Galaxias Zebratus Research Articles

Does thermal history influence thermal tolerance of the freshwater fish Galaxias zebratus in a global biodiversity hotspot?

Compared to other climate regions of the world, Mediterranean regions are likely to experience more severe effects of climate change as rainfall decreases and temperatures increase. Global climate change models predict a reduction in rainfall and rise in the temperature of rivers in South Africa's Cape Fold Ecoregion (CFE) - a Mediterranean region in the south-west corner of the country. In the climate change context and with the prediction that stream temperatures will increase, determining thermal thresholds of freshwater fish in relation to their thermal history is a key element in understanding the potential impacts climate change and a rise in stream temperatures will have on already threatened freshwater fish. The ability of aquatic species to withstand warming in the CFE will be determined by its upper tolerance limit (critical thermal maximum, CTmax). A fish's CTmax can be influenced by several factors, including the thermal characteristics of its environment (thermal history). In this study, we set out to examine whether the thermal tolerance of an endemic CFE fish species, the Cape Galaxias, Galaxias zebratus Castelnau, 1861, is influenced by its thermal history. We hypothesised that CTmax of G. zebratus individuals from warmer sites will have higher CTmax values than individuals from cooler sites. Hourly in situ water temperature data were collected and the CTmax values were determined for fish (n=15 per site) from ten sites on six rivers on the Cape Peninsula of the CFE, and regression analyses revealed that G. zebratus upper thermal tolerance limits are indeed significantly influenced by its thermal history (as characterised by the seven day moving average of daily mean, Mean_7). CTmax was positively related to the thermal history of the rivers, indicating that G. zebratus, and potentially other stenothermic CFE freshwater fish species, is likely to be particularly vulnerable to climate warming. These findings broaden our understanding of thermal history patterns on fish thermal tolerances in Mediterranean rivers, and support G. zebratus conservation by determining its biological temperature thresholds and thermal requirements. Thermal data should be used to monitor and manage stream temperatures to ensure Mediterranean stenotherms can persist in their natural environment.

Successful mechanical eradication of spotted bass (Micropterus punctulatus (Rafinesque, 1819)) from a South African river

Abstract Following the discovery in 2007 of non‐native spotted bass (Micropterus punctulatus (Rafinesque, 1819)) in the Thee River, Olifants‐Doring River system, Western Cape Province, South Africa, a mechanical removal project was initiated in 2010 to eradicate them to protect the unique native fish assemblage in the river. A temporary gabion barrier was constructed to halt spotted bass invasion into upstream reaches and a variety of mechanical removal techniques were used throughout the project. Three hundred and ninety‐nine spotted bass were removed from the river during the project. Three hundred (75%) of these were captured by chasing them into gill nets or by catching them with hand nets. The remainder were removed using spearguns, seine nets and by back‐pack electrofishing. Spotted bass had been depleted to below detection levels downstream of the temporary barrier in the second year of the project in 2013. A subsequent survey of the river in 2014 revealed a bass population in a reach above the temporary barrier that had previously been considered uninvaded. This population of spotted bass was removed in 2014. Subsequent annual surveys of the Thee River in 2015, 2016 and 2017 have not detected spotted bass and the population is considered to have been extirpated. Three years after the extirpation of spotted bass from below the temporary barrier, native fiery redfin (Pseudobarbus phlegethon (Barnard, 1938)) and Cape galaxias (Galaxias zebratus Castelnau, 1861) were observed in pools where they had been absent during the bass invasion.

Variation in thermal tolerances of native freshwater fishes in South Africa's Cape Fold Ecoregion: examining the east-west gradient in species' sensitivity to climate warming.

