Histology-based health assessment and estrogenic effect on Labeobarbus natalensis in the uMgeni River system.

Abstract

The uMgeni River is home to more than 40 fish species and is highly polluted due to anthropogenic activities. The study aimed to assess the overall health and oestrogenic effect on Labeobarbus natalensis in the uMgeni River system and information will benefit the community located along uMgeni River catchment area. The physical parameters of water were measured at Nagle and Inanda dams, and the tributaries feeding the uMgeni River (i.e., uMsunduzi, uMngcweni, and eSikelekehleni rivers) before it empties into the Inanda Dam. Water and sediment samples were also collected for chemical analyses in conjunction with physical parameters. Fish were sampled at the Nagle and Inanda dams riverine using an electro-shocker, and indices such as condition factor, organosomatic, and health assessment index were used to assess the health of fish. Moreover, a histopathologic assessment was done on the liver and gills, and organ indices were calculated. The oestrogenic effect was assessed by measuring vitellogenin concentration in the liver of male Labeobarbus natalensis. A high alkaline pH level was recorded at Inanda Dam and uMsunduzi River with a neutral pH recorded at other sites. Nutrients showed significant differences between sites with Inanda Dam showing significantly higher concentrations for most nutrients. Higher sulphate concentration was recorded in the uMsunduzi River with higher phosphate concentration recorded in the uMngcweni River. Inanda Dam showed significant differences for most metals in the water and sediment with lower concentrations being recorded for Nagle Dam. Coinciding with water quality parameters, the health of fish was generally better at Nagle Dam compared to Inanda Dam. However, negative allometric growth was observed for both Inanda Dam and Nagle Dam populations. The health assessment index and gonadosomatic index (female population) were significantly different between the Inanda and Nagle dams, with the Inanda Dam population exhibiting higher indices than the Nagle Dam population. Histopathologic alterations showed a higher prevalence in the gill and liver for the Inanda Dam population compared to the Nagle Dam population. Gill histopathologies such as necrosis, deposits, oedema, architectural and structural alterations, nuclear alterations, hypertrophy, and hyperplasia were the most common pathologies at Inanda Dam. In the liver, architectural and structural alterations, necrosis, nuclear alterations, vacuolar degeneration, and hypertrophy were the most prevalent pathologies at Inanda Dam. Similarly, organ indices were higher for the Inanda Dam population. However, both populations exhibited gill and liver indices >40, denoting, severe alterations. Nevertheless, no significant difference was observed for vitellogenin (VTG) levels between the Inanda and Nagle dams (p>0.05). However, some individuals showed increased VTG level at Inanda Dam. Generally, the poor water quality from tributaries seems to have impacted the water quality in the Inanda Dam. Although the overall fish health seemed to be in an acceptable state, it is evident that these fish populations are living in stressful conditions, with Inanda Dam showing to be rapidly deviating from normal conditions. There is a need to urgently address the water pollution issue in this river system for the sustainability of Labeobarbus natalensis and possibly other sensitive species.