a lower quality of the residual surfaces. These observations stressed the importance of habitat destruction and decreased quality of remaining habitat for fish stocks renewal.     

Genomic resources for flatfish research and their applications

Flatfishes are a group of teleosts of high commercial and environmental interest, whose biology is still poorly understood. The recent rapid development of different 'omic' technologies is, however, enhancing the knowledge of the complex genetic control underlying different physiological processes of flatfishes. This review describes the different functional genomic approaches and resources currently available for flatfish research and summarizes different areas where microarray-based gene expression analysis has been applied. The increase in genome sequencing data has also allowed the construction of genetic linkage maps in different flatfish species; these maps are invaluable for investigating genome organization and identifying genetic traits of commercial interest. Despite the significant progress in this field, the genomic resources currently available for flatfish are still scarce. Further intensive research should be carried out to develop larger genomic sequence databases, high-density microarrays and, more detailed, complete linkage maps, using second-generation sequencing platforms. These tools will be crucial for further expanding the knowledge of flatfish physiology, and it is predicted that they will have important implications for wild fish population management, improved fish welfare and increased productivity in aquaculture.     

Gill X-cell lesions in American plaice (Hippoglossoides platessoides) concurrent with lymphocystis infection

This paper documents the first report of concurrent infections of lymphocystis lesions and X-cells and the varied associations between multiple, clustered or single lymphocystis lesions and X-cells in a NW Atlantic pleuronectid.     

Lymphocystis in wild plaice Pleuronectes platessa (L.), and flounder, Platichthys flesus (L.), in British coastal waters: A histopathological and serological study

Wild plaice and flounders with lymphocystis were sampled and their lesion distribution noted. Regression of the lymphocystis cells was seen by histology and a host response including macrophages and immune cells occurred. Antibodies were detectable by a double diffusion precipitin test. The epidemiology is discussed with reference to these findings and to the life histories of the two species.     

Flatfish vitellogenin detection using optical waveguide lightmode spectroscopy-based immunosensor

A sensitive optical waveguide lightmode spectroscopy-based immunosensor was developed to detect vitellogenin in seawater flatfish (Paralichthys olivaceus). For this purpose, anion-exchange column chromatography with DE-52 resin was used to purify flatfish vitellogenin from flatfish serum containing vitellogenin that had been induced using an intraperitoneal 17beta-estradiol injection. The anti-flatfish vitellogenin antibody used as the biological component of the above immunosensor was prepared using the purified flatfish vitellogenin. The change in the incoupling angle according to the complexation between the flatfish vitellogenin and its antibody, immobilized over an optical grating coupler sensor chip, was measured to calculate the sensor response. The immunosensor was quite specific to flatfish vitellogenin binding, based on no sensor response in the case of bovine serum albumin immobilization. When plotted using double-logarithmic scales, the sensor responses increased linearly in flatfish vitellogenin concentrations of 0.00675-67.5 nM, with a detection limit of 0.0675 nM. The reusability during seven repetitive measurements was reasonably fair for the preliminary screening of flatfish vitellogenin.     

Long-term dynamics of species composition and abundance of flatfish in waters off Primorye (the Sea of Japan)

Based on the data of trawl surveys, changes in the structure of species composition and flatfish abundance (Pleuronectidae) in waters off Primorye are shown in the period embracing over 20 years (1983 to 2004). In waters off Primorye, 14 flatfish species were recorded in catches. At the present time, the structure of the flatfish part of the fish community in waters off Primorye has undergone considerable changes in comparison with the 1980s: the proportion of deepwater flatfish has considerably increased against the background of a decrease in the abundance of coastal species. A general decrease in the numbers and biomass of flatfish in waters off Primorye is recorded, which is caused by natural reasons against the background of an inconsiderable fishery intensity.     