The Cape Fold Ecoregion (CFE) is a biodiversity hotspot with high levels of endemism in its freshwater fish fauna. This study examined inter and intra-specific variation in critical thermal maxima (TCmax ) for eight native species of freshwater fish from the CFE. Cape galaxias Galaxias zebratus, Breede River redfin Pseudobarbus burchelli, Berg River redfin Pseudobarbus burgi, Clanwilliam redfin Pseudobarbus calidus and fiery redfin Pseudobarbus phlegethon were the most thermally sensitive (TCmax = 29.8-32.8°C). Clanwilliam rock-catfish Austroglanis gilli, Eastern Cape redfin Pseudobarbus afer and Cape kurper Sandelia capensis were moderately sensitive (TCmax = 33.0-36.8°C). An increase in intra-specific thermal sensitivity of S. capensis was observed from east to west. The results were related to in situ water temperature, which influenced TCmax for all species, suggesting that thermal history is a major driver of variation in thermal tolerance amongst populations. These thermal tolerance data for freshwater fishes in the CFE demonstrate that resilience to climate warming follows a geographical cline and that the more sensitive western species and regions are conservation priorities.

Evidence for diet partitioning among three coexisting native freshwater fishes in South Africa's Cape Fold Ecoregion

The partitioning of limited resources commonly explains how different species can coexist within the same ecological community. In this 2010 study, the diets of three coexisting freshwater fishes (Cape galaxias Galaxias zebratus, n = 27; Cape kurper Sandelia capensis, n = 60; Breede River redfin Pseudobarbus burchelli, n = 77) were characterised and compared in three headwater streams in South Africa's Cape Fold Ecoregion using gut contents and stable isotope analyses. These data were analysed to ascertain whether the three species exploit distinct trophic niches. Both approaches provided evidence that these species occupy different trophic niches, though with some overlap. However, dietary differences among sites were not consistent and were probably influenced by site-specific factors like resource availability. Pseudobarbus burchelli had a broader niche breadth at Tierkloof Stream than the other two species, but not at Waaihoek or Tierstel Streams. Our results also suggest that P. burchelli consumed a more omnivorous diet than do the other two species, whereas S. capensis occupied a higher trophic position than the other two species and consumed vertebrates. Our findings suggest that these species occupy non-equivalent feeding niches in Cape Fold Ecoregion headwater streams, and that diet partitioning might facilitate their coexistence in these systems.

The status and distribution of a newly identified endemic galaxiid in the eastern Cape Fold Ecoregion, of South Africa

Abstract DNA‐based studies have uncovered cryptic species and lineages within almost all freshwater fishes studied thus far from the Cape Fold Ecoregion (CFE) of South Africa. These studies have changed the way the CFE is viewed, as almost all stream fishes that were previously considered to be of low conservation priority, because they were perceived to have broad geographical ranges, contain multiple historically isolated lineages, many of which are narrow‐range endemics. As stream fishes of the CFE are of conservation concern owing to threats mainly posed by habitat degradation, invasion by alien species and hydrological modification, re‐evaluation of the distribution and conservation status of newly identified unique lineages is required to inform the development and implementation of effective conservation and management strategies. The present study conducted an IUCN Red List conservation assessment of a newly identified lineage of the Galaxias zebratus species complex (hereafter referred to as Galaxias sp. ‘Joubertina’) to identify key threats and provide recommendations to conservation authorities on appropriate measures to reduce extinction risk. The lineage met the qualifying threshold for the Endangered category because of its very restricted geographic range, few remaining secure populations, small known population sizes and the intensity of threats to most of the populations. Only six populations remain, one of which could be an ‘extralimital’ population potentially established through an inter‐basin water transfer scheme. Galaxias sp. ‘Joubertina’ is threatened by invasive piscivores, habitat degradation and excessive water abstraction. These impacts have fragmented remnant populations, raising concerns about potential long‐term adverse impacts on genetic diversity and evolutionary potential of this lineage. Immediate conservation measures should protect remnant populations from further impacts, while long‐term measures should aim to restore historical connectivity to reduce the potential deleterious effects of inbreeding in the small isolated populations.

Historical abiotic events or human-aided dispersal: inferring the evolutionary history of a newly discovered galaxiid fish.

