Biodiversity and systematics of skates (Chondrichthyes: Rajiformes: Rajoidei)

Skates (Rajiformes: Rajoidei) are a highly diverse fish group, comprising more valid species than any other group of cartilaginous fishes. The high degree of endemism exhibited by the skates is somewhat enigmatic given their relatively conserved body morphology and apparent restrictive habitat, e.g. soft bottom substrates. Skates are primarily marine benthic dwellers found from the intertidal down to depths in excess of 3,000 m. They are most diverse at higher latitudes and in deepwater, but are replaced in shallower, warm temperate to tropical waters by stingrays (Myliobatodei). The number of valid skate species has increased exponentially, with more species having been described since 1950 (n = 126) than had been described in the previous 200 years (n = 119). Much of the renaissance in skate systematics has largely been through the efforts of a few individuals who through author–coauthor collaboration have accounted for 78 of the 131 species described since 1948 and for nine of 13 genera named since 1950. Furthermore, detailed regional surveys and accounts of skate biodiversity have also contributed to a better understanding of the diversity of the skates. A checklist of the living valid skate species is presented.     

Standardized diet compositions and trophic levels of skates (Chondrichthyes: Rajiformes: Rajoidei)

Skates by virtue of their abundance and widespread occurrence appear to play an influential role in the food webs of demersal marine communities. However, few quantitative dietary studies have been conducted on this elasmobranch group. Therefore, to better understand the ecological role of skates, standardized diet compositions and trophic level (TL) values were calculated from quantitative studies, and compared within and among skate and shark taxa. Prey items were grouped into 11 general categories to facilitate standardized diet composition and TL calculations. Trophic level values were calculated for 60 skate species with TL estimates ranging from 3.48 to 4.22 (mean TL = 3.80 ± 0.02 SE). Standardized diet composition results revealed that decapods and fishes were the main prey taxa of most skate species followed by amphipods and polychaetes. Correspondingly, cluster analysis of diet composition data revealed four major trophic guilds, each dominated by one of these prey groups. Fish and decapod guilds were dominant comprising 39 of 48 species analyzed. Analysis of skate families revealed that the Arhynchobatidae and Rajidae had similar TL values of 3.86 and 3.79 (t-test, P = 0.27), respectively. The Anacanthobatidae were represented by a single species, Cruriraja parcomaculata, with a TL of 3.53. Statistical comparison of TL values calculated for five genera (Bathyraja, Leucoraja, Raja, Rajella, Rhinoraja) revealed a significant difference between Bathyraja and Rajella (t-test, P = 0.03). A positive correlation was observed between TL and total length (L _T) with larger skates (e.g. >100 cm L _T) tending to have a higher calculated TL value (>3.9). Skates were found to occupy TLs similar to those of several co-occurring demersal shark families including the Scyliorhinidae, Squatinidae, and Triakidae. Results from this study support recent assertions that skates utilize similar resources to those of other upper trophic-level marine predators, e.g. seabirds, marine mammals, and sharks. These preliminary findings will hopefully encourage future research into the trophic relationships and ecological impact of these interesting and important demersal predators.     

Observations on the venous system of three species of Polypterus (Pisces)

The venous system of Polypterus exhibits general asymmetry. The features that characterize the venous system of this peculiarly African fish are the possession of many blood sinuses, the segmental drainage of blood, the continuation of the posterior cardinal veins as separated vessels and the occurrence of several anastomozes between the latter.
In the absence of any recent comprehensive work on the blood system of this fish, it was thought that investigation of the circulatory system of Polypterus would be valuable. In this paper attention is drawn to Budgettapos;s (1902) original work on a larva of Polypterus senegalus. Contrary to Budgettapos;s findings it is concluded that what he called the "interrenal" vein is in fact the right posterior cardinal vein. It is also found that paired posterior cardinal veins exist in all adults.     

Sexual dimorphism of external morphological characters in some deepwater skates (Rajidae,Rajiformes, Chondrichthyes) of the North Atlantic

Our studies of the external morphology of five species of deepwater skates (Amblyraja jenseni, Bathyraja pallida, B. richardsoni, Rajella bigelowi, and R. kukujevi) showed that their males and females differ significantly in 9 characters in the first species, 14 characters in the second, 11 characters in the third and fourth, and 10 characters in the fifth. Sexual differences occur most frequently in the length of the first gill slit (in four species out of five), the length of the nasal curtain, the mouth width, and the length of the third gill slit (in three species out of five), the width and length of the disc, the length of the first and second dorsal fin bases, the tail height at the tip of the ventral fin, the length of the fifth gill slit, the distance between the first and fifth gill slits, the interspiracular distance, the preanal length, distance from the tip of the snout to the maximum disc width, and the interorbital distance (in two species out of five).     

