The catfish fauna of Lake Victoria after the Nile perch upsurge

Stocks of the indigenous catfish species of Lake Victoria have decreased dramatically since the beginning of the 1980s. This decline coincided with the Nile perch boom and concomitant ecological changes in the lake. In deep water, where Nile perch densities were higher, the decline proceeded more quickly than in shallow water. In the former all catfishes eventually vanished. Of the two largest species, Clarias gariepinus and Bagrus docmak, juveniles disappeared faster than adults. This indicates that predation by Nile perch may have played an important role in their decline. Other possible impacts were the deoxygenation of deepwater areas and the decline of haplochromine cichlids which were an important food source for B. docmak, C. gariepinus and Schilbe intermedius. The various catfish species were not all affected to the same extent. The endemic Xenoclarias eupogon, which lived predominantly in deep water, may have become extinct. B. docmak currently seems to be mainly restricted to refugia in rocky habitats. Synodontis victoriae and S. afrofischeri are still present in small numbers in shallow littoral areas. Schilbe intermedius and C. gariepinus seem to be the least affected of the catfishes in littoral and sublittoral areas. This may be caused, among other reasons, by their smaller habitat overlap with Nile perch than the other species. S. intermedius is partly pelagic, and a considerable part of the C. gariepinus stock lives in bodies of water surrounding the lake. The patterns of decline of the catfishes are very similar to those observed for haplochromine cichlids in the lake. The importance of catfishes for the fisheries in the lake is currently negligible.     

Trophic shifts in predatory catfishes following the introduction of Nile perch into Lake Victoria

This study looked for evidence of trophic shifts in the diet of two predatory catfishes ( Bagrus docmac and Schilbe intermedius ) following the establishment of introduced Nile perch ( Lates niloticus ) into lakes of the Lake Victoria basin. Bagrus docmac exhibited a shift from a primarily piscivorous diet dominated by haplochromine cichlids to a broader diet that included a significant proportion of invertebrates and the cyprinid fish, Rastrineobola argentea , which became abundant following depletion of the haplochromines. Schilbe intermedius exhibited a trophic shift from a piscivorous diet dominated by haplochromines to an insectivorous diet. The flexibility in diet exhibited by these two catfishes may have permitted these species to persist, albeit in reduced numbers, subsequent to the introduction of Nile perch and may facilitate resurgence as fishing pressure reduces numbers of large Nile perch.     

The ecology of the catfish Clarias gariepinus and Clarias ngamensis in the Shire Valley, Malawi

The ecology of two commercially important catfish species, Clarias gariepinus and C. ngamensis , was examined in the Elephant Marsh, southern Malawi. Abundance, distribution, and movements within the marsh system were studied. Growth rates were determined from rings on the vertebrae, with corroborative evidence from length frequency analyses and tagging studies. Breeding seasons, length and age at maturity, and fecundity were determined for both species. Stomach contents were examined and the food preferences of the two species were compared.     

Species succession and the development of a lacustrine fish community in an ephemeral lake

Here, we present a gillnet survey of Lake Liambezi a 370 km² shallow ephemeral floodplain lake situated in north-eastern Namibia, which is fed irregularly by the upper Zambezi and Kwando Rivers during years of high flooding. The lake dried up in 1985 and, with the exception of sporadic minor annual inundation events, remained dry until 2007. We describe the temporal succession of fish species over an 8 year period from initial inundation 2007 to maturation in 2014. The succession of the fish community did not follow the typical pattern of opportunistic strategists during colonisation, to periodic strategists that are eventually succeeded by equilibrium strategists. Instead, the evolution of the fish community was characterised by three distinct phases. The first phase involved the inundation and colonisation of the lake in 2007, followed by its decline until the floods that filled the lake in 2009. During this phase the lake was colonised by fishes from the adjacent upper Zambezi and Chobe River floodplains. Fish communities predominantly comprised floodplain specialists including the barbs Enteromius paludinosus and Enteromius poechii, the mormyrid Marcusenius altisambesi and catfishes Schilbe intermedius and Clarias gariepinus. The filling of the lake in the March 2009 floods marked the beginning of the second, successional phase. The barbs declined in abundance and the alestid Rhabdalestes maunensis underwent explosive population growth between 2009 and 2010, but populations crashed equally rapidly and were replaced by Brycinus lateralis which, together with S. intermedius went on to dominate the fish community 2011–2014. Larger, slower growing tilapiine cichlids increased steadily in abundance and became the dominant components in a 2700 t y^–1 artisanal fishery that developed on the lake. The fish community in the ephemeral Lake Liambezi is clearly influenced by numerous factors including connectivity, lake level fluctuations, competition and the effects of fishing, which may disrupt typical succession processes in floodplain ecosystems.     

