Morphological traits and condition of brown trout Salmo trutta from Žumberak and Samobor mountain streams.
Until now brown trout populations, and their morphological dinstinction in Samobor-Žumberak mountain streams, have not been investigated. The aim of this research was to determine condition factor, length-weight relationship, morphometric and meristic differences between five brown trout populations. In total, 70 specimens of brown trout were analysed. The lowest Fulton condition factor was observed at Kupčina and the highest at the Slapnica stream. Only specimens from Gradna stream demonstrated negative allometric growth. Significant statistical differences between the investigated sites have been identified for head length, mouth width and height, dorsal and pectoral fin height, the number of soft rays in the dorsal fin, and the number of pyloric caeca. The highest similarity between brown trout specimens, based on morphometric and meristic traits, has been observed between the Slapnica and Rudarska Gradna streams. Identified statistically significant morphometric traits suggest genetic variability between analysed specimens and the potential efficacy of stocking with feral brown trout, particularly at the Slapnica and Rudarska Gradna streams. Further research should be focused on the use of molecular analyses to determine the presence of Atlantic lineages (feral) of brown trout, and gene introgression to native wild strains in order to suggest potentially effective conservation measures.