After a successful week of electrofishing in Bråån and Tommarpsån four weeks ago, Laura and I started to prepare an aquaria room at Lunds University for an initial fish-infestation experiment. Cleaning aquaria, buying and arranging equipment or settling up oxygen-pipes were some of our tasks for the week.

This let us continue with a second successful electrofishing-action with Niklas afterwards. With a car full of fish many different species were transported from Klingavälsån and Fyleån to the aquaria room in Lund at several chargings.  Four different fish species were caught in Fyleån, ten in Klingavälsån directly at Hemmerstorps Mölla. What a positive surprise! Bullheads (Cottus gobio) and three-spined sticklebacks (Gasterosteus aculeatus) occurred in both streams, brown trout (Salmo trutta) and minnow (Phoxinus phoxinus) in Fyleån. Roach (Rutilus rutilus), silver bream (Abramis bjoerkna), perch (Perca fluviatilis), stone loach (Barbatula barbatula), common bleak (Alburnus alburnus), pike (Esox Lucius), tench (Tinca tinca) and nine-spined stickleback (Pungitus pungitus) were caught in Klingavälsån. The latter mentioned species were only a few individuals each, but still interesting for testing host-fish suitability. At the end of the week Niklas found 15 gravid mussels in Bråån which we finally transported to the lab.

Since bringing the animals in the aquaria room the tension has been increasing every new morning hoping that all fishes and mussels survived the night. A few bullheads died because of fungal infections, but the general situation is stable now. It was possible to count all fishes and to check their gills for ongoing infestation by mussel glochidia. This was a great balance between anesthetizing baths and fast but still thoroughly looking at the gills with further waking up baths. Between checking the mussels for glochidia release and regularly changing the water, fishes were fed and aquaria were cleaned. It was great to have Deplhine’s help during the week which made it possible to work effectively. Thanks a lot! Many fishes in a small and cold room bring along a lot of work. We now hope to get enough ripe glochidia for starting the experiment. If not, we’ll try with further mussels ;).

During week 26 a second host-fish mapping action could be run by e-fishing in Bråån and Tommarpsån. The weather was sunny! Even if strong wind made it difficult to measure weight and length of fishes in the field, the 210 individuals could be finally conserved. Additional individuals were released in the streams. The fish species did not vary compared to the ones caught during e-fishing at the same stream stretches previously this year. Thanks to the help of Niklas, Laura, Delphine and Peter (friend and photographer/www.kardne.se) this UC4LIFE part was realized in a few days. But following DNA analysis will take many hours in the lab during winter.

At the beginning of the week fish traps were set out in the streams. Their purpose was to catch more different fish species. Unfortunately there were only signal crayfishes, one eel and a lot of dirt in the traps.

However, Laura and I shared the days of field sampling and parallel laboratory work in the aquaria room at Lunds University. One of us always had to take care of the fishes and mussels which were still waiting for the start of a fish-infestation-event. Aquaria must be cleaned, fishes fed and water in the mussel-boxes changed.

Finally, waiting for the glochidia release by mussels payed off! On Wednesday 27^th of June the infestation experiment could be started. Infestation baths including a certain amount of glochidia per fish individual were prepared for different fish species with origin in the streams Fyleån and Klingavälsån. Steering the water in buckets including fishes and glochidia was the task of all my helpers while I organized the glochidia solutions and controlled infestation times. Chocolate was necessary to keep the steering-team alive ;). After the infestation bath fishes were put back in their aquaria to follow the infestation stage of Unio crassus on their potential host-fishes.

For ensuring the survival of the mussels taken in the aquaria room for glochidia collection they were brought back to their stream of origin after marking them with blue-greenish nail polish.

Evaluation of potential host-fishes for Unio crassus needs information of glochidia load and survival on fish gills. Therefore, many fish individuals of different species, hatched and infested in the aquaria room at Lunds University (see previous blog text), were sacrificed and measured in weight and length on a Saturday afternoon/evening. Labeling the fishes was a very important procedure since each individual will be correlated to this data when checking for glochidia infestation rates using a stereomicroscope. Last week a few fish individuals could already be checked for glochidia infestation and many pictures could be taken. On some individuals an immune reaction was visible on the gills. On other individuals successful infestations was indicated by fish-tissue which had been growing over mussel glochidia. This information helps us now to choose fish species for the next UC4LIFE action: re-introduction of U. crassus in the streams Klingavälsån and Fyleån. For this experiment, let’s hope that we still can find gravid mussels in the steams of Skåne!