P. W. Kania

Comparative effects of four feed types on white spot disease susceptibility and skin immune parameters in rainbow trout, Oncorhynchus mykiss (Walbaum)

The effects on rainbow trout, Oncorhynchus mykiss (Walbaum), immune parameters by differently formulated fish feed types containing immunostimulants have been tested in a double-blind, duplicated and controlled study performed over 50 days. A total of 800 rainbow trout (10-12 g) were kept in eight duplicate fish tanks (each containing 100 fish) and fed at a daily feeding rate of 1.5% of the biomass. The feed types were (1) control feed (C) without additives, (2) feed containing beta-glucan, nucleotides, manno-oligosaccharides (MOS), vitamins C and E (GNMCE), (3) feed containing probiotic bacteria and plant extracts (PP) and (4) feed with nucleotides, manno-oligosaccharides, vitamins C and E (NMCE). Plasma lysozyme activity was increased in fish fed two feed types (GNMCE and NMCE) but slightly depressed in fish fed PP. A non-significant trend for a higher mucous cell density at days 30 and 50 was shown in all fish receiving feeds with additives compared to the control group. All fish became infected with Ichthyophthirius multifiliis when exposed, but fish fed GNMCE showed a significantly lower infection both at days 30 and 50. Expression of genes encoding C3 and MHCII was significantly up-regulated in fish fed GNMCE for 50 days, and the expression of genes coding Hepcidin was significantly down-regulated in fish fed NMCE for 50 days. Beta-glucan was the single component, when used in combination with other feed ingredients, which was found associated with increased parasite resistance, increased lysozyme and immune gene up-regulation.

Comparative protection of two different commercial vaccines against Yersinia ruckeri serotype O1 and biotype 2 in rainbow trout (Oncorhynchus mykiss).

Differentially extended specific protection by two commercial vaccines against Yersinia ruckeri serotype O1 biotype 2 was studied following 30s immersion exposure. Rainbow trout were challenged intra-peritoneally (i.p.) with Y. ruckeri serotype O1, biotype 2 (≈10(6) to 10(7)CFU/fish) at 4, 6 and 8 months after vaccination with vaccines containing either biotype 1 (AquaVac(®) ERM) or both biotypes 1 and 2 (AquaVac(®) RELERA™). The specific pattern of vaccine-mediated protection was evaluated by relative percentage survival (RPS) analysis at 4 and 6 months post-vaccination and by obtaining gross pathological observations at 4 and 8 months respectively. We determined specific significant and superior protection in terms of increased survivability in AquaVac(®) RELERA™ vaccinated fish and observed correspondingly fewer pathological changes. The challenge trials indicated a longer protection for at least 6 months without any booster vaccination. A specific and adaptive response induced by AquaVac(®) RELERA™ vaccine against Y. ruckeri biotype 2 was clearly indicated. In addition, some degree of cross protection rendered by AquaVac(®) ERM containing biotype 1 during infection with Y. ruckeri biotype 2 was also noted.

Emerging Pseudoterranova decipiens (Krabbe, 1878) problems in Baltic cod, Gadus morhua L., associated with grey seal colonization of spawning grounds.

