The diet of Brycinus nurse (Pisces: Characidae) from Asa reservoir,Ilorin, Nigeria

From November 1991 to October 1993, 980 specimens of the characid Brycinus nurse were collected from Asa reservoir to examine its diet. The diet was analyzed using the frequency of occurrence, numerical and gravimetric methods. Two hundred and sixty nine (27.45%) of the stomachs examined were empty. The fish was an omnivore feeding extensively on a wide array of plant and animal food items. These consisted of 9 families, 10 genera and 10 species. The most extensively consumed plant food item was aquatic plant parts which occurred in 63.88% of the stomachs, and accounted for 6.06% by number and 12.10% by weight while the ephemeropteran, Povilla adusta was the most dominant animal food item, occurring in 50.92% of the stomachs, and accounting for 11.98% by number and 11.86% by weight. Conversely, the least consumed plant food item was Volvox occurring in 4.49% of the stomachs and accounting for 0.18% by number and 0.35% by weight, while the fish Barbus sp. was the least consumed animal food item occurring in 0.51% of the stomachs, accounting for 0.03% by number and 1.62% by weight. New food items not previously recorded such as a watermite. Aspatharia sinuata and Barbus callipterus were found in the stomach contents. The nonspecific feeding regime of the fish and its ability to utilize different food items effectively was what accounted for the prominence and wide distribution of the fish in the lake.     

A morphological key for the identification of southern African Synodontis species Cuvier, 1816 (Teleostei: Mochokidae)

The identification of the southern African Synodontis species is hampered by variable and overlapping morphological characteristics such as colour, pigmentation patterns and morphometric ratios. Species are often misidentified due to the complicated nature of the present identification keys. The morphological key proposed in this note uses simplified characters including the shape of the humeral process, size of the outer mandibular barbel, teeth rows, position of the mouth, basal membrane of the maxillary barbel and length of the maxillary barbels, plus the natural distribution range of certain species to facilitate positive identification of southern African Synodontis specimens.     

Size,sex and seasonal dynamics in the dietary composition of Brycinus nurse (Pisces: Characidae), from Asa reservoir,Ilorin, Nigeria

Specimens of the characid Brycinus nurse (N = 980) were collected in Asa reservoir, Nigeria, from November 1991 to October 1993. The diet was analyzed from stomach contents using the frequency of occurrence, numerical and gravimetric methods. Fish sex affected occurrence, number and weight of food items. The relative importance index (RI) indicates that diet varied seasonally. There was also a noticeable switch from insectivorous habits in small fish (less than 18 cm) to herbivorous feeding habits in larger fish. The ability of the fish to evolve trophic strategies that ensure optimum foraging despite seasonal changes can account for its success in the lake.     

Electric Discharges in African Upside-Down Catfishes Synodontis (Mochokidae,Siluriformes): Peculiarities and Mechanisms of Electrogeneration

Journal of Ichthyology - The patterns of electric discharges were studied in two species of upside-down catfishes, Synodontis clarias and S. membranaceus. In S. clarias, constant generation of weak...     

埃及尼罗河鲶的精子发生和精子的超微结构

用扫描和透射电子显微镜研究了尼罗河鲶——盾头歧须鮠(Synodontis schall)的精子发生和精子的超微结构。精巢中含有无数肾形的生精小叶,我们将其称为"精原无限型"。尽管其精子发生的大体过程与同类鱼无异。但是,在细节上仍具其独特之处。这些特点未见在其他硬骨鱼中报道过。其特点主要是:生精过程中不发生细胞核的旋转,中心粒复合体和轴丝起始段直接发生在核的基底面垂直线上,有无数的粗的固定纤维将近端中心粒和远端中心粒的近侧部连接到细胞核上。另外,精子发生过程中还包括染色质浓缩,细胞质和线粒体向细胞核的尾端迁移,在核的后端中轴位置上形成中等大小的核后凹,近端中心粒和远端中心粒的一部分嵌在核后凹之内,短的胞质内陷管将线粒体与鞭毛分隔开。精子头部接近圆形,无顶体或顶体泡,鞭毛的中段及胞质内陷管均较短,整个鞭毛却很长,鞭毛侧面无翼膜,轴丝呈典型的9 2结构。上述结果显示,盾头歧须鮠的精子发生具有类型Ⅰ和类型Ⅱ的共同派生特征,这种特征在常见的其他硬骨鱼中也是常有的。但是,正如文献所报道过的另两种尼罗河鲶——金鯵(Chrysichthys auratus)和电鲶(Malapterurus electricus)中的情况一样,盾头歧须的精子发生与类型Ⅲ的精子发生过程更为相似。     

Some aspects of the reproductive biology of Synodontis schall (Bloch-Schneider, 1801) from the White Nile near Khartoum

The biology of reproduction was investigated in 631 specimens of Synodontis schall taken from the White Nile near Khartoum. Morphological changes of the gonads were followed for twelve months and the results used to classify their different developmental stages and maturity. Water and ash content of the gonads varied slightly from month to month and this variation was more pronounced during the breeding season. Gonosomatic indices also varied in the same manner. Synodontis schall spawns from July to September and females are ripe at the early age of I. Absolute fecundity ranged from 10 000 to 90 000 eggs and was highly correlated with growth parameters such as length, weight and age. Variations in the diameter of the eggs during the breeding season were also followed.     

