African Journal of Aquatic Science

Water-quality assessment and spatial distribution of water-quality parameters of Dodoma Urban, Tanzania

O.J. Mdee — 2024-10-29

The study was conducted in 2022 in shallow wells and deep boreholes owned by residents, to investigate the water quality status in the emerging developing area of Dodoma Urban municipality in central Tanzania. Eighteen boreholes and five shallow wells were assessed using the water quality index (WQI), the inverse distance weighting (IDW) method under the ArcGIS environment, and the Euclidean similarity index. The WQI classified the water samples into a good category class with a covered area of 42.5% and an excellent category class with a covered area of 57.5%, indicating that most of the deep boreholes and shallow wells were suitable for residential purposes. The IDW revealed the spatial distribution of the physico-chemical parameters and WQI, indicating that water quality improved from west to east within the study area. Yet, the Euclidean similarity index was dominated by nitrates, pH and heavy metals, with the highest correlation coefficients. Despite the WQI being above the average class, water treatment technologies should be practiced to lower those values of physico-chemical parameters existing above the threshold limits.

Spatial and seasonal variation of microplastics and surface water quality of the Njoro River and Lake Nakuru ecosystems, Kenya

Petra Kienyiy Chui — 2024-10-29

High levels of plastic pollutants threaten aquatic habitats as the plastic materials are ingested by aquatic organisms as food. This study assessed seasonal variations of microplastics and the water quality of the Njoro River and Lake Nakuru, Kenya. Selected water physico- chemical parameters were measured. Microplastic (MP) abundance in the surface water samples in the dry season was recorded as 47– 649 MPs 300 l⁻¹ for sampling points in the Njoro River, and 54–508 MPs 300 l⁻¹ at Fisher’s Point in Lake Nakuru. Abundances during the rainy season were measured as 8–389 MPs 300 l⁻¹ and 28–259 MPs 300 l⁻¹ for the Njoro River and Lake Nakuru, respectively. Our study observed a significant contribution of microplastics from polymers, namely polyester (40%), polypropylene (25%), polyethylene (20%) and polyethylene terephthalate (10%). Recorded ranges of the water parameters were: salinity 0.085–2.59 ± 0.03 ppt; temperature 14.22–23.69 ± 0.07 °C; pH 8.8–9.3; turbidity 13.95–36.03 ± 0.35 NTU; total nitrogen 5.9–8.57 ± 3.24 mg l⁻¹; total phosphorus 7.49–9.41 ± 1.84 mg l⁻¹; electrical conductivity 73.3–533.3 ± 0.64 μs cm⁻¹; and total dissolved solids 46.67–243.33 ± 0.11 ppm. These ranges were within the standards recommended by WHO and U.S. EPA. The results indicate the possibility for the quantity and mass of microplastic particles in Lake Nakuru to surpass those in the Njoro River.

Comparison of the acute toxicity and behavioural effects of two pyrethroids on African catfish Clarias gariepinus fingerlings

E.O. Ogueji — 2024-10-29

Two of the most-commonly used pyrethroid insecticides were subjected to static bioassays to determine their acute toxicity to Clarias gariepinus fingerlings, followed by comparisons of their impact on mortality and behavioural changes in the fish. The LC₅₀ values for deltamethrin (DMT) at exposure durations of 24, 48 and 96 h were 12, 9 and 8 µg l⁻¹, respectively; the LC₅₀ values for cypermethrin (CYP) at the same exposure durations were 55, 44 and 26 µg l⁻¹, respectively. The estimated safe limits ranged from 8×10⁻¹ to 8×10⁻⁵ µg l⁻¹ for DMT, and 26×10⁻¹ to 26×10⁻⁵ µg l^-1 for CYP. The tested substances had an acute toxicity effect on fish development as they caused death, and chronic toxicity effects as they changed fish behaviour. Fish exposed to either one of these pesticides showed behavioural alterations, such as loss of static balance, excessive mucous secretion, irregular swimming, gulping of air and skin discolouration. The results reveal that CYP was less toxic (96-h LC₅₀ = 26 µg l⁻¹) than DMT (96-h LC₅₀ = 8 µg l⁻¹) based on the greater LC₅₀ value and a lower percentage of mortality. To avoid potential ecotoxicological risks to aquatic life, use of these pyrethroids in both terrestrial and freshwater ecosystems must be treated with caution.

