Temporal changes in benthic macrofauna on the west coast of Norway resulting from human activities

Quantitative analyses of soft bottom invertebrate fauna from four Norwegian sill fjords show increased macrofaunal abundance, species richness, and a considerably changed benthic deep water macrofaunal composition in the inner parts of the fjord system. In retrospect, the analyses show significantly altered benthic macrofaunal community structure that was not reflected by the changes in the Shannon-Wiener diversity indices during regular monitoring. The observed changes are mainly due to an increased abundance of opportunistic species, especially of the polychaete Polydora sp. during the last 10-15 years which is correlated significantly to declining dissolved oxygen, rising temperature in the bottom water and increasing total organic matter in the sediment. Possible anthropogenic and climatic impact factors related to the observed macrofaunal changes and environmental consequences of the changes are discussed.

Patterns of Ichthyobodo necator sensu stricto infections on hatchery-reared Atlantic salmon Salmo salar in Norway

Infection patterns with ectoparasitic flagellates belonging to the genus Ichthyobodo were studied in an Atlantic salmon Salmo salar (L.) hatchery in western Norway during an 11 mo period, from eyed eggs to smoltification. Since the earlier species designation Ichthyobodo necator (sensu lato, s.l.) has been shown to represent a complex of several species, the epizootiology of different Ichthyobodo spp. is poorly known. Therefore, we employed molecular methods to ascertain the specific identity of the parasites detected in our study. Only I. necator in the recently redefined and restricted sense occurred (I. necator sensu stricto, s.s.). We observed a 2-peak pattern of infection; the first peak occurred among fry in March and the second peak among fingerlings and pre-smolt in August and September. Skin lesions observed on fingerlings and pre-smolt were significantly associated with Ichthyobodo infections. Also, these infections were negatively correlated with both haematocrit values (Hct) and the condition factor (K) of the fish. The patterns of infection on the farmed salmon suggest that I. necator s.s. is an opportunistic parasite of salmon, flourishing in periods when susceptible hosts are present and the environment favours parasite proliferation. Our study is the first to detect and identify I. necator s.s. on wild-caught adult salmonids (brown trout S. trutta L.). Wild salmonids and sticklebacks Gasterosteus aculeatus (L.) caught in the lakes serving as a water supply to the hatchery were found infected with I. necator s.s., hence these are the likely sources of parasites entering the hatchery via the inlet water.

Occurrence of Francisella piscicida in farmed and wild Atlantic cod, Gadus morhua L., in Norway

Francisellosis, caused by the bacterium Francisella piscicida, has become one of the most serious diseases in Atlantic cod production in Norway. The major aim of this study was to determine the distribution of F. piscicida in farmed and wild fish in areas with cod farming along the Norwegian coast, and its occurrence in cod from areas without cod farming. Two real-time PCR assays, targeting the 16S rRNA gene and the FopA gene of F. piscicida, were developed since sensitive and specific diagnostic tools are required for detecting asymptomatic carriers of the bacterium. A total of 422 wild cod from 13 sampling areas and 955 farmed cod from 10 areas along the coast of Norway were examined. Using the real-time polymerase chain reaction (PCR) assays, F. piscicida was detected in wild populations of cod from all counties examined south of Sogn og Fjordane in southern Norway (overall prevalence 13%, n = 221). Wild cod north of Sogn og Fjordane were negative for the bacterium (n = 201). Farmed cod from most parts of Norway were F. piscicida positive. The apparent absence of the bacterium in wild populations of cod in the northern parts of Norway and its widespread occurrence in wild cod from southern parts of Norway is believed to relate to differences in seawater temperatures.