Pulse trawl fishing: The effects on dab

Wild-caught dab (Limanda limanda) were exposed to two different electrical pulse stimuli both commercially applied in Dutch flatfish trawls. The experiment was conducted at the IMARES-Yerseke facility, where dab were tested in two groups of 51.

The first group was exposed to a Delmeco pulse treatment and the second to a HFK pulse exposure, while a third group was used as "control" group similarly without being exposed electrically. The pulse treatment was given in the closest range of a conductor with a dose extending the commercially applied practice. The fish were kept in observation for five days after the treatment, after they were transferred alive to the Central Veterinary Institute (CVI), Lelystad and analysed for external and internal lesions, possibly attributable to pulse exposure. In case of lesions attributable to infections, bacteriological tests were conducted. During the research samples of fish were taken as references for the condition of the fish directly after the catch and directly after the treatment and analysed likewise.

Of the 102 electrically exposed dab, two fishes died after the treatment with unclear relation to the treatment. Dissection results showed that external and internal anomalies occurred in all groups (including the control group), with no clear differences between the exposed categories. Approximately 12 % of the fish contained a Glugea infection in their gut, and only in two cases, a bacterial disease was found. In the control group a fish gut contained Vibro fortis and in the skin lesion of a HFK exposed fish a primary fish disease Vibrio anguillarum was found.

We conclude, that lesions primarily related to pulse exposure were neither observed in the fish analysed directly after the treatment, nor in the fish that were kept in observation for a period of five days after the treatment.