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.     

A review of the effects of ingredient composition and processing conditions on the physical qualities of extruded high‐energy fish feed as measured by prevailing methods

Feed comprises the biggest cost in intensive fish farming and the quality of feed is therefore important. A vast body of research has been carried out in order to investigate nutritional quality of alternative ingredients. Effects of ingredients on physical quality are seldom included in these investigations. Physical quality of feed varies with ingredient composition and processing condition and may interfere with feed intake, nutrient digestibility and therefore growth performance of the fish. In this review, physical quality of extruded, high energy feed, and how ingredient composition and processing conditions affect the quality will be addressed. Various pellet properties will be discussed and methods used to evaluate physical quality will be reviewed.     

Stocking location and predation by marine fishes affect survival of hatchery‐reared Atlantic salmon smolts

Abstract Release strategies of hatchery‐reared Atlantic salmon, Salmo salar L., smolts were compared by studying survival and migration of smolts (n = 99) and their predators (Atlantic cod, Gadus morhua L., n = 8; and saithe, Pollachius virens (L.), n = 2) during the first 37 km of the marine migration using acoustic telemetry. Survivorship was higher in smolts released at the river mouth (30%) compared with smolts released in the river (12%). This was likely due to mortality or reduced migratory behaviour in fresh water. The marine mortality was 37% during the first 2 km after leaving the river (at least 25% mortality because of predation from marine fishes), and total marine mortality over 37 km was 68%. Detection‐depth data were useful for evaluating whether the tagged smolts were alive or predated; mortality during the first 2 km of outward migration would have been underestimated at 26% instead of 37% without the analysis of depth detection. Transmitters from consumed post‐smolts remained in predators for up to 47 days (average 29 days).     

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.