Trout induces a shift from preferred habitat types for indigenous species: the example of the indigenous catfish, <Emphasis Type="Italic">Amphilius uranoscopus</Emphasis> (Pfeffer, 1889), on an African montane plateau

This study investigated the impact of introduced rainbow trout, Oncorhynchus mykiss, on the distribution and feeding of mountain catfish, Amphilius uranoscopus, on the Nyika Plateau, Malawi. Twenty-four sites were sampled over three different periods in three rivers. Fish habitat units were identified as separate riffle or pool, about 100 m in length, at each site. Each habitat unit was sampled for fish, invertebrates and physical habitat characteristics. Twenty four and 20 habitat units were sampled, respectively, from sites with catfish and sites with trout and catfish. In the absence of trout, the mountain catfish was associated with all depth ranges, with strong preference to shallow and moderate depth, and moderate to fast flow on coarse substratum type (gravel, pebble and boulder). In the presence of trout, the catfish was frequently associated with very shallow depth and slow flow. In its natural habitat, the catfish fed randomly, but preferred the most abundant invertebrate taxa, especially black fly larvae (Simuliidae). In the presence of trout, the catfish preferred mostly the chironomids. The preference by catfish for Simuliidae, also preferred by trout, was less in the trout streams than in its natural habitat. The prey taxa in the catfish stream were diverse, and consisted of large invertebrate predators. Trout streams were dominated by few prey taxa, especially black flies and chironomids. The catfish of the Nyika Plateau may represent genetically unique populations in southern Africa. Introductions of trout into rivers where they currently do not occur on the Nyika should be prevented in order to maintain the genetic diversity of the Amphilius uranoscopus species complex. Handling editor: J. A. Cambray     

Some aspects of the biology of the stargazer mountain catfish,Amphilius uranoscopus (pfeffer); (Siluriformes: Amphiliidae) indigenous to Kenya streams

A study on some biological parameters of the mountain catfish, Amphilius uranoscopus Pfeffer 1889 (Silurifomes: Amphiliidae), was carried out in the Thego stream on the slopes of Mount Kenya from February to December 2002. Physical and chemical profiles of the Thego show that the water quality parameters is typical of high altitude streams with temperatures rarely exceeding 18°C, DO ranging from 7.9 to 8.2 mg l^?1 and relatively high conductivity (97–137 μS cm^?1) typical of perturbed lotic environments. A total of 1010 fish were caught by an electro‐fisher, with sizes ranging between 8 and 24 cm fork length. The population structure had a unimodal distribution with maxima at 14–16 cm. The length–weight relationship showed relatively narrow range in the slope ranging from 2.61 in April to 2.98 in February 2002, thereby suggesting isometric growth pattern. The fitted growth pattern of A. uranoscopus showed an asymptotic length (L_∞) of 28.5 cm and a growth curvature (K) of 0.56 year^?1 resulting in an estimated natural mortality coefficient (M) of 0.90 year^?1. The Fulton’s condition factor (K) was also relatively stable with a peak in April (0.92 ± 0.21) and lowest value in June (0.86 ± 0.10). As A. uranoscopus is not under commercial exploitation, the seemingly depressed population is possibly attributed to the introduced exotic rainbow trout that heavily predates on the species and environmental perturbations arising from changes in land use. The implications of such changes on A. uranoscopus are discussed.     

The impact of non-native rainbow trout within Afro-montane streams in eastern Zimbabwe

Non-native trout species have been associated with many negative effects in receiving ecosystems. The first aim of this study was to determine the impact of non-native rainbow trout Oncorhynchus mykiss on distribution and abundance of native mountain catfish Amphilius uranoscopus within Afro-montane streams in Nyanga Mountains, eastern Zimbabwe. The second aim was to compare macro-invertebrate community responses to the presence of the trout and the catfish. We examined trout impact on catfish’s habitat associations, whereas macro-invertebrate composition was compared using open fish and fish exclosure experiments in habitats with and without trout. Trout influenced both the distribution and abundance of the catfish that occupied shallow reaches possibly to avoid predation from trout that occurred in the deeper habitats. Within trout invaded reaches, most macro-invertebrate taxa were more abundant in exclosure than open treatments. By contrast, within trout-free reaches, most macro-invertebrates either did not differ between treatments or were generally more abundant in open than exclosure treatments. This suggests that the macro-invertebrate communities responded differently within invaded and non-invaded reaches. By influencing distribution and abundance of native biota, non-native rainbow trout may have wider ecological effects, such as influencing trophic interrelationships within invaded habitats.     

