Homology and evolution of the opercular series in the loricarioid catfishes (Pisces: Siluroidei)

Aspects of the morphology of the opercular region of siluroids (catfishes) were examined to determine the homologies of the opercular bones of loricarioid catfishes, a diverse monophyletic neotropical group. Homology of the component structures was inferred by examination of three criteria: (1) functional relations to the jaw abduction mechanism of primitive halecostome fishes; (2) positional relations to the bones of the suspensorium and the path of the preopercular laterosensory canal; and (3) pattern of development of the preopercular canal and lateral cheek plates of loricarioid catfishes. The majority of siluroids have lost one or more of the preopercular canal exit branches to the skin surface present in most primitive siluroids. A number of specializations of the canal pathway and components of the opercular series have occurred in loricariids. Trichomycterids have the preopercular canal reduced to a short branch from the pterotic. Callichthyids share the presence of a preopercular canal with primitive siluroids, but have lost the communication of the canal between the preopercle and pterotic bones. Callichthyids and scoloplacids share one additional loss of a preopercle exit. The second of two subopercular elements of astroblepids is homologous with the interhyal. Astroblepids and loricariids have lost one additional preopercle exit, the interoperculo-mandibular ligament and the corresponding biomechanical couple for lower jaw abduction. Loricariids have probably lost the interopercle as well. These derived features of loricariids and astroblepids are viewed as specializations for a particular feeding behaviour: scraping algae and detritus from the substratum.     

Retinofugal and retinopetal connections in the upside-down catfish (Synodontis nigriventris)

Summary The retinofugal and retinopetal connections in the upside-down catfish Synodontis nigriventris were studied by use of the horseradish-peroxidase (HRP) techniques, autoradiography, and degeneration-silver methods. An unusual retinal projection to the torus semicircularis as well as projections to the retina from three different sources in the brain are described. After intra-ocular injections of HRP, labeled cells were found in the optic tectum, the dorsomedial optic nucleus and one of the pretectal nuclei. These new findings support the basic hypothesis (i) that neuronal connections are more extensive in primitive brains, and (ii) that the evolutionary development of more complex brains involves the loss of some selected connections.     

Postural control mechanisms in the upside-down catfish (Synodontis nigriventris)

The catfishSynodontis nigriventris normally swims upside-down but can assume any posture in response to a substrate it swims close to. Postural reflexes of the body and the eyes, labyrinthine anatomy and passively maintained posture were investigated to obtain indications for possible mechanisms controlling the peculiar postural behavior of this fish. Saccade-like resetting movements of the eyes during counter-roll to body tilt about the longitudinal axis, and maintained tilted swimming positions in blinded fish suggest that these animals reset their vestibular CNS circuits to zero when in tilted positions.Synodontis nigriventris is thus able to maintain any posture without interference from tilt-counteracting vestibular reflexes. The normal upside-down swimming apparently results from a central bias for this position and a supporting ventral light response.We conclude that if the reafference principle applies to the phenomena investigated, the efference copy may be fed through an integrator before reaching vestibular reflex circuits.     

Mitochondrial phylogeny and phylogeography of East African squeaker catfishes (Siluriformes: Synodontis)

Background  

Squeaker catfishes (Pisces, Mochokidae, Synodontis) are widely distributed throughout Africa and inhabit a biogeographic range similar to that of the exceptionally diverse cichlid fishes, including the three East African Great Lakes and their surrounding rivers. Since squeaker catfishes also prefer the same types of habitats as many of the cichlid species, we hypothesized that the East African Synodontis species provide an excellent model group for comparative evolutionary and phylogeographic analyses.     

Relationship between frequency of upside-down posture and space size around upside-down catfish, Synodontis nigriventris.

The catfish Synodontis nigriventris shows a unique habit taking a stable upside-down posture in free water regardless of an above, one-sided illumination. This upside-down posture can be observed when the catfish is apart from objects because the catfish usually orients its ventral side towards the water bottom or objects due to a so-called ventral substrate response. Thus, it is not easy to study the mechanism of the upside-down posture. To resolve this problem, the frequency of the upside-down posture was measured by using various sizes of vessel in which the catfish was kept. Video analysis showed that the frequency of the upside-down posture depended on the space size around the catfish. The smaller the size became, the higher the frequency of the upside-down posture became. Furthermore, the frequency of the upside-down posture depended on the shape of the vessel bottom. Curved-bottom vessels induced the upside-down posture more frequently than flat bottom. These findings suggest that a small, curved-bottom vessel is ideal for researching the upside-down postural control mechanism.     

