Non-parasitized Fish Research Articles

Host-gut microbiota interactions shape parasite infections in farmed Atlantic salmon.

Animals and their associated microbiota share long evolutionary histories. However, it is not always clear how host genotype and microbiota interact to affect phenotype. We applied a hologenomic approach to explore how host-microbiota interactions shape lifetime growth and parasite infection in farmed Atlantic salmon (Salmo salar). Multi-omics data sets were generated from the guts of 460 salmon, 82% of which were naturally infected with an intestinal cestode. A single Mycoplasma bacterial strain, MAG01, dominated the gut metagenome of large, non-parasitized fish, consistent with previous studies showing high levels of Mycoplasma in the gut microbiota of healthy salmon. While small and/or parasitized salmon also had high abundance of MAG01, we observed increased alpha diversity in these individuals, driven by increased frequency of low-abundance Vibrionaceae and other Mycoplasma species that carried known virulence genes. Colonization by one of these cestode-associated Mycoplasma strains was associated with host individual genomic variation in long non-coding RNAs. Integrating the multi-omic data sets revealed coordinated changes in the salmon gut mRNA transcriptome and metabolome that correlated with shifts in the microbiota of smaller, parasitized fish. Our results suggest that the gut microbiota of small and/or parasitized fish is in a state of dysbiosis that partly depends on the host genotype, highlighting the value of using a hologenomic approach to incorporate the microbiota into the study of host-parasite dynamics.IMPORTANCEStudying host-microbiota interactions through the perspective of the hologenome is gaining interest across all life sciences. Intestinal parasite infections are a huge burden on human and animal health; however, there are few studies investigating the role of the hologenome during parasite infections. We address this gap in the largest multi-omics fish microbiota study to date using natural cestode infection of farmed Atlantic salmon. We find a clear association between cestode infection, salmon lifetime growth, and perturbation of the salmon gut microbiota. Furthermore, we provide the first evidence that the genetic background of the host may partly determine how the gut microbiota changes during parasite-associated dysbiosis. Our study therefore highlights the value of a hologenomic approach for gaining a more in-depth understanding of parasitism.

Effects of parasites on growth pattern of African catfish (<i>Clarias gariepinus</i>) in Omi Dam, Omi, Yagba West Local Government Area, Kogi State

The study was carried out using 506 Clarias gariepinus specimens over a period of one year, from Omi Dam (Latitudes 8o34’N – 8o38′N, Longitudes 6o37′E – 6o42′E) Omi, Kogi State, Nigeria. Standard methods were used to determine length-weight relationship, condition factor, and parasitic infestation of the fish in the dam. Generally, fish growth for non-parasitized fishes was positively allometric and condition factor is >1.5, while parasitized fishes had negative allometric growth and condition factor is <1.The negative allometry for parasitized shows the fish weight decreases less quickly than the length while positive allometry for non-parasitized fish mean the fish weight increases than the length of the fish. The effect of parasites in the life of parasitized C. gariepinus was found to probably be a major factor responsible for the loss of weight in parasitized fishes and this affected morphometric values(b) in which body weight was an index.

Occurrence of parasites, length-weight relationship and condition factor of Sarotherodon melanotheron (Ruppel, 1852) in Ilaje Local Government Area of Ondo State, Nigeria