Peculiar hyporheic habitat of some <Emphasis Type="Italic">Rhyacophila</Emphasis> species (Trichoptera; Rhyacophilidae) in Japanese mountain streams

We investigated the distribution patterns of Rhyacophila larvae at 2 habitat scales in mountain streams in central Honshu. One was at a rapid glide within a stream reach and the other was in microvertical layers within each rapid and glide. Cobbles were predominant in rapids, whereas sand and gravels were predominant in glides. Mean sediment particle size was smaller in glides, but evenness of sediment size and porosity were greater. A total of 9 species of Rhyacophila larvae were collected from rapids. On the other hand, in glides, only 4 species, R. nipponica, R. shikotsuensis, R. kawamurae, and R. transquilla, were collected, but they were more abundant than in rapids. The larvae of R. transquilla were found mainly in upper layers of the stream bed, whereas the other 3 species, R. nipponica, R. shikotsuensis, and R. kawamurae, occurred both in upper and lower layers. The latter 3 species belong to R. nigrocephala species group, the larvae of which share several common morphological and behavioral characters adapted to hyporheic habitat, such as slender body shape and vermicular movement. It is suggested that higher porosity in glides provides more microhabitat for them, and small-sized sediment particles are appropriate for their burrowing and creeping movement in hyporheic habitat.     

Population Genetic Structure of Astyanax scabripinnis (Teleostei, Characidae) from an Urban Stream

Despite the great anthropogenic interference on urban streams, information is still scarce about the genetic variability and structure of native fish populations inhabiting such streams. In the present study, random amplified polymorphic DNA (RAPD) markers were used to analyze genetic variability and structure of populations assigned to the Neotropical fish species Astyanax scabripinnis from an urban stream located in Londrina, Paraná State, southern Brazil. Thirty individuals of this species were collected from three sites throughout the upper Cambé stream. A total of 10 primers amplified 159 loci, of which 128 (80.5%) were polymorphic. Each of the three populations showed very similar proportions of polymorphic loci, which ranged from 63.5 to 64.8%. Unbiased genetic distances varied from 0.0612 to 0.0646. Theta_p-test values indicated moderate to high genetic differentiation among individuals from different localities. The number of migrants varied from 1.34 to 1.46, suggesting a low gene flow between populations. The genetic similarity among all individuals studied ranged from 0.424 to 0.848. The results suggest that populations of A. scabripinnis in Cambé stream are undergoing genetic differentiation.     

The fish fauna of mountain streams in the Guanshan National Nature Reserve, Jiangxi, China

Guanshan National Nature Reserve (GNNR) is located in the middle reach of the Jiuling Mountain Range in the southern China and the first national nature reserve within Jiangxi Province. The fish fauna of mountain streams in the GNNR was investigated from September 2006 to August 2007. A total of 379 fish were collected and classified into two families and seven species. Acrossocheilus parallens [relative abundance (RA) 44.3%] was the most abundant fish species. Subdominant species were Onychostoma barbata (RA, 20.3%), Zacco platypus (RA, 14.2%) and Opsariichthys bidens (RA, 12.4%).A greater number of species (7 vs. 2) and individuals (295 vs. 84) were collected from the West Stream compared to the East Stream. Among the seven fish species collected in the GNNR, Acrossocheilus parallens, Onychostoma barbata and Vanmanenia stenosoma are endemic to the Chinese mountain streams. This study suggests that mountain streams in the nation reserves including GNNR are very important for freshwater fish diversity and conservation in Jiangxi Province.     

