R. H. Richards

Phylogenetic and antigenic characterization of new fish nodavirus isolates from Europe and Asia

Nodaviruses are widespread causative agents of viral nervous necrosis in fish. Based on the coat protein sequence, fish nodaviruses are categorized into four different genotypes. In this study, we present data on the phylogenetic and antigenic characterization of 12 new isolates, eight European and four of Asian origin, from farmed and wild species of fish. Phylogenetic analysis based on the nucleotide sequence (688 bases) of the coat protein classified the majority of these new isolates to the RGNNV genotype. Geographic or host-species specificities were not revealed by this study. Neutralizing assay experiments, further confirmed the genotypic classification, supporting the possibility that the different nodavirus genotypes can also be serologically distinguishable.

Attack site and resultant damage during aggressive encounters in Atlantic salmon (Salmo salar L.) parr

Fin rot is a term used to describe a range of changes in fins, from splitting and erosion to nodular thickening. It is common among farmed Atlantic salmon (Salmo salar) parr and is of considerable economic and welfare importance. Fin rot is known to commence when fins become damaged, for example, following attacks by conspecifics; however, not all fins are equally affected, the dorsal fin being much more frequently damaged. This study examined the hypothesis that fin rot is more prevalent in the dorsal fin because it is more frequently attacked during aggressive encounters with conspecifics. Behavioural observations showed that the dorsal and caudal fin areas are much more frequently attacked than other areas of the body and significantly more attacks directed at the dorsal fin area resulted in physical contact than attacks directed at other parts of the body. Fin damage, scored as the total amount of fin splitting was highest in the dorsal and pectoral fins despite the pectoral fins being attacked less frequently than the dorsal or caudal fins. This suggests that pectoral fins may have sustained damage through contact with the tank as well as through attacks. We conclude that at least one reason for the observed prevalence of fin rot in the dorsal fin of Atlantic salmon in aquaculture systems is that it is a preferred site of attack by conspecifics and because attacks are more likely to end in physical contact than attacks on other areas of the body and, thus, they sustain more damage.

Field trials on the efficacy of the organophosphorus compound azamethiphos for the control of sea lice (Copepoda: Caligidae) infestations of farmed Atlantic salmon (Salmo salar)

A study of the efficacy of azamethiphos (S-6-chloro-2,3-dihydro-2-oxo-1,3-oxazolo[4,5-b]pyridin-3-ylmethyl 0,0-dimethyl phosphorothioate) is described when used to treat Atlantic salmon (Salmo salar) infected with sea lice (Lepeophtheirus salmonis and Caligus elongatus) at several salmon farms on the west coast of Scotland. Prior to commencing the cage trials, relative lice sensitivity was evaluated through a series of in vitro exposures which demonstrated differences in the sensitivities of different lice populations to both azamethiphos and dichlorvos. Treatments were carried out by completely enclosing pens within tarpaulins, or by surrounding pens with a tarpaulin skirt, and were l h in duration. A range of treatment concentrations were studied which included 0.05, 0.1 and 0.2 mg−1 L azamethiphos, in addition to reference treatments with dichlorvos (0,0-dimethyl-2,2-dichlorovinyl phosphate) at a concentration of 1.0 mg−1 L. Lice response was measured before treatment, 1 h, 24 h, and 1 week after treatment. Azamethiphos was highly efficacious (85% or better) (Site 3) against adult and pre-adult lice, from a sensitive population, at a concentration of 0.05 mg−1 L where complete tarpaulins were used. Where resistant populations were tested, a concentration of 0.2 mg−1 L (complete tarpaulins) resulted in efficacies ranging from 7.1 to 82.1% (mean 57.1%) (Site 1) and 41 to 96.6% (mean 69.4%) (Site 2) against adult and pre-adult lice, and were generally more variable depending on local treatment conditions. Skirt treatments, tested only on resistant populations of lice, were found to be ineffective. A general trend was observed indicating that pre-adult I male lice were the most sensitive followed by, in order of sensitivity, pre-adult I females, pre-adult II females, pre-adult II males, adult males and adult females. Larval lice numbers, from both sensitive and resistant populations, appeared unaffected by treatment with azamethiphos following treatments with either complete tarpaulins or skirts. When used at the concentrations discussed above, fish tolerated treatments and did not display signs of acute mortality. However, hyperactivity was displayed by several of the treatment groups during treatments.

Minimum inhibitory concentrations of selected antimicrobial compounds against Flavobacterium psychrophilum the causal agent of rainbow trout fry syndrome (RTFS)

Abstract The in vitro susceptibilities of 48 isolates of Flavobacterium psychrophilum, the causal agent of rainbow trout fry syndrome (RTFS), to the major fish farming antimicrobial agents and to a selection of other antimicrobials were assessed using a broth microdilution method. These data were used along with previous published antibiograms for F. psychrophilum, drug serum and tissue levels and reports clinical effect in an attempt to predict the probable therapeutic efficacy. The results indicated that resistance to the most commonly used antimicrobial compounds was significant, but that doxycycline, sarafloxacin, enrofloxacin and florfenicol showed potential as candidate compounds for in vivo trials.