Abstract. Fish parasites immensely affect fish production given their potential impact on profitability and also cause of zoonotic diseases in many parts of the world. This study therefore investigated the effect of fish parasites on growth and well-being. It also evaluated the body variation between parasitized and non- parasitized fish. The study was carried out in five rivers from Ipare, Aboto, Alape, Igbanran and Igbokoda. The length of parasitized fish samples was 13.00±1.26cm, 14.02±1.94cm and 13.51±1.67cm in male, female and combined sexes, respectively, while the weight was 43.29±12.51g, 53.86±21.52g and 48.57±17.92g in male, female and combined sexes, respectively. Also, the average total length (TL) of the non-parasitized fish was 12.92±1.13cm, 14.72±1.53cm and 13.67±1.57cm in male, female and combined sexes, respectively, while the weight was 38.86±9.33g, 62.09±16.50g and 48.49±17.12g in male, female and combined sexes, respectively. The regression coefficient (b) of length and weight of parasitized samples was b=2.12 (male), b=2.15 (female) and b=2.64 (combined sexes), while the regression coefficient ‘b’ recorded for the length-weight relationship of non-parasitized samples was 3.25, 2.49 and 2.78 for male, female and combined sexes, respectively, indicating allometric growth. Also, Senga sp and Nematodes were the most prevalent parasites with average volume of 2.33±0.58 and 2.00±0.00 on both male and female fish, respectively. The regression analysis revealed that the occurrence of parasites did not have significant effect (P>0.05) on the length and weight of S. melanotheron from Ilaje Local Government Area of Ondo State, Nigeria. This study also established similarity in morphology among populations of male and female as well as parasitized and non-parasitized Sarotherodon melanotheron from the study area.

EXPERIMENTAL ELUCIDATION OF THE LIFE CYCLE OF DREPANOCEPHALUS SPATHANS (DIGENEA: ECHINOSTOMATIDAE) WITH NOTES ON THE MORPHOLOGICAL PLASTICITY OF D. SPATHANS IN THE UNITED STATES.

The echinostomatid Drepanocephalus spathans (syn. Drepanocephalus auritus) parasitizes the double-crested cormorant Phalacrocorax auritus. In North America, the marsh rams-horn snail Planorbella trivolvis and ghost rams-horn snail Biomphalaria havanensis serve as snail intermediate hosts, both of which inhabit catfish aquaculture ponds in the southeastern United States. Studies have demonstrated D. spathans exposure can be lethal to juvenile channel catfish Ictalurus punctatus. Two studies were undertaken to elucidate the life cycle of D. spathans to establish a developmental time line. In both studies, D. spathans cercariae collected from naturally infected P. trivolvis individuals were used to infect channel catfish fingerlings, which were then fed to double-crested cormorants (DCCOs) that had been pharmaceutically dewormed. In study 1, laboratory-reared P. trivolvis and B. havanensis individuals were placed in aviary ponds with experimentally infected DCCO and examined bi-weekly for release of cercariae. Trematode eggs were observed in the feces of exposed birds 3 days post-infection. Birds were sacrificed 18 days post-exposure (dpe), and gravid adults morphologically and molecularly consistent with D. spathans were recovered. Snails from the aviary pond were observed shedding D. spathans cercariae 18-54 dpe. In study 2, trematode eggs were observed in the feces of exposed DCCOs beginning 8 dpe. Once eggs were observed, birds were allowed to defecate into clean tanks containing naïve laboratory-reared P. trivolvis individuals. Additionally, eggs from experimental DCCO feces were recovered by sedimentation and placed in an aquarium housing laboratory-reared P. trivolvis individuals. Birds in study 2 were sacrificed after 60 days, and gravid D. spathans specimens were recovered. Snails from the experimental DCCO tanks shed D. spathans cercariae 89-97 dpe. Lastly, trematode eggs were isolated and observed for the hatching of miracidia, which emerged on average after 16 days at ambient temperatures. No D. spathans adults were observed in control birds fed non-parasitized fish. This is the first experimental confirmation of the D. spathans life cycle, resolving previously unknown developmental time lines. In addition, the effects of fixation on adult trematode morphology were assessed, clarifying reports of pronounced morphological plasticity for D. spathans.

