The effects ofTilapia introductions in Lake Luhondo,Rwanda

Synopsis Cyprinid fishes apparently constituted the major part of the original fish fauna in Lake Luhondo, Rwanda, at least until 1934. At that time only three species, all cyprinids, were known from the lake:Barbus neumayeri, a small barbel, very common in the lake (described from the lake asBarbus luhondo) and two larger cyprinid species:Barbus microbarbis andVaricorhinus ruandae. These two large species were probably not very common in the lake. Between 1935 and 1938 some youngTilapia were introduced into Lake Luhondo. Since then and certainly since 1952 the large cyprinids seem to have disappeared completely from the lake. The smallBarbus neumayeri has become extremely rare; at present it survives only in some small tributaries of the lake. In the lake itselfTilapia andHaplochromis species are now the dominant fauna. A survey of the available information is given.Africa-Museum, Steenweg op Leuven, B-1980 Tervuren, Belgium (mailing address)     

Papyrus swamps and the respiratory ecology of Barbus neumayeri

Synopsis In seasonally flooding fresh waters, dissolved oxygen and fluctating water levels combine to create strong seasonal changes in habitat availability and dispersal pathways for fishes. In this study we demonstrate how respiratory mode can affect the use of and dispersal through hypoxic papyrus swamps for a small cyprinid fish, Barbus neumayeri, a species which uses aquatic surface respiration (ASR) in response to severe hypoxia. Monthly records of the distribution and relative abundance of B. neumayeri across 28 stations in a papyrus swamp in Uganda were used to examine seasonal patterns of habitat use and movement. The distribution of B. neumayeri was very restricted during the drier months. Most fish were captured in open pools and channels with large areas of open water surface and higher oxygen. Movement of B. neumayeri was limited to short periods during the wet season when peak water levels produced high levels of oxygen and pathways for movement. Three lines of evidence suggest that these patterns relate to its respiratory mode. These include: the positive :relationship between dissolved oxygen and the number of stations used per month, the positive relationship between fish density at dry season stations and dissolved oxygen, and the absence of fish from stations with. little open water surface area during the dry season. Significant differences in the gill morphology between B. neumayeri from the papyrus swamp and those from the main river suggest that papyrus swamps may contribute to the diversification of B. neumayeri by limiting movement and demanding specialization for extremely hypoxic waters.     

Interdemic variation in the foraging ecology of the African cyprinid, Barbus neumayeri

In the African cyprinid, Barbus neumayeri, populations from hypoxic waters have larger gills than populations from well-oxygenated streams. Differences in trophic morphology and feeding performance between these populations suggest a reduction in feeding efficiency in large-gilled fish that may reflect spatial constraints of the gills. However, this variation may also reflect interdemic variation in diets. In this study, we describe patterns of variation in diet, gut morphology, and prey availability for populations of B. neumayeri from swamp (low-oxygen) and stream (high-oxygen) sites in Kibale National Park, Uganda. Our results indicate that B. neumayeri are omnivorous, feeding primarily on benthic prey items; however, diets differed among swamp and stream sites for certain prey types. The observed dietary differences do not provide direct support for predictions based on variation in trophic musculature; hard-bodied prey were more common in low-oxygen sites. Prey availability also differed among sites; in particular, insect abundance and richness was generally lower in the swamp sites. Gut length was longer in one of the four populations, but did not conform to expectations based on diet differences. Condition and growth rates did not differ between populations from hypoxic and well-oxygenated sites, despite observed differences in prey availability and diet, suggesting that B. neumayeri may be distributed in a way that equalizes fitness among populations in different habitats.     

Geographic variation of Barbus radiatus Peters,a widely distributed African cyprinid fish

Synopsis Barbus radiatus is a widely distributed, polytypic species with three recognized subspecies: radiatus Peters (1853), aurantiacus Boulenger (1910), and profundus Greenwood (1970). A phenetic analysis of relative similarity was conducted for specimens of B. radiatus from throughout its known range. The study focuses on several large population samples taken recently along the presumed central Zambian interface between the subspecies aurantiacus and radiatus. New data on meristic and morphometric variation in B. radiatus and recent rediscovery of typical radiatus in Lake Victoria demonstrate that profundus is a species distinct from radiatus. With respect to the remaining two subspecies, results indicate a populational mosaic of highly variable morphs rather than two discrete, allopatric morphs. Thus, aurantiacus is placed in synonymy of radiatus. It is hypothesized that the populational mosaic of morphology in radiatus reflects adaptive ecotypic responses to water temperature and current velocity. The characters which accounted for most of the geographic variation of radiatus were body depth, caudal peduncle length, longitudinal meristic counts, dorsal fin height, and orbit diameter.     

