Soft Rays Research Articles

Age, growth and maturity of frigate tuna (Auxis thazard Lacepède, 1800) in the Southeastern Brazilian coast

Age, growth and maturity of frigate tuna (Auxis thazard) were studied for the first time in Southeast Brazil. A total of 650 fish (265–494 mm Fork Length) were sampled from beach-seine landings between March 2018 and February 2019. Sectioned fin spines from 548 specimens were processed and age was determined by counting and measuring of increments. Growth parameters were fitted to length-at-age data using the von Bertalanffy growth function and were compared to the literature using the growth performance index (Phi). Macro and microscopic characterization of gonads and physiological indexes were used for the analysis of the reproductive cycle. The length distribution did not differ by sex. Assigned ages were between 0+ and 4 years, with annual increments formed during winter. Coefficient of variation between readings was 11%. Growth differed by sex, and the von Bertalanffy growth parameters were L∞ = 471 mm; k = 0.47 year−1; and t0 = –1.46 year−1 for females; L∞ = 498 mm; k = 0.35 year−1; and t0 = –2.01 year−1 for males. Phi was 5.0 for both sexes. Estimated growth rate is among the lowest recorded for the species, possibly related to the method used for age and growth assessment. Gonadosomatic index peaked in December, associated with the upwelling of the South Atlantic Central Waters, at a temperature of approximately 16 °C. Spawning activity in colder waters has never been reported for this species and may be influenced by a richer habitat caused by the intrusion of more nutritive rich waters during spring-summer, which allows larval development. Length-at-first-maturity (L50) was 345.4 mm for females and 329.8 mm for males.

Heteropneustes fuscus (Siluriformes: Heteropneustidae), a new catfish species from Kerala, India

Abstract. Plamoottil M. 2021. Heteropneustes fuscus (Siluriformes: Heteropneustidae), a new catfish species from Kerala, India. Biodiversitas 22: 87-98. Heteropneustes fuscus, a new catfish species, is described from Kerala, India; it is a close congener of Heteropneustes fossilis (Bloch, 1794) described from Tranquebar in Tamil Nadu. Heteropneustes fuscus has been misidentified as H. fossilis until now, but it differs from Bloch's species in color and many other rigid taxonomic variables. The new species can be distinguished from its relative species in the following combination of characters: deep black body and fins, 4-5 branched dorsal-fin soft rays, 72-75 anal fin rays, 58-60 total vertebrae, 26-32 total gill rakers; deeper and wider body; deeper caudal peduncle; greater pre occipital and post occipital distances and longer anal fin. The new fish is edible and found in freshwater rivers, streams, ponds and paddy fields in Kerala. It is also cultivated in some artificial impoundments. Heteropneustes fuscus is compared with its congeners, scientifically named and taxonomically described.

First Record of Trachipterus trachypterus (Gmelin, 1789) in the Gulf of Antalya (Turkey)

During the research in the grand port area of Antalya (coordinates: 36. 829022N; 30. 603739 E), it was observed that a very rare fish belonging to the Trachipteridae family was stranded in the Mediterranean Sea. The length of the fish, which weighs 400 g (TW = 400g), has been measured as 85cm (TL = 85cm). The fish without anal fin has a dorsal fin with red colour and soft rays, extending from the dorsal to the caudal region. In the examination made; it has been understood that this fish is Ribbon fish, Trachipterus trachypterus (Gmelin, 1789) which are rare fish in the Mediterranean Sea. In a review of previous studies, it was previously understood that this species was not given in the Gulf of Antalya. In the study, the Ribbon fish, Trachipterus trachypterus (Gmelin, 1789), is presented as a new record in the Gulf of Antalya (Turkey).

Stock Composition of the Historical New York Bight Atlantic Sturgeon Fishery Revealed through Microsatellite Analysis of Archived Spines