Effects of jaw adductor hypertrophy on buccal expansions during feeding of air breathing catfishes (Teleostei,Clariidae)

Some species of Clariidae (air breathing catfishes) have extremely well developed (hypertrophied) jaw closing muscles that increase the maximal biting force of these species. As these enlarged jaw muscles tightly cover the suspensoria, which are firmly connected to the neurocranium, we expect diminished lateral expansions during suction for species with hypertrophied jaw muscles. In turn, this could imply a reduced suction performance for these species. Compared to Clarias gariepinus, which has relatively small jaw closers, Clariallabes longicauda shows a clear hypertrophy of the jaw adductors. A kinematic analysis of prey capture in these two species is presented here. As predicted, Clariallabes longicauda shows less lateral expansion (average abduction of the hyoids of 19.0°) than Clarias gariepinus (abduction of 31.1°). However, our data indicate that the decrease in lateral expansion capacity in the species with excessive adductor development is compensated for by a larger and faster ventral expansion of the buccal cavity by depression of the hyoid.     

The food and feeding habits of Physailia pellucida and Schilbe mystus with notes on the diets of S. uranoscopus and Siluranodon auritus, family Schilbeidae (Osteichthyes: Siluriformes) in Lake Kainji, Nigeria

SUMMARY. The food and feeding patterns of four schilbeids in Lake Kainji were studied between November 1974 and October 1975. Physailia pellucida , a small but abundant species, fed on small crustaceans and immature insects, while Schilbe mystus , a larger but less common schilbeid, fed principally on fish, with insects as a supplementary item in its diet. The rare species, Schilbe uranoscopus , was piscivorous, Siluranodon auritus , another small and rare species, is a herbivore feeding mainly on algae, with some crustaceans and immature insects taken as a source of animal protein. Preferential food selection by different length groups was found in S. mystus and P. pellucida . There were seasonal changes in the dietary items. Competition for food within the family was assumed not to occur in view of the different feeding habits of the species.     

Pack-hunting in two species of catfish, Clavias gariepinus and C. ngamensis, in the Okavango Delta, Botswana

During the annual drawdown in the Okavango Delta, Botswana, large shoals of catfish migrate upstream in the main river channels. The examination of samples of the sharptooth catfish Clarias gariepinus and blunttooth catfish C. ngamensis revealed that they were pack-hunting and selectively preying on two species of mormyrids, the bulldog Marcusenius macrolepidotus and the churchill Petrocephalus catostoma . The predation on mormyrids may be related to prey size and abundance. In addition, catfish may sense the electrical discharge given off by the mormyrids when disturbed. The catfish feed intensively for a few months and build up body reserves and reproductive condition prior to spawning on shallow floodplains with the onset of the annual floods from Angola.     

A dynamic model of mouth closing movements in clariid catfishes: the role of enlarged jaw adductors

Some species of Clariidae (air breathing catfishes) have extremely large (hypertrophied) jaw closure muscles. Besides producing higher bite forces, the enlarged muscles may also cause higher accelerations of the lower jaw during rapid mouth closure. Thus, jaw adductor hypertrophy could potentially also enable faster mouth closure. In this study, a forward dynamic model of jaw closing is developed to evaluate the importance of jaw adductor hypertrophy on the speed of mouth closure. The model includes inertia, pressure, tissue resistance and hydrodynamic drag forces on the lower jaw, which is modelled as a rotating half-ellipse. Simulations are run for four clariid species showing a gradual increase in jaw adductor hypertrophy (Clarias gariepinus, Clariallabes longicauda, Gymnallabes typus and Channallabes apus). The model was validated using data from high-speed videos of prey captures in these species. In general, the kinematic profiles of the fastest mouth closure from each species are reasonably well predicted by the model. The model was also used to compare the four species during standardized mouth closures (same initial gape angle, travel distance and cranial size). These simulations suggest that the species with enlarged jaw adductors have an increased speed of jaw closure (in comparison with the non-hypertrophied C. gariepinus) for short lower jaw rotations and when feeding at high gape angles. Consequently, the jaw system in these species seems well equipped to capture relatively large, evasive prey. For prey captures during which the lower jaw rotates freely over a larger distance before impacting the prey, the higher kinematic efficiency of the C. gariepinus jaw system results in the fastest jaw closures. In all cases, the model predicts that an increase in the physiological cross-sectional area of the jaw muscles does indeed contribute to the speed of jaw closure in clariid fish.     

