Desert Pupfish Research Articles

Identification of the Gut Microbiome and its Role in Paradoxical Anaerobism in Desert Pupfish

The Devils Hole pupfish (Cyprinodon diabolis) frequently enters paradoxical anaerobism (PA) in response to endogenously produced or exogenously supplied ethanol in a dose‐dependent manner. PA is characterized by extended periods (e.g. up to 149 min continuous) of negligible oxygen consumption despite its availability. To decipher the role of the gut microbiota in ethanol‐associated paradoxical anaerobism, gut microbial communities of pupfish were depleted using a cocktail of antibiotics. Compared to the fish in the control group, microbiota‐depleted fish spent more time in paradoxical anaerobism. Although the gut microbial communities with and without antibiotic treatment were similarly diverse, they were distinct and the greatest contribution to the dissimilarity (27.38%) was the common fish commensal Cetobacterium. Although Cetobacterium is known as a primary fermenter, we speculate that it may consume ethanol through secondary fermentation and therefore regulate transition from paradoxical anaerobism to aerobic respiration, thereby playing a critical role in regulating the metabolic status of these fish. This study reports the first characterization of gut microbial communities of critically endangered pupfish and suggests the microbiome may play a critical role in regulating metabolic strategies that are critical for survival in extremes of temperature and oxygen concentration. Given the wide distribution and abundance of Cetobacterium in warm‐water fishes, this process may be of broad importance, and suggests that the microbiome be carefully considered for conservation and aquaculture alike.

Oxygen consumption of desert pupfish at ecologically relevant temperatures suggests a significant role for anaerobic metabolism.

Oxygen consumption is oftentimes used as a proxy for metabolic rate. However, pupfish acclimated to ecologically relevant temperatures may employ extended periods of anaerobism despite the availability of oxygen-a process we called paradoxical anaerobism. In this study, we evaluated data from pupfish exhibiting stable oxygen consumption. Routine oxygen consumption ([Formula: see text]) of a refuge population derived from Cyprinodon spp. acclimated to 28 and 33°C was evaluated at the ecologically relevant assay temperatures of between 25 and 38°C. Different interpretations of the data are available depending on normalization. For instance, [Formula: see text] of smaller fish, measured per fish, was remarkably stable over a wide range of assay temperatures and was not different between acclimation groups. However, when measured on a mass-specific basis, [Formula: see text] in these same smaller fish increases more predictably as temperature increased. [Formula: see text] of refuge fish and the closely related pupfish, C. nevadensis mionectes, measured near their respective acclimation temperatures, were essentially identical. However, [Formula: see text] of 28°C acclimated fish of both species, when measured at 34°C, was greater than that of the 33°C acclimated fish measured at 28°C. We suggest that this observed 'efficiency' may result from significant anaerobic metabolism use. Experiments investigating factorial aerobic scope ([Formula: see text]/[Formula: see text]) yielded values less than 1 in 21-36% of the 33°C acclimated fish. These values indicate a substantial contribution of anaerobic metabolism to energy utilization by these fish. However, muscle lactate levels are not elevated in exercising fish-a result that is consistent with paradoxical anaerobism use.

Mitochondrial Respiration In Skeletal Muscle Mitochondria From Desert Pupfish Suggests Limitation Of Metabolic Substrates As A Mechanism For Paradoxical Anaerobism

Skeletal muscle mitochondria were isolated from desert pupfish (Cyprinodon spp) that were acclimated to ecologically relevant temperatures of 28 °C (M28) and 33 °C (M33). The respiratory control ratio (RCR) of M33 pupfish was ~2.6X lower than that of M28 pupfish, initially suggesting mitochondria were damaged by the warmer temperature. However, state 4 respiration was below expected values in both M28 and M33 pupfish suggesting little proton leak. Further, membrane potential was lower in the M33 pupfish than M28 pupfish and did not change with assay temperature. These data suggested a reduced proton motive force in M33 pupfish. Analyses of respiration as a function of membrane potential suggest a block in substrate utilization in M33 pupfish. M33 pupfish also experience reduced production of reactive oxygen species (ROS) from the Q site of complex I. Taken all together, the data suggest pupfish may be limiting mitochondrial use to avoid ROS production by restricting access of substrates to the mitochondrion. These results are consistent with our measurements of oxygen consumption in intact fish. Specifically, fish acclimated to 33 °C demonstrate extended periods of paradoxical anaerobism in which oxygen consumption is absent despite the presence of oxygen.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Genotoxic Assessment of Some Inorganic Compounds in Desert Pupfish (Cyprinodon macularius) in the Evaporation Pond from a Geothermal Plant.

The frequency of micro nucleated erythrocytes in peripheral blood of the desert pupfish (Cyprinodon macularius) from a geothermal effluent pond is determined and compared to organisms kept in an aquarium. The frequency of micronucleated erythrocytes found in pupfish from the geothermal pond is 2.75 (±2.09) and only 0.44 (±0.52) in captivity organisms. Dissolved As in the ponds doubles the 340µgL-1 US-EPA acute quality criteria for aquatic life and Hg equals the 1.77µgL-1 chronic criteria. The organisms with high MNE also have significantly high Se, As and Hg concentrations in muscle and liver. Compared to international maximum allowable limits for fish consumption, there is 81× enrichment for Se, 6× for As and 5× for Hg. Although Se is not significantly enriched in water, it is likely that its bioaccumulation occurs via feeding of detritus. The desert pupfish has a significant resistance to extreme metal accumulations and to recover under unpolluted conditions.

