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During their different life stages, parasites undergo remarkable morphological, physiological, and behavioral “metamorphoses” to meet the needs of their changing habitats. This is even true for ectoparasites, such as the monogeneans, which typically have a free-swimming larval stage (oncomiracidium) that seeks out and attaches to the external surfaces of fish where they mature. Before any obvious changes occur, there are ultrastructural differences in the oncomiracidium’s outer surface that prepare it for a parasitic existence. The present findings suggest a distinct variation in timing of the switch from oncomiracidia epidermis to the syncytial structure of the adult tegument and so, to date, there are three such categories within the Monogenea: (1) Nuclei of both ciliated cells and interciliary cytoplasm are shed from the surface layer and the epidermis becomes a syncytial layer during the later stages of embryogenesis; (2) nuclei of both ciliated cells and interciliary syncytium remain distinct and the switch occurs later after the oncomiracidia hatch (as in the present study); and (3) the nuclei remain distinct in the ciliated epidermis but those of the interciliary epidermis are lost during embryonic development. Here we describe how the epidermis of the oncomiracidium of Discocotyle sagittata is differentiated into two regions, a ciliated cell layer and an interciliary, syncytial cytoplasm, both of which are nucleated. The interciliary syncytium extends in-between and underneath the ciliated cells and sometimes covers part of their apical surfaces, possibly the start of their shedding process. The presence of membranous whorls and pyknotic nuclei over the surface are indicative of membrane turnover suggesting that the switch in epidermis morphology is already initiated at this stage. The body tegument and associated putative sensory receptors of subadult and adult D. sagittata are similar to those in other monogeneans.

Gill parasites on fish are likely to negatively influence their host by inhibiting respiration, oxygen transport capacity and overall fitness. The glochidia larvae of the endangered freshwater pearl mussel (FPM, Margaritifera margaritifera (Linnaeus, 1758)) are obligate parasites on the gills of juvenile salmonid fish. We investigated the effects of FPM glochidia encystment on the metabolism and haematology of brown trout (Salmo trutta Linnaeus, 1758). Specifically, we measured whole-animal oxygen uptake rates at rest and following an exhaustive exercise protocol using intermittent flow-through respirometry, as well as haematocrit, in infested and uninfested trout. Glochidia encystment significantly affected whole-animal metabolic rate, as infested trout exhibited higher standard and maximum metabolic rates. Furthermore, glochidia-infested trout also had elevated levels of haematocrit. The combination of an increased metabolism and haematocrit in infested fish indicates that glochidia encystment has a physiological effect on the trout, perhaps as a compensatory response to the potential respiratory stress caused by the glochidia. When relating glochidia load to metabolism and haematocrit, fish with low numbers of encysted glochidia were the ones with particularly elevated metabolism and haematocrit. Standard metabolic rate decreased with substantial glochidia loads towards levels similar to those of uninfested fish. This suggests that initial effects visible at low levels of encystment may be countered by additional physiological effects at high loads, e.g. potential changes in energy utilization, and also that high numbers of glochidia may restrict oxygen uptake by the gills.

The Na(+), K(+), 2Cl(-) cotransporter (NKCC) is an important gene in ion transport. In order to elucidate its function, and regulatory mechanisms, in salinity acclimation, the complete cDNA sequence of NKCC (4218 bp) from Portunus trituberculatus (PtNKCC) was first cloned and characterized. It was found to encode 1055 amino acids containing conserved AA-permease and SLC12 motifs. Results show that PtNKCC is expressed to the greatest extent in gills. High salinity stress exposure led to significant increases (9.6-fold) of PtNKCC mRNA expression in the gills 12 h after treatment, declining to less than the levels seen in the control group between 48 and 72 h. During low salinity stress, expression levels of PtNKCC in gills were found to be upregulated at each sampling time, reaching their peak after 6 h (a 12.4-fold increase). Eyestalk ablation also triggered an 11.3-fold increase in PtNKCC mRNA, while re-injection with eyestalk homogenates significantly reduced the expression of PtNKCC mRNA. Four single nucleotide polymorphisms (SNPs) were detected in the PtNKCC open reading frame, and one SNP was associated with salt tolerance. Our results indicate that PtNKCC plays an important role in the salinity acclimation of P. trituberculatus, while there may be a compound present in the XOSG that inhibits the expression of PtNKCC.