Range expansion of obligate freshwater fishes in the Cape Floristic Region (CFR) of South Africa has mostly been attributed to river capture events and confluence of rivers following sea-level regression. The role of low drainage divides and interbasin water transfers has received less attention. This study analyzed mitochondrial and nuclear DNA sequences to assess the processes that could have influenced the phylogeographic patterns of a newly discovered lineage of Galaxias zebratus (hereafter Galaxias zebratus “Joubertina”) that occurs across two currently isolated river systems close to the Joubertina area in the eastern CFR. Results from both analyses revealed that observed genetic differentiation cannot be explained by isolation between the two river systems. No genetic differentiation was found between the Krom River system and a population from one of the Gamtoos tributaries. Shallow genetic differentiation was found between the Krom and the other Gamtoos populations. Historical river capture events and sea-level changes do not explain the present distribution of Galaxias zebratus “Joubertina” across the Krom and Gamtoos River systems. Interbasin dispersal during pluvial periods, recent river capture, or recent human-mediated translocation seems to be the most plausible explanations.

Predatory impact of non-native rainbow trout on endemic fish populations in headwater streams in the Cape Floristic Region of South Africa

Non-native rainbow trout Oncorhynchus mykiss have been widely introduced in the Cape Floristic Region (CFR) at the south-western tip of Africa and may pose a serious threat to endemic freshwater fishes in the region. Quantitative information about trout impacts in the CFR is scarce but is urgently needed to guide legislation and management efforts. We used a combination of comparative and experimental approaches to evaluate impacts of introduced trout on native fish populations in headwater streams draining the upper Breede River catchment in the CFR. Fish populations were surveyed, and 19 environmental variables measured, in 24 minimally-disturbed streams, half of which had been invaded by trout. The mean densities of native Breede River redfin Pseudobarbus burchelli, Cape kurper Sandelia capensis and Cape galaxias Galaxias zebratus, were 89–97 % lower in invaded streams than in streams without trout. Furthermore, while native fish were present at all 12 sites without trout, they were not recorded at seven of the 12 invaded sites. None of the measured environmental variables differed significantly between sites with and without trout, and distance-based linear models identified trout density as the best predictor of redfin and kurper density, while galaxias density was best predicted by other environmental variables (riparian vegetation, canopy cover, substrate length, site slope). Native fish ≤40 mm in length were largely absent from invaded streams, but generally abundant in streams without trout, and a field experiment confirmed that trout selectively consume small redfin. Taken together, these findings constitute evidence that trout have depleted the abundance of CFR-endemic fishes through size-selective predation. It is recommended that managers aim to prevent new trout introductions and consider eradicating trout populations where they pose a threat to highly threatened native species.

Conservation status and distribution of freshwater fishes in South African national parks

Thirteen of South Africa’s national parks contain aquatic systems which support 63 indigenous and 11 alien freshwater fishes. Indigenous fishes include 43 species of the Zambezian faunal group (70% of the national total), eight Karroid (47%), five Cape (31%) and seven species of Marine origin (79%). Six represented Zambezian species, two Marine origin, and all of the Cape and Karroid species are endemic to South Africa. Only three threatened species naturally occur within national parks (Serranochromis meridianus, Barbus andrewi, Pseudobarbus afer ) all of which are classified as Endangered. Two extralimital IUCN threatened species (Chetia brevis and Oreochromis macrochir ) have been introduced. At least three of the five lineages of Galaxias zebratus and two of the four lineages of Pseudobarbus afer occur within national parks in the Cape region. Many fish populations within national parks remain threatened, particularly by hydraulic alterations, impoundment, and predation by alien fishes. There are few aquatic systems within national parks where one or more of these threats are not prominent, and these collectively support only half of the freshwater fish species occurring in all national parks. Proposed management actions include determination and implementation of Environmental Flow Reserves in stressed systems, management of existing alien fish populations and prevention of new establishments, and regular assessments of fish communities.

