2.2. Sampling procedure

During the survey, 30 km of the river stretch was sampled, which was divided into two main sections, each covering 15 Km stretch. One section is invaded by O. niloticus, while the other section is uninvaded. The two sections were separated by a unique natural water fall and created a conductive environment to perform good comparison in our study. Both the invaded and uninvaded sections are each located 5.4 km away from the unique natural water fall. At each sampled section, a total of three (3) sampling points were selected with a river distance of about 4.5 km apart from each other. Each sampling point had a total of 200 m stretch covered encompassing all the available five (5) microhabitat type (runs, riffles, vegetative thicket point, open pool (near fisheries landing area) and the tributaries. Sampling of the fish was conducted in the entire 5 selected aforementioned habitat present in each sampling point. Therefore, a total of six sampling points with 30 microhabitats were sampled in both the invaded and uninvaded sections of the upper Kabompo River from December 2019 to February 2020.

Bok and Bills (2012) and DoF (2018) showed that the study area has a greater similarity in native fish species present, rainfall pattern, environmental condition and general water flow regime despite the unique natural barrier that separates them. Due to the proximity of the two sections, it made the two sections of the river easier to compare. The comparison strategy developed here to understand the impact of invasion was a modification from the one proposed by Loiola et al. (2018). This was because the latter comparison was used to compare invasion by terrestrial plants, while here we compared fish invasion. We compared invaded and uninvaded sections to comprehensively investigate the impact of invasion at broader scale (Test 1, Figure 2). As such, TD and FD comparisons between the invaded and uninvaded sections were performed to overall understand the influence of O. niloticus. Secondly, we compared the high or low presence of the O. niloticus in the sampling points of the invaded section (Test 2, Figure 2).

Conceptual model of the two tests comparing taxonomic and functional diversity indices of native species in uninvaded versus invaded sections (Test 1) and native species in sampling points within the invaded section, with high and low presence of exotic species (Test 2) of the upper Kabompo River