Dasyatis Sabina Research Articles

NEW ATPASE FOUND IN ATLANTIC STINGRAY

![Figure][1] An exciting new discovery has been made in the Atlantic stingray that has implications for ion regulation in elasmobranchs. In mammals, an active transport protein (HKα1) is present in the stomach and kidney that mediates proton (H+ or acid) secretion in exchange for potassium

A putative H+-K+-ATPase in the Atlantic stingray, Dasyatis sabina: primary sequence and expression in gills.

In mammals, the gastric H(+)-K(+)-ATPase (HKalpha1) mediates acid secretion in the stomach and kidneys. Like mammals, elasmobranchs also secrete acid from their stomachs, but unlike mammals they primarily use their gills for systemic acid excretion instead of their kidneys. The purpose of this study was to determine if an HKalpha1 orthologue exists in an elasmobranch (Atlantic stingray, Dasyatis sabina), to determine if it is expressed in gills and, if so, to localize its expression and determine if its expression is regulated during hypercapnia or freshwater acclimation. A polyclonal antibody made against an HKalpha1 peptide detected HKalpha1 immunoreactivity in protein isolates and tissue sections of stingray stomachs and gills. Immunohistochemistry demonstrated that HKalpha1 immunoreactivity was present in a subpopulation of epithelial cells in both organs. Double-labeling experiments in the gills showed that HKalpha1 immunoreactivity occurred in Na(+)-K(+)-ATPase-rich cells and not in V-type H(+)-ATPase-rich cells. RT-PCRs were used to deduce the primary sequence of a putative H(+)-K(+)-ATPase from the stomach of Atlantic stingrays. The 3,421-base pair cDNA includes a coding region for a 1,025-amino acid protein that is over 80% identical to HKalpha1 of mammals. RT-PCRs were then used to demonstrate that this transcript is also expressed in the gills. To our knowledge, this is the first H(+)-K(+)-ATPase sequence reported for any elasmobranch and the first full-length sequence for any fish. We also provide the first evidence for its expression in the gills of any fish and demonstrate that its expression increased during freshwater acclimation but not exposure to hypercapnia.

The gill and homeostasis: transport under stress.

in his recent cannon lecture, Cowley ([3][1]) pointed out the parallels between Cannon's time early in the last century and our own, i.e., the challenge facing us now, as then, is that of “systems integration” and understanding how organisms actually achieve homeostasis. We have begun to

Thermal Tolerance Responses of Laboratory-Acclimated and Seasonally Acclimatized Atlantic Stingray, Dasyatis sabina

Abstract Atlantic stingrays, Dasyatis sabina, inhabit shallow bays subject to rapid temperature changes, yet little is known about their thermal tolerance strategies. We quantified critical thermal maxima (CTMaxima) and minima (CTMinima) of Atlantic stingrays from St. Joseph's Bay, Florida. Spiracle contraction cessation for more than one minute was the experimental endpoint. Laboratory-acclimated fish held at 10.8, 20.5, or 35.1 C exhibited CTMaxima of 35.7, 39.3, or 43.2 C, and CTMinima of 0.8, 4.8, or 10.8 C, respectively. Regression analysis revealed that CTMaxima increased by 0.31 C and CTMinima decreased by 0.41 C for every 1.0 C increase in acclimation temperature. Atlantic stingrays exposed to diel thermoperiods of 34.0–37.3 C and 7.0–11.0 C had CTMaxima of 43.1 and 33.4 C and CTMinima of 9.6 and 0.3 C, respectively, suggesting that fish acclimated to low cycle temperatures. A thermal tolerance polygon produced from laboratory data had an area of 978 C2, the third largest ever measured in a fish. ...

Compensation for hypercapnia by a euryhaline elasmobranch: effect of salinity and roles of gills and kidneys in fresh water.