AbstractA targeted commercial fishery for Atlantic Sturgeon Acipenser oxyrinchus oxyrinchus once operated in the New York Bight, where it was assumed that most harvested Atlantic Sturgeon were natal to the Hudson River population. However, more recent evidence suggests that the fishery may have been targeting a mixed‐stock aggregation, in which case harvested Atlantic Sturgeon could have been comprised of individuals from multiple populations throughout the species’ range. Although there is now a moratorium on Atlantic Sturgeon harvest in the New York Bight, modern molecular approaches provide an opportunity to use archived tissues to perform a retrospective mixed‐stock analysis on the fishery. Genomic DNA extracted from archived fin spines from 80 Atlantic Sturgeon collected nearly 30 years ago suggests that the fishery primarily harvested individuals from the Hudson River population. However, based on individual‐based assignment tests, our results indicate that the fishery also harvested individuals from at least eight other populations located throughout the species’ range. This study highlights how archival hard parts that were previously used for age and growth analyses can be employed for retrospective genetic analyses. Further, because the New York Bight harbors relatively high concentrations of Atlantic Sturgeon, the study shows how localized management decisions can influence Atlantic Sturgeon conservation at rangewide scales. When integrated with more recent knowledge of species ecology, these analyses can be used to evaluate the efficacy of previous management strategies and understand the effects of historical processes on contemporary demography.

Spatial variability in strontium to calcium in the Caspian Sea: Recognition of starry sturgeon stocks from the pectoral fin spine chemistry

One of the fundamental hypotheses in aquatic ecology deals with the recognition of fish stocks. The present study tested the spatial dynamics of starry sturgeon stocks across environmental gradients by spatial variability in strontium to calcium in the pectoral fin spine. Forty samples of starry sturgeon were collected from the north and south of the Caspian Sea. A quantitative method was used to examine stocks using digested pectoral fin spine, reflecting habitat characters of fish. Parts of pectoral fin spines from adult starry sturgeon were separated and analyzed using Inductively Coupled Plasma- Mass Spectrometry (ICP-MS). Comparisons of Sr/Ca ratios in digested spines of the fish from north and south of the Caspian Sea demonstrated that Sr/Ca varied in the region and this significance was reflected in the spine as well. Our results for starry sturgeon support the use of spine Sr/Ca as a proxy for ambient levels throughout their life-history, confident interpretation of life history from spine Sr/Ca chronologies, however likely require matching time series of ambient Sr/Ca in the water bodies of interest.

Age, growth, and maturity of little tunny, Euthynnus alletteratus (Rafinesque, 1810) in southeastern Brazil

This is the first attempt to assess life parameters of little tunny Euthynnus alletteratus in the southwestern Atlantic. Fin spines, liver, and gonad information from 345 fishes (330-780 mm fork length) sampled from artisanal landings between March 2018, and February 2019 were used to analyze age, growth, and sexual maturity. Age was estimated by counting and measuring increments in sectioned spines, and the von Bertalanffy growth function was used to fit length-at-age data. There was no significant difference between male and female size distributions. Gonadosomatic index peaked from November to February in both sexes, associated with the South Atlantic Central Water (SACW) upwelling in temperatures between 15-18°C. Reproduction in cold waters has never been reported before and is possibly related to a richer environment for feeding and growth of larvae. The coefficient of variation among successive readings was 9.2%. The oldest fish was 5 years, and one annual increment for 2 and 3-year-old fish was observed to form associated with SACW. Little tunny growing in southeastern Brazil shows a higher growth rate and smaller asymptotic length when compared to most stocks in Mediterranean waters. Growth was not significantly affected by sex, and the von Bertalanffy growth parameters for all fish were L∞ = 791.9 mm, k = 0.42, and t0 = -0.97 yr-1. Length at first maturity is attained by 1-year-old fish of either sex (423-492 mm), suggesting that a small proportion (8%) of juveniles was recorded from fishery landings.

Fin–fin interactions during locomotion in a simplified biomimetic fish model

Fish median fins are extremely diverse, but their function is not yet fully understood. Various biological studies on fish and engineering studies on flapping foils have revealed that there are hydrodynamic interactions between fins arranged in tandem and that these interactions can lead to improved performance by the posterior fin. This performance improvement is often driven by the augmentation of a leading-edge vortex on the trailing fin. Past experimental studies have necessarily simplified fish anatomy to enable more detailed engineering analyses, but such simplifications then do not capture the complexities of an undulating fish-like body with fins attached. We present a flexible fish-like robotic model that better represents the kinematics of swimming fishes while still being simple enough to examine a range of morphologies and motion patterns. We then create statistical models that predict the individual effects of each kinematic and morphological variable. Our results demonstrate that having fins arranged in tandem on an undulating body can lead to more steady production of thrust forces determined by the distance between the fins and their relative motion. We find that these same variables also affect swimming speed. Specifically, when swimming at high frequencies, self-propelled speed decreases by 12%–26% due to out of phase fin motion. Flow visualization reveals that variation within this range is caused in part by fin–fin flow interactions that affect leading edge vortices. Our results indicate that undulatory swimmers should optimize both the positioning and relative motion of their median fins in order to reduce force oscillations and improve overall performance while swimming.

