The evolution of a more virulent pathogen as a consequence of intensive fish farming?
The emergence of
infectious diseases may be triggered by changes in the ecology, epidemiology or
evolution of a pathogen. In aquaculture, pathogen transmission among fish is
radically changed due to high densities of homogenous subsets of fish and
treatments against pathogens. Persistence of several co-occurring pathogen
strains enhance the possibility for repeated outbreaks further. We have studied
an increase in the occurrence and mortality caused by a bacterial fish disease
Flavobacterium columnare in salmon
fingerlings at a fish farm in northern
Increasing Water Temperature and Disease Risks in Aquatic Systems: Climate Change increases the risk of some, but not all, diseases.
Global warming may
impose severe risks for aquatic animal health if increasing water temperature
leads to increase in the incidence of parasitic diseases. Essentially, this
could take place through a temperature-driven effect on the epidemiology of the
disease. For example, higher temperature may boost the rate of disease spread
through positive effect on parasite fitness in weakened host. Increased
temperature may also lengthen the infective season leading to higher total
prevalence of infection and more widespread epidemics. However, to date, general
understanding of these relationships is limited because of scantiness of
long-term empirical data. We are working on one of the first long‑term
multi-pathogen data sets on the occurrence of natural pathogenic bacterial and
parasite infections in relation to increasing temperatures in aquatic systems.
We analyse a time-series of disease dynamics in two fish farms in northern
Vertebrate diets derived from trophically-transmitted fish parasites
Parasites that are transmitted through predator-prey interactions may be used as indicators of trophic relationships between organisms. Yet, they are rarely used as such in the construction of topological (predator-prey) food webs. We are constructing food webs of vertebrate trophic interactions using observed diet alone, trophically-transmitted parasites alone, and the combination of the two based on data from 31 species of fish from the Bothnian Bay, Finland. Standard food web metrics were compared among the three webs. Food web metrics fell within the range of those calculated for other webs elsewhere. The sub-web constructed from parasite data alone had higher mean number of links and connectance than that using observed diet. Connectance and the mean number of links per species increased by 38% using parasites compared versus observed diet as indicators of trophic relationships. Both measurements doubled when parasites and observed diet were considered together compared to observed diet alone, illustrating the complementarity of the two methods. A positive correlation was found between the mean number of parasites and the number of prey taxa in the diet among the fishes. Omnivorous fish had the highest diversity of both parasite species and prey items, while benthophagous fish had among the lowest. Mean total abundance and mean total prevalence of parasites correlated positively with fish size, with piscivores being the largest with the highest abundance and prevalence, while planktivores and benthivores had the lowest. Trophically-transmitted parasites may be used to help construct vertebrate sub-webs and derive information about food web processes. Parasites alone provided equivalent if not more information than observed diet. However, resolution is improved by using parasites and observed diet together.
Transmission patterns of trematodes in the world of narrow opportunities, Ichthyocotylurus pileatus and Australapatemon sp. as models.
Parasites with complex life cycles face two major challenges for transmission in northern latitudes. First, they have to cope with the general unpredictability associated with the series of transmission events required for completion of the cycle, and second, transmission has to be completed within a narrow temporal window because of strong seasonality. Despite this, parasites show high transmission success, suggesting operation of effective transmission mechanisms. We explored the transmission of Ichthyocotylurus pileatus (Trematoda) from its snail (Valvata macrostoma) to fish (Perca fluviatilis) hosts by including some key characteristics in dynamics of the cercarial release from snails. The transmission took place within few weeks mainly in July thus verifying the narrow temporal window for transmission. The output of the short-lived cercariae from the snails was low and variable in magnitude, nevertheless resulted in rapid and high rate of infection in newly hatched fish. The cercarial release showed a strong diurnal rhythm with most of the cercariae released in early evening and night, which might represent the most likely mechanism underlying the high rate of transmission in this species. We emphasise the importance of holistic approaches which combine aspects of multiple host species in studies on transmission of complex life cycle parasites.
multiple parasite species in hosts may lead to interspecific and intraspecific
interactions between the parasites and subsequently shape the structure of the
parasite community. Such interactions are particularly likely in species that
have very high abundances and infect the same location with a host. We also
investigate seasonality of establishment, interspecific interactions and site
segregation in two species of trematodes, Ichthyocotylurus variegatus and
Australapatamon sp. (Trematoda) infection are studied both in the first intermediate host Valvata macrostoma and in two second intermediate leech species, Helodella stagnalis and Erpobdella octoculata. Seasonality in production of cercariaae from Valvata as also metacercariae in leeches have been studied. In laboratory experiments both the susceptibility of the two leech spp as also the differences in activity the these hosts have been studied.