Genetic diversity and population structure of the endangered ripon barbel,Barbus altianalis (Boulenger, 1900) in Lake Victoria catchment,Kenya based on mitochondrial DNA sequences

Approximately 850 bp of the mitochondrial control region was used to assess the genetic diversity, population structure and demographic expansion of the endangered cyprinid Barbus altianalis, a species known to be potamodramous in the Lake Victoria drainage system. The 196 samples taken from the four main rivers draining the Lake Victoria catchment (Nzoia, Yala, Nyando and Sondu–Miriu) yielded 49 mitochondrial DNA haplotypes; 83.7% thereof were private haplotypes restricted to particular rivers. The overall mean haplotype diversity was high (0.93663 ± 0.008) and ranged between 0.566 (Sondu – Miriu) and 0.944 (Nzoia). The overall mean nucleotide diversity was low (0.01322 ± 0.00141), ranging from 0.0342 (Sondu – Miriu) to 0.0267 (Nzoia). Population differentiation tests revealed strong and highly significant (P ≤ 0.001) segregation of populations in the four river basins. F_ST values among the four river‐based populations ranged from 0.05202 to 0.44352. The samples formed two main haplotype networks based on a 95% parsimony criterion, each exhibiting a strong signature of past population expansion. The smaller network was restricted to the River Nzoia, whereas the larger network contained representatives from all four rivers; within this the central haplotypes were found in more than one river, whereas the peripheral haplotypes tended to be river‐specific. The degree of population differentiation and the number of river‐specific haplotypes are too high to be explained by recent anthropogenic impacts alone and suggest that the species has probably existed in the Lake Victoria catchment as two populations: the now ‘extinct’ migratory population and the extant river restricted non‐migratory populations.     

Rare and asymmetrical hybridization of the endemic Barbus carpathicus with its widespread congener Barbus barbus

In endemic species that co-occur with widespread congeners, hybridization can lead to an influx of novel and beneficial genetic variation, but high rates of introgression may cause genetic swamping of the endemic species and have detrimental effects on its survival potential. This study examines hybridization between sympatric populations of the Carpathian barbel Barbus carpathicus , a recently discovered cryptic species with a restricted range, and the widespread common barbel Barbus barbus . Based on six diagnostic allozyme loci, a microsatellite locus and mtDNA, hybrids were found to be present at multiple localities within the Vistula River drainage (Baltic Sea) as well as in the Tisza River system of the Danube River drainage (Black Sea). However, the numbers of hybrids were very low; four individuals of 230 fish sampled from the Vistula drainage. Bayesian assessment of their nuclear genotypes suggested that two hybrids in the Vistula drainage and nine in the Tisza system were F₁ generation, and one in the Vistula drainage and one in the Tisza system were backcrosses (BC) to B. barbus , while no F₂ or BC to B. carpathicus were detected. No hybrid carried B. carpathicus mtDNA and cytonuclear linkage disequilibria showed significant positive associations between hybrid genotypes and B. barbus mtDNA, suggesting unidirectionality in the interspecific mating with a disproportionate contribution of B. barbus mothers. Despite geographically broad occurrence of hybrids, these data provide evidence of strong constraints on hybridization in the native breeding habitats and the lack of introgression towards B. carpathicus .     

Phylogenetic investigations on the haplochromine Cichlidae of Lake Kivu (East Africa), based on lepidological characters*

The phylogeny of the haplochromine cichlids of Lake Kivu was studied using lepidological characters. Only one species, Haplochromis astatodon was found to have a closer relationship to a group outside Lake Kivu, namely Haplochromis sensu stricto. The other 14 species form a monophyletic lineage that is part of a subdivision in the large Lake Victoria-Edward-Kivu flock. The internal phylogeny of this lineage was resolved to the species level.     

A population study of Barbus barbus (L.) in the River Severn, England

The results of the application of Schnabel (Chapman modification), Schumacher & Eschmeyer, Fisher & Ford, and Jolly capture-recapture techniques on the Barbus barbus (L.) population in four areas of the middle Severn are compared. The survival of tagged fish varied in different areas and fish released in some time periods were less vulnerable to recapture than fish released from other samples. It is suggested that the shoaling behaviour of Barbus barbus resulted in non-random mixing of marked fish. The average population size of Barbus barbus greater than 18 cm in length in each of the four sections for the total period of investigation gave population densities ranging from 0.024/m² to 0.202/m².     

Natural hybridization of two species of tetraploid barbels: Barbus meridionalis and Barbus barbus (Osteichtyes, Cyprinidae) in southern France

Natural hybridization of Barbus barbus and B. meridionalis has been demonstrated in southern France. A genetical study (isozyme electrophoresis) of these species and their hybrids revealed the characteristics of hybridization. Ten enzyme markers and five morphological parameters were used to distinguish between the two parent species. Enzymatic divergence between the parent species included fixed allelic differences at certain loci and reduction in enzymatic activity, including the silencing of certain genes. A morphological study revealed a good correlation between the isozyme markers and morphological characters. Backcrosses were observed and this raises the question of the integrity of the parent species.     

