New species of Moenkhausia Eigenmann (Characiformes: Characidae) from Rio Xingu and Rio Tapajos basins, Brazil, with comments on a putative case of polymorphic Batesian mimicry

A new species of Moenkhausia is described from Rio Xingu and Rio Tapajos basins, Brazil. The new species is distinguished from its congeners, except from Moenkhausia moisae, by having more scales in the lateral series, 43-47 (v. 23-41 in the remaining congeners). The new species is distinguished from M. moisae by its colour pattern, which consists of a dark midlateral stripe, and an asymmetrical caudal blotch (inconspicuous or faded in specimens from the Rio Arinos) continuous with the midlateral stripe (v. narrow dark midlateral line and conspicuous, regularly rounded and symmetrical blotch not continuous with the midlateral line). The new species is putatively assumed to be mimetic to Jupiaba apenima, in the Rio Xingu and Rio Teles Pires drainages, and to Jupiaba yarina in the Rio Arinos. The two species of Jupiaba are sympatric and remarkably similar in size, general external morphology and colouration to the new species. A small difference occurs in the colouration between the two species of Jupiaba and is also observed in the two respectively sympatric morphotypes of the new species of Moenkhausia. The occurrence of polymorphic Batesian mimicry is therefore discussed for neotropical freshwater fishes. (C) 2009 The Authors Journal compilation (C) 2009 The Fisheries Society of the British Isles

Taxonomic revision of doubtful Brazilian freshwater shrimp species of genus Macrobrachium (Decapoda, Palaemonidae)

The freshwater prawns of the genus Macrobrachium Spence Bate, 1868 are widely distributed in rivers of tropical and subtropical regions and represent an interesting group with controversial taxonomy. The morphological characters traditionally used to separate species have shown a high intraspecific variation. Doubts about the status of M. birai Lobao, Melo & Fernandes, 1986, M. holthuisi Genofre & Lobao, 1978 and M. petronioi Melo, Lobao & Fernandes, 1986 have been arisen due to the high resemblance of the former two species with M. olfersi (Wiegmann, 1836), and the latter one with M. potiuna (Muller, 1880). Therefore, we performed a detailed morphological analysis of these species, including new characters not usually used in the species recognition. The present results here with molecular data lead us to conclude that M. birai and M. holthuisi are junior synonyms of M. olfersi, and M. petronioi is a junior synonym of M. potiuna. Considering these synonymies, 17 valid species are now reported for the Brazilian territory.

The contrasting role of heterochromatin in the differentiation of sex chromosomes: an overview from Neotropical fishes

During the evolutionary process of the sex chromosomes, a general principle that arises is that cessation or a partial restriction of recombination between the sex chromosome pair is necessary. Data from phylogenetically distinct organisms reveal that this phenomenon is frequently associated with the accumulation of heterochromatin in the sex chromosomes. Fish species emerge as excellent models to study this phenomenon because they have much younger sex chromosomes compared to higher vertebrates and many other organisms making it possible to follow their steps of differentiation. In several Neotropical fish species, the heterochromatinization, accompanied by amplification of tandem repeats, represents an important step in the morphological differentiation of simple sex chromosome systems, especially in the ZZ/ZW sex systems. In contrast, multiple sex chromosome systems have no additional increase of heterochromatin in the chromosomes. Thus, the initial stage of differentiation of the multiple sex chromosome systems seems to be associated with proper chromosomal rearrangements, whereas the simple sex chromosome systems have an accumulation of heterochromatin. In this review, attention has been drawn to this contrasting role of heterochromatin in the differentiation of simple and multiple sex chromosomes of Neotropical fishes, highlighting their surprising evolutionary dynamism.

Egg surface structure of the freshwater toadfish Thalassophryne amazonica (Teleostei: Batrachoididae) with information on its distribution and natural habitat

The egg surface structure of Thalassophryne amazonica, a freshwater toadfish from the Amazon basin is described. Eggs of this species show a remarkable, highly unusual system of parallel ridges and intermittent grooves that originate at the equator of the egg and lead to the micropylar pit, at which they end in a spiralling pattern. A similar egg surface structure has so far been described only from a group of Asian anabantoid percomorphs, obviously not closely related to Thalassophryne. This egg surface pattern may enhance fertilization success by guiding sperm to the micropyle. We review museum records for T amazonica, present an updated map of its occurrence in the Amazon basin, and provide information on its habitat.

Embryonic development and larval stages of Steindachneridion parahybae (Siluriformes: Pimelodidae) - implications for the conservation and rearing of this endangered Neotropical species

