Ultrastructural characterization of gills in juveniles of the Argentinian Silverside, Odontesthes bonariensis (Valenciennes, 1835) (Teleostei: Atheriniformes)

An ultrastructural study was performed on the gills of juvenile Argentinian silverside, Odontesthes bonariensis. The gills are composed of two sets of four holobranchs and, in turn, each holobranch consists of a gill arch and two rows of caudolaterally projecting branchial filaments. From the dorsal and ventral surfaces of each filament, branchial lamellae radiate out as foldings of the epithelial layer. Gill rakers are present on each of the gill arches, on the anteromedial side of the arch opposite to the filaments. Gill rakers, gill arches and branchial filaments are covered by a stratified epithelium, whereas branchial lamellae essentially consist of a thin epithelial envelope containing capillaries. In the stratified epithelium, mucous cells, rodlet cells, granular cells, pavement epithelial cells and mitochondria-rich cells are identified. The thin epithelium that lines the lamellae comprises two cell types, outer and inner epithelial cells, and the capillary walls on the inside of the epithelial envelope are defined by pillar cells. The ultrastructure of all these cell types is described and our findings are discussed in light of the existing data on fish gill morphology. In the gills of juvenile Argentinian silverside is of particular interest the characteristics showed by mitochondria-rich cells, such as their arrangement in clusters of 2-3 cells and their small and depressed surface in contact with the aquatic milieu, features which strongly resemble those of euryhaline species.     

Ultrastructure features of the surface of the gills and the lower pharyngeal jaw of the Tilapia Zilli,redbelly tilapia (Coptodon Zillii,Gervais, 1848)

The present investigation was designed to describe the surface ultrastructure of the gill system of tilapia Zilli. The gill system is formed from four gill arches and each gill arch carries a row of gill filaments on its convex border and two rows of the gill rakers on its concave border. The quadrilateral interbranchial septum has elevated part at the level of the third gill arch. By SEM observations, the gill arch was divided into three regions: rostral, middle and caudal region. The caudal region contained two characteristic structures: oval leaf‐like structure and rounded‐shaped structure. Each oval leaf‐like structure carried two lateral rows of the triangular pointed spines separated by a median groove. All surfaces of gill arches, rakers and filaments were covered with a mosaic of the polygonal pavement cells, in addition to the opening of chloride cells and mucous cells. The gill arch and gill raker had only one appearance of taste buds named type I. Meanwhile, the filaments contained two types of different appearance of the taste buds named: type I and type II. Type I was the main common and similar to that present in gill arch and raker and characterized by its blunt end, while type II had hair‐like structures that projected from the volcano‐shaped depression. The gill rakers were formed from central axis surrounded by two lateral lobulated regions which carry pointed spines, taste buds and the opening of chloride cells. The surface of triangular lower pharyngeal jaw carries numerous teeth‐like papillae which originated from the socket‐like depression.     

Virulence and enterobacterial repetitive intergenic consensus PCR of Vibrio alginolyticus strains isolated from Tunisian cultured gilthead sea bream and sea bass outbreaks

Vibrio alginolyticus was isolated from the internal organs of diseased gilthead sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax) cultured in two fish farms located on the Tunisian Mediterranean coast, from 2003 to 2005. After phenotypic characterisation, a selection of 34 isolates from gilthead sea bream and sea bass were molecularly typed by repetitive intergenic consensus PCR (ERIC-PCR) showing a high polymorphism among the isolated strains (19 genotypes). Most of the isolates were resistant to atleast two antimicrobial agents. All the tested strains were resistant to ampicillin. However, 91.17% were resistant to nitrofurantoin and 35.29% to tetracycline. Several strains isolated from diseased gilthead sea bream and sea bass were tested for virulence in both fish species by intraperitoneal injection. The selected isolates (n=7) were pathogenic for gilthead sea bream and sea bass. LD(50) values ranged from 5.01 x 10(4) to 6.20 x 10(7)CFU/fish. This is the first report on characterisation and virulence of V. alginolyticus for sea bass and sea bream in Tunisia.     