Third-stage larvae of Pseudoterranova decipiens (Krabbe, 1878) and a number of congeneric species (P. krabbei, P. bulbosa, P. azarasi, P. cattani) (McClelland 2002) are anisakid nematodes with the vernacular name cod worm or seal worm. They have a zoonotic potential seen as their ability to infect humans ingesting undercooked infected fish products (Skirnisson 2006). The final hosts harbouring adult worms in their stomachs and intestine comprise various species of seals. Eggs released from the female worm pass with faeces into the marine environment where they hatch and subsequently third-stage larvae (Køie et al. 1995; McClelland 2002) become ingested by freeliving crustaceans and polychaetes which serve as the first transport host. These are then eaten by marine fish in which third-stage larvae penetrate primarily the musculature. A large range of fish species may host this parasite stage (Hafsteinsson & Rizvi 1987; McClelland 2002) and thereby serve as the second transport host. When seals ingest infected fish, the two final moults of the worm occur in their stomach wherein worms obtain maturity. These nematodes have a wide distribution in marine waters worldwide. Thus, the North Sea, East Atlantic, West Atlantic, Pacific, Arctic and Antarctic waters support significant populations of larvae in fish (Jensen, Andersen & Desclers 1994; Due & Curtis 1995; Olafsdottir & Hauksson 1998; Hauksson 2002; McClelland & Melendy 2011) and the adult stages in seals (Aspholm et al. 1995; Marcogliese, Boily & Hammill 1996; Mattiucci et al. 1998; Olafsdottir & Hauksson 1998; Stobo et al. 2002). However, the parasite has been considered absent or extremely rare in the Baltic cod population (Kahl 1939; Möller 1975; Fagerholm 1982; Thulin, Höglund & Lindesjö 1989; Myjak et al. 1994) which may be explained by a low abundance of seals around the main cod spawning and foraging grounds in the Baltic area. However, during the last decade, grey seals, Halichoerus grypus L., have colonized a small group of islets (Ertholmene) located near the main spawning ground of the Baltic cod in ICES subdivision 25. Local fishermen complained about seals feeding on the local fish stocks. In addition, infection of fish in the area with cod worms was considered possible, which made it relevant to implement a preliminary investigation on the occurrence of cod worms in a local cod population caught east of Bornholm. The data were compared to previously unpublished data from the same area in 1982–83. Study area. Fish examined were obtained from local commercial fishermen working in the ICES subdivision 25 immediately east of the island of Bornholm in the Baltic Sea. Fish. The survey in 1982–83 was performed by conducting a full parasitological investigation Correspondence Kurt Buchmann, Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen, Stigbøjlen 7, DK-1870 Frederiksberg C., Denmark (e-mail: kub@life.ku.dk)

Occurrence of gyrodactylids on wild Atlantic salmon, Salmo salar L., in Danish rivers.

Three hundred and one parr of wild salmon, Salmo salar L., from three river systems in Denmark were examined in December 2005 and August 2006 for gyrodactylid infections. The species determination was done by morphological analyses of the opisthaptoral hard parts and molecular analyses of the internal transcribed spacer (ITS) region using PCR restriction fragment length polymorphism (RFLP) and sequencing. Five species of the genus Gyrodactylus were found: Gyrodactylus derjavini, Gyrodactylus teuchis, Gyrodactylus truttae, Gyrodactylus arcuatus and Gyrodactylus salaris. The parasite species G. derjavini dominated over G. teuchis and G. truttae and only one specimen of G. arcuatus and one specimen of G. salaris were recovered. This specimen of G. salaris had the same mutation in the ITS-region as a previously described non-pathogenic Danish G. salaris variant. The prevalence of gyrodactylids on the salmon ranged from 0% to 100% but the mean abundance never exceeded 12.8.

Population dynamics and host reactions in young foxes following experimental infection with the minute intestinal fluke, Haplorchis pumilio