Specimens of the euryhaline elasmobranch, Dasyatis sabina were acclimated to seawater and fresh water, and exposed to normocapnic (air) and hypercapnic (1% CO2 in air) environmental water. Blood pH, PCO2, and [HCO3-], as well as whole-animal net-acid excretion, were measured for up to 24 h of hypercapnia. In a separate experimental series, urine was collected from freshwater acclimated stingrays during 8 h of normocapnia and hypercapnia. Stingrays in both salinities at least partially compensated for the respiratory acidosis by accumulating HCO3- in their extracellular spaces. The degree of compensation for blood pH was 88.5% in seawater, but only 31.0% in fresh water after 24 h of hypercapnia. Whole-animal net-acid excretion was also greater in seawater than in fresh water, as was the increase in extracellular fluid [HCO3-]. Mean urinary net-acid excretion rates were slightly negative, and never increased above normocapnic control rates during hypercapnia. Since whole-animal net-acid excretion rates increased with blood [HCO3-], and urinary excretion was always negative, the gills were probably the primary organ responsible for compensation from environmental hypercapnia. The faster, and more complete, compensation for hypercapnia in seawater than in fresh water for this euryhaline elasmobranch is consistent with data for euryhaline teleosts, and probably reflects Na+-dependent mechanisms of branchial acid excretion.

PENDRIN PROTEIN PRESENT IN EURYHALINE ELASMOBRANCH!

Pendrin is a recently discovered protein in mammals that has the ability to transport chloride ions in exchange for a variety of different molecules including bicarbonate. Chloride/bicarbonate exchange is important in euryhaline organisms and it insures chloride uptake when the animal is in freshwater. David Evans' team presents new evidence that pendrin is present in the Atlantic stingray (Dasyatis sabina) gill tissue, which is believed to be the site of chloride/bicarbonate exchange in the elasmobranch.Bicarbonate and protons are produced in the cell by the enzyme carbonic anhydrase. The active elimination of protons from within the cell by V-ATPases leaves bicarbonate to build-up, creating a favorable bicarbonate gradient for chloride/bicarbonate exchange. Evans' lab recently collected evidence suggesting that pendrin is responsible for chloride/bicarbonate exchange in V-ATPase cells of the mammalian kidney.In elasmobranchs (sharks, skates and rays), the gills are the primary site of acid/base-related ion transport. Up until now, the identity or cellular location of a chloride/bicarbonate exchanger in the elasmobranch gill was not known, even though evidence suggests that net bicarbonate secretion occurs across the gill epithelium. However, there are cells in the elasmobranch gill teeming with V-ATPases, which are similar to the bicarbonate-secreting cells in the mammalian kidney where pendrin is found. Thus, there were three main objectives of the present study. Firstly, the authors sought to determine if pendrin-like transporters were present in elasmobranch gill cells. Secondly,if the presence of this transporter was dependent on whether the stingray was adapted to freshwater or seawater. And thirdly, whether these transporters are associated with cells that are rich in V-ATPases, similar to the bicarbonate-secreting cells of the mammalian kidney.By using semiquantitative immunoblotting, a pendrin or pendrin-like exchanger was located in the gills of both freshwater and marine Atlantic stingrays. The relative abundance of pendrin immunoreactivity was highest in the gills of freshwater stingrays. Immunohistochemical findings demonstrated that the location of these pendrin-like transporters on the gill filament was also influenced by environmental salinity, as freshwater stingrays appeared to have more discrete pendrin immunoreactivity on the apical membrane of the cell, which separates the external environment from the cell's interior. As Piermarini and co-workers point out, greater protein expression and apical membrane association of a pendrin-like exchanger in freshwater stingray gills makes sense, as there is a crucial need for enhanced chloride uptake from freshwater in order to counteract the large diffusional loss of chloride into the environment. Double-labeling experiments clearly demonstrated that pendrin immunoreactivity was found in V-ATPase-rich cells, similar to the mammalian kidney. Therefore, these elasmobranch gill cells could potentially be the site of pendrin-mediated chloride/bicarbonate, similar to chloride/bicarbonate exchange in the mammalian kidney. However, the function of pendrin in the stingray gill is yet to be determined.This study presents the first evidence of a pendrin-like transporter in an ion-transporting tissue from any lower vertebrate and has furthered the development of the Atlantic stingray gill epithelium ion transport model.