Ultrastructural morphology of the gill of the hybrid striped bass (Morone saxatilis x M. chrysops)

The fine structure of the principal cell types found in the gill filaments and secondary, respiratory lamellae of the hybrid striped bass (Morone saxatilis x M. chrysops) was studied by transmission electron microscopy. Most of the cell types generally resembled those observed at this level of resolution in other euryhyaline, teleostean species, and the mucus cells, epithelial cells, and cartilage cells were non-distinctive. Pillar cells were atypically flattened within the lamellae. The extensive cytoplasmic tubular system of the chloride cells was more densely distributed and was less branched than reported for many other teleosts. The vascular endothelial cells of the marginal, lamellar blood vessels were particularly striking because of their prominent, electron-dense cytoplasmic granules. Although the physiological function and chemical composition of these granules remain obscure, their presence suggests an important role of secretion into the vascular lumen. These gill data from normal specimens of this sport and commercial, hybrid species constitute a useful basis for interpreting gill changes in diseased striped bass.     

Contributions to the Functional Morphology of Fishes

From December 1980 to June 1981 a total of 180 specimens of the estuarine round-herring Gilchristella aestuarius were collected for stomach content analysis. Diatoms were the most frequently ingested food item, although the gill raker gap was too large to retain these and other planktonic food items. Mucus-secreting cells within the epithelial layer of the hyoid arch, branchial arches and gill rakers, trap the plankton which accumulate in boluses of mucus-enveloped food too large to pass through the gill rakers. G. aestuarius was found to possess a pair of suprabranchial pouches. The histology of the walls of these organs and the external attachment of six muscle blocks indicates a feeding mechanism involving the accumulation and temporary storage of diatoms and other planktonic food items, which are then coalesced into a pellet large enough to be swallowed by peristalsis into the stomach.     

Host Switch of <Emphasis Type="Italic">Lamellodiscus elegans</Emphasis> (Monogenea: Monopisthocotylea) and <Emphasis Type="Italic">Sparicotyle chrysophrii</Emphasis> (Monogenea: Polyopisthocotylea) between Cage-reared Sparids

Sharpsnout bream (Diplodus puntazzo) has been used in Adriatic aquaculture for less than a decade, but the decreasing trend of rearing this species will probably result in its complete substitution by more exploited sea bream (Sparus aurata). Only two facilities still rear both fish species in neighbouring cages in monoculture. A switch of parasites was observed between sparids during monitoring of the gill monogeneans of farmed fish. In wild fish of the Adriatic Sea, Lamellodiscus elegans (Monogenea: Monopisthocotylea) has previously been reported in annular (Diplodus annularis), and two-banded sea bream (D. vulgaris) and sharpsnout bream (D. puntazzo), and the present study confirmed its presence also in sea bream, in low prevalence and abundance. The exclusively sea bream monogenean Sparicotyle chrysophrii (Monogenea: Polyopisthocotylea) was also isolated from sharpsnout bream, showing prevalence and abundance values even higher than in its resident host. In the occurrence of L. elegans in sea bream, the opportunistic switch resulted in lower abundance and prevalence than in the original host, while in the second case of switching the monogenean S. chrysophrii showed better reproductive capacity on a new host (sharpsnout bream). Both cases point to the possible enlargement of parasite host range.     

The histology and histochemical aspects of gills of the flower fish, <Emphasis Type="Italic">Pseudophoxinus antalyae</Emphasis>

Branchial epithelium of Pseudophoxinus antalyae was lined by both a thick stratified epithelium lining gill arches, gill rakers and primary filaments and a thin epithelium lining the lamellae. Mucous, chloride and rodlet cells, interspersed between pavement cells, were present in the branchial epithelium. With histochemical procedures for the characterization of glycoconjugates, mucous cells showed a strong positive reaction with Periodic acid-Shiff and Alcian Blue at pH 2.5, although with Alcian Blue at pH 0.5 and pH 1.0 the reaction was much weaker. When the combined Alcian Blue (pH 2.5) – Periodic acid-Shiff reaction was performed, most mucous cells were stained purple, whereas by the combined Aldehyde Fuchsin/Alcian Blue (pH 2.5), most cells showed a positive reaction only to Aldehyde Fuchsin. Methylation/ Alcian Blue (pH 2.5) and Methylation/ Saponification/ Alcian Blue (pH 2.5) methods showed the presence of sulphated and carboxylated glycoconjugates in mucous cells. Mucous cells were also detected to stain all metachromatically with Toluidine Blue.     