Predator–prey interactions in river networks: comparing shrimp spatial refugia in two drainage basins

1. Analysis of drainage networks provides a framework to evaluate the densities and distributions of prey species relative to locations of their predators. Upstream migration by diadromous shrimp (Atya lanipes and Xiphocaris elongata) during their life cycle provides access to headwater refugia from fish predation, which is intense in estuaries and coastal rivers. 2. We postulate that geomorphic barriers (such as large, steep waterfalls >3.5 m in height), can directly limit the distribution of predatory fishes and, indirectly, affect the densities of their prey (freshwater shrimps) in headwater streams. 3. We compared densities of shrimp in pools above and below waterfalls, in four headwater tributaries in two river basins of the Luquillo Mountains of northeastern Puerto Rico. We measured shrimp densities twice a year over 8 years (1998–2005) in Prieta, Toronja, Bisley 3 and Bisley 5 streams, which differ in drainage network positions relative to steep waterfalls in Río Espíritu Santo and Río Mameyes. 4. Predatory fishes are absent in the Prieta and Toronja pools and present in Bisely 3 and in lower Bisley 5 pools. Atya lanipes and X. elongata rarely occur in the Bisley streams where predatory fishes are present but these shrimps are abundant in Prieta and Toronja, streams lacking predatory fishes. 5. The mean carapace length of X. elongata is longer in pools where fish are present (Bisley 3 and lower Bisley 5) than in pools lacking fish (Prieta, Toronja, Upper Bisley 5). The increased body size is primarily due to significantly longer rostrums of individuals in stream reaches with fish (below waterfall barriers) than in those reaches lacking fish (above waterfall barriers). Rostrum length may be an adaptation to avoid predation by visually feeding fishes. 6. Atya lanipes and X. elongata distributions and densities were predicted primarily by drainage network position relative to the presence or absence of predatory fishes. High, steep waterfalls effectively impeded fish from moving upstream and created a spatial refuge. Xiphocaris elongata may rely on size refugia (longer rostrum) to minimize predation where spatial refugia are lacking.     

Leaf‐litter colonisation and breakdown in relation to stream typology: insights from Mediterranean low‐order streams

1. Scant information is available on leaf breakdown in streams of arid and semiarid regions, including the Mediterranean, where environmental heterogeneity can be high and the relationship between stream characteristics and leaf breakdown is poorly known. We tested the hypotheses that differences in leaf breakdown metrics would be substantially higher between mountain and lowland Mediterranean streams than among streams within each subregion and that variability among streams would be substantially higher in the lowlands, because permanent reaches in the semiarid lowland streams are rare and isolated. 2. We compared leaf breakdown and associated dynamics of nutrients, fungi and invertebrates in low‐order Mediterranean streams draining sub‐humid forests in the Sierra Nevada Mountains and nearby semiarid lowlands of south‐eastern Spain. Streams differed between the two subregions mainly in water ion content, temperature and riparian tree cover. We detected higher environmental heterogeneity among streams within the lowlands compared to the Sierra Nevada mountain range. In the lowlands, breakdown coefficients (k) of alder leaves spanned almost the entire range reported for this species from temperate streams, overlapping with less variable breakdown coefficients in the Sierra Nevada. 3. The high variability of k values among the lowland sites appeared to be caused primarily by variability in the composition and abundance of a few leaf‐consuming invertebrate taxa, particularly the snail Melanopsis praemorsa. Fungal and nutrient dynamics were less variable among sites within each subregion. 4. These results indicate that the critical condition for stream functional assessment of well‐constrained breakdown rates, or related metrics, could be met at reference sites within homogenous bio‐geo‐climatic regions such as the Sierra Nevada. By contrast, in heterogeneous areas such as the semiarid lowland streams, natural variability of breakdown rates can greatly exceed the magnitude of effects expected in response to anthropogenic disturbances.     