Conservation Status and Distribution of Freshwater Fishes in South African National Parks

Thirteen of South Africa's national parks contain aquatic systems which support 63 indigenous and 11 alien freshwater fishes. Indigenous fishes include 43 species of the Zambezian faunal group (70% of the national total), eight Karroid (47%), five Cape (31%) and seven species of Marine origin (79%). Six represented Zambezian species, two Marine origin, and all of the Cape and Karroid species are endemic to South Africa. Only three threatened species naturally occur within national parks (Serranochromis meridianus, Barbus andrewi, Pseudobarbus afer) all of which are classified as Endangered. Two extralimital IUCN threatened species (Chetia brevis and Oreochromis macrochir) have been introduced. At least three of the five lineages of Galaxias zebratus and two of the four lineages of Pseudobarbus afer occur within national parks in the Cape region. Many fish populations within national parks remain threatened, particularly by hydraulic alterations, impoundment, and predation by alien fishes. There are few aquatic systems within national parks where one or more of these threats are not prominent, and these collectively support only half of the freshwater fish species occurring in all national parks. Proposed management actions include determination and implementation of Environmental Flow Reserves in stressed systems, management of existing alien fish populations and prevention of new establishments, and regular assessments of fish communities.

Present status and historical changes in the fish fauna of the Berg River, South Africa

The Berg River system in the southwestern Cape South Africa was historically populated by at least four species of highly endemic fish species. A litany of anthropogenic changes, including large-scale land transformation, invasion by alien plant species, modification of the natural flow regime of the river, changes to water chemistry, siltation, and introduction of alien fish species, has transformed the system to the extent that some of these species were believed to have been completely eradicated from the system while others had become severely restricted in terms of the ranges they now occupy. This paper pulls together all available data and information (mostly anecdotal) on historical abundance and distribution patterns of indigenous fish species in the system and on the introduction and spread of alien fish species through the system. It also presents results of a series of surveys undertaken in recent years which provide a snapshot of present day abundances and distributions patterns of both the indigenous and alien fish species in the system. These recent surveys are focussed mostly on the main stem of the system but cover the full length of the river from the upper reaches to the estuary. Methods employed in the recent surveys included beach seine netting, gill netting, electrofishing and snorkelling. These surveys have revealed the presence of only three indigenous fish species in the system—the Berg River redfin, Pseudobarbus burgi, the Cape kurper, Sandelia capensis, and the Cape galaxias, Galaxias zebratus. In spite of once being abundant and widespread in the system these species are now confined to the extreme upper reaches of the mainstem and in the upper tributaries where alien species have not yet managed to penetrate and water quality remains pristine. A fourth indigenous species, once reported as being widespread through the system, the witvis, Barbus andrewi, appears to have been extirpated from the system in its entirety. At least ten species of alien species are present in the system and include rainbow trout, Onchorhynchus mykiss, smallmouth bass, Micropterus dolomieu, spotted bass, M. punctulatus, large mouth bass, M. salmoides, Mozambique tilapia, Oreochromis mossambicus, banded tilapia, Tilapia sparrmanii, sharptooth catfish, C. gariepinus, bluegill sunfish, Lepomis macrochirus, carp, Cyprinus carpio, and mosquito fish, Gambusia affinis. These species are most abundant in the mainstem of the river and lower portions of the tributaries, being prevented from penetrating further upstream by a combination of physical barriers, low winter temperature, and turbulent flow patterns which characterise the upper reaches of the Berg River system. Historical surveys of freshwater fish populations in the Berg River system relied mostly on surface observations and angling as survey methods, and thus most of the results of these studies are of an anecdotal nature. However, using these as a base, it has been possible to pinpoint with a reasonable degree of accuracy the time at which most of the alien species were originally introduced into the Berg River system as well as their spread through the system, and the simultaneous decline of indigenous species in the river. We conclude from this analysis that the strong correlation between the spread of alien species through the Berg River system and the concomitant decline of indigenous species is strongly suggestive of a causative relationship. The paper concludes with some speculation on the prognosis for both indigenous and alien fish species in the Berg River system, focusing on the impacts that the newly constructed Berg River Dam may have on these fauna, as well as potential opportunities this may present for their conservation.

