Males of some species of Eurycea exhibit gross morphological shape changes of their heads throughout the year because of hypertrophy of jaw musculature during the mating season, although glandular swelling of the integument has not been rejected for all taxa. We assessed head shape variation of a species from the Eurycea quadridigitata complex, E. chamberlaini, throughout the year to examine seasonal variation in head shape in a diminutive species where this has never been reported. We found that male specimens differed from females in terms of morphospace and, similar to other species of Eurycea, male heads were wider posterior to the orbital region relative to anterior. Interestingly, we also recovered the same result for females, demonstrating that head shape varies seasonally in both sexes of E. chamberlaini. Collectively, these results indicate that hypertrophy and atrophy of jaw muscles, or potentially integumentary glands, not only occurs in males and females of the Eurycea bislineata complex, but also may be more ubiquitous within the genus. The previous lack of this observation within the E. quadridigitata complex is most likely the result of difficulty in observing head shape variation in a diminutive species similar to E. chamberlaini without the use of large datasets and morphometric analysis.

Dussumieria apollo, new species, is described based on 34 specimens collected from the southern coast of Papua New Guinea and northern coast of Australia. The unique combination of characters including forms of body scales (numerous longitudinal striae on posterior part), teeth on mouth roof (numerous rows of conical teeth on anterior parts of palatine and pterygoids forming a band), deep body, low number of gill rakers, and several proportional measurements separated the new species from all congeners. To evaluate the validity of the new species, four barcode sequences (three of them newly determined for this study) of the mitochondrial DNA (mtDNA) cytochrome oxidase I (COI) gene were compared with those of 35 specimens belonging to seven other valid species of Dussumieria. Our molecular analysis corroborated the validity of D. apollo, new species, which forms a monophyletic group diverging from any congener by >8.0% mean uncorrected genetic distances.

The Eastern Red-Backed Salamander (Plethodon cinereus) is one of the most abundant vertebrate species in the forests of eastern North America and is considered an important species for ecological processes. Two phenotypes most commonly coexist in most populations, but in different proportions: the red-backed (striped) and lead-backed (unstriped) morphs. Recent large-scale studies suggested that both color morphs of P. cinereus occur in and beyond the species' current northern range. The presence of lead-backed morphs in this area would contradict some previous studies that link the lead-backed morph with warmer conditions. To test this hypothesis, we conducted inventories in the boreal forest of northwestern Quebec (Canada), outside or at the edge of the species' known northern range, where temperatures are among the coldest encountered by this species. We documented 11 sites with the lead-backed morph, including five sites in the Parent area that fill a large gap in the species' known distribution. Among the latter, we found three distinct populations in which the lead-backed morph reached frequencies of 43–96%. These occurrences of P. cinereus are noteworthy given the harsh climatic conditions that prevail throughout the year and the recurrence of large-scale disturbances in these far-north forests. Although a previous study observed relatively high frequencies of the lead-backed morph in the northern part of the species' range, this is the first report of such high frequency findings so far north, outside of the known species' range. Our findings agree with the mounting evidence that variation in color morph frequency is not related only to temperature or shifts in climate.

The Sicklefin Redhorse is perhaps the largest truly new North American species discovered in the last century, and the species is herein described as Moxostoma ugidatli, new species. Sicklefin Redhorse differ from other red-tailed redhorse based on the presence of elongate first through third dorsal-fin rays, and from all other redhorse by having plicate lips with deep, branching grooves distally (vs. lips papillose or unbranching) and by having moderately molariform pharyngeal teeth (vs. molariform or chisel-like teeth). The Sicklefin Redhorse is found in the upper Tennessee River basin of North Carolina and Georgia in the Little Tennessee and Hiwassee River subbasins. Although the species is not federally protected, it is threatened in North Carolina and endangered in Georgia. The species is known to live to 22 years, with the largest preserved female 500 mm SL, 633 mm TL, 2.561 kg and the largest preserved male 463.2 mm SL, TL unknown, 2.024 kg.