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。     

Extensive chromosomal rearrangements and nuclear DNA content changes in the evolution of the armoured catfishes genus Corydoras (Pisces, Siluriformes, Callichthyidae)

Karyotypes and nuclear DNA content were studied in 11 species of the genus Corydoras from rivers in South America: C . sp. from Caripi river 2 n =60, C . cf. simulatus 2 n =62, C . simulatus 2 n =62, C . reticulatus 2 n =74, C . sp. from Galheiro river 2 n =84, C . aff. punctatus from Negro river 2 n =102, C . flaveolus 2 n =58, C . arcuatus 2 n =46, C . trilineatus 2 n =46, C . schwartzi 2 n =46, and C . metae 2 n =92. Extensive chromosome diversity and differences in DNA content were detected among species. The high variability in chromosome counts was not exclusively related to chromosomal structural rearrangements, but also to large changes in DNA content. Species could be grouped using their shared cytogenetic characteristics, suggesting that within the genus Corydoras different groups of species followed distinct evolutionary trends. Chromosomal rearrangements in Corydoras are, apparently, more frequent that morphological modifications, so cytogenetic data may be very useful for species delimitation and for the understanding of interrelationships among species.     

Correlation between body color and behavior in the upside-down catfish,Synodontis nigriventris

• 1.1. Unlike common fishes and as its Latin name implies, the upside-down catfish, Synodontis nigriventris, possesses dark ventral skin. Microscopic observation reveals that melanophores are present on both the ventral and the dorsal skin but differ in size and density of distribution.
• 2.2. The darkness of both sides of the fish changes in accordance with that of the background.
• 3.3. At night, the fish are very active and the body becomes pale. The change in color is more noticeable in the dorsal than the ventral skin.
• 4.4. When melatonin was added to the bathing water, the fish became pale and swam restlessly even when they were exposed to the black background.
• 5.5. It was found that the catfish preferred the black background to the white one.

     

Multilocus phylogenetic analysis of the genus Atherina (Pisces: Atherinidae)

Sand-smelts are small fishes inhabiting inshore, brackish and freshwater environments and with a distribution in the eastern Atlantic and Mediterranean Sea, extending south into the Indian Ocean. Here, we present a broad phylogenetic analysis of the genus Atherina using three mitochondrial (control region, 12S and 16S) and two nuclear markers (rhodopsin and 2nd intron of S7). Phylogenetic analyses fully support the monophyly of the genus. Two anti-tropical clades were identified, separating the South African Atherina breviceps from the north-eastern Atlantic and Mediterranean Atherina' species. In European waters, two groups were found. The first clade formed by a well supported species-pair: Atherina presbyter (eastern Atlantic) and Atherina hepsetus (Mediterranean), both living in marine waters; a second clade included Atherina boyeri (brackish and freshwater environments) and two independent lineages of marine punctated and non-punctated fishes, recently proposed as separate species. Sequence divergence values strongly suggest multiple species within the A. boyeri complex.     

Catfishes of the genus Sperata (Pisces:Bagridae) in India

DNA barcode data of the South Asian bagrid catfish genus Sperata indicate the presence of at least five species in the Indian subcontinent. Those results, which are supported by morphological data, show a marked increase in species diversity from the recent taxonomic and fishery literature, although each of the five species had been previously named. Two species are restricted to rivers of peninsular India south of the Godavari: Sperata aorides from the Cauvery river basin and S. seenghala from the Krishna river basin. Most literature records of S. seenghala from the Ganges-Brahmaputra-Meghna river basins likely refer to S. lamarrii, a species which appears to also be present in the Indus river basin. Some genetic data reported as S. seenghala from the Ganges-Brahmaputra-Meghna river basins refer to S. aorella. S. aor is widespread in the Ganges-Brahmaputra-Surma river basins in India and Bangladesh, extending southwards to the Godavari river.     

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.     