Sound production to electric discharge: sonic muscle evolution in progress in Synodontis spp. catfishes (Mochokidae)

Elucidating the origins of complex biological structures has been one of the major challenges of evolutionary studies. Within vertebrates, the capacity to produce regular coordinated electric organ discharges (EODs) has evolved independently in different fish lineages. Intermediate stages, however, are not known. We show that, within a single catfish genus, some species are able to produce sounds, electric discharges or both signals (though not simultaneously). We highlight that both acoustic and electric communication result from actions of the same muscle. In parallel to their abilities, the studied species show different degrees of myofibril development in the sonic and electric muscle. The lowest myofibril density was observed in Synodontis nigriventris, which produced EODs but no swim bladder sounds, whereas the greatest myofibril density was observed in Synodontis grandiops, the species that produced the longest sound trains but did not emit EODs. Additionally, S. grandiops exhibited the lowest auditory thresholds. Swim bladder sounds were similar among species, while EODs were distinctive at the species level. We hypothesize that communication with conspecifics favoured the development of species-specific EOD signals and suggest an evolutionary explanation for the transition from a fast sonic muscle to electrocytes.     

A large-scale phylogeny of Synodontis (Mochokidae,Siluriformes) reveals the influence of geological events on continental diversity during the Cenozoic

To explain the spatial variability of fish taxa at a large scale, two alternative proposals are usually evoked. In recent years, the debate has centred on the relative roles of present and historical processes in shaping biodiversity patterns. In Africa, attempts to understand the processes that determine the large scale distribution of fishes and exploration of historical contingencies have been under-investigated given that most of the phylogenetic studies focus on the history of the Great Lakes. Here, we explore phylogeographic events in the evolutionary history of Synodontis (Mohokidae, Siluriformes) over Africa during the Cenozoic focusing on the putative role of historical processes. We discuss how known geological events together with hydrographical changes contributed to shape Synodontis biogeographical history. Synodontis was chosen on the basis of its high diversity and distribution in Africa: it consists of approximately 120 species that are widely distributed in all hydrographic basins except the Maghreb and South Africa. We propose the most comprehensive phylogeny of this catfish genus. Our results provide support for the ‘hydrogeological’ hypothesis, which proposes that palaeohydrological changes linked with the geological context may have been the cause of diversification of freshwater fish deep in the Tertiary. More precisely, the two main geological structures that participated to shape the hydrographical network in Africa, namely the Central African Shear zone and the East African rift system, appear as strong drivers of Synodontis diversification and evolution.     

Description of a new small-sized Synodontis species (Siluriformes: Mochokidae) that is important for local subsistence fisheries in the middle Lufira (upper Congo River,DR Congo)

Synodontis denticulatus sp. nov. is an endemic from the middle Lufira Basin and its associated tributaries and lakes. The species shows close morphological resemblance to Synodontis greshoffi and Synodontis unicolor, which are widespread Congo Basin and Bangweulu-Mweru endemic species, respectively. However, it differs from both S. greshoffi and S. unicolor by its non-villous skin (v. villous skin), strong and numerous serrations on the posterior margin of the dorsal spine (v. weak and fewer serrations), weak and few serrations on the posterior margin of the pectoral spine (v. strong and numerous serrations), relatively short maxillary barbels (v. long) and its small maximum standard length (89.1 mm L_S v. 148.0 and 190.7 mm L_S respectively). A DNA barcoding study (coI, mtDNA) revealed that S. denticulatus forms a distinct genetic clade with a genetic distance of 2.18% with S. greshoffi and 0.84% with S. unicolor. Synodontis denticulatus is caught regularly and abundantly as a by-catch in the gillnet fisheries in the middle Lufira lakes. Owing to its small overall size and large bony head, the species has usually no real commercial value but is an important food fish for the fishermen's families.     

Ontogeny of the catfish pectoral-fin spine (Teleostei: Siluriformes)

The characteristic and morphologically variable pectoral-fin spine of catfishes (order Siluriformes) has been well-investigated based on later developmental stages (juveniles and adults) but information on the earliest life stages are lacking. Here, we document the ontogeny of pectoral-fin spines in four siluroid (Ictalurus punctatus, Noturus gyrinus, Silurus glanis and Akysis vespa) and two loricarioid catfishes (Corydoras panda and Ancistrus sp.). To further our understanding of pectoral-fin spine development, we also examined adult and juvenile specimens representing 41 of the currently 43 recognized families of catfishes. Development of the pectoral-fin spine is similar in all catfishes and resembles the development of a typical soft fin ray. Fusion between hemitrichia of the anteriormost lepidotrichium occurs proximally first, forming the spine proper, with growth of the spine occurring through the subsequent fusion of developing distal hemitrichial segments that comprise the spurious ray. The variation of pectoral-fin spine morphology observed is largely attributed to the presence/absence of five traits, which either develop as part of the hemitrichial segments that are added to the distal tip of the spine during growth (distal rami, anterior/posterior serrae) or develop independent of these segments (denticuli and odontodes).     