A new species of stingray belonging to the genus Hypanus is described in this study based on data collected in the Eastern Tropical Pacific (ETP) region of Colombia. This new species stands out within the genus by its unique spade-shaped disc with a width-to-length ratio ranging from 1.0 to 1.1, whereas its obtuse snout extends 29–30% of the disc width (DW). This species also stands out due to its large size (125 cm DW). Notably, it has three distinctive rows of enlarged denticles on its mid-scapular area, with the central row extending back to the caudal sting. Additionally, it possesses a long tail that measures 2.2–2.5 times the DW, tapering smoothly. Molecular data also revealed significant differences between this new species and its congeners using COI. The phylogenetic analysis recovered Hypanus rubioi, new species, as the sister species to the western Atlantic Longnose Stingray H. guttatus, with an uncorrected genetic distance of 2.27 to 2.94%. The preliminary ecological niche modeling further indicates that this newly described species is likely associated with coastal regions in the ETP, ranging from central Mexico to northern Peru, with backlight and salinity as the most influential variables. These findings contribute to our understanding of the biodiversity within the genus Hypanus and the ecological distribution of this novel species in the ETP.

Se describe una nueva raya del género Hypanus del Pacífico oriental tropical (POT) a partir de material colectado en el Pacífico de Colombia. La nueva especie es única dentro del género por ser de gran tamaño (125 cm de ancho de disco [AD]) con un disco romboidal en forma de pala, su anchura 1,0 a 1,1 veces su longitud, un hocico obtuso, rostro prolongado de punta extendida, 29–30% en AD, tres filas de dentículos agrandados en la parte media de la escapula, la hilera central se extiende hacia atrás hasta el aguijón caudal, cola larga, 2,2–2,5 veces el AD, estrechándose suavemente. Se diferencia de todos sus congéneres también por diferencias moleculares del gen COI. El análisis filogenético encontró que Hypanus rubioi sp. nov. es la especie hermana de la raya laya látigo hocicona del Atlántico occidental H. guttatus, con una distancia genética no corregida de (2,27 a 2,94%). El modelado preliminar del nicho ecológico indica además que esta especie recién descrita está probablemente asociada a regiones costeras del POT, que abarcan desde el centro de México hasta el norte de Perú y donde la luz de fondo y la salinidad fueron las variables con mayor influencia en el resultado. Estos resultados contribuyen a nuestra comprensión de la biodiversidad dentro del género Hypanus y la distribución ecológica de esta nueva especie en el POT.

A majority of ichthyological research on Sulawesi is focused on the island's ancient lakes, whereas many, even large, river systems remain unstudied. This is particularly true for the Lariang River in the central highlands of Sulawesi, the island's longest river with the largest drainage basin. Recent collection efforts there revealed a previously unknown species of ricefish (Teleostei: Adrianichthyidae: Oryzias), which is described herein. It is distinguished from its congeners by its high, non-overlapping scale count in lateral series. Interestingly, it occurs in sympatry with another recently described ricefish species. A phylogenetic analysis based on mitochondrial ND2 gene sequences recovered both species as sister lineages, making them the first known case of a riverine species pair in this family. The new species is further separated from its close relatives because it is a transfer-brooding species within a clade of pelvic-brooding species, suggesting a secondary reversal of reproductive modes. Possibly related to this, it also has the most pronounced rheophilic ecology of all known ricefish species. This discovery highlights the diversity of evolutionarily derived lineages found on Sulawesi and stresses the importance of additional explorative surveying to record it.

Turtles experience numerous threats and high mortality in urban areas. Mass-mortality events (MMEs) are localized, sudden events resulting in a catastrophic increase in mortality rate. Turtles are susceptible to MMEs because their long generation times do not permit density-dependent compensation. We retrospectively investigated an MME in 2020 that affected two species, headstarted Blanding's Turtles (Emydoidea blandingii) and naturally occurring Midland Painted Turtles (Chrysemys picta marginata) in Rouge National Urban Park (RNUP) in Ontario, Canada, where we monitored the freshwater turtle community from 2014 to 2022. In 2020, 48 juvenile headstarted Blanding's Turtle and 57 Midland Painted Turtle carcasses were found, most (75%) of which were females. The turtles were likely depredated by Raccoons (Procyon lotor) or American Minks (Neogale vison). Documented mortalities were highest in release sites for headstarted turtles, possibly due to increased monitoring efforts at those sites. Conservation initiatives such as headstarting are useful to recover turtle populations, but MMEs may disrupt and delay population stabilization, especially in areas where other threats (e.g., subsidized predators, road mortality) are prevalent. We emphasize the importance of long-term monitoring of turtle populations, especially after conservation interventions, to detect challenges that affect their persistence.