Morphologic and genetic variability in the Barbus fishes (Teleostei,Cyprinidae) of Central Italy

Italian freshwaters are highly biodiverse, with species present including the native fishes Barbus plebejus and Barbus tyberinus that are threatened by habitat alteration, fish stocking and invasive fishes, especially European barbel Barbus barbus. In central Italy, native fluvio‐lacustrine barbels are mainly allopatric and so provide an excellent natural system to evaluate the permeability of the Apennine Mountains. Here, the morphologic and genetic distinctiveness was determined for 611 Barbus fishes collected along the Padany–Venetian (Adriatic basins; PV) and Tuscany–Latium (Tyrrhenian basins; TL) districts. Analyses of morphological traits and mitochondrial DNA sequence data explored the natural and anthropogenic factors that have shaped their distribution ranges. Over 100 alien B. barbus were recorded in the Tiber basin (TL district) and Metauro basin (PV district). Comparisons of genetic and morphometric data revealed that morphometric data could identify alien B. barbus from native Barbus, but could not differentiate between B. tyberinus and B. plebejus. Genetic analyses revealed ~50 D‐loop mtDNA haplotypes and identified a distinct Barbus lineage present only in the Vomano River at the southern boundary of PV district. Demographic expansion and molecular variance analyses revealed a lack of geographic structuring across the sampling regions. While the contemporary B. plebejus distribution has been driven primarily by anthropogenic fish translocations, the dispersal of B. tyberinus has been via natural dispersion, including their crossing of the Apennine Mountains via temporary river connectivity. The results also revealed that the Barbus fishes of the mid‐Adriatic region of Europe have a complex pattern of local endemism. To conserve these patterns of genetic uniqueness, especially in the mid‐Adriatic basins, Barbus fishes should be managed by treating them as unique evolutionary units and ceasing translocations of all Barbus fishes between river basins.     

A behavioural study of hybridization between Barbus barbus and Barbus meridionalis

The reproductive behaviour of two species of barbel ( Barbus barbus and Barbus meridionalis ) was investigated by means of aquarium experiments in several matings of six combinations. The reproductive behaviour of the two species appears to be similar and hybridizations were observed, showing that no complete behavioural barrier blocks the mating of the two species.     

Migratory behaviour shapes spatial genetic structure of cyprinid fishes within the Lake Malawi catchment

• Genetic differences among freshwater fish populations are dependent on life‐history characteristics of the species, including the range of adult dispersal and the extent of homing to natal breeding grounds. However, the effects of variation in such characteristics on population genetic connectivity are rarely studied comparatively among closely related species.
• We studied population genetic structure within three congeneric cyprinid species from the Lake Malawi catchment that differ substantially in life‐history traits and conservation status, using a combination of microsatellite and mitochondrial DNA markers. Mpasa (Opsaridium microlepis) is a large (70 cm total length) migratory species that spawns in rivers, but as an adult is exclusively known from the main lake body. Sanjika (Opsaridium microcephalum), is a medium size (30 cm total length) species that exists in lake breeding, river‐lake migratory and apparently landlocked populations. Dwarf sanjika (Opsaridium tweddleorum) is a small non‐migratory species (15 cm total length) that persists in small tributaries surrounding the main lake and adjoining rivers.
• The results revealed striking differences among the three species in spatial genetic structuring. The river‐lake migratory mpasa showed only weak yet significant population genetic structure within the main Lake Malawi catchment, suggesting that there is no strong natal homing. The habitat‐generalist sanjika showed only weak spatial genetic differentiation at microsatellite loci within the Lake Malawi catchment, but moderate structure in mitochondrial DNA, potentially reflecting male‐biased dispersal. The river‐restricted dwarf sanjika showed strong genetic structure in both microsatellite and mitochondrial DNA, suggesting strictly limited dispersal at both adult and juvenile stages.
• We conclude that contrasting migration life histories have resulted in dramatically different patterns of population genetic structure among these congeneric species. The observed patterns demonstrate how divergent life‐history evolution may strongly influence broader patterns of population genetic connectivity in freshwater fish, with consequences for management and conservation. Specifically the results suggesting gene flow among Lake Malawi populations of mpasa, an IUCN red‐listed ‘Endangered’ species endemic to the lake catchment, imply that conservation initiatives operating at both local and catchment scales are needed to reverse local population decline.