Myxobolus infection of the gills of common bream (Abramis brama L.) in Lake Balaton and in the Kis-Balaton reservoir, Hungary

During a five-year survey including studies on the parasite fauna of bream (Abramis brama), four gill-parasitic Myxobolus species (M. bramae, M. hungaricus, M. impressus and M. macrocapsularis) were recorded in a total of 313 breams from Lake Balaton. The commonest species, M. bramae showed a prevalence of 33%, while the other species occurred sporadically. Myxobolus bramae and M. macrocapsularis infected the tips of the gill filaments and caused both intralamellar and interlamellar infection. Intralamellar plasmodia of small size developed in the capillary network of the gill lamellae whereas the much larger interlamellar plasmodia were formed in the arteria afferens. The intralamellar plasmodia of M. hungaricus always infected the basal or central part of the gill filaments. In contrast to the above species developing in the blood vessels, M. impressus proved to be an epithelial parasite, as its plasmodia always developed in the adjacent gill filaments of two opposite haemibranchia, in the stratified epithelium between the respiratory plates, causing changes of the haemibranchium which were well visible even by the naked eye.     

Experimentally induced glochidiosis in smallmouth bass (Micropterus dolomieu)

Necropsy was performed on 2 smallmouth bass (Micropterus dolomieu) that died 8 days after experimental gill inoculation with Actinonaias pectorosa glochidia. The salient feature at necropsy was ragged gills containing multiple petechial hemorrhages and numerous white, iridescent dust-like particles easily confirmed as glochidia in squash preparations of the gill filaments. Microscopically, the gills contained multiple rounded glochidia encysted at the tips or along the length of the filaments. Parasitized filaments were thickened, blunted, and often fused. Lamellae were extensively fused and obliterated, with proliferation of the epithelial cells giving the filament a smooth outline. Sometimes glochidia were associated with necrosis and/or hemorrhage. These fish most likely died due to asphyxia associated with the severe branchial lesions caused by the glochidia.     

The Post-larval Development of Lateral Musculature in Gilthead Sea Bream Sparus aurata (L.) and Sea Bass Dicentrarchus labrax (L.)

Fibre-type differentiation of lateral musculature has been studied in gilthead sea bream Sparus aurata (L.) and sea bass Dicentrarchus labrax (L.) during post-larval development using ultrastructural, histochemical and morphometric techniques. The study showed three muscle layers: red, intermediate (or pink) and white. Initially, most of the red muscle showed low myosin ATPase (m-ATPase) activity fibres, whereas near the transverse septum some small high m-ATPase activity fibres appeared and later acquired a rosette aspect. Afterwards, during adult growth the red muscle showed a histochemical mosaic appearance. The pink muscle in sea bass was observed at the beginning of juvenile development by the oxidative technique (NADH-RT reaction) whereas in gilthead sea bream it was also observed at the end of larval development. The pink layer consists of high m-ATPase activity fibres. However, along the muscle development other low and moderate m-ATPase activity fibres were observed close to the red and white muscles, respectively. The white muscle of juvenile fish showed a histochemical mosaic appearance near the pink muscle. In adult specimens the mosaic white muscle spread out occupying the whole of the myotome. Morphometric analysis shows a significant increase in mean fibre diameter during post-larval development, as shown by the Student's t-test (hypertrophic growth). Skewness and kurtosis values of fibre diameters point to the generation of a new fibres from the myosatellite cells (hyperplastic growth).     

Myxobolus infections of common carp (Cyprinus carpio) in Syrian fish farms

During a survey on Myxobolus infection of pond-cultured common carp in Syria three Myxobolus spp. were found. Myxobolus dispar infected the gill arteries, forming large elongated plasmodia in the gill filaments. The plasmodia of M basilamellaris were located in the gill arches at the base of the filaments. Elongated filiform plasmodia of M. encephalicus were found in the blood vessels of the brain. Despite the common occurrence of the above parasites, no disease symptoms were observed in the infected fish specimens. This is the first report on myxosporean infection of fish from Syrian waters.     