A thromboxane A 2 system in the Atlantic stingray, Dasyatis sabina

Thromboxane B 2 ( TXB 2) is the stable metabolite of thromboxane A 2 ( TXA 2) and thromboxane B 2-like immunoreactivity (iTXB 2) has been identified in the plasma of the Atlantic stingray, Dasyatis sabina (0.57±0.03 ng/ml). Plasma levels of iTXB 2 increase if the blood is allowed to clot (3.0±0.27 ng/ml). When clotting occurs in the presence of indomethacin, this increase is partially inhibited (1.5±0.17 ng/ml), indicating the presence of a cyclooxygenase activity. Radioligand binding analysis using the TXA 2 analog [ 125 I ]BOP in isolated kidney membranes revealed a receptor of K d=2.88±0.51 nM and B max=25.6±5.9 fmol/mg protein. [ 125 I ]BOP binding was displaced by the TXA 2 receptor (TP receptor) agonists U46619 (IC 50=106.4±15.7 nM) and U44069 (IC 50=88.7±13.0 nM), and the antagonist SQ29548 (IC 50=51.0±12.9 nM). Binding was also displaced stereoselectively by the antagonists (−)L657925 (IC 50=18.9±3.8 nM) and (+)L657926 (IC 50=2025±280 nM). Tissue bath studies revealed that U46619, a stable TXA 2 mimetic, elicited concentration-dependent contractions in the ventral aorta which were inhibited in a concentration-dependent manner by the TP receptor antagonist SQ29548. Using a human TP receptor riboprobe, Northern blotting of mRNA isolated from the stingray kidney identified transcripts of 2.8 and 6 kb. The 2.8 kb transcript is similar to a 2.8 kb transcript found in human cells or tissues, but the 6 kb transcript may be unique. These data indicate the presence of a TXB 2-like substance in the blood, a TP receptor in the kidney, TXA 2 biological activity in the ventral aorta, and expression of a TP receptor-like gene.

Morphological and histological changes in the genital ducts of the male Atlantic stingray, Dasyatis sabina, during the seasonal reproductive cycle

Changes inthe morphology and histologyofthe epididymis and seminal vesicle in male Atlantic stingrays (Dasyatis sabina) were examined in relation tothe seasonal reproductive cycle. Observations onthe size and structureofthese organs were accompanied by analysisof cell proliferation in genital duct epithelia using proliferating cell nuclear antigen (PCNA) as a marker for mitotic activity. No signsof reproductive tract growth or histological alteration were apparent duringthe initial stagesof spermatogenesis. However, increased PCNA expression inthe seminal vesicle epithelium was observed during this period, suggesting that this organ begins to undergo preparatory changes at an early stage inthe reproductive cycle. During late spermatogenesis, heightened expressionof PCNA in epithelial cellsofthe epididymis and seminal vesicle was observed in conjunction with dramatic increases in size and semen contentofthese organs. Extensive changes inthe histological architectureofthe genital ducts also were evident at this time, including regressionofthe stroma and an increase in size and secretory activityofthe epithelium. Althoughthe epididymis regressed in size and structure shortly after sperm production was completed,the seminal vesicle retained its appearance and activity forthe durationofthe 7-month copulatory period. Afterwards, immune cell content increased considerably in both ducts, likely reflecting clearanceof residual spermatozoa in preparation forthe subsequent reproductive season.the present study provides a basis for future reports onthe physiological regulationof reproductive tract function in elasmobranchs, and establishes PCNA immunocytochemistry as a novel tool for such investigations.

Molecular and functional characterization of a urea transporter from the kidney of the Atlantic stingray.

In general, marine elasmobranch fishes (sharks, skates, and rays) maintain body fluid osmolality above seawater, principally by retaining large amounts of urea. Maintenance of the high urea concentration is due in large part to efficient renal urea reabsorption. Regulation of renal urea reabsorption also appears to play a role in maintenance of fluid homeostasis of elasmobranchs that move between habitats of different salinities. We identified and cloned a novel 2.7-kb cDNA from the kidney of the euryhaline Atlantic stingray Dasyatis sabina (GenBank accession no. AF443781). This cDNA putatively encoded a 431-amino acid protein (strUT-1) that had a high degree of sequence identity (71%) to the shark kidney facilitated urea transporter (UT). However, the predicted COOH-terminal region of strUT-1 appears to contain an additional sequence that is unique among cloned renal UTs. Injection of strUT-1 cRNA into Xenopus oocytes induced a 33-fold increase in [(14)C]urea uptake that was inhibited by phloretin. Four mRNA bands were detected in kidney by Northern blot: a transcript at 2.8 kb corresponding to the expected size of strUT-1 mRNA and bands at 3.8, 4.5, and 5.5 kb. Identification of a facilitated UT in the kidney of the Atlantic stingray provides further support for the proposal that passive mechanisms contribute to urea reabsorption by elasmobranch kidney.

Pendrin immunoreactivity in the gill epithelium of a euryhaline elasmobranch.