Implications of Certain Biochemical Metabolites and Meta-analysis on the Fish Liza parsia (Hamilton, 1822) with Isopod Parasite Norileca indica

Liza parsia (Goldspot Mullet) is an important fishery resource in estuarine areas. This fish is in high demand among the local consumers due to its affordability in price and deliciousness. Unfortunately, this fish population is also highly affected by crustacean isopod parasites. One of the most important parasites is Nerolica indica which causes economic loss to fishermen. The mechanical damages to parasitized fish and secondary biochemical metabolites in the diseased fish will cause serious complications to consumers. The obligate isopod ectoparasites vary in size, and many of them continue their complete or partial life cycle in the host and affect the host's anatomy and physiology. The isopod parasites attach to the body surface, buccal cavity, and branchial cavity. These surface-attached parasites scratch the skin and feed on the blood; buccal cavity parasites often cut the tongue and replace it; the brachial cavity parasites harbour between the gills and make a serious effect on fish respiration. The affected fish loses its weight and body fluid continuously and eventually dies. The aim of this study was primarily to assess the biochemical variations between healthy and parasite-infested fish. A significant reduction in total proteins, glucose, and cholesterol levels were observed in the infected fish. The monounsaturated fatty acid (MUFA) and polyunsaturated fatty acid (PUFA) of parasitized fish were also significantly reduced when compared to non-parasitized fish. The objective of this study was to analyse these biochemical metabolite’s variations and critically assess the metabolites roles in the physiology and biochemistry of the infected fish.

Ectoparasites infecting Mugil curema (Mugiliformes: Mugilidae) in Amapá state estuary, in the northern Brazilian coast region.

In fish, one of the most important interactions is that occur between parasite species and environment. Wild fish interactions with parasites of different taxa can result in diseases for fish and consequently damages to the fishing industry. This study investigated the ectoparasite fauna in Mugil curema (Valenciennes, 1836), in Amapá state estuary, in Brazilian coast region. The parasite prevalence was 51.4%, and a total of 282 parasites were collected among Ligophorus brasiliensis (Abdallah, Azevedo & Luque 2009), Excorallana longicornis (Lemos de Castro, 1960), larvae of Gnathia sp. and Ergasilus atafonensis (Amado & Rocha, 1995), but L. brasiliensis was the dominant parasite. The parasites presented highly aggregated dispersion, except for Gnathia sp. that had a random dispersion. There was a predominance of hosts non-parasitized and parasitized by one species. The relative condition factor did not differ between parasitized and non-parasitized fish. The body size of hosts did not influence the parasite abundance. The community of ectoparasites consisted of low species richness with low infection levels. This is the first study on parasites of fish from the coast of the State of Amapá and is the first report of Gnathia sp. for M. curema.

Effects of the cranial parasite Tylodelphys sp. on the behavior and physiology of puye Galaxias maculatus (Jenyns, 1842).

Diplostomatid digeneans are well-known manipulators of the behavior of their intermediate hosts. Unencysted metacercariae of Tylodelphys sp. inhabit the cranial cavity of the fish Galaxias maculatus; however, to date they have not been documented to alter their host behavior. The goal of this study was to evaluate the potential effects of Tylodelphys sp. inhabiting the cranial cavity of Galaxias maculatus on host physiology and swimming behavior as well as its reaction to a simulated predation attempt. Blind experiments in the lab were carried out on 56 fish that were filmed individually. The Fulton condition factor (K) was used as an approximation of nutritional status and a respirometry chamber was used to evaluate oxygen consumption rates of fish. Of the 56 fish, 21 were parasitized by Tylodelphys sp. (mean intensity = 30, range from 1 to 101). Parasitized and non-parasitized fish were similar in condition factor and oxygen consumption rates. Furthermore, the oxygen consumption rate of G. maculatus was not correlated with the abundance of Tylodelphys sp. However, parasitized fish more frequently swam close to the water surface, whereas non-parasitized fish more frequently swam at intermediate depths. When faced with a simulated predator attack, unparasitized fish showed more frequent fleeing behavior as well as a more intense post-fleeing activity. Collectively, these results suggest that Tylodelphys sp. inhabiting the cranial cavity of fish may alter their behavior predisposing them to predation by birds.