Although sculpin can play important ecological roles, serving as abundant key meso-predators in freshwater aquatic systems, much remains to be learned about their development and ecology. Depth discrete light traps effectively captured larval sculpin from Lookout Point Reservoir in the Willamette Basin, Oregon, USA. We confirm that these larvae were Prickly Sculpin (Cottus asper) based on morphology and genetics. We also document larval size and development and examine monthly vertical distributions and sympatric invertebrate taxa. We captured 1,048 pelagic larval Prickly Sculpin from 4.21 to 42.0 mm total length. Sampling occurred in traps set up to 20 m above the substrate, with Prickly Sculpin captured at all sampled depths. Captures shifted toward deeper reservoir habitats corresponding to increases in average body sizes as the season progressed from early spring to fall. We found most larval Prickly Sculpin at locations within the main reservoir body, several kilometers downstream of riverine areas. In addition to trap location, the abundance of larval Prickly Sculpin per trap was strongly associated with aquatic mites (absent from Prickly Sculpin stomachs). These findings suggest potentially shared ecological drivers of the observed distributions of larval Prickly Sculpin and mites. Collectively, we demonstrate that light trapping can be a useful method for collecting pelagic juvenile sculpins from reservoirs, in this case Prickly Sculpin, with the potential to improve our understanding of distribution, life-history patterns, and ecology throughout their range.

The lower Rio Grande watershed below Falcon Dam has been 95% developed for agriculture, urban, and industrial uses. The river has been extremely altered to make this possible, with the addition of two more downstream dams, a series of five rock weirs, and numerous water diversions. This regulation has resulted in an extremely altered flow regime and fish fauna since the early 1950s. There has been a significant general retreat and decline of primary freshwater fishes over time, and we identified three significantly different faunal groups across the fragmented watercourse. However, the overall species richness of the region did not change significantly over time, likely due to an ongoing upstream intrusion of estuarine and marine-derived taxa, as well as the increase in the number and spread of non-native taxa. Despite no overall change in species richness within the region, we identified a significant trend in the species richness of the two most diverse primary freshwater fish families, Leuciscidae and Centrarchidae. Leuciscid richness significantly declined and centrarchid richness significantly increased over the 68-year period. Fluvial native leuciscid species that require a natural flow regime became extirpated or extinct, while lentic-adapted native and introduced centrarchids have thrived. The flow regime of the lower Rio Grande has been severely altered since impoundment of Falcon Reservoir. Median monthly flows have declined for all months, maximum flows and high flow pulses have declined, and base flows have increased. Also noteworthy were the increased number of hydrograph reversals post-impoundment. The streamflow regime is of central importance in sustaining the ecological integrity of rivers, and its disruption in the lower Rio Grande corresponds to a vastly different contemporary fish fauna than what historically occurred.

Biofluorescence in tetrapods has rapidly become a captivating area of study. This phenomenon was previously identified to be widespread across amphibian diversity, but few studies have investigated biofluorescence in early life history stages. The aquatic environments inhabited by the early developmental stages of biphasic amphibians are different from those of terrestrial, post-metamorphic individuals. This could translate to differences in the presence and function of biofluorescence. In our study, we explored the biofluorescence of developing embryos and larvae of three species of mole salamander (Ambystoma) and one species of newt (Notophthalmus) in response to different excitation wavelengths. We discovered that the colors, intensity, and locations of maximal fluorescence varied ontogenically and by species. Although fluorescence occurred in response to both blue and green light, it was more prevalent and intense under blue excitation. Under blue excitation, we observed predominantly green fluorescence, but orange-red wavelengths were emitted in some taxa and developmental stages. We discuss intrinsic and external mechanisms that may be contributing to fluorescence in the eggs, embryos, and larvae of salamanders. We also use previously published criteria to generate hypotheses about the potential ecological significance of fluorescence in the aquatic life history stages of salamanders.