Freshwater fugu or pufferfishes of the genusTetraodon from the Mekong basin, with descriptions of two new species

The fresh waters of the Mekong basin are inhabited by five species of the pufferfish genusTetraodon Linnaeus, 1758 (sensu lato): the widely distributedT. leiurus Bleeker, 1851; two previously described species endemic to the Mekong,T. baileyi Sontirat, 1989 andT. suvattii Sontirat & Soonthornsathit, 1985; one new species endemic to the Mekong basins.Tetraodon baileyi has now been collected numerous times but only in or near rapids;T. abei, T. barbatus andT. suvattii are often but not exclusively associated with rapids or at least swift flowing streams; whileT. leiurus is found in almost all habitats except rapids.Tetraodon abei andT. barbatus are closely related toT. leiurus, from which they differ most strikingly in coloration.Tetraodon survattii differs from all of the others in having a strongly upturned mouth and light and dark stripes or spots radiating outwards from the eye.Tetraodon baileyi, the most distinctive Mekong pufferfish, has head and body more or less extensively covered with dermal cirri and is entirely scaleless.     

Future increase in temperature may stimulate litter decomposition in temperate mountain streams: evidence from a stream manipulation experiment

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Diel Habitat Partitioning by Bull Charr and Cutthroat Trout During Fall and Winter in Rocky Mountain Streams

We used underwater observation to determine diel habitat partitioning between bull charr, Salvelinus confluentus, and cutthroat trout, Oncorhynchus clarki, during fall and winter (0.1–8.3°C) in two Rocky Mountain streams that differed in habitat availability. The majority (>70%) of both species emerged from concealment cover at night, though bull charr exhibited a greater tendency for nocturnal behavior than cutthroat trout. Differences in day and night counts were most pronounced at temperatures <3°C, when very few fish of either species were observed in the water column during the day, but both species were common at night. Both species used concealment cover of large woody debris and boulder substrate crevices in deep pools during the day. At night, fish emerged from cover and habitat use shifted to shallow water with low cover. Microhabitat partitioning among species and size classes occurred at night, cutthroat trout moving into shallower, faster water that was farther from cover compared to bull charr. Smaller fish of both species occupied focal positions in slower, shallower water closer to the substrate than larger fish. Large, mixed-species aggregations also were common in beaver ponds both day and night. High variation in diel and site-specific winter habitat use suggests the need for caution in developing habitat suitability criteria for salmonids based solely on daytime observations or on observations from a few sites. Our results support the need to incorporate nocturnal habitat use and partitioning in studies of salmonid ecology.     

Comparison of Antipredator Responses of Two Related Water Striders to a Common Predator

This study compares the antipredator responses of two congeneric water striders that live in different habitats yet share a common predator. Aquarius nebularis and A. remigis are stream-dwelling species of water striders found in close association in central Kentucky. Aquarius nebularis typically inhabit third- and fourth-order streams that support diverse and complex fish communities; A. remigis inhabit adjacent first- and second-order tributaries that tend to have either no fish or relatively few fish patchily distributed. The ecological conditions for these two species are distinctly different, yet the green sunfish (Lepomis cyanellus) is a surface-feeding predator and a potential risk to both species. In experimental pools with sunfish, an initial fish strike caused A. remigis to move to the edge of the pool and become inactive. For the rest of the observation period, A. remigis reduced behaviour patterns that attract predators such as skating on open water, mating and male–male aggression. The proportion of A. remigis missing from sunfish pools was 5 times higher than in pools lacking fish, suggesting that 20% of water striders were killed by predation. In contrast, an initial fish strike caused A. nebularis to exhibit a burst of activity as individuals erratically skated over the open water. They then resumed the less active pre-attack behaviours a short time later. Aquarius nebularis showed none of the antipredator behaviours typical for A. remigis. Furthermore, the proportion of A. nebularis missing from sunfish pools did not differ from that in pools without fish. Although antipredator behaviour has been examined for relatively few species of water striders, this study suggests that the behaviour of the most commonly studied species, A. remigis, may not be indicative for water striders in general., Corresponding author: James J. Krupa, School of Biological Sciences, University of Kentucky, Lexington, KY 40506-0225, U.S.A. E-mail: bio149@pop.uky.edu bio149@pop.uky.edu     

Spatial and temporal variation of fish assemblage in two intermittent streams in north‐western Zimbabwe

