Electric fishing survey data from Walloon streams, Belgium (autumn 2025)

This dataset contains the results of an electric fishing survey conducted in Walloon rivers (southern part of Belgium) in October 2025. Sampling took place between 6–9 October 2025 at 13 stream locations across the Walloon region, covering a total of 2,956 individual fish observations from 24 species. Data were collected using standardised point electrofishing methodology (single pass). This dataset is intended to support freshwater biodiversity monitoring and conservation assessments in the Walloon hydrographic network, and by extension in similar waters across EU Member States. Dataset Data_FishingWalloonRivers2025_SITES.csv, created on the 27th of April 2026. This is the cleaned, ready-to-use dataset containing the details of the different sampling sites, containing the following columns: ID: numerical identification of the data row. Date: Date of sampling and electric fishing, format DD/MM/YYYY. Location: Name of the sampling location. Latitude: Coordinates from the general sampling location. Longitude: Coordinates from the general sampling location. Distance_m: Detailed point within the 100 fishing transect (either 0, 50 or 100m from the downstream start). Width_m: Width of the stream in meters. Depthx/y/z_cm: Up to three different depth measurements. D_length_m: Transect length over which the stream velocity was measured with floaters. Ts/t/u/v/w/x/y/z_sec: Up to eight time measurements for the floaters to reach the end of the transect defined in D_length_m. Data_FishingWalloonRivers2025_FISH.csv, created on the 27th of April 2026. This is the cleaned, ready-to-use dataset containing the digital records of all the fish caught, measured and weighted during the field campaign. It consists of the following columns: ID: numerical identification of the data row. Date: Date of sampling and electric fishing, format DD/MM/YYYY. Location: Name of the sampling location. Species_NL: Species name in Dutch. Species_ENG: Species name in English. Species_FR: Species name in French. Length_mm: Length of the individual fish. Weight_g: Weight of the individual fish. Total_weight_g: Weight of a number of fish (when a subsample of multiple individuals is weighted). For_ind: The amount of individuals weighed in that record. Remarks: Additional information regarding the caught fish. Besides the affiliated institutes, this work was performed in collaboration with SPW Wallonie and DEMNA. Note that C. gobio as reported in this dataset refers to the formerly broadly circumscribed species complex, which has since been revised into 15 European species including, in the Belgian context, the two co-occurring species C. rhenanus and C. perifretum (Freyhof et al., 2005); given the study area, detections most likely represent C. rhenanus, though this cannot be confirmed with certainty based on the 12S marker alone (Colleye et al., 2013). Freyhof J., Kottelat M. & Nolte A. (2005). Taxonomic diversity of European Cottus with description of eight new species (Teleostei: Cottidae). Ichthyologia Explorans Freshwaters 16: 107–172. Colleye O., Ovidio M., Salmon A. & Parmentier E. (2013). Contribution to the study of acoustic communication in two Belgian river bullheads (Cottus rhenanus and C. perifretum) with further insight into the sound-producing mechanism. Frontiers in Zoology 10 (1): 71. https://doi.org/10.1186/1742-9994-10-71