DIETARY COMPOSITION OF LARGEMOUTH BASS, Micropterus salmoides (Lacepède, 1802) IN THE LOWER COURSE OF THE NERETVA RIVER IN CROATIA

The aim of this study was to determine the composition of the diet of the largemouth bass (Micropterus salmoides) in the lower course of the Neretva River and whether this species feeds on any endemic fish . The research was conducted at the beginning of May 2021. Samples were collected from a boat by electrofishing from Krvavac near Opuzen to the mouth of the Neretva River into the Adriatic Sea near Rogotin. Ten locations were sampled and the length of each transect was 100 m. In the laboratory, the digested material was separated and determined to the lowest possible taxonomic group. In the processing of prey, the percentage of abundance (N%) and frequency of occurrence (F%) were determined. In total, 37 largemouth bass were sampled, with their diet including prey from Decapoda, Amphipoda, Coleoptera and five fish species. The results on relative abundance shows: decapods of the suborder Caridea with 46.9%, fish with 37.5%, Coleoptera with 12.5% and amphipodes represented by Gammarus balcanicus with 3.1%. In regard to frequency of occurrence, the most significant are fish with 40%, followed by Caridea with 35%, Coleoptera with 20% and G. balcanicus with 5%. The endemic fish species Orsinigobius croaticus and Ninnigobius canestrinii are determined in the diet of largemouth bass. The largemouth bass in the lower course of the Neretva River also feeds on non-native fish species Gambussia hoolbrooki and Lepomis gibossus ; cannibalism has also been recorded. Due to its fast adaptability, predation and food choice the largemouth bass could have a significant negative impact on the ichthyofauna in the lower course of the Neretva River in the future, in particular on endemic species from the Gobidae family.