FjordFish FjordFish is an underwater imagery dataset (3002 images, 6350 annotated objects) across 27 classes (table 1) designed for training object detection models to detect and classify underwater marine fauna. The dataset focuses on North Atlantic coastal fish species inhabitating the Norwegian and Swedish coasts. Images were collected from videos taken during baited and unbaited remote underwater video surveys along the Swedish and Norwegian coasts. Images of coastal cod were also collected from a semi-natural mesocosm at the Institute of Marine Research Flødevigen research station. All images are fully framed to include diverse backgrounds and species assmeblages. Labels are provided in the YOLO format for YOLOv8 and newer, but can be converted to other formats. Data managers: David Poling - University of Agder, Norway - james.d.poling@uia.no Tonje Knutsen Sørdalen - Institute of Marine Research, Norway - tonjesordalen@gmail.com If using this dataset for research, please cite: Poling, J. D., Sørdalen, T. K., Halvorsen, K., Thormar, J., Perry, D., & Larsen, T. (2025). FjordFish [Data set]. Zenodo. https://doi.org/10.5281/zenodo.17496689 Files: FjordFish.zip: images: 6350 images with numerical naming e.g. "1.jpg", "50.jpg" labels: label files in YOLO .txt format with naming identical to their associated image e.g. "1.txt", "50.txt" Table 1. Class ID Class Name Common Name Latin Name Total Annotations 0 ballan Ballan Wrasse Labrus bergylta 93 1 cuckoo_female Cuckoo Wrasse Female Labrus mixtus 47 2 cuckoo_male Cuckoo Wrasse Male Labrus mixtus 31 3 corkwing_female Corkwing Wrasse Female Symphodus melops 456 4 corkwing_male Corkwing Wrasse Male Symphodus melops 1215 5 goldsinny Goldsinny Wrasse Ctenolabrus rupestris 1433 6 rock_cook Rock Cook/Small-mouthed Wrasse Centrolabrus exoletus 152 7 labrids_unknown Labrids Unknown Labridae sp. 333 8 cod Atlantic Cod Gadus morhua 811 9 cod_yoy Cod Young of the Year Gadus morhua 181 10 haddock Haddock Melanogrammus aeglefinus 7 11 pollack Pollack Pollachius pollachius 149 12 poor_cod Poor Cod Trisopterus minutus 22 13 saithe Saithe Pollachius virens 39 14 whiting Whiting Merlangius merlangus 101 15 gadids_unknown Gadids Unknown Gadinae sp. 200 16 spiny_dogfish Spiny Dogfish Squalus acanthias 684 17 sharks_unknown Sharks Unknown Squalidae sp. 0 18 brown_crab Brown Crab Cancer pagurus 190 19 green_crab Green Crab Carcinus maenas 38 20 hermit Hermit Crab Paguridae sp. 15 21 lobster European Lobster Homarus Gammarus 1 22 decapods_unknown Decapods Unknown Decapoda sp. 5 23 ling Ling Molva molva 30 24 two_spot_goby Two Spot Goby Pomatoschistus flavescens 113 25 black_goby Black Goby Gobius niger 1 26 sand_goby Sand Goby Pomatoschistus minutus 3