Fishes of the family Cichlidae are well known for their capacity to exploit trophic niches in their environments through rapid speciation and morphological diversification, with the best-documented cases of such diversification occurring in the lakes of the African Rift Valley. Numerous species of cichlids are established outside of their native ranges, with reproducing populations of many species occurring in southern Florida (U.S.). The purpose of this study was to examine morphological differences between native and non-native (Floridian) populations of three cichlid species (Pelmatolapia mariae, Parachromis managuensis, and Mayaheros urophthalmus) to better understand how these species have managed to invade so successfully. Using linear measurements, we found that all three species have diverged in multiple characteristics: Pe. mariae in head length (HL), snout length (NL), and interorbital width (IO), Pa. managuensis in maximum body depth (MD), NL, and IO, and M. urophthalmus in MD and IO. Analyses of 2D-landmark data also revealed that Pe. mariae and Pa. managuensis collected from non-native populations display morphological variation beyond the ranges of variation exhibited by specimens from native populations. The observed morphological differences may be the result of natural selection, morphological plasticity, or some combination of the two; further work is needed to test these hypotheses. This study suggests that the conditions exist to promote rapid morphological change in introduced populations of cichlids in Florida.

A new species of Psalidodon without an adipose fin and with an interrupted lateral line and scaleless caudal fin is described from a marshland area in headwater tributaries of Rio Paraopeba, Rio São Francisco basin, Minas Gerais, Brazil. The new species can be promptly distinguished from all members of the Acestrorhamphidae by the presence of an ossified canal segment on the dorsal portion of the preopercular laterosensory canal running across the posterodorsal tip of the fourth infraorbital and posterior portion of the fifth infraorbital (vs. preopercular laterosensory canal lacking an ossified canal segment in the fourth and fifth infraorbitals). The new species fits the classical definition of the genus Hasemania; however, a comprehensive phylogenetic analysis carried out herein to assess its phylogenetic relationships revealed it as the sister group of Psalidodon crenuchoides, new combination. Further, both species are deeply nested within the genus Psalidodon, as recently redefined, which led to the generic reallocation of the latter. Comments on the phylogenetic position of the new species, as well as its conservation status, are presented.

Uma nova espécie de Psalidodon sem nadadeira adiposa, com linha lateral interrompida e nadadeira caudal sem escamas é descrita de áreas pantanosas de afluentes de cabeceira do rio Paraopeba, bacia do rio São Francisco, Minas Gerais, Brasil. A nova espécie pode ser prontamente distinguida de todos os membros de Acestrorhamphidae por apresentar um segmento de canal ossificado da porção dorsal do canal laterossensorial pré-opercular passando pela extremidade póstero-dorsal do quarto infraorbital e porção posterior do quinto infraorbital (vs. canal laterossensorial pré-opercular sem um segmento de canal ossificado no quarto e quinto infraorbitais). A nova espécie se enquadra na definição clássica do gênero Hasemania, no entanto, uma análise filogenética abrangente realizada para avaliar suas relações filogenéticas revelou tratar-se do grupo irmão de Psalidodon crenuchoides, nova combinação, e que ambas espécies estão profundamente aninhadas dentro do gênero Psalidodon, como recentemente redefinido, o que levou à realocação genérica da última. Comentários sobre a posição filogenética da nova espécie, bem como seu status de conservação, são apresentados.

Imparfinis is a genus of small catfishes with 21 valid species broadly distributed throughout the main river basins of the Neotropical region. Here, a new species of Imparfinis is described from the headwaters of the Rio Xingu. The new species is distinguished from its congeners by the presence of a wide dark stripe from snout tip to caudal peduncle sharply contrasting pale underside and aligned with dark stripe centered on dorsal portion of lower caudal-fin lobe, 11–12 gill rakers on the first ceratobranchial, 39 vertebrae, maxillary barbel surpassing vertical through dorsal-fin origin, and absence of short, flexible extension of the anteriormost pectoral, dorsal, and upper caudal-fin rays. In addition, assemble species by automatic partitioning (ASAP) and the Poisson tree processes model (bPTP) analyses support the validity of this new species. Our molecular phylogeny based on the cytochrome c oxidase subunit 1 mitochondrial gene (COI) corroborates the placement of the new species in Imparfinis and its close relationship with I. guttatus. Species delimitation in Imparfinis is discussed.

The short-tail eel family Colocongridae is a group of small to moderately large eels found in the mid- to upper-continental slope of all oceans except the eastern and central Pacific. The taxonomy of this group is still poorly known, and many diagnostic characteristics have never been tested and verified. Museum specimens were examined, and data were taken by following methods provided in previous studies, as well as some newly introduced. A total of seven species are recorded for the only genus, Coloconger, including a new species described herein from the Solomon Islands and Vanuatu. The diagnostic characters distinguishing species of Coloconger are discussed, comments are made on previous records, and a key to all known species is provided. Morphology of the post-metamorphic stage and transforming leptocephalus is also provided.