Influence of largemouth bass, Micropterus salmoides, on abundance and habitat selection of Cape galaxias, Galaxias zebratus, in a mountain stream in the Cape Floristic Region, South Africa

Predatory alien fishes have been widely introduced into streams in the Cape Floristic Region (CFR), South Africa, but little is known about their effect on native fishes. Results from this 2006 study suggest that the presence of alien predatory largemouth bass, Micropterus salmoides, may have influenced abundance and habitat selection of the native Galaxias zebratus at one location in a small CFR mountain stream. Numbers of adults, but not of juveniles, were significantly lower where M. salmoides was present, suggesting a size-specific influence on G. zebratus abundance. Because other studies have found the influence of a predator to be affected by prey size and the diel activity of predator and prey, we measured microhabitat use by adult and juvenile G. zebratus by day and by night. Galaxias zebratus selected deeper, faster-flowing microhabitats more strongly where M. salmoides was present than where it was absent. This suggests that G. zebratus adjusts its habitat use in the presence of M. salmoides, although differences in available habitat, or in interactions with other indigenous species, could be partly responsible for the observed differences. In-stream vegetation presence was strongly positively related to depth and strongly negatively related to velocity at positions where G. zebratus was observed, suggesting that the deeper, slower-flowing microhabitats occupied by G. zebratus were structurally more complex than the shallower, faster-flowing ones.

Aquatic systems in and adjacent to Agulhas National Park with particular reference to the fish fauna

The study aimed to determine the distribution and relative abundance of freshwater fishes in and adjacent to Agulhas National Park. Fourteen fish species were collected during surveys carried out in the Heuningnes and Ratel river systems and a variety of endorheic pans from 2003 to 2005. Seven of the species are marine fishes tolerant of low salinity (Mugil cephalus, Liza richardsonii, Monodactylus falciformis, Caffrogobius gilchristi, Rhabdosargus holubi, Solea bleekeri, Gilchristella aestuaria) with the remaining seven species being primary freshwater fishes. Three are indigenous, including Pseudobarbus burchelli, Sandelia capensis, and Galaxias zebratus of which two morphological forms were recorded within Agulhas National Park. The remaining four species are invasive aliens (Cyprinus carpio, Lepomis macrochirus, Micropterus salmoides, Micropterus punctulatus). Classification using physico-chemical variables indicated four major wetland groups, with fishes occurring predominantly in the group comprising palustrine, lacustrine and riverine wetlands, and in one instance in a brackish endorheic pan. Management actions which should facilitate conservation of indigenous fishes in the Agulhas region are suggested.

Extreme levels of intra-specific divergence among Cape Peninsula populations of the Cape galaxias, Galaxias zebratus Castelnau 1861, reveals a possible species complex

The Cape galaxias, Galaxias zebratus, is part of the paleao-endemic fauna characteristic of the south-western Cape, South Africa, and is the only galaxiid found in continental Africa. A 284-bp fragment of the cytochrome b region of the mtDNA was sequenced from 48 individual galaxiids, representing 10 populations from the Cape Peninsula. Five sequences, for four additional populations sampled at the extremes of the species range, were obtained from the literature. Analysis of cyt b mtDNA from these 14 populations of G. zebratus revealed five distinct and highly divergent lineages with low levels of intra-population mtDNA haplotype diversity. A new and distinct genetic lineage is described from the southern part of the Cape Peninsula. Estimates of genetic divergence between populations ranged from <1% to >17%. The observed level of sequence divergence represents the largest yet reported for any single fish species. The distribution of these lineages and their degree of sequence divergence refutes a model of isolation by distance. Results suggest that periods of low sea level may have been important in creating opportunities and alternative routes for dispersal and migration for Cape Peninsula populations.