Heat shock proteins (Hsps) are a class of highly conserved proteins produced in virtually all living organisms from bacteria to humans. Hsp60 and Hsp10, the most important mitochondrial chaperones, participate in environmental stress responses. In this study, the full-length complementary DNAs (cDNAs) of Hsp60 (PmHsp60) and Hsp10 (PmHsp10) were cloned from Penaeus monodon. Sequence analysis showed that PmHsp60 and PmHsp10 encoded polypeptides of 578 and 102 amino acids, respectively. The expression profiles of PmHsp60 and PmHsp10 were detected in the gills and hepatopancreas of the shrimps under pH challenge, osmotic stress, and heavy metal exposure, and results suggested that PmHsp60 and PmHsp10 were involved in the responses to these stimuli. ATPase and chaperone activity assay indicated that PmHsp60 could slow down protein denaturation and that Hsp60/Hsp10 may be combined to produce a chaperone complex with effective chaperone and ATPase activities. Overall, this study provides useful information to help further understand the functional mechanisms of the environmental stress responses of Hsp60 and Hsp10 in shrimp.

MicroRNAs (miRNAs) are small noncoding RNAs that post-transcriptionally regulate gene expression in organisms. To understand the underlying mechanisms behind the molecular response of the crab to low salt-stress, high-throughput Illumina/Solexa deep sequencing technology was used to investigate the expression profiles of miRNAs under low salinity challenged. Two mixed RNA pool libraries of gill tissues from low salinity challenged (LC) and the control groups (NC) were sequenced on the Illumina platform. A total of 6,166,057 and 7,032,973 high-quality reads were obtained from the NC and LC libraries, respectively. Sixty-seven miRNAs consisting of 16 known and 51 novel ones were identified, among which, 12 miRNAs were differentially expressed in LC compared to NC. Thirty-four of the target genes predicted were differentially expressed in the opposite direction to the miRNAs, which were involved in crucial processes related to osmoregulation by gene ontology (GO) functional enrichment analysis, such as anion transport processes (GO:0006820) and chitin metabolic process (GO:0006030). These results provide a basis for further investigation of the miRNA-modulating networks in osmoregulation of Portunus trituberculatus.

Certain wrasse species (Labridae) are used as cleaner fish in salmon farms on the Norwegian coast, reducing salmon louse intensities. The pathogen repertoire of wrasse in Norway is poorly known, and the objective of the present study is to describe a novel intracellular bacterium detected in Norwegian Labrus bergylta. Histological examination of gill tissues from ballan wrasse, L. bergylta, revealed epitheliocysts occurring basally to the secondary lamellae in the interlamellar epithelium. Ultrastructurally, these had bacteria-filled inclusions with thickened membranes and radiating ray-like structures (actinae). 16S rRNA gene sequences from the gill bacteria showed the highest (97.1 %) similarity to Candidatus Similichlamydia latridicola from the gills of the latrid marine fish Latris lineata in Australia and 94.9 % similarity to Candidatus Actinochlamydia clariae, causing epitheliocystis in the freshwater catfish Clarias gariepinus in Uganda. A total of 47 gill samples from L. bergylta from Western Norway were screened by real time RT-PCR with an assay targeting Candidatus Actinochlamydiaceae 16S rRNA. Prevalence was 100 %. We propose the name Candidatus Similichlamydia labri sp. nov. for this new agent producing gill epitheliocysts in L. bergylta. publishedVersion

The striated darter (Etheostoma striatulum Page & Braasch) is a rare fish species restricted to the Duck River system in Maury County, Tennessee, USA. In this paper we describe Aethycteron striatuli n. sp., a gill parasite from a genus that has specialised on darters as the parasites' preferred hosts. Aethycteron striatuli morphologically resembles A. malleus (Mueller, 1938), A. robisoni Cloutman & McAllister, 2017, A. chlorosomus (Harrises & Vickery, 1970) and A. micropercae Suriano & Beverley-Burton, 1982. It is distinguished from other species in that it is one of the smallest described parasites in this genus to date and possesses a small male copulatory organ with a distinct accessory piece. This is the first monogenean parasite reported from E. striatulum, a species that is currently under threat due to its restricted range and the potential for habitat loss. It is essential to expand our knowledge of the host and the pressures it faces in its limited habitat, including disease and parasite pressures, so that measures can be taken to preserve this vulnerable native species.