This study examined the spatial and temporal variation in fish assemblage composition within two intermittent streams in north‐western Zimbabwe. Eight sites were sampled during three different periods of flow. Twenty‐five species in eight families, dominated by cichlids and cyprinids, were collected. Redundancy analysis (RDA) was used to explore the relationship between species and their environmental correlates. According to variation partition, 68.1% of assemblage variation was explained by both habitat and temporal variables. Most species were associated with large pools, whereas small species were associated with habitats that had gravel and boulders. The temporal aspect suggested a pattern associated with high catch per unit effort (CPUE) for the mormyrids, Clarias gariepinus and Labeo altivelis, during the early rain period. By comparison, the late rain period was associated with high CPUE for Labeo cylindricus, Labeobarbus marequensis, Chiloglanis neumanni and Oreochromis mortimeri, whereas the rest of the species had high CPUE during both the late rain and dry periods. The assemblage composition was more diverse during the late rain period. Refuge availability during the dry period appeared to be essential for the assemblage of the intermittent streams. Protection of these temporal habitats is therefore important in conserving fish assemblages within intermittent streams of the Lake Kariba area.     

Importance of landscape context for post‐restoration recovery of riparian vegetation

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Information spiraling: Movement of bacteria and their genes in streams

Bacteria in transport in streams are largely derived from other parts of the ecosystem. Here we review factors that influence transport of bacteria and their movement between habitats (such as sediment, water column, rocks, wood, and leaves) and consider the role of these movements in ecosystem processes. Bacteria enter the water column by sloughing, scouring, as a consequence of changes in morphology or hydrophobicity, or dislodgment by invertebrates and fish or other aquatic vertebrates. Transported cells (which may be planktonic or particle-associated) that colonize surfaces may establish new gene pools through cell division (vertical transfer) or genetic exchange (lateral transfer). Genetic information is also transported in streams as free or protected DNA or in bacteriophages. Movement of these vectors causes genetic information to spiral along a stream in a manner analogous to that of nutrients and organic carbon. Spiraling refers to the pattern of transport, uptake or attachment, and release of a molecule or cell. The flow of water in streams causes this cycle of attachment and release to be displaced downstream resulting in a spiral rather than a closed, stationary loop. Offprint requests to: L. G. Leff.     

皖南凹耳臭蛙地理分布格局与生境选择

凹耳臭蛙(Odorrana tormota)是一种小型山溪蛙类,由于叫声独特,种内具有超声通讯功能而引起国内外相关专家的广泛关注。首次针对皖南凹耳臭蛙地理分布、生境选择以及人为干扰强度对种群密度的影响进行了研究。共调查了9县1区32条不同的山溪,发现其中的16个有凹耳臭蛙分布,除黄山区的香溪和浮溪具文献记录外,其余14个分布点均为首次报道。基于现存凹耳臭蛙分布点的水系关系,推测该物种在皖南的分布呈现出以青弋江、新安江和水阳江三大水系为纽带、间断分布的格局。对其中10个分布点222只凹耳臭蛙生境选择的统计结果表明,在夜晚活动周期内,该物种对乔木、灌木丛、草本植物、岩石、沙滩和倒伏朽木等不同生境的选择具有显著差异(F5,54=25.75,P0.001),栖息在草本植物和灌丛中蛙的数量明显多于栖息在其它几种生境类型中的蛙类。暗示溪流沿岸的草本植物和灌丛对该物种的生存和繁衍具有重要意义,乔木对其非活动周期的隐蔽可能具有不可替代的作用。根据人类活动对其栖息地破坏程度,将人为干扰程度划分为强、中和弱3种不同强度,对不同干扰强度下种群相对密度进行单因素方差分析。结果表明,中等干扰强度下的种群密度显著高于其它两种强度下的种群密度(F2,13=8.155,P=0.005)。推测适度的人为干扰可能增加了栖息地内昆虫的种类和数量,对蛙类的生存和繁衍更为有利。但随着人为干扰强度的增强,对溪流沿岸植被的破坏更为剧烈,种群密度显著下降。     

FIRST RECORD OF OREOCHROMIS MACROCHIR (BOULENGER, 1912) (PISCES:CICHLIDAE) FROM THE LIMPOPO RIVER IN SOUTHERN AFRICA.