Diversity of gobioid fishes in the late middle Miocene of northern Moldova, Eastern Paratethys \u2013 part I: an extinct clade of Lesueurigobius look-alikes

Studies of otoliths suggest that Gobioidei, which are among the most species-rich groups of modern-day vertebrates, were prominent elements of late middle Miocene (early Sarmatian sensu lato) fish faunas in Europe and Western Asia. However, few complete skeletons have come to light. Here, we report an assemblage of six marine gobiid species, based on skeletons preserved with otoliths in situ, from the lower Volhynian (lower Sarmatian s.l.) of Karpov Yar, Naslavcea, northern Moldova (Eastern Paratethys). Previously only one of these species had been reported from the Central Paratethys, based on its otoliths alone. Five new species representing four new genera are described: †Katyagobius prikryli gen. et sp. nov., Pseudolesueurigobius manfredi gen. et sp. nov., †Sarmatigobius compactus gen. et sp. nov., †Yarigobius decoratus gen. et sp. nov., and †Y. naslavcensis gen. et sp. nov. All six species share the following set of characters, suggesting that they represent a monophyletic clade: 27–29 vertebrae (of which 10 are abdominal); spines of first dorsal fin distally filamentous; second dorsal fin with spine and 14–16 soft rays; anal fin with spine and 13–15 soft rays; caudal fin longish-to-lanceolate; otoliths (sagittae) with rounded, trapezoid-to-squarish shape. Their skeletal features suggest that they are closely related to Lesueurigobius Whitley, 1950, but the otoliths preserved in situ do not support such a classification. The new fossils most likely represent a stem lineage of the European Aphia lineage, and indicate that the diversity of gobiid lineages 12 million years ago differed clearly from that observed today.

Marking fin spine of juvenile sturgeon (acipenseriformes: acipenseridae) using oxytetracycline and the comparing of growth performance

ABSTRACT This study aimed to describe and validate the formation of the rings in the spine of the pectoral fin and to determine the coherence of the OTC mark with the rings of three species of Caspian Sea sturgeon, the Persian sturgeon (Acipenser persicus), the Starry sturgeon (Acipenser stellatus) and Ship sturgeon (Acipenser nudiventris). Validation was achieved by comparing the total radius of the fin spine of fish of known age after one and two years of growth with the measured radius of the first and second rings in the zone. There was no overlap between the measured radius for the first year and the increase for the second. The Ship sturgeon showed the largest width of the second ring followed by the Persian sturgeon and Stellate sturgeon. The results indicate that the highest growth parameter belongs to the juvenile Ship sturgeon. This research showed that chemically marking the fin spines of juvenile Acipenseridae leads to unbiased estimates and contributes to the knowledge of the population dynamics of these species. The study found that the combination of the dial ring of the pectoral fin spine with growth validated the age estimation in juvenile sturgeon Ship, Persian, and Starry sturgeon.

HETEROPNEUSTES FOSSILIS (ASIAN STINGING CATFISH)

This air sac catfish can be reported from India, Bangladesh, Pakistan, Nepalese, Asia, Thailand, Myanmar, and Bhutan, where it is known as the Asian stinging catfish (Heteropneustes fossilis). H. fossilis can be found in muddy rivers as well as ponds, canals, swamps, and marshes. It is able to survive in mildly salted water. It can eat anything. During the monsoon, this species breeds in restricted water, although it can also breed in ponds, abandoned ponds, and ditches if there is enough rainwater. Due to its supposed medical properties, it is in high demand. Humans can be stung to death by the stinging catfish. Known to cause severe agony is a gland on its dorsal fin spine that secretes poison. Fisheries in the area depend heavily on this species, which reaches a maximum length of 30 cm (12 in). It is also cultivated for the aquarium trade and available there. In Kerala, India, it's known as kadu or karri in local dialects (Malayalam). Assamese people call it singhi and it is very popular. In Dhaka, this fish is known as singi mach, whereas in Sri Lanka, it is known as hunga.

