Abstract
Freshwater leeches are benthic invertebrates whose population assemblages depend on the abundance of food, depth, and water quality. Leeches may function as suitable bio-indicators of water pollution. The study aims to 1) identify the leech species found in the sampling sites, 2) determine if leeches preferred specific water quality parameters, and 3) determine if the leeches had a preferred depth in Emmarentia Dam, Padda Dam, Westdene Dam and Albert’s Farm Dam, with the latter acting as a relative reference site. The aforementioned study sites are found in the Westdenespruit and the Montgomery spruit., Ten sets of two boards (green and white) in the field were lowered 5 m apart into the water at specific points along a transect and left for 20 minutes. The number of leeches on each board was then counted. Once enumerated, some of the leeches were fixed for identification purposes. The leeches were fixed in 70% ethanol or Acetic acid-formalin-alcohol (AFA) by dropping 1 drop of the solution into a petri dish every 1 minute until the leech no longer moved. The process was repeated three 3 times on three different days for comparison purposes. In the laboratory, only the first 30 specimens were fixed and used from each dam for identification (light microscopy and wholemount). The abundance, prevalence, and mean intensity were calculated and compared to board depth, and depth profiles were generated for the length of the transects.
Total dissolved oxygen, light intensity, temperature (surface and bottom), salinity, and pH were measured using a Euclite Elite and then statistically analysed. The leech species collected from all four dams were identified as Helobdella stagnalis. The parasite mean abundance was significantly higher on the white boards in Emmarentia and Westdene dams. In comparison, the mean abundance was higher on the Padda Dam and Albert's Farm Dam green boards. The leeches in Emmarentia Dam had the highest prevalence on the green boards (55.56%), followed by the leeches in Padda Dam on the green boards (40.26%), while at Albert’s Farm Dam, leeches chose the white boards (3.33%). In Westdene Dam, the leeches indicated had an equal prevalence (42.22%) for both the green and white boards. The Thus leeches in Westdenespruit, and Montgomery spruit preferred the green and white boards. In conclusion, rainfall influences the ecology of the leech species; the deeper the boards are suspended in the water, the darker the environment will be, and the mean intensity of the leeches increases.