Dataset of Morphometry and Metal Concentrations in Coptodon rendalli and Oreochromis mossambicus from the Shongweni Dam, South Africa

Abstract

The uMlazi River receives effluents from wastewater work before feeding the Shongweni Dam. However, local communities are consuming fish from this dam for protein supplements. This study was undertaken to investigate the metal concentrations in the water and sediment, the general health of Coptodon rendalli and Oreochromis mossambicus, and metal bioaccumulation. Sampling was conducted during the dry (July–August) and wet seasons (November and December) in 2021. Water was sampled using acid-pre-treated sampling bottles, whereas sediment was collected using the Van Veen grab at the inflow, middle, and dam wall. Fish were collected, and their tissues were digested using aqua regia. Metal concentrations were measured using inductively coupled plasma optical emission spectroscopy (ICP-OES). This data manuscript reports the physical parameters of the water and concentrations of antimony, arsenic, cadmium, copper, iron, manganese, lead, selenium, and strontium in the water and sediment from the Shongweni Dam. Moreover, the fish morphometric data and metal concentrations observed in the muscle are also presented. This data could be used as baseline information on metal concentrations in the Shongweni Dam. Moreover, it provides insight into the potential impact of wastewater effluents on metal increases in freshwater bodies.

Dataset: https://doi.org/10.5281/zenodo.15846281 (accessed on 7 July 2025).

Dataset License: CC-BY-NC

1. Summary

Metal pollution in freshwater ecosystems has become a cause for concern due to increasing industrialization and urbanization [1,2]. Rivers and dams are now showing signs of water quality degradation, which compromises the potential to provide good quality ecosystem services [3]. There are uncertainties regarding the ecological health of aquatic biota, the cost of treating water, and the edibility of fish from rivers that are receiving effluents from industrial and domestic wastewater plants. Although some fish exhibit metal concentrations below permissible limits and low carcinogenic risks [4,5], there is immense evidence that wastewater effluents have the potential to cause metal pollution in freshwater bodies [6,7]. The Shongweni Dam in South Africa (29°51′24.984″ S, 30°43′19.992″ E) is primarily impacted by effluents from wastewater treatment work [8,9]. The dam is bordered by economically disadvantaged communities, which are opting for fish to supplement their protein needs. Moreover, the health of these fish and their edibility have been poorly explored.

This paper contains data on the physical variables, nutrients, and metal concentrations in the water, and metal concentrations in the sediment and fish muscle from the Shongweni Dam impacted by effluents from wastewater works in South Africa. The surface water, sediment, and two fish species, Oreochromis mossambicus and Coptodon rendalli, were sampled during the dry and wet seasons in 2021. The two selected fish species are known to be good indicators of metal contamination [10,11], and they are abundant in the Shongweni Dam. Moreover, the two fish species are targeted and preferred by subsistence fishermen. To obtain this data, the physical variables were measured, and 1 L of each of the water and samples were collected during each survey. Water was acidified, whereas the sediment was over-dried and digested using aqua regia. Metal concentrations in the water and sediment fish tissue samples were measured using ICP-OES. The fish sample size was determined by the number of fish that we could catch during each sampling season; however, the target was 10 for each species at each season. Fish and the livers were weighed, and fish lengths were measured. These morphometries were used to work out the length–weight relationship and calculate the fish condition factor and hepatosomatic index. Nutrients were measured in the water to determine the trophic status of the dam. Metal concentrations in the fish were also used to calculate the metal pollution index (MPI) to estimate the severity of pollution.

This dataset presents the nutrients, metal pollution levels, and fish morphometry observed in the Shongweni Dam and the metal concentration in inhabitant fish, which is linked to Ncayiyana et al. [12]. The data showed that effluents from wastewater works have the potential to increase metal concentrations in aquatic environments and the biota. The Cr and Pb concentrations in fish muscle showed high carcinogenic and non-carcinogenic risks for human communities, which is a cause for concern. These results could be used by other scientists exploring the effect of wastewater effluences in aquatic environments and their association with public health. Moreover, this dataset could be of particular significance to responsible authorities, including policymakers, as it provides a baseline for metal concentrations in the dam and inhabitant fish that could be used to make a predictive argument when developing fish advisories for communities using the Shongweni Dam as a source of food.

2. Data Description

This dataset comprises the physical parameters of the water as well as metal concentrations in the water and sediment. Moreover, data on the morphometry of the two fish species and metal concentration in the muscle is also presented.

2.1. Water and Sediment Quality

This dataset was generated from water and sediment samples collected during dry (July–August) and wet (November–December) seasons in 2021 from the following three sites: the inflow, middle, and dam wall in the Shongweni Dam. The data also reports the levels of physical parameters, i.e., temperature, dissolved oxygen (DO), pH, total dissolved solids (TDS) and electrical conductivity (EC). The concentrations of nutrients and ion concentrations, i.e., nitrite (NO₂), nitrate (NO₃), ammonia (NH₃), sulfate (SO₄), and orthophosphate (PO₄³⁻) are also reported. Moreover, the concentrations of metals, namely antimony (Sb), arsenic (As), cadmium (Cd), chromium, iron (Fe), lead (Pb), manganese (Mn), selenium (Se), and strontium (Sr) in the water and sediment for wet and dry seasons are reported. The TDS and EC showed higher levels during the dry season, whereas other physical parameters showed no seasonal variations. No seasonal variations were observed for nutrients and metals. However, notable metal concentrations were observed in the sediment, with higher concentrations observed during the dry season.