Regional patterns in prevalence of principal external diseases of dab Limanda limanda in the North Sea and adjacent areas 1992-1997

The prevalence and spatial distribution of major diseases of dab Limanda limanda in the North Sea and adjacent areas were studied in the summers 1992 to 1997. Areas covered were the North Sea, Irish Sea, northern and northeastern British Waters and the English Channel. The diseases studied were lymphocystis, epidermal hyperplasia/papilloma and skin ulceration. To standardise data, results were analysed for females >15 cm (>3 yr old). Data were subjected to median polish, and additive, extended and additive plus multiplicative models were applied to best account for effects of region and year. Annual differences in disease prevalence were low whilst differences between areas were pronounced. For lymphocystis higher prevalence was observed in the northwestern sector of the North Sea, at the northern tip of Scotland and in an area south of Iceland. Prevalence was low in the Irish Sea, the English Channel and the southern North Sea, and intermediate in the German Bight. For epidermal hyperplasia/papilloma, levels were low at Icelandic stations, in the northern Irish Sea, in the southern North Sea and the English Channel, whilst levels were high in the northwestern part of the North Sea and the German Bight. Elevated levels of skin ulceration were found on the Dogger, at 1 station in the Irish Sea (off Sellafield) and at 1 station to the south of Iceland. Lower levels were detected west of Iceland. Prevalence in all other areas was intermediate. It is concluded that a detailed analysis of available data on disease prevalence and putative causative factors is desirable and, given the good availability of data, would be a promising step forward toward elucidating possible cause and effect relationships between diseases and anthropogenic factors.     

Whitespotted puffer Arothron hispidus, a new host for lymphocystis in Qingdao Aquarium of China

In April 2004 white nodular lesions were found on the fins of whitespotted puffer Arothron hispidus (Linnaeus). Diagnostic studies were carried out to confirm the disease using light and electron microscopy, histochemical methods and PCR. The results revealed that the nodules were composed of giant cells up to 400 microm in diameter. These cells were surrounded by a periodic acid-Schiff (PAS)-positive hyaline capsule containing dot-shaped, Feulgen-positive inclusion bodies in the cytoplasm and an irregular nucleus. Numerous virus particles 200 nm in diameter and with hexagonal profiles were observed in the cytoplasm. These features were consistent with those of lymphocystis disease. Additionally, based on the gene sequences of major capsid protein (MCP) of lymphocystis disease virus (LCDV) from Japanese flounder Paralichthys olivaceus, 2 pair primers were designed; after a nested PCR was performed for detection of LCDV in A. hispidus, a positive amplified product was obtained showing the presence of LCDV. Therefore, the white nodules were the lymphocystis lesions caused by LCDV infection and A. hispidus was demonstrated to be a new host for LCDV.     

Hair Cell Polarization in the Flatfish Inner Ear

The hair cell polarization of the various sensory epithelia in the inner ear was examined in two species of flatfish, the Plaice (Pleuronectes platessa) and the Dab (Limanda limanda). The hair cells in the macula utriculi are polarized in the pattern usually seen for this macula in vertebrates. In the macula sacculi and macula lagenae the hair cell polarization is different from that hitherto described from bony fishes and other vertebrates. The polarization seen in these maculae in the flatfish explains their ability to sense movements in all directions, which is necessary if these sensory areas are the most important inner ear organs in the regulation of postural orientation.     

Annual variation in lymphocystis infection frequency in flounder, Platichthys flesus (L.)

The infection frequency of the virus induced lymphocystis disease has been registered in flounder from the Oslofjord, Norway, during a 4 year period. The disease has a clear regular seasonal variation, and also an annual variation. The percentage infection in the summer was 1–10%, and in the winter up to 57%. The possibility that the high pollution level of the inner Oslofjord could be the reason for the high frequency of lymphocystis disease, is discussed.     

Iridovirus infections in farm-reared tropical ornamental fish

A systemic viral infection in both gourami Trichogaster spp. and swordtail Xiphophorus hellerii and an outbreak of lymphocystis in scalare Pterophyllum scalarae and gourami are reported to have occurred in fish reared in ornamental fish farms in Israel. The systemic infection developed in endothelial cells that became hypertrophic and their contents were modified. The presence of such cells in light-microscopically examined stained smears and sections provides an initial indication for this systemic viral infection. Infection in gourami caused hemorrhagic dropsy. Transmission electron microscopic (TEM) images of iridovirus-like particles recovered from gouramies showed them to be 138 to 201 nm from vertex to vertex (v-v); those from swordtails were 170 to 188 nm v-v. TEM images of lymphocystis virions from scalare were 312 to 342 nm v-v and from gourami 292 to 341 nm v-v. Lymphocystis cells from the gourami were joined by a solid hyaline plate, which was lacking in the infection in scalare where the intercellular spaces between the lymphocystis cells consisted of loose connective tissue.     