Morphology–diet relationships in four killifishes (Teleostei, Cyprinodontidae, Orestias) from Lake Titicaca

This study explores the relationship between morphology and diet in four Andean killifishes ( Orestias ) from Lake Titicaca that are known to differ in habitat use. Species that fed preferentially on amphipods ( Orestias albus ) or molluscs ( Orestias luteus ) separated in multivariate space from other species that feed on cladocera and algae ( Orestias agassii and Orestias jussiei ). Generally, specimens feeding on cladocera were characterized by a short, blunt nose with a small mouth; whereas, specimens feeding on amphipods exhibited a long snout with a large mouth. Specimens including molluscs in their diet tended to have a larger posterior part of the head and the larger opercles than others; while the occurrence of substratum in gut content was generally related to a short but deep head. The present analysis suggests that the littoral O. jussiei has an intermediate phenotype and diet between the pelagic ( O. agassii ) and benthic ( O. albus and O. luteus ) species. Results suggest that resource partitioning was occurring and that several morphological traits relate to characteristics of the diet, and it is inferred that the benthic, the pelagic and the littoral zones in the lake host different prey communities constituting distinct adaptive landscapes.     

A revision of the genus Labidochromis (Teleostei: Cichlidae) from Lake Malawi

The diagnosis of the genus Labidochromis is revised to include species with bicuspid outer teeth. Sixteen species, of which 13 are new, are described and illustrated and the validity of five others is discussed. The interrelationships between members of the genus and the relationship of the genus to other genera are discussed. No clearly defined sister group to the genus has been found either within or outside the Lake Malawi cichlid species flock. A key based on the coloration of known species is included.     

Validation of Alburnus timarensis from the Lake Van basin,eastern Anatolia (Teleostei: Cyprinidae)

The Lake Van basin located in eastern Anatolia is inhabited by two species of Alburnus: Alburnus tarichi is a migratory species foraging in the lake and spawning in all tributaries, while A. timarensis is resident in streams and is known only from one tributary of the lake, the Karasu. It could be shown that A. timarensis is a valid species, which is rediagnosed here. Both species are syntopic during the spawning season, but are well distinguished by size, gill raker and lateral line scale counts.     

A revised synonymy of Telmatochromis temporalis (Teleostei, Cichlidae) from Lake Tanganyika (East Africa)

The taxonomic status of the nominal species Telmatochromis temporalis , T. lestradei , T. burgeoni and Julidochromis macrolepis has been reviewed. The synonymy of T. lestradei with T. temporalis is confirmed. A comparison of Telmatochromis burgeoni with Telmatochromis temporalis revealed no significant differences either. Hence T. burgeoni is considered synonymous with T. temporalis . Examination of the type of Julidochromis macrolepis showed it to be conspecific with Telmatochromis dhonti and not with T. temporalis , as had been suggested.     

Midwater spawning inHaplochromis chrysonotus (Boulenger) (Teleostei: Cichlidae) in Lake Malawi

Synopsis Haplochromis chrysonotus, a semipelagic shoaling cichlid from Lake Malawi, has been observed spawning in open water up to ten metres above the substratum. It is suggested that open water spawning without the establishment of a substratum-based territory eliminates competition with other species for breeding space and that it may be a stage in the evolution of a totally pelagic mode of life.     

Correlating head shape with ecological variables in rock-dwelling haplochromines (Teleostei: Cichlidae) from Lake Victoria

An exploratory analysis was made of the head shape of cichlid fishes. A 3-D head truss was used, which allowed approximations of the volumes of three compartments of the head. We applied the method to six species of rock-dwelling haplochromine cichlids, of which we studied 12 populations from four rocky islands in the southern part of Lake Victoria. Head shape was correlated with eight environmental variables. Truss distances and compartment volumes correlated with these variables, e.g. volumes of the compartments containing the gills correlated (negatively) with oxygen levels; truss distances, including the oral jaws and their musculature, correlated with food composition; and eye size correlated with width of the transmission spectrum. Another finding was the likely architectonic interactions between anatomical elements. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 76 , 39–48.     

Cyclomorphosis in Keratella tropica (Apstein) of Lake Asejire,Nigeria

Of one thousand, one hundred and four (1104), Keratella tropica collected with a 55 m mesh plankton net from the surface of Lake Asejire from February 1974 to February 1976 lorica length and width, and the lengths of the posterior spines were measured.Lake Asejire K. tropica are among the smallest in Africa. Variations in the patterns of spine length development were independent of season as individuals without left posterior spines and with relatively long left and right posterior spines occurred as commonly in the rainy as in the dry season months.Correlations between K. tropica dimensions and thirty environmental factors underscore the importance of physical environmental factors and point to biological and genetic factors as determinants of the patterns of cyclomorphosis in K. tropica.