Spiny and soft-rayed fin domains in acanthomorph fish are established through a BMP-gremlin-shh signaling network

With over 18,000 species, the Acanthomorpha, or spiny-rayed fishes, form the largest and arguably most diverse radiation of vertebrates. One of the key novelties that contributed to their evolutionary success are the spiny rays in their fins that serve as a defense mechanism. We investigated the patterning mechanisms underlying the differentiation of median fin Anlagen into discrete spiny and soft-rayed domains during the ontogeny of the direct-developing cichlid fish Astatotilapia burtoni Distinct transcription factor signatures characterize these two fin domains, whereby mutually exclusive expression of hoxa13a/b with alx4a/b and tbx2b marks the spine to soft-ray boundary. The soft-ray domain is established by BMP inhibition via gremlin1b, which synergizes in the posterior fin with shh secreted from a zone of polarizing activity. Modulation of BMP signaling by chemical inhibition or gremlin1b CRISPR/Cas9 knockout induces homeotic transformations of spines into soft rays and vice versa. The expression of spine and soft-ray genes in nonacanthomorph fins indicates that a combination of exaptation and posterior expansion of an ancestral developmental program for the anterior fin margin allowed the evolution of robustly individuated spiny and soft-rayed domains. We propose that a repeated exaptation of such pattern might underly the convergent evolution of anterior spiny-fin elements across fishes.

MORPOMETRIC AND MERISTIC FEATURES OF THE CARP POPULATION (Cyprinus carpio) IN ÖZLÜCE DAM LAKE (ELAZIĞ-BİNGÖL)

This study was carried out to determine some metric and meristic characteristics of the Cyprinus carpio population captured from Özlüce Dam Lake at different times. For this purpose, the average, maximum, minimum, standard deviation, standard error and the coefficients of variation of 47 metric measurements and their ratio to each other belong to 60 scale and mirror carp samples captured from the dam lake are calculated. At the same time, 8 meristic features (the number of scales in the lateral line, the number of transversal scales, the number of spines in the first gill arch, the row and number of pharyngeal teeth and the number of simple and soft rays in the dorsal, ventral, pectoral and anal fins) were examined.

Natural hybridization between species of the cichlid genus Oreochromis (Cichlidae, Perciformes) in ponds of the low Ruzizi River (DR Congo)

Between 1948 and 1975, 3 species Oreochromis niloticus, O. leucostictus and O. macrochir were introduced into the Ruzizi plain, the natural distribution area of the subspecies Oreochromis niloticus edouardianus. Hybridization is observed between these species. The Mann-Whitney U test revealed significant differences between O. niloticus and its hybrids for the number of brachiospines; length of the last dorsal soft ray; and length of the lower jaw; O. macrochir differs from its hybrids in the number of branchiospines and length of the lower jaw; and O. leucostictus differs from its hybrids in the number of scales in the longitudinal line, the upper lateral line, the number of gill rakers, the length of the last dorsal soft ray, the length of the snout and the diameter of the eye. These characteristics are not sufficient to distinguish these three species from their hybrids without recourse to quality characteristics.

Gamma ray burst studies with THESEUS

Gamma-ray Bursts (GRBs) are the most powerful transients in the Universe, over–shining for a few seconds all other γ-ray sky sources. Their emission is produced within narrowly collimated relativistic jets launched after the core–collapse of massive stars or the merger of compact binaries. THESEUS will open a new window for the use of GRBs as cosmological tools by securing a statistically significant sample of high-z GRBs, as well as by providing a large number of GRBs at low–intermediate redshifts extending the current samples to low luminosities. The wide energy band and unprecedented sensitivity of the Soft X-ray Imager (SXI) and X-Gamma rays Imaging Spectrometer (XGIS) instruments provide us a new route to unveil the nature of the prompt emission. For the first time, a full characterisation of the prompt emission spectrum from 0.3 keV to 10 MeV with unprecedented large count statistics will be possible revealing the signatures of synchrotron emission. SXI spectra, extending down to 0.3 keV, will constrain the local metal absorption and, for the brightest events, the progenitors’ ejecta composition. Investigation of the nature of the internal energy dissipation mechanisms will be obtained through the systematic study with XGIS of the sub-second variability unexplored so far over such a wide energy range. THESEUS will follow the spectral evolution of the prompt emission down to the soft X–ray band during the early steep decay and through the plateau phase with the unique ability of extending above 10 keV the spectral study of these early afterglow emission phases.