Phylogenetic relationships in a small group of diminutive galaxiid fishes and the evolution of sexual dimorphism

Analysis of diverse morphological characters supports combined monophyly of the diminutive galaxiid genera Brachygalaxias (Chile) and Galaxiella (Australia), both of which are monophyletic. However, equally parsimonious trees vary in the suggested relationships among the three species of Galaxiella, and in no instance is there strong support for any particular association among them. The African Galaxias zebratus may also form a monophyletic clade when added to [Brachygalaxias + Galaxiella], though character analyses that include a wider representation among galaxiids are needed to clarify that question. Brachygalaxias and Galaxiella are distinctive among all galaxiids in having longitudinal coloration, including bright yellow to orange stripes. Brachygalaxias gothei is not sexually dimorphic (orange stripes are present in both sexes), whereas among Galaxiella species, the eastern Australian G. pusilla is dimorphic (only the smaller male has bright red stripes). The western Australian G. nigrostriata may also be dimorphic (males are sometimes described as having more vivid stripes than females), but it seems less likely in G. munda. Retention of what seems to be a juvenile character in Galaxiella, in G. munda, may suggest that it is a neotenous derivative of another Galaxiella species. Known morphological characters do not identify the sister species of G. munda, though on zoogeographic grounds it is perhaps more likely to share closest ancestry with G. nigrostriata.

A preliminary assessment of the impact of alien rainbow trout (Oncorhynchus mykiss) on indigenous fishes of the upper Berg River, Western Cape Province, South Africa

Impacts of alien rainbow trout (Oncorhynchus mykiss) on critically endangered Berg River redfin (Pseudobarbus burgi), Cape kurper (Sandelia capensis) and Cape galaxias (Galaxias zebratus) in the upper Berg River were investigated in terms of predation and spatial interactions. Trout stomach contents revealed that invertebrates dominate trout diet within the study area, whilst only six fish were recovered from 45 stomachs. The apparent low fish predation success of O. mykiss within the stream suggests a smaller impact compared to that of other alien piscivores such as bass (Micropterus spp.). Galaxias zebratus was the only fish species identified as prey, and its conservation status in the river requires further investigation. Snorkelling surveys revealed that rainbow trout co-exist with S. capensis and adult P. burgi within pools on this river. Galaxias zebratus was absent from the pools, while P. burgi juveniles were segregated from rainbow trout along a depth gradient, possibly indicating avoidance behaviour. Sandelia capensis juveniles may avoid predation by hiding under rocks. Rainbow trout probably compete with indigenous fish for food and space in the pools, though this could not be quantified. The impacts of O. mykiss on all indigenous fauna within the river are likely to be density-dependent.

Freshwater fishes of Tsitsikamma National Park

This study aimed to determine the distribution and relative abundance of freshwater fishes in the Tsitsikamma National Park. Fish assemblages in six river systems were sampled in 2001, with a total of 323 fish from eight species recorded. Indigenous fish collected included four freshwater species (Pseudobarbus afer, Pseudobarbus tenuis, Sandelia capensis, Anguilla mossambica), three estuarine species (Monodactylus falciformis, Caffrogobius gilchristi, Myxus capensis), and one alien (Micropterus salmoides). One additional indigenous species (Galaxias zebratus) and two aliens (Salmo trutta, Oncorhynchus mykiss) could potentially occur within the park. The topography and locality of the park presents a unique opportunity to meaningfully conserve the endangered P. tenuis as well as other fish characteristic of the eastern reaches of the Cape Floristic Region. Management action is required to minimise opportunities for further establishment and spread of alien fish species and to conserve indigenous fish assemblages within the park.

Combined effects of predatory fish and sublethal pesticide contamination on the behavior and mortality of mayfly nymphs

