Maxwell Barson

The impact of water hyacinth ( Eichhornia crassipes) in a eutrophic subtropical impoundment (Lake Chivero, Zimbabwe). II. Species diversity

We compared abundance and diversity of phytoplankton, zooplankton, and fishes among limnetic (P: always without macrophytes) and littoral habitats with (L +) and without (L- ) hyacinths in Lake Chivero, a man-made hypertrophic reservoir near Harare (Zimbabwe). In addition, the littoral macrophyte community, and macro-inver- tebrates associated with hyacinth mats were inventoried. The phytoplankton commu- nity was dominated by blue-green algae (mainly Microcystis aeruginosa ), typical for a hyper-eutrophic lake. Total absolute densities were about 10 to 30 times higher at the L+ sites than at the unvegetated L- and P sites. On the basis of relative species abun- dances the L- zones were more similar to the P than to the L + zones. There was an in- creasing importance of chlorophytes ( Staurastrum sp. and Pandorina morum ) and di- atoms (Cyclotella meneghiniana and pennales) and a decreasing dominance of Mycro- cystis along the discriminant axis from L +, L- to P. The zooplankton community was most dense in the unvegetated zones. Daphnids and bosminids were more abundant in the pelagic than in both littoral zones. Calanoids and Diaphanosoma were dominantly represented in the unvegetated zones. The two littoral zones were characterised by higher densities of chydorids, while they could be discriminated by the dominance of cyclopoids in the vegetated site. Seventeen different fish species were captured by at least one of the different fishing methods. Apparent habitat preferences differed ac-

Parasite hybridization in African Macrogyrodactylus spp. (Monogenea, Platyhelminthes) signals historical host distribution

Macrogyrodactylus spp. from the gills of Clarias gariepinus in Zimbabwe and Kenya, and C. anguillaris in Senegal were identified using haptoral sclerite morphology and by sequencing the nuclear ribosomal DNA internal transcribed spacers (ITS) 1 and 2, partial 18S and the complete 5.8S rRNA gene. A molecular phylogeny was constructed using all sequenced Macrogyrodactylus species to date. Based on morphology, Macrogyrodactylus congolensis, M. heterobranchii, M. clarii, and M. karibae were identified, with one specimen from Zimbabwe displaying morphological features that were intermediate between M. heterobranchii and M. clarii. In the intermediate form, the partial 18S and ITS1 sequence was identical to that of M. clarii while the remaining ITS1 and complete ITS2 region was almost identical to M. heterobranchii as was the partial cox1 fragment, thus strongly suggesting a hybrid origin. At present, the catfish host of M. heterobranchii and M. clarii do not co-occur in southern Zimbabwe; this hybridization event is therefore proof of historical sympatry of both fish species.

Taxonomy and Faunistics of the Helminth Parasites of Clarias gariepinus (Burchell, 1822), and Oreochromis mossambicus (Peters, 1852) from Temporary Pans and Pools in the Save-Runde River Floodplain, Zimbabwe

Abstract Two freshwater fish species, Clarias gariepinus and Oreochromis mossambicus, were collected from pans, dry-season pools, and tributaries of the Save and Runde rivers in the southeastern lowveld of Zimbabwe from December 2004 until June 2006. Helminth parasites infecting these fish were isolated from the gills, skin, muscles, body cavity, gall bladder, stomach, and intestines and were examined microscopically. Adult helminths were collected from the darter, Anhinga melanogaster, a piscivorous bird, to compare and possibly link them to the larvae recovered from fish. Stomach contents of the birds were analyzed, and their prey fish species were identified. Larval helminths collected include digenean metacercariae (clinostomes and strigeids), larval cestodes (gryporhynchids), and juvenile nematodes (Contracaecum). Adult worms include the monogeneans Macrogyrodactylus clarii, Macrogyrodactylus karibae, and Macrogyrodactylus congolensis; the digenean Clinostomum complanatum; the nematodes Paracamallanus cyathopharynx, Contracaecum rudolphi, Contracaecum multipapillatum, and Contracaecum rodhaini; and the cestodes Polyonchobothrium clarias and Echinorhynchotaenia tritesticulata. Many of these observations are the first record of that particular parasite species in Zimbabwe or southern Africa. Morphological measurements were made and compared with the original species description, and some unique morphological features are here described.