A revision of Vernicomacanthus Miles with comments on the characters of stem‐group chondrichthyans

AbstractThe ‘acanthodian’ fishes provide key anatomical insights into the deepest branches of the chondrichthyan stem group. We review the anatomy of the acanthodian Vernicomacanthus uncinatus from the Lochkovian (Lower Devonian, 419.2–410.8 Ma) of Scotland based on eight articulated fossils, one of which is newly described. Broadly, the anatomy of V. uncinatus fits with that of contemporaneous acanthodians such as Climatius and Parexus, with a head covered by robust tesserae, an enlarged postorbital scale, an armoured shoulder girdle, and many pairs of ventrolateral spines. However, it departs from this anatomy in key respects. Its pectoral fin spines are obliquely ridged and posteriorly denticulated, similarly to Carboniferous gyracanth stem‐group chondrichthyans. Its scales consist of multiple anteroposteriorly aligned odontodes, similarly to many Palaeozoic ‘sharks’. And its endoskeletal shoulder girdle may have a posterolateral angle, previously observed only in shark‐like chondrichthyans. We propose that the differences between V. uncinatus and its congeneric, V. waynensis, which include potentially phylogenetically significant characters of the shoulder girdle and spines, are sufficient to erect a new genus for V. waynensis: Dobunnacanthus gen. nov. The scales of Vernicomacanthus are identical to those of the ‘shark’ scale genus Altholepis, suggesting that some such scales may instead belong to taxa with acanthodian‐like gross anatomies. Based on these scales we highlight potential patterns in chondrichthyan scale evolution, in particular the axial addition of odontodes. Anatomical similarities between Vernicomacanthus and gyracanths, highlighted by previous authors, may indicate the existence of a grade including these and similar acanthodian‐grade taxa placed relatively crownwards in the chondrichthyan stem‐group.

A new species of pikeblenny (Blenniiformes: Chaenopsidae: Chaenopsis) from the tropical eastern Pacific and a key to all species.

The genus Chaenopsis presently includes 10 species, four in the eastern Pacific and six in the western Atlantic. Five individuals of an undescribed species of this genus were obtained at Gorgona Island in the eastern Pacific of Colombia, in depths between 3 and 5m. This new species differs from all the Eastern Pacific species in an array of traits including meristic, coloration and morphometric characters. Chaenopsis celeste new species differs from its only sympatric species, C. deltarrhis, in having fewer pectoral rays, fewer dorsal spines and more dorsal-fin soft rays and anal-fin elements. This new species is found over shallow sandy, rubble and small rocks bottoms from Costa Rica to Colombia.

Durnonovariaodus maiseyi gen. et sp. nov., a new hybodontiform shark-like chondrichthyan from the Upper Jurassic Kimmeridge Clay Formation of England.

A partial skeleton of a hybodontiform shark-like chondrichthyan from the Upper Jurassic Kimmeridge Clay Formation of Dorset, England, is described and designated as a new genus and species, Durnonovariaodus maiseyi gen. et sp. nov. The holotype and only known specimen, which is represented by disarticulated splanchnocranial elements with associated teeth, a single dorsal fin spine, the pelvic girdle, as well as unidentifiable cartilage fragments, plus countless dermal denticles, exhibits a puzzling combination of dental and skeletal features, providing important new insights into the morphological and ecological diversity of hybodontiforms. Durnonovariaodus gen. nov. displays a unique set of dental characters, showing close morphological resemblance to Secarodus from the Middle Jurassic of England, which was erected for distinctive, strongly labio-lingually compressed multicuspid cutting teeth originally described as Hybodus polyprion. Skeletally, Durnonovariaodus gen. nov. resembles Hybodus and Egertonodus in having a palatoquadrate with a palatobasal process and an ethmoidal articular surface, combined with the possession of dorsal fin spines ornamented with costae. Therefore, and given the absence of any conclusive phylogenetic framework, Durnonovariaodus maiseyi gen. et sp. nov. is here tentatively referred to Hybodontidae until more complete material becomes available in order to enable a more reliable suprageneric identification. The holotype of Durnonovariaodus maiseyi gen. et sp. nov. contains two separate pelvic half-girdles, a feature previously considered as evolutionarily primitive among hybodontiforms. However, unfused pelvic half-girdles also occur in the supposedly closely related species Hybodus hauffianus and may in fact have been more widely distributed among hybodontiforms than previously thought, thus rendering the phylogenetic utility of separated pelvic half-girdles for inferring hybodontiform interrelationships difficult and unresolved.