Steindachneridion parahybae is a freshwater catfish endemic to the Paraiba do Sul River and is classified as an endangered Neotropical species. An increasing number of conservation biologists are incorporating morphological and physiological research data to help conservation managers in rescue these endangered species. This study investigated the embryonic and larval development of S. parahybae in captivity, with emphasis in major events during the ontogeny of S. parahybae. Broodstocks were artificially induced to reproduce, and the extrusion occurred 200-255 degree-hours after hormonal induction at 24 degrees C. Larval ontogeny was evaluated every 10 minutes under microscopic/stereomicroscopic using fresh eggs samples. The main embryogenic development stages were identified: zygote, cleavage, including the morula, blastula, gastrula phase, organogenesis, and hatching. The extruded oocytes showed an average diameter of 1.10 +/- 0.10 mm, and after fertilization and hydration of eggs, the average diameter of eggs increased to about 1.90 +/- 0.60 mm, characterized by a large perivitelline space that persisted up to embryo development, the double chorion, and the poles (animal and vegetative). Cell division started about 2 minutes after fertilization (AF), resulting in 2, 4, 8 (4 x 2 arrangement of cells), 16 (4 x 4), 32 (4 x 8) and 64 (2 x 4 x 8) cells. Furthermore, the blastula and gastrula stages followed after these cells divisions. The closed blastopore occurred at 11 h 20 min AF; following the development, the organogenetic stages were identified and subdivided respectively in: early segmentation phase and late segmentation phase. In the early segmentation phase, there was the establishment of the embryonic axis, and it was possible to distinguish between the cephalic and caudal regions; somites, and the optic vesicles developed about 20 h AF. Total hatching occurred at 54 h AF, and the larvae average length was 4.30 +/- 0.70 mm. Gradual yolk sac reduction was observed during the first two days of larval development. The first feeding occurred at the end of the second day. During the larval phase, cannibalism, heterogeneous larval growth and photophobia were also observed. This information will be important in improving the artificial reproduction protocols of S. parahybae in controlled breeding programs.

Ontogenetic and evolutionary change of external morphology of the neotropical shrimp potimirim (Holthuis, 1954) explained by a molecular phylogeny of the genus

A phylogenetic analysis of a fragment of the mitochondrial gene 16S was used to test the monophyletic status of Potimirim. Existing doubts on the taxonomic status of brasiliana (once P glabra) and P potimirim (once P mexicana) were clarified. Potimirim mexicana and P potimirim are distinct species according to molecular data and appendix masculina morphology. A new species (Potimirim sp. 1) from Puerto Rico was revealed with molecular data, and it is evolutionarily related to P potimirim and P mexicana according to our analysis. We found out three distinct species under the name P glabra. Then, we recommend the application of the name P glabra for the populations of the Pacific slope of Central America and revalidation of P brasiliana for the Brazilian ones. The need for a new name to those "P glabra" of the Caribbean is highlighted, and it was provisionally referred as Potimirim sp. 2. The ontogenetic (juveniles to adults) development of the appendix masculina of P brasiliana was observed and compared to the other species of Potimirim (adults). In the light of our phylogenetic hypothesis, we postulate a pattern of character addition for the evolution of the appendix masculina of Potimirim. This hypothesis is plausible for two key reasons. First. Potimirim is a monophyletic group according to our hypothesis. Second, the shape of appendix masculina found in adults of P. americana is similar and comparable to those found in the earliest juvenile stages of P brasiliana, a derived species according to our phylogeny (P americana, ((P mexicana, Potimirim sp. 1. P potimirim), (P glabra, (brasiliana, Potimirim sp. 2)))). As so, the basal P americana retain the ancestral morphological state of the appendix masculina when compared to the other species of Potimirim. In our interpretation the ontogeny of the appendix masculina recapitulated the proposed phylogeny, giving further support to it.

Embryonic development and larval stages of Steindachneridion parahybae (Siluriformes: Pimelodidae): implications for the conservation and rearing of this endangered Neotropical species

Steindachneridion parahybae is a freshwater catfish endemic to the Paraíba do Sul River and is classified as an endangered Neotropical species. An increasing number of conservation biologists are incorporating morphological and physiological research data to help conservation managers in rescue these endangered species. This study investigated the embryonic and larval development of S. parahybae in captivity, with emphasis in major events during the ontogeny of S. parahybae. Broodstocks were artificially induced to reproduce, and the extrusion occurred 200-255 degree-hours after hormonal induction at 24°C. Larval ontogeny was evaluated every 10 minutes under microscopic/stereomicroscopic using fresh eggs samples. The main embryogenic development stages were identified: zygote, cleavage, including the morula, blastula, gastrula phase, organogenesis, and hatching. The extruded oocytes showed an average diameter of 1.10 ± 0.10 mm, and after fertilization and hydration of eggs, the average diameter of eggs increased to about 1.90 ± 0.60 mm, characterized by a large perivitelline space that persisted up to embryo development, the double chorion, and the poles (animal and vegetative). Cell division started about 2 minutes after fertilization (AF), resulting in 2, 4, 8 (4 x 2 arrangement of cells), 16 (4 x 4), 32 (4 x 8) and 64 (2 x 4 x 8) cells. Furthermore, the blastula and gastrula stages followed after these cells divisions. The closed blastopore occurred at 11 h 20 min AF; following the development, the organogenetic stages were identified and subdivided respectively in: early segmentation phase and late segmentation phase. In the early segmentation phase, there was the establishment of the embryonic axis, and it was possible to distinguish between the cephalic and caudal regions; somites, and the optic vesicles developed about 20 h AF. Total hatching occurred at 54 h AF, and the larvae average length was 4.30 ± 0.70 mm. Gradual yolk sac reduction was observed during the first two days of larval development. The first feeding occurred at the end of the second day. During the larval phase, cannibalism, heterogeneous larval growth and photophobia were also observed. This information will be important in improving the artificial reproduction protocols of S. parahybae in controlled breeding programs.