Investigation of a parasitic outbreak of Lernaea cyprinacea Linnaeus (Crustacea: Copepoda) in fish from Zimbabwe

ABSTRACT Infestation of fish by the crustacean ectoparasite Lernaea cyprinacea Linnaeus, 1758 was investigated to establish the extent of infestation, potential effects of the parasite and its ecological adaptations. Fish samples were collected from impoundments in the Malilangwe Wildlife Reserve in the southeastern lowveld of Zimbabwe and these included the cichlids Oreochromis mossambicus, Oreochromis placidus and Tilapia rendalli, the cyprinids Labeo altivelis and Barbus paludinosus, the clariid Clarias gariepinus, the centrarchid Micropterus salmoides and the characid Hydrocynus vittatus. All the cichlids and one cyprinid (L. altivelis) were infested with L. cyprinacea. The two Oreochromis species exhibited prevalence as high as= 100% and mean intensity up to 149 parasites per fish. Lernaea cyprinacea exhibited an aggregated distribution in host populations and were attached mostly to the ventral and caudal regions of hosts, while the head was the least preferred attachment site. With a few exceptions, there was no significant correlation between parasite prevalence and intensity with host size, sex, condition factor, gonadosomatic index or fecundity.

Invertebrate communities in dry-season pools of a large subtropical river: patterns and processes

Dynamics of flooding and drying resulting in fragmentation of lotic habitats are a yearly phenomenon in subtropical floodplain rivers but their ecological significance is not known for invertebrate communities. We studied the response of zooplankton and macroinvertebrate communities in 48 dry-season river pools in the Save-Runde river system (Lowveld, Zimbabwe). Patterns and ecological processes influencing invertebrate communities, taxon richness and macroinvertebrate functional richness were investigated with focus on the role of regional (connectivity) and local processes (habitat characteristics). Local factors accounted for 15% of the variability in the zooplankton community but only 3.4% for the macroinvertebrate community. Important factors affecting zooplankton densities in the pools were depth, vegetation cover and presence of fish (planktivorous and omnivorous). The presence of fish in pools can infer predation risk. Macroinvertebrate abundances were affected by the presence of fish only. Zooplankton densities increased in pools with fish while macroinvertebrate densities declined in the presence of fish. Macroinvertebrates could exert top-down pressure on zooplankton either by competition for resources or predation in pools. Regional factors significantly explained zooplankton but not macroinvertebrate community variability. Connectivity had no significant effect on local pool habitat characteristics. There were no significant differences in water quality variables between flowing river sites and the pools. Zooplankton and macroinvertebrate α- and γ-diversity in dry-season pools was higher than in the flowing river. Species additions rather than species replacements by processes that include dispersal and possibly dormancy may explain increased zooplankton and macroinvertebrate taxon diversity in pools. Functional feeding group (FFG) analysis showed that the proportion of macroinvertebrate predator taxa increased significantly in pools compared to the flowing river. Pools create a more suitable and diverse habitat for these widely dispersing taxa. The other FFG were comparable between the river and pools. The pools are strongly heterotrophic. Our results confirm that habitat fragmentation may actually be beneficial for zooplankton and macroinvertebrate biodiversity in dryland rivers.