Morphological characteristics of three species in the genus Upeneus (Cuvier and Valenciennes, 1829) in the coastal sea of Nghi Son Town, Thanh Hoa Province

The study was conducted based on the analysis of specimens collected in the coastal sea of Nghi Son Town, Thanh Hoa Province, from December 2019 to December 2020. The results identified three species in the genus Upeneus (Mullidae): Upeneus tragula Richardson, 1846, Upeneus sulphureus Cuvier, 1829, and Upeneus japonicus Houttuyn, 1782. The study also analysed the differences of above specimens in comparison with the previous studies of FAO (2001) [1], Nguyen et al. (2007) [6], although there are some differences in the ratios of the body part with the standard length (Lo) and head length (T) but insignificant. Analysis of the morphological characteristics of the three species also showed that the differentiation was most clearly expressed in the number spines of the first dorsal fin, the soft rays of pectoral fin, lateral scales, colour and pattern on the body; the combination of these features can be used as a standard for classifying species, among them the differences in color and pattern are important classification characteristics.

A new jawfish of the genus Opistognathus/ (Perciformes: Opistognathidae) from Japan.

A new species of jawfish, Opistognathus ocellicaudatus, is described based on a single specimen collected at 67 m depth in Sagami Bay (near the mouth of Tokyo Bay), Honshu Island, Japan. The new species can be separated from all other Indo-West Pacific jawfish species in having 3 longitudinal dark brown stripes on the body, a large dark whitish-rimmed ocellus on the caudal fin, a small black blotch on the opercular flap, the dorsal fin with 11 spines and 11 soft rays, the anal fin with 2 spines and 11 soft rays, 21 pectoral-fin soft rays, 26 vertebrae, 42 oblique scale rows, and 2 supraneurals. The holotype is a female containing mature eggs, suggesting summer spawning. The type locality was close to the northern distributional limit of Opistognathidae in the Indo-West Pacific. [http://zoobank.org/urn:lsid:zoobank.org:act:00DCADDA-BE92-4C33-B7EB-1DA8348BA02A].

Two new catfish species of typically Amazonian lineages in the Upper Rio Paraguay (Aspredinidae: Hoplomyzontinae and Trichomycteridae: Vandelliinae), with a biogeographic discussion

Two new species of particular biogeographic significance are described from the upper rio Paraguay basin, one of the genus Paracanthopoma (Trichomycteridae, Vandelliinae) and the other of the genus Ernstichthys (Aspredinidae, Hoplomyzontinae). The two species occur sympatrically in the Rio Taquarizinho, tributary of the Rio Taquari, in the upper Paraguay system. Paracanthopoma saci is distinguished from its only congener, P. parva, by a spatulate caudal peduncle; a minuscule premaxillary dentition (reduced to three delicate teeth); the supraorbital latero-sensory canals opening as two separate s6 pores; the caudal fin slightly convex or truncate with round edges; the skull roof entirely open, unossified; the origins of dorsal and anal fins approximately at same vertical; and the pelvic fin with three rays. Ernstichthys taquari is diagnosed among congeners by the narrow bony shields on dorsal and ventral series, not overlapping or contacting each other; by the presence of seven or eight serrations on the posterior margin of the pectoral spine; and by the pectoral-fin spine only slightly larger than subsequent soft rays. Both Paracanthopoma and Ernstichthys were previously unknown outside of the Greater Amazonian river systems (Amazon, Orinoco, Essequibo and smaller surrounding drainages). Their presence restricted to the Rio Taquari is unexpected and suggests a peculiar biogeographical history. Ancestral geographic distributions were reconstructed using S-DIVA and BBM methods in RASP. A majority of resulting hypotheses support that the two species reached the Paraguay from the Amazon. The alternative explanation accounts for their presence in the Paraguay by vicariant events. In no case, their presence in the Paraguay is an ancestral distribution with subsequent Amazonian dispersal. Though unusual, this pattern is also seen in a few other fish taxa, showing that the Rio Taquari is biogeographically hybrid, combining elements from both the Paraguay and Amazon drainages.