Non-native and invasive fish species of Lake Batur in Bali, Indonesia

Lake Batur is one of the priority lakes for the government initiative to control the damage, and to restore the condition and function of the critical lakes. The degradation in biodiversity due to the invasive and non-native species could raise ecological, economic, and socio-cultural problems for the community. In Lake Batur, there are several fish introduction activities since 1935. Many introduced fish species have turned invasive and could alter the structure of fish communities. It is important to have a solid understanding of how invasive species affect an ecosystem and its biodiversity. Despite numerous studies on fish diversity in Lake Batur, the accurate information on fish diversity and the presence of non-native species in Lake Batur is still not completely known. This paper aims to investigate the diversity of fish in Lake Batur to provide accurate information about the composition of fish species and the presence of existing non-native and invasive fish in Lake Batur. We collected fish samples during the dry season from 30 August-5 September 2022. We used experimental gillnets (30 x 2 m, with mesh size of 16 mm; 25 mm; 37.5 mm; 50 mm; 62.5 mm; and 75 mm), fish nets from the fishing communities (mesh size of 50-75 mm), fishing rods, and scoops. Direct identifications were conducted for the fish samples in the location. For unidentified fish, we preserved the fish sample for further identification. A total of 1104 fish samples from lakes and floating net cages with five different stations were collected. In contrast to the others station, station 4 Abangsongan has all fish species. We obtained 17 species distributed among 8 families. Cichlidae is the most dominant fish family, including the non-native species Nile tilapia (Oreochromis niloticus) and Midas cichlids (Amphilophus citrinellus). Furthermore, Midas cichlid has become invasive with a very rapid increase during the last 10 years in Lake Batur. For Poecilidae family, Bonylip barb (Cyclocheilichthys apogon) is clearly identified for the first time in this study. This study concludes that the invasive species, or non-native Indonesian species represented by Cichlidae species, are a significant issue for fish diversity in Lake Batur.