2.2. Fish Morphometry

The dataset was generated from a total number of 29 fish, as per

Table 1. The sample size of both Coptodon rendalli and Oreochromis mossambicus collected at the Shongweni Dam during the dry and wet seasons in 2021.

Species	Sample Size		Total
	Dry Season	Wet Season
C. rendalli	9	6	15
O. mossambicus	7	7	14

. The length, weight, and liver weight of the fish are reported. There was variability with each population; however, no seasonal variations were observed in both species for the length and fish weight. Moreover, the length–weight relationship also showed negative allometric growth for both species.

2.3. Metal Concentrations

This dataset presents metal concentrations in fish and the permissible guidelines for human consumption. The mean moisture content ranged from 73.12 to 83.71%, with a mean of 79.99%; therefore, the dry weight concentration was multiplied by the factor of 0.2 to convert to wet weight. Metals showed no seasonal variation, whereas inter-species variations were observed for Cr, Fe, and Mn. Moreover, C. rendalli showed significantly higher concentrations for the three metals compared to O. mossambicus. Antimony, As, and Cd concentrations were below the permissible limits, as per the FAO [13], MOHSAC [14], and FAO [13], respectively, for both species. In contrast, Cd and Cr exceeded the WHO’s [15] and MOHSAC’s [14] permissible limits of 1 mg/kg and 2 mg/kg, respectively. Moreover, Pb also exhibited concentrations exceeding the MHSAC’s [16] permissible level of 0.5 mg/kg.

3. Methods

3.1. Study Area

The Shongweni Dam is an impoundment that serves as a repository for contaminants from the entire uMlazi River catchment (Figure 1). The catchment is characterized by human settlements and wastewater treatment work [9].

3.2. Water and Sediment Sampling and Processing

The physical variables of the water, namely temperature, DO, pH, TDS, and EC, were measured in situ at the inflow (29°51′30″ S, 30°42′56″ E), middle (29°51′20″ S, 30°43′19″ E), and dam wall (29°51′37″ S, 30°43′10″ E) to cover the spatial variability across the dam. The HANNA multi-parameter instrument (Model: HI98494) was used to measure physical variables. Concurrently, the water was sampled using acid-pre-treated bottles and kept in the fridge, whereas the sediment was sampled using the Van Veen grab and stored in an acid-pre-treated 1-liter bottle, kept in a cooler box and later transferred into a freezer until analysis. During analysis, water was acidified with nitric acid (HNO₃) and kept in the fridge until analysis. The sediment was processed following the protocol described in the research of Wu et al. [17] and Misra et al. [18]. The sediment was oven-dried overnight at 110 °C and ground using a pestle and mortar. Approximately 0.2 g of the sample was digested using aqua regia, 3-hydrochloric acid/1-nitric acid (3HCL:1HNO₃) and hydrogen peroxide (H₂O₂) on a hotplate for 2 h. The solution was filtered with 0.45 µm membranes, transferred to a 250 mL volumetric flask, and deionized water was added up to the mark. A 15 mL solution from the volumetric flask was syringe-filtered into a 15 mL Falcon tube and kept in the fridge until analysis. Both the water and sediment solution were analyzed using inductively coupled plasma optical emission spectroscopy (ICP-OES). The chemical used for this study was of analytical grade and supplied by Merck (Darmstadt, Germany).

3.3. Fish Sampling and Processing

Fish sampling was carried out using gill nets, fyke nets, and electro-shockers at the three sites: Site A1 (29°51′26″ S, 30°42′59″ E), Site A2 (29°51′13″ S, 30°43′19″ E), and Site A3 (29°51′21″ S, 30°43′28″ E). Approval was sought from the University of KwaZulu-Natal Animal Research Ethics Committee (Ref: AREC/019/018). Fish were euthanized as per CCAC [19] by severing the spinal cord. During processing, fish were weighed, and their lengths were measured before opening them up ventrally. The liver was dissected out and weighed. A fish muscle was sectioned out, wrapped in aluminum foil, and frozen until digestion and metal analysis.

3.4. Muscle Digestion and Metal Analysis

Muscle processing was carried out following the protocol described by Biswas et al. [20] and Misra et al. [18]. Approximately 0.2 g of muscle sample was oven-dried over 48 h at 95 °C. The dried sample was ground with a pestle and mortar and digested with aqua regia for 1 h on a hotplate. The solution was filtered with a 0.45 µm membrane into a 100 mL volumetric flask, and deionized water was added up to the mark. The diluted solution was syringe-filtered into 15 mL Falcon tubes and kept in the fridge until analysis. The metal analysis was carried out using ICP-OES with blanks and certified reference materials.

3.5. Quality Assurance and Control

Both sediment and muscle samples were digested with blanks. Analyses were carried out with blanks and certified reference materials supplied by Merck. The recovery ranged from 93 to 105% (

Table 2. The linear concentration, the limit of detection, the limit of quantification, and the recovery percentage observed during analysis.

Metals	Recovery %
Sb	93–102
As	96–105
Cd	94–103
Cr	93–103
Fe	94–102
Mn	94–99
Pb	94–103
Se	96–101
Sr	93–102

).