Pendrin is an anion exchanger in the cortical collecting duct of the mammalian nephron that appears to mediate apical Cl(-)/HCO3(-) exchange in bicarbonate-secreting intercalated cells. The goals of this study were to determine 1) if pendrin immunoreactivity was present in the gills of a euryhaline elasmobranch (Atlantic stingray, Dasyatis sabina), and 2) if branchial pendrin immunoreactivity was influenced by environmental salinity. Immunoblots detected pendrin immunoreactivity in Atlantic stingray gills; pendrin immunoreactivity was greatest in freshwater stingrays compared with freshwater stingrays acclimated to seawater (seawater acclimated) and marine stingrays. Using immunohistochemistry, pendrin-positive cells were detected on both gill lamellae and interlamellar regions of freshwater stingrays but were more restricted to interlamellar regions in seawater-acclimated and marine stingray gills. Pendrin immunolabeling in freshwater stingray gills was more apical, discrete, and intense compared with seawater-acclimated and marine stingrays. Regardless of salinity, pendrin immunoreactivity occurred on the apical region of cells rich with basolateral vacuolar-proton-ATPase, and not in Na(+)-K(+)-ATPase-rich cells. We suggest that a pendrin-like transporter may contribute to apical Cl(-)/HCO3(-) exchange in gills of Atlantic stingrays from both freshwater and marine environments.

Renal water and solute excretion in the Atlantic stingray in fresh water

Renal water and solute excretion in the Atlantic stingray in fresh water

Renal water and solute excretion in the Atlantic stingray in fresh water

Freshwater, male Atlantic stingrays Dasyatis sabina, from Lake Jesup, Florida, U·S·A·, excreted a dilute urine similar in composition to freshwater teleosts and lampreys with the exception that urea was the primary osmolyte. Urine flow rate was 2·5 to 10 fold higher than that reported for freshwater teleosts resulting in high free‐water clearance. Mass‐specific free‐water clearance values from euryhaline elasmobranchs inhabiting freshwater environments greatly exceed those for freshwater teleosts and are nearly equivalent to those of freshwater lampreys.

Ontogenetic Changes in the Response Properties of the Peripheral Electrosensory System in the Atlantic Stingray (Dasyatis sabina)

Adult stingrays use their ampullary electroreceptors to detect prey and locate mates, but the response properties and function of their electrosensory system in the pre-adult stages are unknown. We examined the response properties of Atlantic stingray (Dasyatis sabina) electrosensory primary afferent neurons through ontogeny to determine whether encoding of electrosensory information changes with age, and how it relates to the ontogenetic encoding of biologically relevant electric stimuli. We show that during development electrosensory primary afferents increase resting discharge regularity, show an upward shift in best frequency (BF), an increase in neural sensitivity, and a decrease in bandpass. These ontogenetic changes in the response properties of the stingray electrosense are consistent with sensory adaptations to enhance the avoidance of large predators as young, and increase the location of prey and mates as adults.

European sea bass ( Dicentrarchus labrax L.) cytochrome P450arom: cDNA cloning, expression and genomic organization

Cytochrome P450arom, a key enzyme in the hormonal steroidogenic pathway, mediates the conversion of androgens to estrogens. This work describes the molecular cloning of the cDNA encoding the European sea bass ( Dicentrarchus labrax L.) cytochrome P450arom by means of reverse transcriptase and polymerase chain reaction (RT–PCR) and 5′ and 3′-rapid amplification of cDNA ends (RACE) analyses. The cDNA is 1822 bp in length and encodes a putative protein of 517 amino acids. Northern blot analysis revealed that the ovary expressed a transcript of about 2.2 kb in size. Analysis of the deduced amino acid sequence indicated 62–86% identity with ovarian P450arom of other teleost fish, the highest identity being found with the Japanese flounder, Paralichthys olivaceous. Identity was lower (56–65%) with the P450arom forms first reported in teleost brain. Only 52% identity was observed with the corresponding fragment of the cartilaginous fish, Dasyatis sabina. RT–PCR revealed that the sea bass P450arom mRNA was also expressed, at low levels, in testis and brain. Between the 5′ and 3′-untranslated terminal regions (UTR), the sea bass CYP19 gene contains eight introns. All introns conform to the GT/AG rule for RNA splicing and are inserted in exactly the same positions as those found in Oryzias latipes and the human CYP19 gene.

