Effects of rainbow trout (Oncorhynchus mykiss) introduction on the diversity of aquatic insects in andean streams

Abstract

Introduction. Freshwater fish have been widely introduced into aquatic ecosystems, resulting in diversity losses, ecological alterations, and socioeconomic impacts. Among these species, the rainbow trout (Oncorhynchus mykiss) has been introduced in multiple regions, including the Colombian Andes, where it is presumed to negatively affect aquatic insect communities. Objective. To evaluate the effect of rainbow trout introduction on the diversity of aquatic insects in Andean streams. Materials and methods. The study was conducted on the eastern flank of the Central Cordillera, in Tolima (Colombia), between 2000 and 2600 m above sea level, in the upper Magdalena River basin. Stratified random sampling was used, on land cover (forest and non-forest), selecting 13 streams during the low rainfall season. The streams were divided into four treatments based on cover (forest or pasture/crops) and the presence of Astroblepus micrescens, A. trifasciatus, and rainbow trout. Results. 9,095 individuals were recorded, distributed across the orders Diptera, Ephemeroptera, Plecoptera, and Trichoptera, 31 families, and 58 genera, with rock and leaf litter being the preferred substrates for these organisms. Diptera and Trichoptera recorded the highest number of genera in all the treatments evaluated. The abundance of insects recorded by treatment was T1 = 1585 individuals, T2 = 980 individuals, T3 = 2482 individuals, and T4 = 4048 individuals. No significant differences were found in the abundance of the orders, but there were significant differences in aquatic insect richness between treatments. Conclusions. This study shows how the introduction of rainbow trout influences aquatic insect diversity, providing information to inform management strategies for this introduced species.