Nodavirus infection in Atlantic cod and Dover sole in the UK

E. (1992) Pathological changes in kidneys of dogs with natural Leishmania infection. Veterinary Parasitology 45, 33-47 POLI, A., ABRAMO, F., MANCIANTI, F., NIGRO, M., PIERI, S. & BIONDA, A. (1991) Renal involvement in canine leishmaniasis. Nephronl 57,444-452 PUMAROLA, M., BREVIK, L., BADIOLA, J., VARGAS, A., DOMINGO, M. & FERRER, L. (1991) Canine leishmaniasis associated with systemic vasculitis in two dogs. Journal of Comparative Pathology 105, 279-286 REAGAN, W. J. & REBAR, A. H. (1995) Platelet disorders. In Textbook of Veterinary Internal Medicine. Philadelphia, W. B. Saunders. pp 1964-1976 SAINZ, A., TESOURO, M. A., RODRIGUEZ, F., MAYORAL, I. & MAZZUCHELLI, F. (1995) Seroprevalence of Ehrlichia canis infections in police dogs in Spain. Preventive Veterinary Medicine 23, 179-182 SLAPPENDEL, R. J. (1988) Canine leishmaniasis. A review based on 95 cases in the Netherlands. Veterinary Quarterly 10, 1-16 SLAPPENDEL, R. J. (1989) Disseminated intravascular coagulation. In Kirks Current Veterinary Therapy X. Small Animal Practice. Philadelphia, W. B. Saunders. pp 451-457 SLAPPENDEL, R. J. & FERRER, L. (1998) Leishmaniasis. In Infectious Diseases of the Dog and Cat. Philadelphia, W. B. Saunders. pp 450-458 SLAPPENDEL, R. J., FRIELINK, R. A., MOL, J. A., NOORDZIJ, A. & HAMER, R. (1992) An enzyme-linked immunosorbent assay (ELISA) for von Willebrand factor antigen (vWf-Ag) in canine plasma. Veterinary Immunology and Immunopathology 33, 145-154 TABOADA, J. & MERCHANT, S. R. (1995) Protozoal and miscellaneous infections. In Textbook of Veterinary Internal Medicine. Philadelphia, W. B. Saunders. pp 384-397 TESOURO, M. A. (1984) Aspectos clinicos y laboratoriales de la leishmaniosis canina. Estudio epizootiologico en la provincia de Madrid. PhD thesis, Universidad Comlutense de Madrid, Madrid TESOURO, M. A., RODRIGUEZ, F., SAINZ, A. & JIMENEZ, F. (1992) Contribuciones al diagnostico y patocronia de la leishmaniosis canina (I). Informacion Veterinaria 125,40-46 VALLADARES, J. E., RUIZ DE GOPEGUI, R., RIERA, C., ALBEROLA, J., GALLEGO, M., ESPADA, Y., PORTUS, M. & ARBOIX, M. (1998) Study of haemostatic disorders in experimentally induced leishmaniasis in Beagle dogs. Research in Veterinary Science 64, 195-198 VARELA, F. (1992) Immunopatologia de la leishmaniosis canina: bases teoricas y aspectos practico. Premios Fundacion Purina, Columna Ediciones SA. pp11 -54 WARDROP, K. J., DHEIN, C. R., FRENIER, S. & MEYERS, K. M. (1989) Altered hemostasis in a dog with chronic renal failure. Journal oftheAmerican Animal Hospital Association 25, 325-329 WERNER, L. L., TURNWALD, G. H. & BARTA, 0. (1994) Immunologic and plasma protein disorders. In Small Animal Clinical Diagnosis by Laboratory Methods. Philadelphia, W. B. Saunders. pp 253-272 WILLIS, S. E., JACKSON, M. L., MERIC, S. M. & ROUSSEAUX, C. G. (1989) Whole blood platelet aggregation in dogs with liver disease. American Journal of Veterinary Research 50, 1893-1897

In situ hybridisation identifies the gill as a portal of entry for PKX (Phylum Myxozoa), the causative agent of proliferative kidney disease in salmonids.

Abstract PKX (Phylum Myxozoa) is an important pathogen affecting salmonid culture in Western Europe and North America. All of the available oligonucleotide probes developed for the PCR amplification of PKX DNA were examined for their ability to detect PKX in fixed tissue sections using in situ hybridisation. Out of the 12 probes examined, only four stained PKX in tissue sections. The specificity of these probes to PKX was examined by testing them individually against a range of myxosporean infections. One of the probes (1032) cross-reacted with Sphaerospora truttae infecting brown trout kidney and stained this parasite in tissue sections, while probe 6R stained stickleback DNA. The results from these studies allowed for an optimised, relatively rapid, in situ hybridisation protocol to be developed for PKX detection. Using this protocol, a preliminary study was conducted on the life history of the parasite in the rainbow trout Oncorhynchus mykiss. This demonstrated the presence of PKX in the gill arch 3 days after initial exposure in an enzootic river. It is suggested that a portal of entry for PKX is the gill. From here, it migrates to the kidney where the disease progresses as previously described.