Parasites in Leporinus macrocephalus (Anostomidae) of four fish farms from the western Amazon (Brazil).

This study evaluated the presence of metazoan parasites in Leporinus macrocephalus from four fish farms from the western Amazon (Brazil). In 160 fish examined, prevalence was 61.9%, and parasites found were: Urocleidoides paradoxus, Urocleidoides eremitus, Tereancistrum parvus, Jainus leporini, Procamallanus (Spirocamallanus) inopinatus, Rhabdochona (Rhabdochona) acuminata, Dolops discoidalis and Ergasilus sp., but U. paradoxus was the dominant parasite. Jainus leporini and Ergasilus sp. occurred only in L. macrocephalus from one fish farm, while U. paradoxus, U. eremitus and T. parvus were found in fish from three fish farms. Dolops discoidalis, P. (S.) inopinatus and R. (R.) acuminata occurred only in L. macrocephalus from two fish farms. Higher infection levels were caused by U. paradoxus, U. eremitus and P. (S.) inopinatus, which had an aggregated dispersion. There was positive correlation between abundance of parasites and the length of hosts. No difference in the condition factor of parasitized and non-parasitized fish were found. Such differences between fish farms were attributed to differences in management and quality of cultivation environments, and data indicate the need to adopt prophylactic measures in the fish farms to prevent diseases in the future. This was the first report of D. discoidalis and Ergasilus sp. for L. macrocephalus.

Parasites in farmed Piaractus brachypomus (Serrasalmidae) in the state of Acre, western Brazilian Amazonia

ABSTRACT This study investigated the parasite fauna in Piaractus brachypomus grown in fish farms in the state of Acre, in the western Brazilian Amazon. We examined 160 fish from four farms. Overall parasite prevalence was 66.9%. The fish were parasitized by Anacanthorus spathulatus, Mymarothecium viatorum, Anacanthorus penilabiatus, Clinostomum marginatum, Echinorhynchus jucundus and Henneguya sp., but monogenean species were the dominant parasites. Monogeneans showed an aggregated distribution pattern and there was a weak correlation between host size and abundance of M. viatorum and A. penilabiatus. No difference in the condition factor of parasitized and non-parasitized fish was detected. The fish of all farms had the gills parasitized by A. spathulatus and M. viatorum, but A. penilabiatus was found only in fish from two farms. Echinorhynchus jucundus, C. marginatum and Henneguya sp. were found in only one farm. The differences in parasitism level among the farms are attributable to differences in management and quality of cultivation environments.

Disruption of gut integrity and permeability contributes to enteritis in a fish-parasite model: a story told from serum metabolomics

BackgroundIn the animal production sector, enteritis is responsible for serious economic losses, and intestinal parasitism is a major stress factor leading to malnutrition and lowered performance and animal production efficiency. The effect of enteric parasites on the gut function of teleost fish, which represent the most ancient bony vertebrates, is far from being understood. The intestinal myxozoan parasite Enteromyxum leei dwells between gut epithelial cells and causes severe enteritis in gilthead sea bream (Sparus aurata), anorexia, cachexia, growth impairment, reduced marketability and increased mortality.MethodsThis study aimed to outline the gut failure in this fish-parasite model using a multifaceted approach and to find and validate non-lethal serum markers of gut barrier dysfunction. Intestinal integrity was studied in parasitized and non-parasitized fish by immunohistochemistry with specific markers for cellular adhesion (E-cadherin) and tight junctions (Tjp1 and Cldn3) and by functional studies of permeability (oral administration of FITC-dextran) and electrophysiology (Ussing chambers). Serum samples from parasitized and non-parasitized fish were analyzed using non-targeted metabolomics and some significantly altered metabolites were selected to be validated using commercial kits.ResultsThe immunodetection of Tjp1 and Cldn3 was significantly lower in the intestine of parasitized fish, while no strong differences were found in E-cadherin. Parasitized fish showed a significant increase in paracellular uptake measured by FITC-dextran detection in serum. Electrophysiology showed a decrease in transepithelial resistance in infected animals, which showed a diarrheic profile. Serum metabolomics revealed 3702 ions, from which the differential expression of 20 identified compounds significantly separated control from infected groups in multivariate analyses. Of these compounds, serum inosine (decreased) and creatine (increased) were identified as relevant and validated with commercial kits.ConclusionsThe results demonstrate the disruption of tight junctions and the loss of gut barrier function, a metabolomic profile of absorption dysfunction and anorexia, which further outline the pathophysiological effects of E. leei.