Effect of long-term oral administration of an immunostimulant diet on innate immunity in sea bass (Dicentrarchus labrax)

Immunostimulants represent a modern and promising tool in aquaculture, enhancing the resistance of cultured fish to disease and stress. This study investigated the effect of a combination of dietary glucans, alpha-tocopherol and ascorbic acid on the innate immune response of cultured sea bass (Dicentrarchus labrax). After 5 weeks of adaptation on a commercial diet containing 100 p.p.m. ascorbic acid and 200 p.p.m. alpha-tocopherol, sea bass were switched to a diet supplemented with 2% beta-1.3/beta-1.6 glucans and ascorbic acid and alpha-tocopherol at 500 p.p.m. The supplemented diet was given at 2% of body weight per day over a 2-week period, every 3 months. Plasma lysozyme concentration, content and distribution of major plasma proteins and complement activity were measured prior to feeding the supplemented diet and after 40 weeks. Alternative pathways of complement activation and lysozyme activity were both significantly enhanced in fish fed on glucans and elevated doses of vitamins. No significant differences were observed in protein content or in albumin/globulin ratio. Compared to lysozyme activity, which showed marked individual variation, complement-mediated haemolytic activity has been shown to be a more reliable indicator of sea bass immunocompetence. Further studies are in progress to clarify the effect of each dietary component on the innate immune response and disease resistance.     

Characterization of the probiotic strain Vagococcus fluvialis in the protection of European sea bass (Dicentrarchus labrax) against vibriosis by Vibrio anguillarum

Aquaculture is one of the main sources of income in many countries worldwide. Intensive farms are often affected by different infectious diseases that can decrease their final production. To control this situation, several antibiotics are frequently used with known environmental consequences. The aim of this study was to analyze different bacterial strains isolated from of gilthead sea bream, sea bass, sole and meagre guts, for use as probiotics in aquaculture. The strains were evaluated in vitro through various mechanisms of selection, such as the production of antagonistic effects against pathogens, production of antibacterial substance, adhesion to the intestinal mucus, competition for nutrients or binding site, and growth in intestinal mucus. A total of 50 bacterial strains were analyzed and only one showed excellent in vitro results for consideration as a candidate to be analyzed in vivo. The strain, identified as Vagococcus fluvialis, showed good protection against Vibrio anguillarum 975-1 in vivo in the experimental challenge, showing a relative percent survival of 42.3% higher than positive control group. Therefore, in conclusion we consider this strain to be a good candidate for use as a future probiotic in aquaculture.     

Amoeba-like infections in cultured marine fishes: systemic infection in pompano Trachinotus falcatus L. from Singapore and gill disease associated with Paramoeba sp. in sea bream Sparus aurata L. from Greece

Two cases of Amoeba-like infections in cultured warmwater marine fish are described, an unusual systemic infection in pompano Trachinotus falcatus L. from Singapore and a gill infection in Mediterranean sea bream Sparus aurata L. All pompano showed marked systemic infection of Amoeba-like parasites in gills, kidney, intestine, pancreas and spleen. The most severe lesions were in the gills and renal tissue with minimal tissue reaction in other organs.     

Gill epithelium of an angler catfish,Chaca chaca (Siluriformes,Chacidae): Enzyme and glycoprotein histochemistry

A series of histochemical techniques have been employed to localize alkaline phosphatase, acid phosphatase, non-specific esterase, catalase and peroxidase; and to visualize and characterize glycoprotein (GPs) moieties in the epithelium of gill arch, gill filaments and secondary lamellae of an angler catfish Chaca chaca. The epithelium of gill arch and gill filament shows strong alkaline phosphatase activity in the deeper layer epithelial cells; strong non-specific esterase activities in the outer layer epithelial cells; and weak acid phosphatase activity throughout the epithelium. The activity of these enzymes in the secondary lamellae is weak. The catalase and peroxidase show strong activities in the blood cells of the secondary lamellae. Various classes of GPs have been identified and characterized in the mucous secretions of the gill epithelium of C. chaca. These include—GPs with oxidizable vicinal diols, GPs with sialic acid residues without O-acyl substitution and GPs with O-sulphate esters. The functional significance of different enzymes in gill epithelium and the GPs in the mucus secreted on the surface has been discussed with the physiology of the gills in relation to the characteristic habit and habitat of the fish.     