Insights into the phylogenetic position of genus Synodontella (Monopisthocotylea) among some other Dactylogyridea gill parasites of African catfishes and the importance of haptoral elements

Jonathan A. Mbondo — 2024-10-29

This work provides new molecular data on seven species representing three genera (Protoancylodiscoides, Schilbetrema and Synodontella) in the order Dactylogyridea. The results help to explain the origin of Synodontella spp. and to elucidate the phylogenetic position of Synodontella in relation to the other genera. The findings also highlight the importance of the haptoral elements in determing phylogenetic relationships between and within Dactylogyridea taxa, which are monogenean parasites of mostly cyprinid fishes in fresh water. A total of 36 catfish specimens representing five species in three genera (Synodontis, Schilbe and Chrysichthys) were collected from two rivers in Cameroon: the Sanaga River (at Edéa and Nachtigal, in the Littoral and Cental regions, respectively) and Boumba River (at Mang-kaka, East Region), and examined for gill parasites. The novel 28S rDNA sequences of seven species belonging to Dactylogyridea were obtained and their phylogenetic relationships inferred. Synodontella resulted as a monophyletic lineage; the samples obtained from the catfish in Cameroon were well-differentiated into two groups. Synodontella appears to be more closely related to Schilbetrema than to the other Dactylogyridea species investigated here. The shape of the ventral bar should be considered an important feature for distinguishing among Dactylogyridea genera. The existence of two or more lineages within the genus Synodontella, as suggested by previous morphological studies, is here molecularly confirmed, indicating speciation as likely an outcome of ecological influences or the phylogenetic relationships among parasites and/or hosts.

Distribution and host preference of a potential biocontrol agent with a new association for the alien water lily Nymphaea mexicana in South Africa

M.K. Reid — 2024-10-29

Although classical biological control makes use of natural enemies from the native range of an invasive alien species, there are occurrences in which species in the invaded range expand their host range and form new associations with the invader. Bagous longulus Gyllenhal (Coleoptera: Curculionidae) is a South African native weevil hosted by the native water lilies Nymphaea nouchali Burm. f. and Nymphaea lotus L. (family Nymphaeaceae), and it has formed a new association with the invasive alien water lily Nymphaea mexicana Zuccarini. Host range expansions of more-specialist native herbivores on alien invasive plant species occur relatively infrequently; therefore, we investigated the potential of this weevil as another means of managing N. mexicana in South Africa through augmentative biological control. Field surveys were conducted in 2021 and 2022 to determine the distribution of the weevil, and host-specificity tests were conducted under greenhouse conditions to understand its preference for its natural host as compared with N. mexicana and an exotic Nymphaea hybrid. The weevil was widely distributed at 31 surveyed sites across the country but was found feeding and completing lifecycles on only Nymphaea species, including the native hosts and the alien invasive N. mexicana. Additionally, there were no major differences in feeding preference for its natural host when compared with N. mexicana, but the Nymphaea hybrid tested was less preferred. The narrow host range of this weevil, its presence and impact on N. mexicana at three invaded sites, and the fact that a classical biological control agent has not yet been approved, all suggest a potential for B. longulus to be released augmentatively to manage N. mexicana in South Africa. Even so, possible risks such as increased herbivory on native Nymphaea species with augmented populations of its natural enemy should be carefully considered and tested before implementation.

Potential for a commercial inland fishery or just another water storage facility at Spring Grove Dam, KwaZulu-Natal, South Africa?