Summary

During 1973/74, Barbus poechii, Oreochromis macrochir, O. andersonii, Serranochromis angusticeps, S. codringtonii, S. robustus and S. thumbergi from the Okavango System were introduced into the Shashe Dam (Limpopo System, Botswana). These species are alien to the Limpopo System. A fish survey during September 1991 disclosed the presence of two specimens of the greenhead tilapia O. macrochir in a large natural pool in the Limpopo River 7 tan downstream from the Shashe/Limpopo confluence. In August 1992 another specimen was caught in this pool. It is surmised that the likely origin of these specimens is the Shashe Dam. There is a possibility that the greenhead tilapia may interbreed with the indigenous Mocambique tilapia O. mossambicus. Consequently the genetic integrity of O. mossambicus in the Limpopo River may become suspect. If the other alien species introduced into the Shashe Dam reach the Limpopo River, O. andersonii may also interbreed with O. mossambicus while the Serranochromis spp. could be detrimental for feeding relationships in the Limpopo River and its tributaries. The impact that B. poechii could have is uncertain but it does not appear to co-exist with the closely related B. trimaculatus of the Limpopo System. Eradication of O. macrochir in the Limpopo River is not practical. Further stocking of the Shashe Dam as well as other impoundments in the Limpopo System with alien fish species should be discouraged.     

The ecology of the calanoid copepod Eurytemora affinis in salt marsh tide pools

We describe selected aspects of the ecology of the copepod Eurytemora affinis in tide pools of an inland salt marsh near L'Isle-Verte, Québec along the southern shore of the St. Lawrence estuary. E. affinis performed daily horizontal migrations moving from the centers of pools to the banks and into dense algae. Male E. affinis were mainly found in the center of the pools during twilight (21 : 00 hrs) and in dense algae in daylight (12: 00 hrs) whereas most females and copepodites were found near the banks at all three sampling periods. Although these daily movements among sites may have minimized predation by diurnally foraging sticklebacks (Pisces: Gasterosteidae), other explanations for the movements can not be excluded. We also quantified the effects of fish predation upon the population structure of E. affinis. Densities of all stages (nauplius, copepodite, adult) were significantly lower in pools with fish than in pools without fish. Female E. affinis were significantly smaller (mean length) in pools with fish than in pools without fish, indicating that the sticklebacks selectively ate larger females. Male-biased sex ratios were found in both types of pools, which excluded the possibility that biased ratios in this species are caused by selective predation upon the females.     

Refugia and habitat partitioning among midges (Diptera: Chironomidae) in rain-pools

ABSTRACT.

• 1 Rain-pools on granite exposures are common in tropical Africa and they are inhabited by the larvae of two midge species, Chironomus imicola Kieffer and Chironomus pulcher Wiedemann.
• 2 These pools differ from other ephemeral island habitats such as carrion, fallen fruit, sap flows, mushrooms and dung in their high degree of spatial predictability. Most pools are predictably inhabited by either C.imicola or C.pulcher. This finding is considered in the light of contemporary competition theory.
• 3 An arrangement whereby the same species repeatedly invades the same temporary habitat indicates that there is something about the habitat itself causing the discrimination. I suggest that degree of exposure to sunlight may provide a cue allowing females to discriminate between pools as oviposition sites.
• 4 Both species survive the long dry season by retreating to pools of river water left by receding rivers. Dispersal to rain-pools by emerging adults occurs during the following season with imicola occupying rain-pools remote from shaded rivers. Appropriately, measured against pulcher, the biology of imicola is that of a colonizing species.
• 5 The possibility is discussed that the chironomids in rock-pools do not survive to breed. Instead, these populations may be maintained externally, for example by invasions from breeding populations in the Great Lakes of Africa, where larval densities may be too low to be detected by sampling. The evolutionary implications of such a situation are considered.

     

Life Cycle of Himalopsyche japonica (Morton) (Trichoptera: Rhyacophilidae) in Two High Mountain Streams in Nagano, Central Japan

The life cycle of Himalopsyche japonica (Morton) was studied in two high mountain streams at about 1500 m a.s.l. from September 2000 to May 2002 in central Japan. The life cycles in both streams are univoltine. Larval development in upper streams with cooler water is slower than in lower streams with warmer water. The relationships between voltinism or larval size and water temperature are discussed.