Metal concentrations in water, sediment and sharptooth catfish Clarias gariepinus from three peri-urban rivers in the upper Manyame catchment, Zimbabwe

Concentrations of zinc, cadmium, chromium, nickel, lead, copper and iron were measured in flowing water, riverbed sediments and tissues of sharptooth catfish Clarias gariepinus from three rivers in the upper Manyame catchment over seven months in 2008–2009. The Manyame and Mukuvisi rivers are severely polluted by industrial and domestic effluent, whilst the Gwebi River is not influenced by urban effluent. Key water quality parameters, including dissolved oxygen and conductivity, clearly showed a pollution gradient in the Mukuvisi and Manyame rivers, but water quality in the Gwebi River was good. Levels of zinc, iron, copper, nickel and lead in fish tissues from the three rivers sampled were unusually high, with zinc and iron concentrations being the highest in all the tissues. This was also positively correlated with the concentrations of these metals in water and sediments. Notable differences existed between the water (zinc and copper) and sediments (iron and zinc) of each river. The relatively high metal concentrations in the Gwebi River, as well as conductivity and dissolved ions, were explained by the geological influence of the Great Dyke in its subcatchment. Metals are bound in the sediment but these can be rapidly mobilised into water if environmental changes occur, therefore efforts to monitor and prevent further water quality deterioration are required. The results of this study may have significant negative implications for aquatic organisms and for human health through fish consumption and therefore risk assessment investigations are imperative.

Species of Gyrodactylus von Nordmann, 1832 (Platyhelminthes: Monogenea) from cichlids from Zambezi and Limpopo river basins in Zimbabwe and South Africa: evidence for unexplored species richness.

New findings on Gyrodactylus spp. parasitising African cichlids in southern Africa are presented, comprising data from Zimbabwe and South Africa. Morphometry of opisthaptoral hard parts in combination with nuclear ribosomal DNA sequences confirmed the presence of six species of Gyrodactylus von Nordmann, 1832. Three new species are described from fishes in Zimbabwe: Gyrodactylus chitandiri n. sp. from the gill arches of Coptodon rendalli (Boulenger) and Pseudocrenilabrus philander (Weber); Gyrodactylus occupatus n. sp. from the fins of Oreochromis niloticus (L.), Pharyngochromis acuticeps (Steindachner) and P. philander; and Gyrodactylus parisellei n. sp. from the fins of O. niloticus, P. philander and Tilapia sp. Gyrodactylus nyanzae Paperna, 1973 was also identified from the gills of O. niloticus and C. rendalli collected from two localities in Zimbabwe; these findings represent new host and locality records for this parasite. Gyrodactylus sturmbaueri Vanhove, Snoeks, Volckaert & Huyse, 2011 was identified from P. philander collected in South Africa and Zimbabwe thereby providing new host and locality records for this parasite. Finally, Gyrodactylus yacatli García-Vásquez, Hansen, Christison, Bron & Shinn, 2011 was collected from the fins of O. niloticus and P. philander studied in Zimbabwe; this represents the first record of this species from the continent of Africa. Notably, this study improves upon the knowledge of Gyrodactylus spp. parasitising cichlids from these southern African regions. All species studied were recorded from at least two different cichlid host species indicating trend for a wide range of Gyrodactylus hosts in Africa. Accordingly, this supports the idea of intensive host switching in the course of their evolution.

Metal Correlations and Mobility in Sediment and Water from the Gwebi River in the Upper Manyame Catchment, Zimbabwe

Intermetallic correlation and the ameliorative effects of metals (Cd, Cr, Cu, Fe, Ni, Pb and Zn) were determined in water and sediments in the Gwebi River, a major tributary to Lake Manyame, which is a source of potable water to the City of Harare. Water and sediment were sampled at four selected sites in the wet (December- March) and dry (April-November) seasons and metal concentrations were analysed by flame atomic absorption spectroscopy (FAAS). Significantly high concentrations of zinc and copper were observed in water in both the wet and dry season. Concentrations of chromium, copper, zinc iron and nickel in water in both the wet and dry seasons surpassed World Health Organization (WHO) thresholds. The significant difference (ANOVA, p < 0.05) in seasonal/temporal variation in metal concentrations in water indicate different pollutant sources within the catchment of the river. Ameliorative effects of metals were also observed seasonally in the Gwebi River, with