     

Role of thyroid hormone in the ontogeny and morphological diversification of <Emphasis Type="Italic">Barbus intermedius sensu</Emphasis> Banister, 1973 of Lake Tana in Ethiopia

The role of thyroid hormone in the ontogeny of the Large African barb Barbus intermedius sensu Banister, 1973 (Teleostei; Cyprinidae)—the presumed ancestral species for the species flock of the large African Barbs of Lake Tana (Ethiopia)—has been studied. It has been shown that the thyroid hormone influences the timing and rate of many morphogenetic processes and a change in its level causes heterochronies, affecting the definitive morphology of fish. Thus, it can be assumed that even a slight change in activity of the thyroid axis during ontogeny can be the cause of wide morphological variability in B. intermedius and may underlie explosive diversification of the species flock of Large African Barbs of Lake Tana.     

The North Mediterranean Barbus lineage: phylogenetic hypotheses and taxonomic implications based on allozyme data

On the basis of distinct ecological and morphological characters, the European Barbus taxa have been clustered in two groups: a fluvio-lacustrine and a rheophilic or strictly riverine one. These two groups (or ecophenotypes) were recognized in different parts of Europe, and formed either a species assemblage ( Barbus barbus group) or a polytypic species ( Barbus meridionalis ). The hypothesis was that species of the same group belong to the same phylogenetic lineage (clade) and are the result of the same transcontinental colonization event. The analysis, using allozyme markers, of 10 taxa of the genus Barbus from France, Italy, Greece, the Czech Republic and Slovakia, showed that the taxa thought to belong to the fluvio-lacustrine and the rheophilic groups are not monophyletic. The results suggest that probably in each sub-region, the founding taxon has diverged independently to form species of two different ecophenotypes, one occupying the upstream rivers and the other the lowland rivers. Accordingly, Barbus species groups represent clusters of morphologically convergent taxa living in equivalent biotopes.     

Physiological advantages may contribute to successful invasion of the exotic Cyprinus carpio into the Xingyun Lake, China

Feeding and growth traits of Cyprinus carpio and Cyprinus pellegrini (both at age-0) were compared in three experiment, in an attempt to analyze potential causes for the displacement of the native C. pellegrini in the Xingyun Lake, Yuxi, Yunan, China. Experiment I was conducted in water which fluctuated between 15 and 20°C. Experiment II and III were conducted in a laboratory and water temperature was maintained between 20°C and 25°C, respectively. Three common trends were noted for all three experiments: (1) feeding rate of C. carpio was lower than that of C. pellegrini, and this difference was found to be significant in experiment I; (2) growth rate of C. carpio was higher than C. pellegrini, and the difference was found to be significant in experiment II; (3) food conversion efficiency and energy retention efficiency for C. carpio were higher than those of C. pellegrini, and significant differences were noted in experiment I and II. Since the growth period for fish in the Xingyun Lake generally occurs when water temperatures are between 15 and 25°C, it can be suggested that C. carpio has advantages over C. pellegrini in growth and food utilization efficiency, and lower food consumption than C. pellegrini. These physiological traits of C. carpio might allow this species to be more resistant to food shortage and predation, and may be partially responsible for the displacement of C. pellegrini by C. carpio.     

Changes of Skull Proportions in Ontogeny of Barbus canis from Lake Kinneret and of the Lake Tana large-mouthed barbs, Barbus intermedius Complex

Skull proportions of Barbus canis individuals drastically change during their life. Yearlings have skull proportions characteristic for barbs of the NEC phenetic group (sensu Mina et al. 2001 Environ. Biol. Fish. 61: 242–252), but with age become similar to those of the Lake Tana large-mouthed morphotypes which acquire their specific features at 3–7 years old while at earlier ages they have skull proportions of a NEC form identified as 'intermedius' sensu Nagelkerke et al. (1994 Environ. Biol. Fish. 39: 1–21). The large-mouthed Lake Tana barbs originated from an ancestral NEC form through peramorphosis, but in relation to B. canis they are paedomorphic in skull proportions. B. canis supposedly originated from a NEC form as a consequence of an adaptive radiation that took place in western Asia.     

Length–weight relationships for five fish species caught in Keban Dam Lake,Turkey

Length–weight relationships (LWR) are presented for five commercial freshwater fish species (Luciobarbus esocinus, Heckel, 1843; Capoeta trutta, Heckel, 1843; Barbus lacerta, Heckel, 1843; Luciobarbus mystaceus, Pallas, 1814 and Capoeta umbla, Heckel, 1843) collected from Keban Dam Lake located in eastern Anatolia, Turkey. Studied samples were obtained between July and December 2008 using commercial gill nets. For each species the sample size, length range, weight range, length‐weight relationships, 95% confidence intervals of a and b, coefficient of correlation and growth type are given. Values of b were between 2.915 (Luciobarbus esocinus) and 3.079 (Copoeta trutta) and r² values from 0.919 (Copoeta trutta) to 0.987 (Barbus lacerta) in the study. New maximum length and length–weight relationships are reported for Barbus lacerta and Luciobarbus mystaceus.