Feeding-site utilization in three sympatric species of Petrotilapia (Pisces, Cichlidae) from Lake Malawi

Three sympatric sibling species of Petrotilapia , with similar dietary and macrohabitat requirements, occur near Monkey Bay, Lake Malawi. Males and females of all three species fed selectively on the rocky shores. Males utilized less than 6% of the space they defended as a breeding territory for feeding and although interspecific overlap of territories was considerable, only 2.5% of the feeding space used by territorial males was shared. Males primarily utilized rich food patches which occurred within the territories of highly aggressive Pseudotropheus species, whereas females tended to feed in undefended areas. Although Petrotilapia species are not highly aggressive fishes, there was a well-defined social dominance hierarchy amongst them and it is suggested that feeding-site utilization is dependent on social rank. Inter-and intraspecific differences in feeding-site utilization probably facilitate species coexistence and thus contribute to the maintenance of the high species diversity which is a characteristic of the ichthyofauna of Lake Malawi.     

Biology and ecology of three species of Australian Dragonets (Pisces: Callionymidae)

Callionymus sublaevis, C. calcaratus and C. calauropomus collected from Moreton Bay and offshore Queensland, were studied biologically and ecologically and the findings compared with other callionymid fishes from Australian waters and other areas. Predominant preys types included penaeid prawns, pelecypods and poly-chaetes. Differences in temporal feeding intensity and prey types eliminated competition in some cases. Through brain pattern analyses, these callionymids were shown to be predominantly sight feeders even at depth, although gustatory feeding also increased slightly with depth. Sex ratios in C. sublaevis were almost even, while C. calauropomus had a predominance of males. C. calcaratus had a predominance of females, but considerable variation occurred on a seasonal basis. Although considerable variation was found in spawning times and spawning period length, the histological changes that occurred in the development of oocytes was similar. The ovarian cycle in C. sublaevis was studied in detail and found to be typical of most teleosts. Length-weight regression coefficients in all species were significantly higher than 3.0, indicating that the weight increased faster than the cube of their length. In all cases females were heavier in older fish with the least difference in length-weight occurring between the males and females of C. calcaratus. Otoliths were found to be satisfactory and reliable for use as a method for age and growth determinations in two of the callionymids studied. Overlap of age groups was found in all species and this was mostly attributed to the length of spawning period. The dragonets studied here all reached age group IV+ and attained maturity usually by the second year. No evidence was found to indicate that males die after spawning as has been shown in C. lyra. Observations on predation by benthic piscivorous fishes and by one avian predator are reported.     

Food and feeding of three Distichodus species (Pisces: Characiformes) in Lake Kainji,Nigeria

The food and feeding of three Distichodus species in Lake Kainji, Nigeria was studied. Sixty 140 and 528 specimens of Distichodus brevipinnis, D. engycephalus and D. rostratus respectively were examined. All three species were exclusively herbivorous. Their feeding was intense in the evening until dusk but declined during the day. All exhibited some seasonal variation in their food preferences.     

Description of egg capsules of Rasptail Skate Rostroraja velezi (Chondrichthyes: Rajiformes: Rajidae) from northern Peru

Environmental Biology of Fishes - Nine egg capsules of the Rasptail Skate (Rostroraja velezi) were collected from their southernmost distributional range in northern Peruvian waters for their...     

Clasper morphology of skates of the tribe Riorajini (Chondrichthyes: Rajiformes: Arhynchobatidae) and its systematic significance

Claspers of adult specimens of the skate tribe Riorajini, family Arhynchobatidae, comprising Atlantoraja and Rioraja , are described, compared, and systematically reinterpreted based on material collected off southeastern and southern Brazil. For the first time the external components and musculature of the clasper of members of this tribe are described and related to internal (skeletal) structures. The component pecten is present in all species of Atlantoraja but absent in Rioraja . The new external component grip , an autapomorphy of A. cyclophora fully developed in adults, is described. Rioraja presents dorsal terminals 1 and 2, ventral marginal distally extended and ventral terminal cartilages. Dorsal terminals 1 and 2, ventral marginal distally extended, accessory terminals 2 and 3, and ventral terminal cartilages occur in Atlantoraja . A new interpretation of the ventral marginal distally extended is discussed. The dorsal terminal 1 of Atlantoraja has an inverted U shape but is triangular in Rioraja . The accessory terminal 2 cartilage is reported for the first time in Atlantoraja cyclophora . The accessory terminal 3 is present only in A. platana and A. cyclophora , and absent in Rioraja and A. castelnaui . Many of our findings concerning the clasper skeleton do not agree with previous interpretations. The arrangement, distribution and systematic significance of many of the terminal clasper components are discussed among rajoids.     

A new species of Argyrosomus (Pisces, Sciaenidae) from Natal, South Africa

Argyrosomus thorpei sp. n. is described from 11 specimens and compared with its closest relatives A. hololepidotus and A. amoyensis.     