Background African tetras (Alestidae) belonging to Brycinus Valenciennes are known to be parasitized with monogeneans attributed to two genera, Annulotrema Paperna & Thurston, 1969 and Characidotrema Paperna & Thurston, 1968 (Dactylogyridae). During a survey of monogeneans parasitizing alestids, species of Characidotrema were collected in Cameroon, D. R. Congo, Senegal, South Africa, Sudan and Zimbabwe. This paper provides new morphological data and the first molecular analysis broadening our knowledge on the diversity of these parasites. Results Seven species (four known and three new) of Characidotrema are reported from two species of Brycinus: C. auritum n. sp. and C. vespertilio n. sp. from B. imberi (Peters); and C. brevipenis Paperna, 1969, C. nursei Ergens, 1973, C. pollex n. sp., C. spinivaginus (Paperna, 1973) and C. zelotes Kritsky, Kulo & Boeger, 1987 from B. nurse (Rüppell). Species identification was based on morphological analysis of the sclerotized structures supported by nuclear ribosomal DNA (partial 18S rDNA, ITS1, and 28S rDNA) sequence data. Morphological analysis confirmed that the most apparent character distinguishing species in the genus is the morphology of the male copulatory organ and vagina. Observations on the haptoral sclerotized elements of these parasites by means of phase contrast microscopy revealed the presence of a sheath-like structure relating to the ventral anchor, a feature that supplements the generic diagnosis of Characidotrema. Maximum Likelihood and Bayesian analyses of the large subunit (28S) rDNA sequences recovered Characidotrema species isolated from the two Brycinus hosts as monophyletic, and indicated a closer relationship of this group to monogeneans parasitizing African cyprinids (Dactylogyrus spp.) and cichlids (species of Cichlidogyrus Paperna, 1960, Scutogyrus Pariselle & Euzet, 1995, and Onchobdella Paperna, 1968) than to those from catfishes (species of Quadriacanthus Paperna, 1961, Schilbetrema Paperna & Thurston, 1968 and Synodontella Dossou & Euzet, 1993). The overall agreement between the morphological diversification of the MCOs and the molecular tree observed in this study indicates that significant phylogenetic signals for clarifying relationships among species of Characidotrema are present in the characteristics of the MCO. Conclusions It seems that intra-host speciation is an important force shaping the present distribution and diversity of Characidotrema but further studies are necessary to confirm this hypothesis and assess questions related to the phylogeny of these parasites. To identify potential co-speciation events, co-phylogenetic analyses of these monogeneans and their alestid hosts are required.

Mass mortality of fishes was reported at the Adyar estuary, South India, during November 2017. The probable reasons for fish mortality are analyzed in this paper. Critical assessments on water quality parameters including the metal concentrations, nutrients, and histology of gills and liver of fish (Mugil cephalus) isolated from the impact zone were performed. Among the metals observed, chromium showed levels (3.64 ± 0.001 mg L-1) much above the average permissible limits (0.1 mg L-1). The measured values of physico-chemical parameters in the impact zone are as follows: dissolved oxygen 4.7 ± 0.22 mg L-1, total alkalinity 132 ± 4 CaCO3 mg L-1, salinity 5.3 ± 0.3 PSU, temperature 27.8 ± 0.16 °C, nitrate, 1.66 ± 0.48 mg L-1, nitrite 0.01 ± 0.0008 mg L-1, ammonia 0.03 ± 0.001 mg L-1, phosphate 1.52 ± 0.002 mg L-1, and silicate 13.85 ± 3.1 mg L-1. The low salinity could have escalated the toxicity of the metal. In addition, histology of gills and liver showed cellular necrosis, epithelial lifting, hyperplasia, edema, mucous cell proliferation in the gills, cytoplasmic vacuolation of hepatocytes, and degeneration of liver which reveal that chromium toxicity is the most probable cause for mass mortality.

The paper presents a description of Paradiplozoon bingolensis sp. n. from the gills of Garra rufa Heckel, 1843 (Cyprinidae) collected from the Göynük Stream, a tributary of the Murat River, Turkey. This is the first diplozoid species to be described from G. rufa. P. bingolensis is distinguished from the other valid species in the genus by the combination of the morphology of the sclerites of its clamps and by the size of the central hooks. Even molecular characterization based on variability of the second internal transcribed spacer (ITS2) of the ribosomal DNA region provided additional support of separation of this new species from the valid ones. The sequences were compared with previously published ITS2 sequences of other diplozoid species. Subsequent analysis demonstrated the uniqueness of this new parasite species and revealed uncertainties in the current taxonomic division of the Diplozoidae that are commented in the text.