Review on the immunology of European sea bass Dicentrarchus labrax

European sea bass (Dicentrarchus labrax L.) is a marine species of great economic importance, particularly in Mediterranean aquaculture. However, numerous pathogenic viruses, bacteria, fungi and parasites affect the species, causing various infectious diseases and thereby leading to the most heavy losses in aquaculture production of sea bass. In this respect, knowledge on molecular and genetic mechanisms of resistance to pathogens and specific features of immune response against various infectious agents should greatly benefit the development of effective vaccines and proper vaccination strategies in marker-assisted selection of fish resistant to a range of infections. To date, genetic knowledge on sea bass immune regulatory genes responsible for resistance to pathogens is relatively poor but tends to accumulate rapidly. In this review, we summarize and update current knowledge on the immune system and immune regulatory genes of the sea bass.     

Viral encephalopathy and retinopathy of Dicentrarchus labrax and Sparus aurata farmed in Tunisia

Viruses belonging to the Nodaviridae family cause disease worldwide among a large number of species of marine fish, and have been described in all continents. In the present study, a total of 69 farmed Tunisian sea bass (Dicentrarchus labrax) and 24 sea bream (Sparus aurata) samples were tested monthly for the detection of betanodavirus. The virus was identified in both species using indirect immunofluorescence assays (IFAT) and RT-PCR. In addition sequence analysis of part of the coat protein gene indicated that both species were infected by highly related, but distinct, strains belonging to the RGNNV genotype. The sequence of the coat protein gene of several strains was identical but up to 9 different sequences were detected in a single farm. In addition, viral sequences obtained from fish that were held at lower temperature (<20°C) were distinct from the rest of the sequences.     

Electron spin resonance (ESR) detection of irradiated fish containing bone (gilthead sea bream,cod, and swordfish)

Food irradiation is a preservation method that has been approved by the European Union for a limited number of foods or food products and within a limited range of doses. European Community legislation states that all foods or food ingredients treated in this manner and authorized for sale in the European Union must be clearly labeled, and that market-level inspections must be carried out to ensure compliance with this regulation. To improve detection of irradiated foods, we evaluated the efficacy of electron spin resonance (ESR) spectroscopy for the identification of seafood that had been subjected to irradiation. Three fish species were tested: gilthead sea bream, cod, and swordfish. For each species, 18 samples of flesh-containing bone were analyzed after either irradiation at 0.5, 1, or 3 kGy or no irradiation (control). Induced radicals in irradiated samples produced distinct ESR signals that allowed differentiation from non-irradiated samples. Within the dose range tested, a linear dose-response relationship was observed (R ² > 0.94). The gilthead sea bream displayed the highest radiosensitivity. The analytical procedure was validated and successfully used for the routine monitoring of locally marketed seafood. The main aims of the study were to develop a reliable tool for the enforcement of the proper labeling of irradiated foods and to obtain preliminary data on compliance with current laws in the Italian market.

     

Immersion booster vaccination effect on sea bass (Dicentrarchus labrax L.) juveniles

In each challenge 30 sea bass juveniles (mean weight 3.3 +/- 0.2 g SD) were used. During the whole experiment (water T: 18 +/- 1 degrees C) the fish were held in four 50l seawater independent recirculation systems (one fish group per 50l system). The protection to the pathogen Vibrio anguillarum was tested on booster vaccinated sea bass (Dicentrarchus labrax L.) juveniles. The vaccination was performed by immersion for 60 s in a commercial anti-V. anguillarum vaccine suspension. Booster vaccination took place 60 days after the initial immunization. Thirty days after the booster vaccination all the fish received intraperitoneally (IP) 3.0 x 10(6) cfu/fish (colony forming units) virulent V. anguillarum bacteria. The booster vaccination showed a strong protection effect on the challenged sea bass. In the next 20 days after the challenge the mortality was 0% among the booster vaccinated sea bass, 10% among the once vaccinated fish and 50% in the control group (unvaccinated fish). No mortality was observed among the unvaccinated sea bass injected IP with sterile normal saline by the challenge.