Immunochemical analysis of the vacuolar proton-ATPase B-subunit in the gills of a euryhaline stingray (Dasyatis sabina): effects of salinity and relation to Na(+)/K(+)-ATPase.

In the gills of freshwater teleost fishes, vacuolar proton-ATPase (V-H(+)-ATPase) is found on the apical membrane of pavement and chloride (Na(+)/K(+)-ATPase-rich) cells, and is an important transporter for energizing Na(+) uptake and H(+) excretion. In the gills of elasmobranch fishes, the V-H(+)-ATPase has not been extensively studied and its expression in freshwater individuals has not been examined. The goals of this study were to examine the effects of environmental salinity on the expression of V-H(+)-ATPase in the gills of an elasmobranch (the Atlantic stingray, Dasyatis sabina) and determine if V-H(+)-ATPase and Na(+)/K(+)-ATPase are expressed in the same cells. We found that gills from freshwater stingrays had the highest relative abundance of V-H(+)-ATPase and greatest number of V-H(+)-ATPase-rich cells, using immunoblotting and immunohistochemistry, respectively. When freshwater animals were acclimated to sea water for 1 week, V-H(+)-ATPase abundance and the number of V-H(+)-ATPase-rich cells decreased significantly. Atlantic stingrays from seawater environments were characterized by the lowest expression of V-H(+)-ATPase and least number of V-H(+)-ATPase-rich cells. In contrast to teleost fishes, localization of V-H(+)-ATPase in freshwater stingray gills was not found in pavement cells and occurred on the basolateral membrane in cells that are presumably rich in mitochondria. In freshwater stingrays acclimated to sea water and seawater stingrays, V-H(+)-ATPase localization appeared qualitatively to be stronger in the cytoplasm, which may suggest the transporter was stored in vesicles. Using a double-immunolabeling technique, we found that V-H(+)-ATPase and Na(+)/K(+)-ATPase occurred in distinct cells, which suggests there may be two types of mitochondrion-rich cells in the elasmobranch gill epithelium. Based on these findings, we propose a unique model of NaCl and acid-base regulation where the V-H(+)-ATPase-rich cells and Na(+)/K(+)-ATPase-rich cells are the sites of Cl(-) uptake/HCO(3)(-) excretion and Na(+) uptake/H(+) excretion, respectively.

Phylogenetic Relationships within the Stingray GenusDasyatis(Chondrichthyes: Dasyatidae)

Abstract Phylogenetic relationships for 14 of 35 currently recognized Dasyatis species (Dasyatis americana, Dasyatis brevis, Dasyatis centroura, Dasyatis geijskesi, Dasyatis guttata, Dasyatis kuhlii, Dasyatis lata, Dasyatis longus, Dasyatis margaritella, Dasyatis pastinaca, Dasyatis sabina, Dasyatis say, Dasyatis violacea, and Dasyatis zugei), Pastinachus sephen (sometimes referred to as Dasyatis sephen), one Indo-West Pacific Himantura (Himantura gerrardi), and four outgroups (Gymnura micrura, Urobatis jamaicensis, Taeniura lymma, and amphi-American Himantura schmardae) were elucidated using parsimony analysis of 32 morphological characters. One most-parsimonious tree of 116 steps (CI = 0.345, HI = 0.655, RI = 0.64) was found. The analysis refutes monophyletic Dasyatis and Himantura and reveals Dasyatis kuhlii, D. violacea, and P. sephen to be basal among other ingroup species, with D. kuhlii as the most basal species. The genus Himantura is paraphyletic, with amphi-American H. schmardae as sister to a c...

Contractile properties of the elasmobranch rectal gland.

The importance of the rectal gland in elasmobranch osmoregulation is well established. The rate of secretion by the gland is under the control of a variety of secretagogues and inhibitors. Early morphological work suggested that a band of smooth muscle cells surrounds the periphery of the shark rectal gland between the secretory tubules and the connective tissue capsule. To confirm the presence of the muscle ring, we examined histological sections from two species of shark, Squalus acanthias and Carcharodon carcharius, and from the stingray Dasyatis sabina and stained sections from S. acanthias with the actin-specific ligand phalloidin. In all three species, a distinct band of what appeared to be smooth muscle cells was evident, and the putative muscle ring in S. acanthias stained specifically with phalloidin. Moreover, isolated rings of rectal gland tissue from S. acanthias constricted when acetylcholine or endothelin was applied and responded to nitric oxide with an initial dilation, followed by a more substantial constriction. Subsequent addition of porcine C-type natriuretic peptide dilated the rings, but two prostanoids (carbaprostacyclin and prostaglandin E(1)) did not change ring tension significantly. The rings did not respond to the endothelin-B-specific agonist sarafotoxoin S6c, suggesting that the response to endothelin was mediated via endothelin-A-type receptors. Our data confirm the presence of a smooth muscle ring in the periphery of the elasmobranch rectal gland and demonstrate that the gland responds to a suite of smooth muscle agonists, suggesting that changes in the dimensions of the whole rectal gland may play a role in its secretory function.