Mining effluents are a potential source of toxic metals in the surrounding aquatic ecosystem and pose a potential health risk to humans from fish consumption. The objective of this paper is to assess the impact of the long-term Dabaoshan mining operation on heavy metal accumulation in different fish species. Heavy metal accumulation (lead (Pb), cadmium (Cd), zinc (Zn), and copper (Cu)) in four tissues (liver, muscle, intestine, and gills) of five carp species (Hypophthalmichthys molitrix, Ctenopharyngodon idellus, Megalobrama amblycephala, Aristichthys nobilis, and Carassius auratus auratus) from two fishponds exposed to effluent waters from Dabaoshan mine, South China. The bioaccumulation factor (BAF) and target hazard quotients were calculated to assess potential health risks to local residents through fish consumption. Levels of heavy metals varied depending on the analyzed tissues. C. auratus auratus accumulated the higher Pb, Cd, Zn, and Cu in the intestine compared with other fish species. Liver of all five species contained high concentrations of Pb, Cd, Zn, and Cu. The BAF for the studied metals showed a descending order of Cd > Zn > Cu > Pb for fishpond 1 and Zn > Cd > Cu > Pb for fishpond 2. Risk assessments suggested that potential human health risk may be present due to high Pb and Cd concentration in the muscle of some fish species exceeding the national and international limits, although the target hazard quotients were less than one.

In this study, a total of 120 fish specimens of common carp (Cyprinus carpio), were caught at four different stations in Shatt Al-Arab (Hareer, Garmat Ali, Al-Maqal and Abual-Khasib). The histological changes in the gills of fish were detected microscopically. Results show that the Shatt Al-Arab is polluted by some different sources of pollutants including power stations, paper industry, oil refineries, petrochemical industry, chemical fertilizer companies and the sewage system and overfishing and the application of pesticides. As a result of these analyses, histopathological changes in the gills of fish specimens, such as hyperplasia, loss of regular shape of secondary lamellae, separation of lamellar epithelium, clavate structure, atrophy of secondary gills lamellae, necrosis, dilation of lamellar capillaries, loss of secondary lamellae, fusion of secondary lamellae, edema, proliferation of cartilage in primary lamellae and curving of primary lamellae, were observed. The histopathological changes in fish gill samples from the Hareer region were much more prevalent than samples caught from other stations.

Dongting Lake is located in the northeastern part of Hunan Province in the People’s Republic of China. The lake covers about 2,740 km 2 , making it the second-largest freshwater lake in China. The lake is an important source of freshwater fish. However, it is also an endemic region of schistosomiasis. Oncomelania hupensis gredler is the only lodging host of schistosome and plays a vital role in schistosomiasis spread. To kill Oncomelania hupensis gredler large amounts of sodium pentachlorophenate (NaPCP), which was found containing polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) impurities, had been sprayed for over 30 years (Bao et al., 1995). PCDD/Fs are chemically stable, persistent hydrophobic organic chemicals and are thought to be biomagnified via the food chain. Those isomers with chlorinated substitutions in the 2, 3, 7, and 8 positions are thought to pose a risk to human health due to their toxicity, carcinogenic potency, and potential effects on animal reproductive and immunological systems. Although the spraying of Na-PCP has been prohibited in the region since 1996, recent studies have indicated that the sediments, soils, and breast milk around Dongting Lake area are contaminated by PCDD/Fs (Zheng et al., 1997; Gao et al., 2005; Zheng et al., 2003). Fish are usually used as bioindicators for the environmental medium and food webs, and can reflect the PCDD/ Fs contaminant status. Moreover, humans are consumers of fish, and exposure assessments now routinely consider fish ingestion as a potential route of human exposure to chemicals in the environment. Consequently, monitoring programs establish limits for the maximum content of these toxicants in a variety of foods. An important regulation is that the European Community (EC) has set a limit of 4 pg/g wet weight of toxic equivalents (WHOPCDD/F-TEQ) for the muscle meat of fish and fishery products (EC, 2001). As do most organic contaminants, PCDD/Fs accumulate in certain organs with the highest proportions found in the fish liver (Wu et al., 2001). This paper describes the levels and bioaccumulation profiles of PCDD/Fs in different fish species livers and gills from Dongting Lake region.

