An atypical biotype I Actinobacillus pleuropneumoniae serotype 13 is present in North America

Atypical Actinobacillus pleuropneumoniae serotype 13 strains present in North America are described here for the first time. Different from serotype 13 strains described in Europe, North America strains are biotype I and antigenically related to both, serotypes 13 and 10. Chemical and structural analysis of the capsular polysaccharide (CPS) and lipopolysaccharide (LPS) of a representative strain revealed that the CPS is almost identical to that of the reference strain of serotype 13, having a slightly higher degree of glycose O-acetylation. However, it produces an O-PS within the LPS antigenically and structurally identical with that of the reference strain of A. pleuropneumoniae serotype 10. The O-PS was characterized as a homopolymer of 1,2 linked β-D-galactofuranosyl residues, a structure unrelated to that of the O-PS produced by the reference strain of serotype 13. Strains from Canada and United States are antigenically, phenotypically and genotypically similar. Animals infected by one of these strains induced antibodies that were detected by a LPS-based ELISA diagnostic test using either the homologous antigen or that of serotype 10. Based on the LPS and toxin profile, these strains might be misidentified as A. pleuropneumoniae serotype 10.     

Multi‐decadal variations in spawning ground use in Northeast Arctic haddock (Melanogrammus aeglefinus)

Despite the importance both in an ecological and management context, much uncertainty remains about the underlying factors controlling spawning ground use in marine fish. Here, we investigate how spawning ground use of Northeast Arctic (NEA) haddock (Melanogrammus aeglefinus) has changed over time. By combining data from a Soviet‐Russian egg survey conducted over a 35 year period (1959–1993) with a biophysical drift model, we estimate annual median spawning latitudes of NEA haddock. Furthermore, we test for statistical association between the median latitude of spawning and covariates that are candidates for shaping the spawning distribution of haddock. The results indicate no association with temperature, as measured at the Kola transect, or demographic structure, as measured by the mean weight of spawners. However, we find a positive and significant association between spawning latitude and spawning stock biomass, indicating that density‐dependence may be more important in shaping spawning location than other factors such as temperature and demographic structure. A potential mechanism for the reported effect of spawning stock biomass may act through the distribution at the feeding grounds, which is reported to expand north‐ and eastwards at high population density.     

Festulolium fibre characteristics and digestibility as affected by maturity

This study compared the forage quality of Festulolium entries of festucoid (Hykor) and loloid attributes (Felopa and Norwegian candivars) with major cultivars of the parent species perennial ryegrass and meadow fescue, and with timothy. Forage NDF, iNDF, kdNDF and DDM were analysed at vegetative stage, early heading, heading and anthesis during spring growth (SG) and two subsequent regrowths over two production years at two locations in Norway. NDF and iNDF increased and kdNDF and DDM decreased with advancing maturity, mostly expressed in SG, with negative correlations between DDM and NDF and iNDF and ADL, and strong positive correlations with kdNDF. In SG, across years and locations, the content of NDF at heading stage was 30% higher and iNDF 400% higher in stems than in leaves, while stem kdNDF was about 50% of that in leaves. In general, timothy cv. Grindstad and Festulolium cv. Hykor had the highest NDF and iNDF and the lowest kdNDF values. Loloid entries of Festulolium were quite similar to perennial ryegrass, although the tetraploid entry proved better than the others with respect to forage quality. Regarding nutritive value, the festucoid and loloid types of Festulolium should be considered separate groups. The effect of year was more pronounced than that of location, for which the ranking of entries was quite similar. Loloid Festulolium is prone to winter damage, and, although it has higher nutritive value than the parent species, its use will depend on the conditions for winter survival.     

Transmission dynamics of the monogenean Gyrodactylus salaris under seminatural conditions

Tracking individual variation in the dynamics of parasite infections in wild populations is often complicated by lack of knowledge of the epidemiological history of hosts. Whereas the dynamics and development of Gyrodactylus salaris Malmberg, 1957, on Atlantic salmon, Salmo salar L., are known from laboratory studies, knowledge about infection development on individual wild fishes is currently sparse. In this study, the dynamics of an infection of G. salaris on individually marked Atlantic salmon parr was followed in a section of a natural stream. During the 6‐week experiment, the prevalence increased from 3.3 to 60.0%, with an average increase in intensity of 4.1% day^?1. Survival analyses showed an initially high probability (93.6%) of staying uninfected by G. salaris, decreasing significantly to 37% after 6 weeks. The results showed that even at subarctic water temperatures and with an initially low risk of infection, the parasite spread rapidly in the Atlantic salmon population, with the capacity to reach 100% prevalence within a short summer season. The study thus track individual infection trajectories of Atlantic salmon living under near‐natural conditions, providing an integration of key population parameters from controlled experiments with the dynamics of the epizootic observed in free‐living living populations.     

The efficacy of Aqui‐S vet. (iso‐eugenol) and metomidate as anaesthetics in European eel (Anguilla anguilla L.), and their effects on animal welfare and primary and secondary stress responses

The effects of 40 mg/L metomidate and 300 mg/L iso‐eugenol (i.e. 600 mg/L Aqui‐S vet.) anaesthesia on the stress response in European silver eel during a process of complete anaesthesia, recovery and long‐term survival were studied. Metomidate is a hypnotic agent with no analgesia, whereas Aqui‐S vet. is a true anaesthetic. There was no difference between fish exposed to Aqui‐S vet. and metomidate, with respect to time to anaesthesia (mean 3.8 and 2.6 min respectively) and recovery (mean 7.6 and 6.5 min respectively). For the metomidate group, the plasma cortisol concentration increased to a peak during the recovery phase, and was significantly higher than for the Aqui‐S vet. group, which showed no such increase. Fish were kept in tanks with seawater for monitoring of long‐term survival (4 months) after anaesthesia treatment, and no mortality was observed in either group. The results indicate that metomidate is a potential stressor to European eels during exposure, and we do not recommend using metomidate in this species. Aqui‐S vet., however, seems promising as a stress‐reducing anaesthetic for European eel, and if used properly could improve animal welfare and survivability during and after common ecology‐related procedures, as capture, tagging and size measuring.     

Comparative assessment of Vibrio virulence in marine fish larvae

Vibrionaceae infections are a major obstacle for marine larviculture; however, little is known about virulence differences of Vibrio strains. The virulence of Vibrio strains, mostly isolated from vibriosis outbreaks in farmed fish, was tested in larval challenge trials with cod (Gadus morhua), turbot (Scophthalmus maximus) and halibut (Hippoglossus hippoglossus) using a multiwell dish assays with single‐egg/larvae cultures. The strains differed significantly in virulence as some caused a high mortality of larva reaching 100% mortality after a few days, while others had no or only marginal effects on survival. Some Vibrio strains were pathogenic in all of the larva species, while some caused disease only in one of the species. Twenty‐nine of the Vibrio anguillarum strains increased the mortality of larvae from at least one fish species; however, pathogenicity of the strains differed markedly. Other Vibrio species had no or less pronounced effects on larval mortalities. Iron uptake has been related to V. anguillarum virulence; however, the presence or absence of the plasmid pJM1 encoding anguibactin did not correlate with virulence. The genomes of V. anguillarum were compared (D. Castillo, P.W. D'Alvise, M. Middelboe & L. Gram, unpublished data) and most of the high‐virulent strains had acquired virulence genes from other pathogenic Vibrio.