Bite performance in clariid fishes with hypertrophied jaw adductors as deduced by bite modeling

Within clariid fishes several cranial morphologies can be discerned. Especially within anguilliform representatives an increase in the degree of hypertrophy of the jaw adductors occurs. The hypertrophy of the jaw adductors and skeletal modifications in the cranial elements have been linked to increased bite force. The functional significance of this supposed increase in bite force remains obscure. In this study, biomechanical modeling of the cranial apparatus in four clariid representatives showing a gradual increase in the hypertrophy of the jaw adductors (Clarias gariepinus, Clariallabes melas, Channallabes apus, and Gymnallabes typus) is used to investigate whether bite force actually increased. Static bite modeling shows that the apparent hypertrophy results in an increase in bite force. For a given head size, the largest bite forces are predicted for C. apus, the lowest ones for C. gariepinus, and intermediate values are calculated for the other species. In addition, also in absolute measures differences in bite force remain, with C. apus biting distinctly harder than C. gariepinus despite its smaller head size. This indicates that the hypertrophy of the jaw adductors is more than just a correlated response to the decrease in absolute head size. Further studies investigating the ecological relevance of this performance difference are needed.     

Morphometric and genetic characterization of sympatric populations of Clarias gariepinus and C. anguillaris from Senegal

A sample of African Clarias catfishes from the Senegal River was studied using morphometry, allozyme variation, microsatellites and RFLPs of mitochondrial DNA. They all confirmed the presence of two species , C. gariepinus and C. anguillaris . The two species were closely related genetically and no diagnostic loci were found in allozymes and microsatellites studies. Two of the 11 haplotypes of mtDNA observed were shared by both species. Three of the four assays (morphometry, allozymes and microsatellites) allowed a precise characterization of both. One specimen occupied an intermediate position in the analysis of the data; it was considered an F_l hybrid whose possible origin is discussed.     

The African sharptooth catfish Clarias gariepinus can tolerate high levels of ammonia in its tissues and organs during four days of aerial exposure

The African sharptooth catfish Clarias gariepinus lives in freshwater, is an obligatory air breather, and can survive on land during drought. The objective of this study was to elucidate how C. gariepinus defends against ammonia toxicity when exposed to terrestrial conditions. During 4 d of aerial exposure, there was no accumulation of urea in its tissues, and the rate of urea excretion remained low. Thus, exposure to terrestrial conditions for 4 d did not induce ureogenesis or ureotely in C. gariepinus. Volatilization of NH(3) was not involved in excreting ammonia during aerial exposure. In addition, there were no changes in levels of alanine in the muscle, liver, and plasma of C. gariepinus; nor were there any changes in the glutamine levels in these tissues. However, there were extraordinarily high levels of ammonia in the muscle (14 micromol g(-1)), liver (18 micromol g(-1)), and brain (11 micromol g(-1)) of fish exposed to terrestrial conditions for 4 d. This is the first report on a fish adopting high tolerance of ammonia in cells and tissues as the single major strategy to defend against ammonia toxicity during aerial exposure. At present, it is uncertain how C. gariepinus tolerates such high levels of ammonia, especially in its brain, but it can be concluded that, contrary to previous reports on two air-breathing catfishes (Clarias batrachus and Heteropneustes fossilis) from India, C. gariepinus does not detoxify ammonia to urea or free amino acids on land.     