Hematological parameters of three freshwater stingray species (Chondrichthyes: Potamotrygonidae) in the middle Rio Negro,Amazonas state

This paper aimed to study and compare the hematology of newborns, young, subadults, adult males, adult females and pregnant females of Potamotrygon wallacei (cururu stingray), Potamotrygon motoro and Paratrygon aiereba. Newborn cururu stingrays had lower red blood parameters than those of other development stages. Thrombograms and leukograms showed a conservative pattern between development stage, sexual dimorphism and pregnancy. In P. motoro and P. aiereba, variables relating to red blood parameters, biochemistry and leukograms showed little variation between the species' biological characteristics, thus showing that these variables are not good criteria for differentiating them within the same species. In conclusion, the development stage is an important factor for differentiating hematological properties in the cururu stingray, while this has not been observed in P. motoro and P. aiereba stingrays.     

A karyological study of three species of Scincidae (Reptilia)

In this paper the Authors decribe the karyogram of three species of Scincidae (Chalcides chalcides chalcides, Chalcides ocellatus tiligugu, and Mabuya striata). The diploid number of these species is 2n=28. It is not possible to subdivide the chromosome set in micro- and macrochromosomes or to recognize the heterochromosomes morphologically. Ch. ocellatus and M. striata have very similar karyograms; that of Ch. ch. chalcides is different in that chromosomes 6, 7, 8, 9, and 10 are acrocentric. Pericentric inversion is probably involved in the karyotypic evolution of these species.     

A cytogenetic study on three Chilean species of Chrysomelinae (Coleoptera, Chrysomelidae)

Three species of Chilean leaf beetles were chromosomally analyzed. The endemic Araucanomela wellingtonensis displays a male meioformula of 13 + Xyp with 2n = 28 chromosomes and an asymmetric karyotype with two large autosome pairs and 12 medium/small pairs of autosomes and sex-chromosomes, a diploid number which had not been found among the other species of the subtribe Paropsina sensu lato studied to date. Strichosa eburata presents a meioformula of 11 + Xyp, 2n = 24 chromosomes, as occurs in many species of chrysomelines belonging to different subtribes. Furthermore, Phaedon cyanopterum has a 16 + Xyp meioformula, that is 2n = 34 chromosomes, of small size mostly, also in agreement with the karyological findings obtained in all the other congeneric species so far examined. These cytogenetic data are discussed with respect to the previous ones in this subfamily and with other characters of taxonomic and evolutionary value.     

A new species ofPalaeospinax (Chondrichthyes,Neoselachii) from the Lower JurassicPosidonia Shale of Southern Germany

The diagnosis of the fossil neoselachian genusPalaeospinax Egerton 1872 is revised. A new species from the Lower ToarcianPosidonia Shale of Southern Germany is described asPalaeospinax politus n. sp. It differs from all other known members of the genus in having smooth anterior and lateral teeth.     

Chromosomes of three freshwater stingrays (Rajiformes Potamotrygonidae) from the Rio Negro basin, Amazon, Brazil

Potamotrygonidae is the representative family of South American freshwater elasmobranchs. It is a monophyletic group containing 20 species grouped into three genera. Three species belonging to two genera of this family were collected from the middle Negro River, Amazonas, Brazil, and studied cytogenetically: Paratrygon aiereba, Potamotrygon motoro and Potamotrygon orbignyi. Paratrygon aiereba presented 2n = 90 chromosomes and 4M+2SM+10ST+74A. Both species of Potamotrygon presented 2n = 66 chromosomes and differed in their chromosomal formulas: P. motoro had 18M+12SM+10ST+26A and P. orbignyi had 22M+10SM+8ST+26A. No sex heteromorphism was detected. The Fundamental Number (FN) was 106 for the three species. A system of multiple NORs was found in the three species, but with interspecific differences in terms of location and position of the active Ag-NORs sites. Paratrygon aiereba presented only four sites on the short arms of two chromosomal pairs, both in terminal regions. Potamotrygon motoro presented seven sites, on the long and short arms, all in terminal regions of non-homologous chromosomes; P. orbignyi presented eight sites on the long arms, all in terminal regions, of non-homologous chromosomes. The constitutive heterochromatin was in pericentromeric regions of all chromosomes, and no significant interspecific difference was found in relation to this marker.     

Molecular differentiation of three loach species (Pisces, Cobitidae) based on the nuclear 5S rDNA marker

The diversity of the 5S rDNA fragment among three loach species: Cobitis taenia, C. elongatoides and Sabanejewia aurata was investigated using universal PCR primers for this gene. Three amplification products were obtained: 220 bp length for C. taenia and C. elongatoides, and 330 bp for S. aurata. Two amplicons with the same length (in Cobitis) were digested with TaqI restriction endonuclease. This enzyme found one restriction site T/CGA in the C. elongatoides fragment, while in the case of C. taenia no cleavage effect was observed. On this basis we constructed an easy and cheap method for loach species discrimination. It seems adequate for effective support of conservation initiatives for endangered loaches.