Androgen-Induced Changes in the Response Dynamics of Ampullary Electrosensory Primary Afferent Neurons

Male stingrays use their ampullary electroreceptors to locate mates, but the effect of gonadal androgens on electrosensory encoding during the reproductive season is unknown. We tested the hypothesis that gonadal androgens induce neurophysiological changes in the electrosense of male Atlantic stingrays. During the primary androgen increase in wild males, the electrosensory primary afferent neurons show an increase in discharge regularity, a downshift in best frequency (BF) and bandpass, and a greater sensitivity to low-frequency stimuli from 0.01 to 4 Hz. Experimental implants of dihydrotestosterone in male stingrays induced a similar lowered BF and bandpass and increased average neural sensitivity to low-frequency stimuli (0.5-2 Hz) by a factor of 1.5. Primary afferents from long ampullary canals (>3 cm) were more sensitive and had a lower bandpass and BF than did afferents from short canals (<2 cm). We propose that these androgen-induced changes in the frequency response properties of electrosensory afferents enhance mate detection by male stingrays and may ultimately increase the number of male reproductive encounters with females. Furthermore, differences in primary afferent sensitivity among short and long canals may facilitate detection, orientation, and localization of conspecifics during social interactions.

Effects of environmental salinity on Na(+)/K(+)-ATPase in the gills and rectal gland of a euryhaline elasmobranch (Dasyatis sabina).

Changes in Na(+)/K(+)-ATPase activity and abundance associated with environmental salinity were investigated in the gills and rectal gland of the Atlantic stingray Dasyatis sabina. Using a ouabain-specific ATPase assay and western blotting, we found that stingrays from fresh water had the highest activity and highest relative abundance of Na(+)/K(+)-ATPase in the gills. Using immunohistochemistry, we also found that gills from freshwater stingrays had the greatest number of Na(+)/K(+)-ATPase-rich cells. When freshwater stingrays were acclimated to sea water for 1 week, the activity and abundance of Na(+)/K(+)-ATPase and the number of Na(+)/K(+)-ATPase-rich cells decreased in the gills. In seawater stingrays, the branchial activity and abundance of Na(+)/K(+)-ATPase and the number of Na(+)/K(+)-ATPase-rich cells were further reduced. In rectal glands, the activity and abundance of Na(+)/K(+)-ATPase were lower in freshwater animals than in seawater-acclimated and seawater stingrays, both of which had equivalent levels. These findings suggest that salinity-associated changes in gill and rectal gland Na(+)/K(+)-ATPase activity are due to changes in the abundance of Na(+)/K(+)-ATPase. We conclude that the gills may be important for active ion uptake in fresh water, while the rectal gland is important for active NaCl excretion in sea water. The results from this study are the first to demonstrate an effect of environmental salinity on Na(+)/K(+)-ATPase expression in the gills and rectal gland of an elasmobranch.

Dasyatis marianae: The Correct Name for a Recently Described Stingray (Chondrichthyes: Dasyatidae) from the Southwestern Atlantic

Abstract The southwestern Atlantic Stingray Dasyatis macrophthalma Gomes, Rosa, and Gadig was described under two different names which appeared in the original publication by mistake. By using the First Reviser principle, according to the provisions of the International Code of Zoological Nomenclature, we select Dasyatis marianae as the valid name for the species. The name D. macrophthalma previously had been published by other authors in its homonym form D. macrophtalma, without reference to a formal description (a nomen nudum). It is herein treated as the junior objective synonym of D. macrophthalma. To avoid the repetition of similar cases, we recommend the authors preparing descriptions of new taxa refrain from publicizing manuscript names in the Web, scientific meetings, news media, or museum labels.