Schilbetrematoides manizani n. sp. (Dactylogyridea) monogenean parasite of Schilbe mandibularis (Günther, 1867) (Schilbeidae) in the Ivory Coast

The authors describe a new species in the genus Schilbetrematoides Kritsky & Kulo, 1992 from the gills of Schilbe mandibularis (Günther, 1867) (Schilbeidae) caught in the rivers Bia and Agneby in Ivory Coast. S. manizani n. sp. differs from S. pseudodactylogyrus Kritsky & Kulo, 1992, a parasite of Schilbe intermedius Rüppell, 1832 by having morphologically distinct gripi.     

Morphometric and allozyme variation in the African catfishes Clarias gariepinus and C. anguillaris

This study investigated morphological characters and electrophoretic polymorphism at 25 protein loci in nine wild populations of the African clariid catfish Clarias gariepinus and seven wild populations of C. anguillaris. Two other clariid species, Clarias albopunctatus and Heterobranchus longifilis , were used as outgroups in the allozyme study. Morphometric and allozyme data are congruent for the Nilo-Sudanian populations of C. gariepinus and C. anguillaris. Both approaches also distinguished two groups amongst the C. gariepinus populations, one containing Nilo-Sudanian populations and the other including Lake Victoria and southern African populations. However, allozyme data suggest that C. gariepinus is not a monophyletic group and show that C. albopunctatus is more divergent from C. gariepinus and C. anguillaris than it is from H. longifilis , stressing the need for a revision of clariid systematics. The variation observed in C. gariepinus is discussed in terms of palaeogeographical events and its use in aquaculture.     

A new genus and species of proteocephalidean (Cestoda) from Clarias catfishes (Siluriformes: Clariidae) in Africa

A new proteocephalidean cestode is described from 2 catfishes, Clarias gariepinus (type host) and C. cf. anguillaris (Siluriformes: Clariidae), from Ethiopia (type locality), Sudan, Tanzania, and Zimbabwe, and a new genus, Barsonella, is proposed to accommodate it. The genus belongs to the Proteocephalinae because its genital organs (testes, ovary, vitellarium, and uterus) are situated in the medulla. Barsonella lafoni, the type and only species of the new genus, is characterized mainly by the possession of an additional opening of each sucker; circular musculature on the anterior margin of suckers, serving as a sphincter; a small thin-walled glandular apical organ; absence of well-developed osmoregulatory canals in mature, pregravid, and gravid proglottids; and a large strobila, up to 173 mm long and 3.2 mm wide. Species of Marsypocephalus Wedl, 1861 (Marsypocephalinae), other large-sized proteocephalidean tapeworms occurring sympatrically in African catfishes (Clarias and Heterobranchus) and also possessing a sphincter-like, circular musculature on the anterior part of suckers, differ from B. lafoni in the absence of an additional sucker opening and glandular apical organ, the cortical position of the testes, well-developed osmoregulatory canals throughout the strobila, and a large cirrus sac. Proteocephalus glanduligerus (Janicki, 1928), another cestode parasitic in Clarias spp. in Africa, is much smaller than B. lafoni (maximum length 15 mm), has suckers without additional opening and circular musculature on the suckers, a large-sized glandular organ, much larger than suckers, and well-developed osmoregulatory canals. Comparison of partial sequences of the 28S rRNA gene for 7 samples of B. lafoni from 2 different hosts and 4 localities in Ethiopia, Sudan, and Tanzania has shown a very low genetic variability. In a limited phylogenetic analysis, B. lafoni formed a clade with Corallobothrium solidum Fritsch, 1886 (Proteocephalidae: Corallobothriinae), an African electric catfish parasite. This clade was the sister group of almost all Neotropical taxa from pimelodid and other catfishes.     

Enzymatic variation in African clariid catfishes

Enzymatic polymorphism was examined at 13 protein loci in four African clariid catfish species: Clarias anguillaris (Linnaeus, 1758), C. ebriensis Pellegrin, 1920, C. gariepinus (Burchell, 1822) and Heterobranchus longifilis Valenciennes, 1840. The latter appears to be closer to C. anguillaris and C. gariepinus than C. ebriensis . These results correspond with recently published karyological and morphometrical data.
Reproductive compatibility, under laboratory conditions at least, is demonstrated between C. gariepinus and H. longifilis . The hybrids were shown to be completely intermediate between the parental strains.     