The parasitic isopod Mothocya nana drives dietary shifts and poorer condition of Brazilian silversides Atherinella brasiliensis.

Cymothoids are ectoparasites that may attach to various parts of the fish for molting and reproductive purposes, thus increasing the energetic costs of the host. This study investigated the influence of the parasitic isopod Mothocya nana on the physiological condition and diet of adult Brazilian silversides Atherinella brasiliensis at a sandy beach in southeastern Brazil. We collected 268 A. brasiliensis individuals, of which 230 fish were non-parasitized (mean ± SE total weight [TW] = 16.92 ± 0.38 g; total length [TL] = 127 ± 0.88 mm) and 38 were parasitized by up to 2 isopods (TW = 15.89 ± 0.79 g; TL = 126 ± 1.96 mm). Parasitic prevalence (P) and intensity (I) reached highest values in June 2015 (P = 20.88%; I = 1.31) and were slightly higher on males (P = 17.39%; I = 1.33) than on females (P = 13.07%; I = 1.27). Parasitized fish revealed poorer condition than non-parasitized ones, among which male hosts were especially burdened by M. nana's attachment. The condition factor, the eviscerated condition factor and the fullness index each showed a decreasing trend according to the parasite's development and offspring weight (i.e. increase in egg and larval weight). Parasitized and non-parasitized Brazilian silversides fed mainly on microcrustaceans, but the first group showed reduced phytoplankton intake and was associated with fewer trophic categories in comparison to non-parasitized fish. These dietary shifts revealed correlation with the poorer physiological condition reported for infected A. brasiliensis, whose decreased feeding efficiency is likely related to potential impairment of the filter-feeding mechanism and/or altered behaviour due to pressure atrophy and the increased energetic costs imposed by M. nana's development.

Parasitic Isopod Cymothoa eremita (Brünnich 1783) (Isopoda: Cymothoidae) Affects the Growth of Black Pomfret Parastromateus niger (Bloch 1795) in the Southeast Coast of India

The black pomfret Parastromateus niger is often favored host for infestation by the cymothoid, buccal attaching ectoparasite Cymothoa eremita. This investigation aimed to evaluate the health status of black pomfret by means of relative condition factor under the existing parasitic cymothoids. Prevalence of C. eremita on black pomfret fish was high (42%) but large (>300 mm) and small fish (< 250) showed significantly lesser prevalence than intermediate-sized host fish. The harmful effects of parasite infection on their hosts include basihyal damage, a loss in buccal cavity volume as a result of female cymothoid infestation, and a severe impact on host growth. The diet composition examination was a small indication to suggest a change in either feeding habits or diet of fish where parasitized and non-parasitized fish occupied the similar tropic niche. Due to an infestation of C. eremita in P. niger, the relative condition factor in infested was found to be lower than that of the uninfested fish. C. eremita infestation can impair growth and decrease feeding efficiency in hosts, subsequently affecting health condition and survival.

