Sperm motility and testicular histology as reproductive indicators of fish health of two feral fish species from a currently DDT sprayed area, South Africa

Sperm motility and testicular histology were studied as reproductive indicators of the reproductive capacity for two wild, indigenous fish species (Oreochromis mossambicus and Clarias gariepinus) from a currently DDT sprayed area in South Africa. An important component of fish health is an optimally functioning reproductive system. Computer assisted sperm analysis (CASA), based on open-source software, was used to assess sperm motility parameters including percent motile sperm (% MOT), velocity curvilinear (VCL μm-s^-1) and progression (PROG). Both species were sampled at a reference site, Albasini dam (AD), and at two exposed sites, Nandoni Dam (ND) and Xikundu weir (XW). DDT and its metabolites were found in varying concentrations in the water from all three sites (0.1-1.2μg-L^-1). The CASA results showed a general trend of a decrease in all parameters from the reference site (AD) to the exposed sites (ND and XW) for both species [O. mossambicus: % MOT: 69.89 (AD), 65.92 (ND), 56.62 (XW); VCL: 89.24 (AD), 117.05 (ND), 82.49 (XW); PROG: 2922.06 (AD), 2734.14 (ND), 2431.52 (XW); C. gariepinus: % MOT: 39.90 (AD), 20.25 (ND), 39.10 XW); VCL: 99.93 (AD), 80.72 (ND), 88.61 (XW); PROG: 2502.72 (AD), 2340.89 (ND), 1915.73 (XW)], however few significant differences were observed. The histological results revealed alterations to testis tissue of both species at all three sites. The testes were assessed through the identification of alterations and an organ index was calculated: Testes Index (I_T). The index is indicative of the histological response in the respective tissue type. O. mossambicus at XW had the highest mean I_T value (5.47±4.63), primarily due to the occurrence of testicular oocytes (intersex). There is a vital need for a dependable method or indicator to assess reproduction of fish in situ in order to relate impacts of environmental EDCs with changes in reproductive success of indigenous fish populations.