Redescription of Proteocephalus glanduligerus (Cestoda: Proteocephalidea), a parasite of clariid catfishes in Africa with a unique glandular apical organ

The tapeworm Proteocephalus glanduligerus (Janicki, 1928) Fuhrmann, 1933 (Cestoda: Proteocephalidea), a parasite of clariid catfishes (Clarias spp.) in Africa, is redescribed on the basis of an evaluation of voucher material and newly collected specimens from Clarias gariepinus and C. cf. anguillaris from the Sudan, Ethiopia, and South Africa. The most typical characteristic of P. glanduligerus (previously misspelled as P. glanduligera or P. glanduliger) is the presence of an extremely large glandular apical organ, the size of which is 1.6-3.5 times larger than that of the suckers. In addition, other morphological characteristics unreported in previous accounts are provided, such as an unusual position of osmoregulatory canals (situated close to each other, with the dorsal canal latero-ventral to testes), the presence of a vaginal sphincter, several (usually 3-5) uterine pores, and eggs with paired lateral auricular swellings (extensions) of the outer envelope.     

Isozyme variation among four species of the catfish genus Clarias

Native Thai species of Clarias catfishes and one species introduced from Africa can be easily distinguished by horizontal starch gel electrophoresis of allozymes. An undescribed species of Clarias was collected from Thailand and found to possess several fixed allelic differences from the Clarias previously studied.     

Sixteen EST-linked microsatellite markers in Günther's walking catfish, Clarias macrocephalus

Twenty-seven new microsatellite sequences were identified by screening 2029 expressed sequence tags from Günther's walking catfish, Clarias macrocephalus. Sixteen loci were polymorphic with the number of alleles ranging from two to 16 per locus and the observed and expected heterozygosities ranging from 0.4667 to 0.9333 and from 0.427 to 0.8819 per locus, respectively. Cross-species amplifications of all 16 primer pairs were tested in four other species of catfish including Clarias gariepinus, Pangasius hypophthalmus, Pangasius larnaudii and Pangasianodon gigas. Eleven loci were found to amplify in other species, with the number of polymorphic loci ranging from one in P. larnaudii to nine in C. gariepinus.     

Analyses of the stomach contents of the piscivorous fishes of the Upper Ogun River in Nigeria

The stomach contents of the fishes of the Upper Ogun River were scrutinised for three consecutive years. 8 out of the 36 species resident in the river are predominantly piscivorous. These are Mormyrops deliciosus, Hydrocynus forskahlii, Hepsetus odoe, Bagrus docmac, Lates niloticus and Hemichromis fasciatus. Piscivorous habits in Schilbe mystus and Eutropius niloticus are less developed. Three others, viz: Clarias lazera, Heterobranchus longifilis and Channa obscura, which were classified as piscivores by other workers, were caught. The stomachs of C. obscura examined were all empty while those of C. lazera and H. longifilis contained mainly aquatic invertebrates. The major prey of these piscivores are small sized Barbus spp. Other prey fishes include mormyrids, characids, cyprinids, citharinids, catfishes and cichlids. The relationships between the piscivorous and prey fishes and the partitioning of the available resources by these piscivores are discussed.     

Diversity of Lactobacillus and Bifidobacterium in feces of herbivores, omnivores and carnivores

The Lactobacillus and Bifidobacterium population in the feces of 26 animals (16 species) were studied by culture-dependent and culture-independent techniques. Lactobacilli were detected from a few herbivores, all carnivores and some omnivores. Lactobacillus johnsonii, Lactobacillus reuteri, Lactobacillus salivarius, Lactobacillus vaginalis and Lactobacillus ingluviei were the most dominant lactobacilli in carnivores. These species were, however, not predominant in herbivores and omnivores. Lactobacillus brevis, Lactobacillus casei, Lactobacillus parabuchneri, Lactobacillus plantarum, Lactobacillus sakei, Leuconostoc mesenteroides and Leuconostoc pseudomesenteroides, usually present in raw plant material, were present in omnivores but not in carnivores. Bifidobacteria were detected in only four herbivores and two omnivores. Bifidobacterium pseudolongum was the only Bifidobacterium species detected in herbivores. Bifidobacteria detected in the two omnivores are phylogenetically not closely related to known species and are possible novel species in the genus.