WOS: 000352820300006 PubMed: 25877641 In this paper, concentrations of trace metals such as Cr, Mn, Fe, Ni, Cu, As, Se, Ag, Cd and Pb were determined in Mugil cephalus of the middle Black Sea coasts by employing inductively coupled plasma mass spectrometry (ICP-MS) and microwave digestion technique. Different parts of fish samples were analysed separately such as the gill, muscle and liver. The accuracy of the results has been checked by using a certified reference material (DORM-4). The highest trace metal values determined in different parts of fish were Cr in muscle tissue (0.416 mu g/g), Mn in gill tissue (52.246 mu g/g), Fe in muscle tissue (11.899 mu g/g), Ni in muscle tissue (108.057 mu g/g), Cu in liver tissue (261.911 mu g/g), As in liver tissue (4.162 mu g/g), Se in liver tissue (11.418 mu g/g), Ag in liver tissue (0.323 mu g/g), Cd in liver tissue (1.11 mu g/g) and Pb in gill tissue (3.047 mu g/g). These results were also compared with various relevant literature and guidelines. Giresun UniversityGiresun University [FEN-BAP-A-220413-49] This study was supported by Giresun University ( No: FEN-BAP-A-220413-49) Scientific Research Project.

Redescription of Myxobolus pyramidis Chen, 1958, from gill lamellae of allogynogenetic gibel carp, Carassius auratus gibelio (Bloch), is presented in this paper to complete Chen's description. The diagnostic characters of the myxosporidia are: ovoid round, greyish-white polysporous plasmodia, averaging (159 +/- 21)x(72 +/- 6.5) mu m in size; spore pyriform in front view with smooth surface and symmetrical valves, convex-shaped in sutural view with straight and thick sutural line, averaging (10.5 +/- 1.1)x(10.3 +/- 0.9)x(6.1 +/- 0.2) mu m in size; two equal pyriform polar capsules averaging (5.5 +/- 0.7)x(3.5 +/- 0.2) mu m in size with distinct intercapsular process and polar filament wounded in five to six coils. The histological effects of the pathogen were observed by light microscopy, and the parasite-host relationship was discussed.

Prolonged exposure of fish to a variety of pollutants can induce stress (Adams 1990). These include municipal effluent, PCBs, pesticides, polycyclic aromatic hydrocarbons (PAHs), heavy metals in mine tailings, effluent from pulp and paper mills, etc. Manifestations of stress, which might culminate in a change of homeostasis, include reduced feed intake and impairment of growth and reproductive potential accompanied by immunosuppression. All of these factors could influence survival. Biomonitoring methods have been devised to assess the impact of pollution on fish health by comparing potentially contaminated and reference samples of the same species. These include body and organ indices, histopathological and hematological methods and the prevalence, abundance and diversity of parasites (Adams 1990; Khan and Thulin 1991; Overstreet 1993).

Chromatographic and immunological evidence indicates that a vasopressin-like peptide might be present in the CNS of Aplysia californica, and that this peptide may be involved in modulating the behaviour of the gill. Immunocytochemical techniques using antisera raised against various vasopressin-like peptides were used to localize the sites containing these peptides in the CNS of Aplysia. Vasopressin-like immunoreactivity was found to be restricted to one single neuron in the abdominal ganglion and two small neurons located bilaterally in each pedal ganglion. Immunoreactive fibres were present in the neuropile of the abdominal, pedal, pleural and cerebral ganglia, but not in the buccal ganglion. The identification of these neurons provides a morphological localization for vasopressin-like substances detected previously in CNS extracts of Aplysia californica. In addition, the possibility of electrophysiological studies involving the immunoreactive neurons identified in the present paper will allow a more direct approach to study the physiological role of vasopressin-like peptides in Aplysia.

The brown shrimp, Penaeus californiensis Holmes, is an Eastern Pacific species which is geographically distributed from San Francisco, California, USA, including the Gulf of California, to Callao, Peru. In Mexico and particularly in the Pacific Coast, this crustacean supports 75% of the commercial catch of shrimp. Knowledge of the distribution of metals in isolated tissues of marine organisms is useful in order to identify specific organs that may be particularly selective and sensitive to accumulation of heavy metals. This paper presents data on the levels of Fe, Mn, Ni, Cu, Cd, and Zn in five different tissues of the P. californiensis populations from the northwest coast of Mexico. Additionally, the accumulation of metals by males and females is examined. 16 refs., 2 figs., 1 tab.