Hematology and biochemistry of Colossoma macropomum co-infected with Aeromonas hydrophila and monogenean Anacanthorus spathulatus after treatment with seed extract of Bixa orellana

This study evaluated the use in vitro and in vivo of Bixa orellana seed extracts on the hematological and biochemical parameters of Colossoma macropomum co-infected with bacterium and monogenean, Anacanthorus spathulatus. The extract presented antimicrobial and antiparasitic activity in vitro against the pathogens. Fish supported the toxicity test and in vivo assay used 180 fish distributed in six treatments in triplicate: non-parasitized fish non-injected with A. hydrophila; non-parasitized fish non-injected exposed to acetone 0.2%; parasitized fish injected non-treated with the extract; parasitized fish injected treated with 125 μg mL−1 of extract in 2 h bath for two consecutive days; parasitized fish injected treated with 250 μg mL−1 of extract in 2 h bath for two consecutive days; parasitized fish injected treated with 125 μg mL−1 of extract for 12 h. After last bath, the fish were examined. Acetonic extract showed minimal inhibitory concentration of 125 μg mL−1 against A. hydrophila in the in vitro test and 100% efficacy against monogenean with therapeutic baths in relation to control non-treated in the in vivo test. Aeromonas hydrophila infection did not cause mortality. The gross pathology analysis showed ascites and hemorrhagic liver, kidney and spleen. Increased hemoglobin concentration, mean corpuscular hemoglobin concentration and total number of erythrocytes was followed by a decrease in hematocrit percentage in non-treated fish compared to basal group. Lymphocytes from fish in the control group were higher than in the other groups. Glucose was higher in treated fish than that found in those of basal and control. The results demonstrated that B. orellana bath was an effective alternative to treat fish diseases.

Hematology and condition factor of tui chub and fathead minnow parasitized by nematode from Upper Klamath Lake, Oregon, USA.

This study evaluated the hematological profile and condition factor (Kn) of tui chub Siphateles bicolor and fathead minnow Pimephales promelas and their associations with larvae of Contracaecum sp. infection of the heart. A total of 30 tui chub and 17 fathead minnow were collected from Upper Klamath Lake, Oregon, USA, measured, and weighed and blood was drawn for hematological analysis. Nematode larvae parasitized tui chub with a prevalence of 50% and mean intensity of 1.40, while 11.8% of fathead minnow were parasitized at a mean intensity of 1.0. Non-parasitized tui chub were significantly larger than the parasitized fish, indicating that small fish could be easily predated by the definitive host, a piscivorous bird. Although the relatively large worm occupied a large portion of the atrium, the presence of the larvae did not affect tui chub Kn, possibly associated with low parasite intensity and a harmonic co-evolution. Only parasitized fathead minnow showed significant differences in red blood cell measurements (greater cell width and larger nuclei) compared to non-parasitized fish. Lymphocytes were the most common white blood cells found in tui chub, followed by neutrophils, monocytes, and periodic acid-Schiff positive granular leukocytes; in fathead minnow lymphocytes were followed by heterophils, monocytes, neutrophils and eosinophils. This study is the first report of Kn and description of blood cells and hematological parameters in these fish species.

Putative Roles for Metallothionein and HSP70 Genes in Relation with Heavy Metal Accumulation and Parasitic Cymothoid in the Fish Nemipterus furcosus.

To assess stress level induced by multiple stressors in aquatic organism, biomarkers have been adopted as early warning indicator due to their high accuracy, rapidity, and sensitivity. We investigated the effects of ectoparasitic isopod infection on heavy metal bioaccumulation (Fe, Cu, Zn, and Cd) in the fish Nemipterus furcosus and profiled the expression of metallothionein (MT) and heat shock proteins 70 (HSP70) genes of the fish host. Sixty individuals (parasitized and nonparasitized with Cymothoa truncata) were collected from three sites differing in the levels of anthropogenic activities off the South China Sea. Our results revealed no significant difference in heavy metal concentrations between infected and nonparasitized fish. We observed a positive correlation between heavy metal bioaccumulation in the fish host and anthropogenic activities. Accordingly, expression analysis of MT genes in fish liver showed significant differences in expression level between sampling sites, with lowest level in the least exploited site (Batu Rakit). A reverse pattern in HSP70 gene expression was demonstrated in fish muscle, showing the highest expression at Batu Rakit. While cymothoid infection in N. furcosus had no significant impact on fish MT gene expression, it resulted in a reduction of HSP70 level in liver of parasitized fish. These findings highlight the putative roles of MT in heavy metal assessment. Future studies should determine the kinetics of cymothoid infection and other potential stressors in characterizing the HSP70 gene expression profile.