BackgroundInfections with fish-borne zoonotic trematodes (FZT) including the minute intestinal fluke, Haplorchis pumilio, are highly prevalent in Southeast Asia. However, little is known about the infection dynamics and clinical symptoms in the final hosts which include a range of animal species and man. We aimed to generate such information using an experimental model with H. pumilio in foxes.MethodEight commercially bred foxes were each orally infected with 2000 H. pumilio metacercariae. Another three foxes served as uninfected controls. Faecal examination for eggs was performed twice weekly. The body weight was measured, standard haematological and biochemical analysis were performed regularly. All foxes were euthanized at day 56 post infection (p.i.). Adult worms were quantified and location in the small intestine noted.ResultsAnorexia was observed in all infected foxes starting day 12 p.i. and lasting for approximately a week. A weight loss was noticed in the infected group in weeks 3–6 p.i. Five of eight infected foxes excreted H. pumilio eggs day 9 p.i. onwards, the remaining three started on day 13 p.i. Mean (± SD) faecal egg counts showed an initial peak at day 16–20 with a maximum of 1443 ± 1176 eggs per gram of faeces (epg), where after a stable egg output around 4–500 epg was seen. Worm burdens ranged between 116–2070 adult flukes with a mean (± SD) worm recovery of 948 ± 666. The majority of worms were found in the lower part of the jejunum. Total white blood cell and lymphocyte counts were significant lower in the infected group from first week p.i. onwards and throughout the study period. A significantly lower level of eosinophils was found in week 2 p.i. and transient anaemia was seen in week 2 and 4 p.i.ConclusionThis study showed a short prepatency period, an initial peak in egg excretion, establishment of infection in all animals with predilection site in the lower jejunum and a marked but transient clinical effect of the infection. The findings on egg output and prepatency should be taken into consideration when control programs targeting dogs and other reservoir hosts are to be established.

Contracaecum osculatum and other anisakid nematodes in grey seals and cod in the Baltic Sea: molecular and ecological links

Populations of grey seals (Halichoerus grypus), sprats (Sprattus sprattus) and cod (Gadus morhua) in the Baltic Sea are relatively stationary. The present work, applying classical and molecular helminthological techniques, documents that seals and cod also share a common parasite, the anisakid nematode Contracaecum osculatum, which uses seals as the final host and fish as transport hosts. Sequencing mitochondrial genes (COX1 and COX2) in adult worms from seals and third-stage larvae from livers of Baltic fish (sprats and cod), showed that all gene variants occur in both seals and fish. Other anisakid nematodes Pseudoterranova decipiens and Anisakis simplex are also found in both seals and cod in the Baltic Sea, but at much lower rates. The Baltic grey seal population was left at a critically low level (comprising a few hundred individuals) during the latter part of the 20th century, but since the year 2000 a marked increase in the population has been observed, reaching more than 40,000 individuals at present. Ecological consequences of the increased seal abundance may result from increased predation on fish stocks, but recent evidence also points to the influence of elevated parasitism on fish performance. Contracaecum osculatum larvae preferentially infect the liver of Baltic cod, considered a vital organ of the host. Whereas low prevalences and intensities in cod were reported during the 1980s and 1990s, the present study documents 100% prevalence and a mean intensity of above 80 worms per fish. Recent studies have also indicated the zoonotic potential of C. osculatum larvae in fish, following the consumption of raw or under-cooked fish. Therefore the present work discusses the impact of parasitism on the cod stock and the increasing risk for consumer health, and lists possible solutions for control.

Positive correlation between Aeromonas salmonicida vaccine antigen concentration and protection in vaccinated rainbow trout Oncorhynchus mykiss evaluated by a tail fin infection model

Rainbow trout, Oncorhynchus mykiss (Walbaum), are able to raise a protective immune response against Aeromonas salmonicida subsp. salmonicida (AS) following injection vaccination with commercial vaccines containing formalin-killed bacteria, but the protection is often suboptimal under Danish mariculture conditions. We elucidated whether protection can be improved by increasing the concentration of antigen (formalin-killed bacteria) in the vaccine. Rainbow trout juveniles were vaccinated by intraperitoneal (i.p.) injection with a bacterin of Aeromonas salmonicida subsp. salmonicida strain 090710-1/23 in combination with Vibrio anguillarum serotypes O1 and O2a supplemented with an oil adjuvant. Three concentrations of AS antigens were applied. Fish were subsequently challenged with the homologous bacterial strain administered by perforation of the tail fin epidermis and 60-s contact with live A. salmonicida bacteria. The infection method proved to be efficient and could differentiate efficacies of different vaccines. It was shown that protection and antibody production in exposed fish were positively correlated to the AS antigen concentration in the vaccine.