Matthew J. Burnett — 2024-10-29

South Africa's inland fisheries are generally undervalued, though there is developing interest in the sector. Spring Grove Dam in the KwaZulu-Natal Midlands became operational as a water storage facility in 2013 to provide water to the growing urban population in the province. We assessed whether the impoundment could potentially support commercial fisheries as had been proposed during its design and construction. We conducted seasonal fish community surveys from 2020 to 2021 at sites along the impoundment and in the mainstem of the Mooi River which feeds into the impoundment. We recorded a total of nine fish species, including six non-native fishes with invasive characteristics. Only three of 10 expected native species were found, namely the KwaZulu-Natal yellowfish Labeobarbus natalensis, chubbyhead barb Enteromius anoplus and African longfin eel Anguilla mossambica. Catch per unit effort (CPUE) was low in the sampling surveys using mostly gillnets and fyke nets, and relatively low yields (14.97 tonnes yr⁻¹) were subsequently calculated for the impoundment, making commercial fisheries unviable. However, the existing subsistence and recreational fisheries for non-native salmonids and the native L. natalensis would benefit by controlling the distribution range and abundances of non-native centrachids Micropterus spp. We offer recommendations and suggestions for management plans for Spring Grove Dam in the context of local fish diversity, a changing climate, further construction of water storage facilities on east-flowing rivers in the province, and a nationally neglected inland fishery industry.

The impact of printing industry effluent on the growth and antioxidant response of the freshwater green microalga Chlorella sorokiniana

I.Y. Okpanachi — 2024-10-29

Contamination of aquatic ecosystems with printing industry wastewater is a serious concern because of the toxicity associated with the effluent components and a tendency to create cascading ecological effects. The influence of printing-press effluent on the freshwater microalga Chlorella sorokiniana strain UTEX2714 was studied under controlled laboratory conditions. The microalga was subjected to various effluent concentrations prepared by diluting printingpress effluent with bold basal medium (BBM) in the following ratios (effluent:medium): 1:149, 1:119, 1:99, 5:95 and 10:90, reflecting greater concentrations of the effluent. The control BBM had no effluent added. Higher effluent concentrations had a negative impact on the cell density of C. sorokiniana; at low effluent concentrations the algae displayed a high growth rate and high chlorophyll a production (p < 0.05), although total chlorophyll content did not differ significantly among treatments (p ≥ 0.05). This study also discovered an increase in peroxidase activity in this microalga in response to higher concentrations of printing-press effluent, which indicated an increase in oxidative stress that prompted antioxidant defence mechanisms. We conclude that printing-press effluent adversely affects the physiology of C. sorokiniana, indicating the potential of printing wastewater to harm phytoplankton in freshwater environments.

Variations in the heart rate of Mediterranean mussels Mytilus galloprovincialis and brown mussels Perna perna under thermal stress on rocky shores of South Africa

K. Beine — 2024-10-29

Intertidal mussels experience prolonged emersion during low tide, followed by rapid submergence cooling during high tide, causing temperature-induced stress responses. This study examined variations in heart rate to investigate the relationship between emerged and submerged thermal stress in Mediterranean mussels Mytilus galloprovincialis and brown mussels Perna perna from one site on a south coast warm-water coastline and two sites on a west coast cold-water coastline in South Africa. Gaping behaviour in air displayed by P. perna appears to contribute towards their survivability under warmer conditions, as their flatline temperature was higher as compared with M. galloprovincialis, which do not display gaping behaviour. Warm-water acclimatised mussels of both species appeared better able to survive higher temperatures than cold-water acclimatised mussels. However, both mussel species are possibly living at their upper thermal tolerance based on their sublethal Arrhenius breakpoint temperature (ABT). The values of ABT were higher while exposed to air than when submerged, revealing physiological mechanisms at work to cope with changes in the intertidal zone.