AbstractWe evaluated the potential interaction of pesticide effect and predatory fish on behavior and mortality of a stream mayfly. Experiments in laboratory stream microcosms compared the activity, drift, and mortality of Baetis mayfly nymphs in the absence of fish with that in the presence of Cape galaxias (Galaxias zebratus), both species inhabiting the same stream environments in the Western Cape of South Africa. These two predator treatments were combined with exposure either to no pesticide or to 0.2 μg/L of the organophosphate insecticide azinphos‐methyl (AZP) or 0.2 μg/L of the pyrethroid insecticide fenvalerate (FV). Such pesticide levels are known from transient spraydrift‐ or runoff‐related pesticide input into running waters. Each of the six combinations was replicated six times as 30‐min trials during the day and effects were analyzed using 2 × 2 factorial analysis of variance (ANOVA). A single exposure to either fish or pesticide significantly increased the absolute activity of mayflies, measured as number of animals visible on top of stones, and the absolute mayfly drift in the fish treatment and in the FV treatment but did not increase the mortality above 0.8%. The combination of predator presence and sublethal pesticide exposure resulted in a significant increase in the mortality rate, to about 9% in the AZP × fish and 25% in the FV × fish treatment, although the activity and drift rates were not increased compared with the single‐stressor treatments. Two‐by‐two factorial ANOVA and the comparison of expected and measured responses indicated that the mortality resulted from a synergistic interaction of the two stressors. The observed mortality was without exception caused by predation of the fish on drifting mayflies. The relative drift rate in the FV × fish treatment was decreased, again due to a synergistic interaction, which suggests an active drift avoidance reaction of the mayflies exposed to the combined pesticide × fish treatment, in contrast with those exposed just to FV. We conclude that the drift response of mayflies to transient sublethal pesticide exposure results in a synergistically increased adverse effect in the presence of predatory fish.

Combined effects of predatory fish and sublethal pesticide contamination on the behavior and mortality of mayfly nymphs.

We evaluated the potential interaction of pesticide effect and predatory fish on behavior and mortality of a stream mayfly. Experiments in laboratory stream microcosms compared the activity, drift, and mortality of Baetis mayfly nymphs in the absence of fish with that in the presence of Cape galaxias (Galaxias zebratus), both species inhabiting the same stream environments in the Western Cape of South Africa. These two predator treatments were combined with exposure either to no pesticide or to 0.2 microg/L of the organophosphate insecticide azinphos-methyl (AZP) or 0.2 microg/L of the pyrethroid insecticide fenvalerate (FV). Such pesticide levels are known from transient spraydrift- or runoff-related pesticide input into running waters. Each of the six combinations was replicated six times as 30-min trials during the day and effects were analyzed using 2 x 2 factorial analysis of variance (ANOVA). A single exposure to either fish or pesticide significantly increased the absolute activity of mayflies, measured as number of animals visible on top of stones, and the absolute mayfly drift in the fish treatment and in the FV treatment but did not increase the mortality above 0.8%. The combination of predator presence and sublethal pesticide exposure resulted in a significant increase in the mortality rate, to about 9% in the AZP x fish and 25% in the FV x fish treatment, although the activity and drift rates were not increased compared with the single-stressor treatments. Two-by-two factorial ANOVA and the comparison of expected and measured responses indicated that the mortality resulted from a synergistic interaction of the two stressors. The observed mortality was without exception caused by predation of the fish on drifting mayflies. The relative drift rate in the FV x fish treatment was decreased, again due to a synergistic interaction, which suggests an active drift avoidance reaction of the mayflies exposed to the combined pesticide x fish treatment, in contrast with those exposed just to FV. We conclude that the drift response of mayflies to transient sublethal pesticide exposure results in a synergistically increased adverse effect in the presence of predatory fish.

Intraspecific phylogeography of the Cape galaxias from South Africa: evidence from mitochondrial DNA sequences

Intraspecific phylogeography of the Cape galaxias from South Africa: evidence from mitochondrial DNA sequences

Intraspecific phylogeography of the Cape galaxias from South Africa: evidence from mitochondrial DNA sequences

Mitochondrial cytochrome b gene sequences were obtained from representatives of five populations of the Cape galaxias Galaxias zebratus. Four highly distinct genotypes were revealed, with sequence divergence values ranging from 5.8 to 13.8%. Some of the pairwise divergences are the highest yet reported for cytochrome b within a fish species, and are more typical of interspecific and intergeneric comparisons. In contrast, the low genetic divergence (0.3%) between two recently recorded populations from the Krom and Gamtoos (Kouga) Rivers indicates recent gene flow. Parsimony analysis consistently produced a tree with the population from the Olifants River on the west coast as ancestral and eastern populations as progressively more derived. Estimated divergence times for the Olifants population range from 4.4 to 6.6 million years ago. The findings suggest that another detailed revision is required to determine whether these divergent populations represent a single species or a species complex.