Methylation pattern of fish lymphocystis disease virus DNA.

The content and distribution of 5-methylcytosine in DNA from fish lymphocystis disease virus was analyzed by high-pressure liquid chromatography, nearest-neighbor analysis, and with restriction endonucleases. We found that 22% of all C residues were methylated, including methylation of the following dinucleotide sequences: CpG to 75%, CpC to ca. 1%, and CpA to 2 to 5%. Comparison of relative digestion of viral DNA with MspI and HpaII indicated that CCGG sequences were almost completely methylated at the inner C. The degree of methylation of GCGC was much lower. The methylation pattern of fish lymphocystis disease virus DNA differed from that of the host cell DNA.     

Feeding biology of the flatfish Citharichthys spilopterus (Bothidae) in a tropical estuary of Mexico

The flatfish Citharichthys spilopterus Günther 1862 is the most common bothid in the coastal lagoons of the Gulf of Mexico. The objective of the present study was to describe the trophic biology of this species in the tropical coastal lagoon of Tampamachoco, Mexico. For the diet analysis, we used multivariate discriminant analysis and trophic niche breadth. The morphological analysis showed that the features of the bucco-pharyngeal cavity, the large stomach and the short intestine of this flatfish relate to a carnivorous habit. The overall diet showed that this species is a third-order consumer, feeding mainly on fish (52%, mainly gobies) and crustaceans (36%, mostly decapods). Diet and trophic niche breadth showed no significant differences between sexes (P > 0.1). By contrast, there were significant ontogenetic differences in the diet and trophic niche breadth, where larger C. spilopterus were almost entirely piscivorous and showed the narrowest trophic niche. As the flatfish grew in size there was a trend toward the consumption of larger prey. The importance of copepods and peracarids correlated inversely with flatfish size (P < 0.001), but fish prey correlated directly to flatfish size (P < 0.001). Likewise, there was an inverse significant correlation between niche trophic breadth and flatfish size (P < 0.005). There were also significant seasonal differences in the diet (P < 0.02), related to the availability and vulnerability of prey in the lagoon during the dry and rainy seasons. However, the trophic niche showed no significant differences between seasons. Finally, we discuss the advantages of discriminant analysis applied to evaluate differences among diets of fish groups when compared with other bivariate and multivariate techniques.     

Seasonal changes in frequency of diseases in dab,Limanda limanda,from the southern North Sea

Infestation rates of flatfishLimanda limanda from the southern North Sea (German Bight) were investigated in 1981 and 1982. At three stations, including a dumping area of acid-iron wastes northwest of Helgoland, dabs were examined for the occurrence of lymphocystis and epidermal papillomas. Marked seasonal changes of infestation rates were observed with maxima of diseased fish in March and May (epidermal papillomas 2 % in 1981, 4.1 % in 1982; lymphocystis 7.5 % in 1981, 17.2 % in 1982). Infestation minima were found from June to October. Differences in incidence rates were observed between stations in winter and spring, but not in summer. Both diseases turned out to be size-dependent. Seasonality of the two diseases is discussed in relation to spawning cycle and water quality, including pollution.     

Eye movements of flatfish for the changes of gravity (II)

In this study, we analysed the eye movements of flatfish for body tilting and compared with that of goldfish. The fish was fixed on the tilting table controlled by computer. The eye movements for body tilting along the different body axis were video-recorded. The vertical and torsional eye rotations were analysed frame by frame. In normal flatfish, vertical eye movement of left eye to leftward tilting was larger than that to rightward tilting. For head up or head down tilting, clear vertical eye movements were observed. On the other hand, torsional eye movements showed similar characteristics as goldfish. These results suggested that sacculus and lagena were important for otolith-ocular eye movements in flatfish.