Fine structure and distribution of epidermal projections associated with taste buds on the oral papillae in some loricariid catfishes (Siluroidei: Loricariidae)

Two morphologically distinct structures occur on the surfaces of the oral papillae in several loricariid catfish species; namely, (1) typical vertebrate taste buds composed of receptor and sustentacular cells and (2) brushlike projections, termed epidermal brushes, that represent specialized epidermal cells containing keratin. Both of these structures were studied with the combined use of light microscopy and scanning and transmission electron microscopy. The general body surface, fins, and rostral cutaneous processes of some loricariid catfishes are covered with taste or terminal buds but lack the epidermal brushes. It is suggested that the epidermal brushes found on the oral papillae serve as protective devices for the taste buds and as abrasive surfaces for substrate scraping during feeding. The taste buds on the oral papillae may detect any gustatory stimuli from the resulting substrate disturbance. Comparative studies reveal many differences in the number and spatial arrangement of these two structures on the oral papillae among the several species of the Loricariidae examined. These differences may represent functional adaptations to the various modes of life in the Loricariidae.     

Haematology and habits in catfish of the genus Synodontis

African catfish of the genus Synodontis vary in their habits, from inverted plankton eaters to normally oriented benthos eaters. Haemoglobin concentrations and red cell counts vary between populations of one species, and between species of differing habits. Synodontis schall from the well-aerated White Nile had lower haemoglobin concentrations than members of the same species from Lake Kainji, Nigeria. Synodontis membranaceus , an inverted plankton eater, had lower haemoglobin concentrations than the bottom dwelling S. filamentosus and S. nigrita. Species with intermediate habits, such as S. batensoda and S. ocellifer had intermediate concentrations of haemoglobin.
It is suggested that these differences in haemoglobin concentration are a result of differing habits. Those species that enter poorly aerated water are stimulated to make more haemoglobin.     

Dual bioluminescent systems in the anglerfish genus Linophryne (Pisces: Ceratioidea)

Females of the anglerfish genus Linophryne bear barbels containing luminous organs, in addition to an escal light organ. Luminescence has been observed from the barbels of four species of Linophryne , and the morphology of the luminous organs investigated. The barbel light organs do not contain bacteria but complex paracrystalline photogenic granules. The esca contains luminous bacteria. The esca is ectodermal in origin whereas the barbel organs may be derived from the mesoderm.
The possible significance of this unique dual system of luminous organs is discussed.     

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.     

Phylogenetic analysis of the loricariid subfamily Hypoptopomatinae (Pisces: Siluroidei: Loricariidae), with comments on generic diagnoses and geographic distribution

A survey of 55 osteological and myological features provided the basis for a phylogenetic analysis of the genera of the loricariid subfamily Hypoptopomatinae. Eleven genera are recognized. Aceslridium, Hypoptopoma, Microlepidogaster, Otocinclus (sensu stricto), Otothyris, Oxyropsis, Par otocinclus, Pseudotocinclus, Schizolecis and an unnamed new genus from Venezuela are each hypothesized as monophyletic on the basis of at least one uniquely derived, unreversed character stale. Pseudotothyris is diagnosed by one character state representing evolutionary convergence. Otocinclus , as presently defined (Isbriicker, 1980), is paraphyletic. Species related to Otocinclus vestitus , the type species, are more closely related to other Hypoptopomatinae than to other Otocinclus species. The hypothesis of generic relationships described herein is based on the consensus among three equally parsimonious trees of length 89 steps (c = 0.652). Distribution of character states on that tree and character-state evolution are discussed in terms of support for each lineage. Thirty-three trees were found one step longer (length = 90, c = 0.644) than the shortest, most parsimonious trees. The consensus among these 33 trees revealed two additional unresolved polychotomies involving members of the tribe Otothyrini and a clade composed of Hypoptopoma, Oxyropsis and Aceslridium. A preliminary framework for the analysis of historical biogeography of the Hypoptopomatinae is discussed.     

The Lusitania Province as a center of diversification: the phylogeny of the genus Microlipophrys (Pisces: Blenniidae)

The Lusitania Province has been considered a transition zone between the Atlantic northern cold waters and Tropical warm waters. Tropical species have expanded their ranges during warm periods and either retreated during cold periods or survived in local refuges. Successive waves of dispersion into this Province could have favored diversification through geographic isolation. Taxa that remained in this large Province may also have diversified in loco. We analyzed molecular markers of the genus Microlipophrys (family Blenniidae) that confirm the validity of this genus and of the seven recognized species. Microlipophrys and its sister clade apparently originated within Lusitania and dispersed into the tropics at a later stage.