Sea lampreys elicit strong transcriptomic responses in the lake trout liver during parasitism.

BackgroundThe sea lamprey (Petromyzon marinus) is a jawless vertebrate that parasitizes fish as an adult and, with overfishing, was responsible for the decline in lake trout (Salvelinus namaycush) populations in the Great Lakes. While laboratory studies have looked at the rates of wounding on various fish hosts, there have been few investigations on the physiological effects of lamprey wounding on the host. In the current study, two morphotypes of lake trout, leans and siscowets, were parasitized in the laboratory by sea lampreys and the liver transcriptomes of parasitized and nonparasitized fish were analyzed by RNA-seq (DESeq2 and edgeR) to determine which genes and gene pathways (Ingenuity Pathway Analysis) were altered by lamprey parasitism.ResultsOverall, genes encoding molecules involved in catalytic (e.g., enzymatic) and binding activities (factors and regulators) predominated the regulated gene lists. In siscowets, the top upregulated gene was growth arrest and DNA-damage-inducible protein and for leans it was interleukin-18-binding protein. In leans, the most significantly downregulated gene was UDP-glucuronosyltransferase 2A2 - DESeq2 or phosphotriesterase related - edgeR. For siscowets, the top downregulated gene was C-C motif chemokine 19 - DESeq2 or GTP-binding protein Rhes - edgeR. Gene pathways associated with inflammatory-related responses or factors (cytokines, chemokines, oxidative stress, apoptosis) were regulated following parasitism in both morphotypes. However, pathways related to energy metabolism (glycolysis, gluconeogenesis, lipolysis, lipogenesis) were also regulated. These pathways or the intensity or direction (up/downregulation) of regulation were different between leans and siscowets. Finally, one of the most significantly downregulated pathways in both leans and siscowets was the kynurenine (tryptophan degradation) pathway.ConclusionsThe results indicate a strong transcriptional response in the lake trout to lamprey parasitism that entails genes involved in the regulation of inflammation and cellular damage. Responses to energy utilization as well as hydromineral balance also occurred indicating an adjustment in the host to energy demands and osmotic imbalances during parasitism. Given the role of the kynurenine pathway in promoting immunotolerance in mammals, the downregulation observed in this pathway during parasitism may signify an attempt by the host to inhibit any feedback suppression of the immune response to the lamprey.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2959-9) contains supplementary material, which is available to authorized users.

Can the behaviour of threespine stickleback parasitized with Schistocephalus solidus be replicated by manipulating host physiology?

Sticklebacks infected by the parasitic flatworm Schistocephalus solidus show dramatic changes in phenotype, including a loss of species-typical behavioural responses to predators. The timing of host behaviour change coincides with the development of infectivity of the parasite to the final host (a piscivorous bird), making it an ideal model for studying the mechanisms of infection-induced behavioural modification. However, whether the loss of host anti-predator behaviour results from direct manipulation by the parasite, or is a by-product (e.g. host immune response) or side effect of infection (e.g. energetic loss), remains controversial. To understand the physiological mechanisms that generate these behavioural changes, we quantified the behavioural profiles of experimentally infected fish and attempted to replicate these in non-parasitized fish by exposing them to treatments including immunity activation and fasting, or by pharmacologically inhibiting the stress axis. All fish were screened for the following behaviours: activity, water depth preference, sociability, phototaxis, anti-predator response and latency to feed. We were able to change individual behaviours with certain treatments. Our results suggest that the impact of S. solidus on the stickleback might be of a multifactorial nature. The behaviour changes observed in infected fish might result from the combined effects of modifying the serotonergic axis, lack of energy and activation of the immune system.