Field trials to evaluate the efficacy of emamectin benzoate in the control of sea lice, Lepeophtheirus salmonis (Krøyer) and Caligus elongatus Nordmann, infestations in Atlantic salmon Salmo salar L.

Abstract Three field trials were conducted to evaluate the efficacy of emamectin benzoate as a treatment for sea lice, Lepeophtheirus salmonis (Kroyer) and Caligus elongatus (Nordmann), infestations on Atlantic salmon Salmo salar (L.). Trials were carried out at sea temperatures of 13.0–15.5°C and 7.2–8.5°C. Salmon naturally infested with sea lice, with mean weights of 438, 513 and 2662 g, respectively, were held in experimental pens on commercial sites. At day −1 or −2, 20 or 30 fish were sampled from each pen to determine pre-treatment numbers of lice. Emamectin benzoate was administered in-feed at a dose of 50 μg kg −1 biomass day −1 for 7 consecutive days. Sea lice were counted again on days 7, 14 and 21, and comparisons made with untreated control fish. Treatment with emamectin benzoate was effective against chalimus and motile stages of sea lice. In all three trials, treated groups were surrounded by pens of heavily infested fish and L. salmonis numbers increased over time on control fish by 87–284%, whereas over the same period, L. salmonis were reduced on treated fish by 68–98%. In the low temperature trial, reductions were slower but numbers were still 90% lower than on control fish at day 21. At the end of the third trial, both control pens were treated with hydrogen peroxide owing to heavy lice burdens. However, L. salmonis numbers rapidly increased again and at day 55, fish treated only with emamectin benzoate still had 80% fewer lice than control fish. In the two summer trials, large numbers of C. elongatus were rapidly reduced by treatment with 82–84% efficacy by day 21. Despite the potential for continuous re-infestation, oral treatment with emamectin benzoate presented an effective means of controlling all parasitic stages of L. salmonis and C. elongatus on farmed salmon, and in one trial, numbers remained lower on treated fish for at least 55 days.

Proliferative kidney disease (PKD) in rainbow trout Salmo gairdneri: Further observations on the effects of water temperature

Abstract The seasonality of proliferative kidney disease (PKD) and the effects of water temperature on the development of the disease in naturally-infected fingerling rainbow trout, Salmo gairdneri , were investigated. Fingerling rainbow trout became infected from May to October, but those infected in October did not develop clinical disease. In naturally-infected fish subsequently held under laboratory conditions, clinical PKD occurred at 12–18°C, but not at 9°C. The disease progressed more rapidly and was more severe as temperatures increased. On re-exposure to infection, rainbow trout previously held at 9°C developed clinical PKD, whereas in those previously held at 12°C it did not develop. Possible implications of these findings for the control of PKD are discussed.

Pyridoxine requirements of the gilthead bream, Sparus aurata☆

Abstract Minimal dietary pyridoxine requirements of the gilthead bream ( Sparus aurata Linnaeus) were determined. Partially defined test diets containing graded levels of pyridoxine were fed to groups of fish of average initial weight 2.7 g and 70 g. The criteria used to measure pyridoxine requirements were growth, mortality, food conversion, fish behavior, liver alanine aminotransferase (AAT; EC 2.6.1.2) activity and histopathology. At the lowest dietary pyridoxine level used with the small fish (1.15 mg/kg dry diet) and at the two lowest levels used with the bigger fish (1.15 and 1.46 mg/kg dry diet), vitamin deficiency symptoms were evident in all parameters examined. Signs of deficiency were manifested as growth retardation, high mortality, poor food conversion, hyperirritability coupled with erratic swimming behavior and degenerative changes in peripheral nerves. In both experiments, the dietary level at and above which no deficiency signs appeared was 1.97 mg/kg dry diet. Liver AAT activity was a more conservative parameter, indicating pyridoxine insufficiencies in both groups of fish also at the level of 1.97 mg/kg dry diet.

Induction of nodavirus disease in seabass, Dicentrarchus labrax, using different infection models.

The aim of this study was to investigate the susceptibility of juvenile and adult seabass, which are generally thought to be refractory to nodavirus. Moreover, preliminary immunological studies were performed to examine the immune response of adult seabass. Successful transmission of the disease was experimentally demonstrated in juvenile and adult seabass as ascertained by the presence of the clinical signs of the disease, re-isolation of the virus in the SSN-1 cell line and subsequent confirmation by histopathology and immunohistochemistry. Bigger seabass not only developed the clinical disease but also suffered mortalities. Serum neutralisation titres were considered low in this study.