Introduction

The population growth of grey seals and harbour seals in Danish marine waters has implications for performance of populations of various fish species. Evidence for a serious impact of parasitism on cod physiology and growth is presented. Further, the risk of human infections with the zoonotic anisakids is increased.

Methods

A series of field investigations on fish populations (Atlantic cod, Atlantic salmon) occurring in the Baltic Sea and adjacent waters has been conducted during the time period from 1982 to 2020. The prevalence and mean intensity of parasites in the fish populations were calculated.

Experimental infection experiments in the laboratory supplemented the field investigations. The studies involved both cod and mammals (pigs).

Standard parasitological methods were applied to recover the parasites in the hosts. Molecular methods (PCR and sequencing) were used to diagnose the recovered parasites.

Results

Occurrence of the anisakid nematode larvae Pseudoterranova decipiens and Contracaecum osculatum originating from seals (final hosts) have been recorded with increasing prevalence and intensity of infection in wild cod (Gadus morhua) in Danish waters since the 1980s.

The occurrence of C. osculatum larvae in the liver of Baltic cod is associated with a 50 % reduction of cod muscle mass.

We have documented that P. decipiens can infect humans, and by conducting pig infection studies it has been indicated that also C. osculatum has a zoonotic potential.

Conclusions

The increasing occurrence of grey seals and harbour seals in Danish marine waters is associated with an elevated infection of cod with zoonotic nematode larvae. The high infection level has implications for cod performance and fish meat quality. The risk of infection for consumers is increased.

Introduction

Aquaculture production, currently covering 50 % of the human consumption of fish, is challenged by infections by parasitic, bacterial and viral pathogens. Management, chemotherapy and vaccination are control tools applied with some success. We here suggest that marker assisted and targeted breeding of disease resistant fish strains may in the future secure a sustainable development of World aquaculture. We applied such an approach and here describe quantitative trait loci (QTL) for resistance traits in rainbow trout against the skin parasitic ciliate Ichthyophthirius multifiliis (ICH) causing White Spot Disease (WSD).

Methods

We performed controlled ICH infection experiments with 1,059 rainbow trout as host. All fish were SNP genotyped by the 50 K Affymetrix Trout Axiom microarray. Based on the described QTL, located on trout chromosomes 16 and 17 (Omy 16 and 17), we selected male parent fish homozygous for the QTL and produced a new generation of QTL fish (homozygous and heterozygous for the allele) and tested these (263) fish in comparison to outbred control (non-QTL) fish (263) in a subsequent ICH challenge.

Results

We showed that Omy 16 and 17 carried genes associated with lowered infection intensity and prolonged time to death after infection. When then we compared QTL fish with non-QTL fish in triplicate trials (common garden) challenge experiments we confirmed that the QTL was associated with higher resistance.

Conclusions

Marker assisted breeding of disease resistant rainbow trout is a cost-effective solution for future management and control of WSD in freshwater aquaculture.

Introduction

In the year 2012 a total of seven individuals (one bull and six cows) of European bison (Bison bonasus), originating from a population in the Polish Bialowieza forest, were introduced into a fenced 200 ha forest area in a nature reserve (Almindingen, Island Bornholm, Baltic Sea). In 2017 the herd was supplemented by introduction of another bull.

Methods

Faecal samples were recovered with regular intervals and examined for parasite eggs and larvae by means of flotation (McMaster), sedimentation, and Baermann-technique. Parasites sampled at necropsy of three animals were identified by morphometric and molecular methods (PCR and sequencing).

Results

The introduced animals carried a variety of helminths including trematodes (liver fluke Fasciola hepatica, rumen flukes), cestodes (Moniezia), nematodes (Dictyocaulus, Trichuris, Capillaria and other gastrointestinal nematodes). The trematodes did not establish a life cycle in the recipient area (probably due to lack of suitable snail intermediate hosts), but the cestode and the nematodes became established. This was indicated by examination of calves born in the new area. Especially Dictyocaulus viviparus was successfully spread and occurred at high infection intensities at most sampling times. In early 2022 the total number of animals was ten (seven males and three females).

Conclusions

A high mortality (up to 66 %) occurred during the study period and parasite infections may be associated, at least partly, with the mortality. Further detailed investigations of the health status of the flock are needed.

Introduction

A bacterial lipopeptide surfactant isolated from Pseudomonas H6 SPH6), previously known to eliminate Saprolegnia oomycetes, was recently tested for its capacity to control White Spot Disease (WSD) in freshwater fish caused by the parasitic ciliate Ichthyophthirius multifiliis. This parasite has a low host specificity and is considered the main parasitic problem in both wild and cultured freshwater fish worldwide.

Methods

In vitro and in vivo tests were performed in order to elucidate if the surfactant could kill the different lifecycle stages (theronts, trophonts, tomonts and tomocysts) of the parasite and prevent infection of rainbow trout Oncorhynchus mykiss.

Results

We first performed in vitro tests, using dilution series, and documented that even a low SPH6 concentration (10 mg/L) was able to kill all external life cycle stages of I. multifiliis. Subsequently we conducted in vivo studies, using rainbow trout as host, and showed that fish exposed to high numbers of infective theronts remained un-infected if SPH6 (10 mg/L) was present in the fish tank. Further toxicity studies documented a high therapeutic index as SPH6 effects on the host were minimal up to a concentration of 40 mg/L. Toxicological studies indicated that the environmental effects of the compound is limited and the possible future usage of the products should be further tested in field studies. A patent application has been submitted and a novel start-up company (Sundew) has obtained the license to produce the product.

Conclusions

The discovery in the laboratory of the antiparasitic effects of a bacterial surfactant (performed both in vitro and vivo) is now the basis for a novel start-up company, which has upscaled the production to industry level.