Effect of Nanophyetus salmincola and Bacterial Co-Infection on Mortality of Juvenile Chinook Salmon.

The freshwater trematode Nanophyetus salmincola has been demonstrated to impair salmonid immune function and resistance to the marine pathogen Vibrio anguillarum, potentially resulting in ocean mortality. We examined whether infection by the parasite N. salmincola similarly increases mortality of juvenile Chinook Salmon Oncorhynchus tshawytscha when they are exposed to the freshwater pathogens Flavobacterium columnare or Aeromonas salmonicida, two bacteria that juvenile salmonids might encounter during their migration to the marine environment. We used a two-part experimental design where juvenile Chinook Salmon were first infected with N. salmincola through cohabitation with infected freshwater snails, Juga spp., and then challenged with either F. columnare or A. salmonicida. Cumulative percent mortality from F. columnare infection was higher in N. salmincola-parasitized fish than in nonparasitized fish. In contrast, cumulative percent mortality from A. salmonicida infection did not differ between N. salmincola-parasitized and nonparasitized groups. No mortalities were observed in the N. salmincola-parasitized-only and control groups from either challenge. Our study demonstrates that a relatively high mean intensity (>200 metacercariae per posterior kidney) of encysted N. salmincola metacercariae can alter the outcomes of bacterial infection in juvenile Chinook Salmon, which might have implications for disease in wild fish populations.

Dactylogyrus intermedius parasitism enhances Flavobacterium columnare invasion and alters immune-related gene expression in Carassius auratus.

The monogenean Dactylogyrus intermedius and the bacterium Flavobacterium columnare are 2 common pathogens in aquaculture. The objective of the present study was to examine the effect of prior parasitism by D. intermedius on the susceptibility of goldfish to F. columnare and to explore the potential immune mechanisms related to the parasite infection. A F. columnare challenge trial was conducted between D. intermedius-parasitized and non-parasitized goldfish. The F. columnare load in gill, kidney, spleen and liver were compared. The expression of immune-related genes (IL-1β2, TNF-α1, TGF-β, iNOS-a, C3 and Lyz) in gill and kidney of D. intermedius-only infected and uninfected control fish were evaluated. D. intermedius-parasitized goldfish exhibited higher mortality and significantly higher loads (3051 to 537,379 genome equivalents [GEs] mg(-1)) of F. columnare, which were 1.13 to 50.82-fold higher than non-parasitized fish (389 to 17,829 GEs mg(-1)). Furthermore, the immune genes IL-1β2, TNF-α1, iNOS-a and Lyz were up-regulated while the TGF-β and C3 were down-regulated in the gill and kidney of parasite-infected fish compared to the non-parasitized controls. The down-regulation TGF-β and C3 was especially noteworthy, as this might indicate the suppression of the host immune functions due to the parasitism by D. intermedius. Taken together, these data demonstrate that parasite infection can enhance bacterial invasion and presents a hypothesis, based on gene expression data, that modulation of host immune response could play a role.

Efecto del endoparásito Prosorhynchoides sp. (Trematoda: Bucephalidae) en la capacidad de nado sostenido del baunco Girella laevifrons (Osteichthyes: Kyphosidae)

This study analyzed whether the trematode Prosorhynchoides sp., at metacercaria stage, affects the sustained swimming capacity of the intertidal juvenile sea chub Girella laevifrons. Fifteen non-parasitized and 15 experimentally infested fish were used in this study. Wild fish were infested under laboratory conditions by cercaria from an infected mussel Perumytilus purpuratus. The parasite mainly infested the tail muscles of the fish. The maximum time of sustained swimming of each fish was measured through a swimming camera. Parasitized fish showed less time of sustained swimming and traveled less distance estimated than non-parasitized fish. This result was independent of fish body size, condition factor and trematode abundance. Therefore, Prosorhynchoides sp. affects the swimming capacity of juvenile G. laevifrons that might influence the migration and distribution of the fish.