Randhawa, HaseebErzini, KarimPubert, Eve-Marine2025-04-092025-04-092024-10-12http://hdl.handle.net/10400.1/26992Understanding the stock structure of a commercial species is essential for sustainable management. Failure to do so can lead to the depletion of regional sub-populations, genetic diversity erosion, and ecosystem services loss. Plaice, Pleuronectes platessa, are a commercially important species for the Icelandic economy and are found in warm southern and cold northern waters. However, plaice is managed as a single stock. Over the last three decades, the use of parasites as biological markers has proved effective in distinguishing between different fish stocks. The use of otolith shapes for stock discrimination has gained popularity in recent years thanks to advances in image analysis tools and geometric methods. The study on 82 individuals of plaice from different geographical locations and seasons in Iceland showed that the community of parasites and the morphology of otoliths varied significantly between regions and periods, constituting several sub-populations in Icelandic waters. A notable differentiation between Icelandic plaice stocks was observed according to otolith shape and parasitic diversity. Otolith shape showed significant differences between the four geographical and seasonal groups (North-Summer, North-Winter, South-Summer, and South-Winter). Plaices collected in the southern region during the winter had otoliths with distinct shapes compared with the other groups. The parasite study confirmed the otolith shape results. The South-Winter group was also distinguished by a higher abundance of parasites and a different parasite composition than the other groups. Hysterothylacium aduncum was a candidate to be a parasite tag due to its constant presence throughout the year and in all regions but with notable variations in abundance and prevalence.engStock identificationParasiteOtoliths shapeFisheries managementmaster thesis203802772