Oxygen Consumption of Desert Pupfish at Ecologically‐Relevant Temperatures Suggests a Significant Role for Anaerobic Metabolism

Oxygen consumption is oftentimes used as a proxy for metabolic rate. Routine oxygen consumption (RVO2) of a refuge population of Cyprinodon diabolis acclimated to ecologically relevant temperatures of 28 °C and 33 °C was evaluated at assay temperatures between 25 °C and 38 °C. Different interpretations of the data are available depending on normalization. For instance, RVO2 of smaller fish, measured per fish, was remarkably stable over a wide range of assay temperatures and was not different between acclimation groups. Measured on a mass‐specific basis, RVO2 in larger fish increased more predictably as temperature increased. RVO2 of refuge fish and the closely related pupfish, C. nevadensis mionectes, measured near their respective acclimation temperatures of either 28 °C or 33 °C were essentially identical. However, RVO2 of 28 °C acclimated fish of both species, when measured at 33 °C, was greater than that of the 33 °C acclimated fish measured at 28 °C. We suggest this observed ‘efficiency’ may result from significant anaerobic metabolism use. Experiments investigating metabolic scope (MaxVO2/RVO2) yielded values less than 1 in 33 °C acclimated fish. These values indicate a substantial contribution of anaerobic metabolism to energy utilization by these fish. However, muscle lactate levels are not elevated in exercising fish‐ a result that is consistent with paradoxical anaerobism use.Support or Funding InformationSupported by grants from the US Fish and Wildlife Service and Nevada Department of Wildlife

Ecologically‐relevant Temperatures and Stress in Desert Pupfish

The Southwest United States was much wetter in its recent past. For instance, Death Valley was inundated with the 100m deep Lake Manley just 10,000 years ago. As the waters receded, pupfish were isolated to the warm springs and spring outflows that characterize their current habitats. These fish spent much of their recent evolutionary history in cooler waters and now reside in waters that may be > 33 °C. We asked if rearing or acclimating fish at the ecologically relevant temperature of 33 °C would result in stress as compared to when fish are reared at 28 °C. Heat shock protein 90 was increased 4 fold during both a 4 h acute exposure as well as >3 week chronic exposure to 33 °C. Similarly, hypoxia‐induced factor alpha was increased ~3X at 33 °C. However, cortisol was reduced 2‐fold in 33 °C chronically acclimated fish but not in acute exposure as compared to 28 °C acclimated controls. The Cdk inhibitory protein, p21 was increased during acute exposure but not during chronic exposure to 33 °C. Taken together, these data suggest that stress may be differentially managed and processed in context. For instance, while it may be possible for p21 to repress cell cycle for 4 h, it is less likely that cell cycle may be inhibited for 3 weeks even in the face of environmental insult.

Oxygen consumption in single eggs of a desert pupfish

Pupfish of the genus Cyprinodon live in environments that may be very warm (>35 °C) and hypoxic. In order to address how these conditions might affect the metabolism of fish eggs, we developed an approach that allowed for the measurement of oxygen consumption of a single egg. Eggs were classified into one of 4 groups depending on the stage of development and reared at either 28 or 33 °C. Expected increases in oxygen consumption as the result of development were found for the first three stages of development. However in well developed embryos, exposure to 33 °C resulted in an unexpected decrease in oxygen consumption. Interestingly, oxygen consumption spiked when eggs hatched during the assay suggesting that eggs are oxygen‐limited by the end of development. Critical partial pressures of oxygen were relatively high (~112 to 125 torr). These data call into question what role oxygen might have in the development of pupfish eggs in the wild.

Evaluating the influence of connectivity and distance on biogeographical patterns in the south‐western deserts of North America

AbstractAimTo examine the role of geological history, connectivity and distance in shaping the biogeographical structure of North American desert clades that are restricted to habitat islands (sand dunes and relictual aquatic habitats), using statistical model choice on old and new probabilistic biogeographical models.LocationNorth America, Mojave, Sonoran and Chihuahuan Deserts.Materials and methodsDated phylogenies were estimated for three field‐sampled insect clades (Trigonoscuta,Rhaphiomidasand sand treader crickets), and five other literature‐sampled clades (the snailsAssiminea,PyrgulopsisandTryonia; the desert fringe‐toed lizardUma; and the desert pupfishCyprinodon).BioGeoBEARSwas used to statistically compare biogeographical models assuming unconstrained or connectivity‐constrained dispersal, with or without founder‐event speciation (jump dispersal) permitted. Finally, we introduce and test a novel distance‐based dispersal model (+x) where dispersal probability is multiplied by distance to the powerx.ResultsWe observed little concordance between biogeographical patterns and timing of geological events. Model comparisons were decidedly in favour of inclusion of founder‐event speciation in the models for most taxa, with only a small taxon,Uma, showing support for the model favouring vicariance. The inclusion of a constrained‐dispersal matrix was favoured by three of the eight taxa examined (Cyprinodon, sand treader crickets, andTrigonoscuta). Surprisingly, tests for distance influencing dispersal probability were mostly negative.Main conclusionsOur results do not show support for any one geological event shaping the biogeographical patterns of these desert taxa. Instead, the histories of desert dune and aquatic taxa are largely products of rare jump dispersal events, and can be considered island‐like systems. Although results are negative for the distance‐based dispersal model, this in itself demonstrates the superiority of explicit statistical model testing overa prioriassumption of fixed models in historical biogeography.

Environmentalism in the Interstices: California's Salton Sea and the Borderlands of Nature and Culture

Environmentalism in the IntersticesCalifornia’s Salton Sea and the Borderlands of Nature and Culture Traci Brynne Voyles (bio) Introduction: A Dying Sea In the lowlands of Southern California’s Riverside and Imperial Counties, the state’s largest body of water, the Salton Sea, is rapidly evaporating under a hot desert sun. Runoff from the Imperial Valley and Coachella Valley agricultural districts, which has sustained the sea’s water level since the 1920s, has been cut back to an anemic trickle in the wake of a 2003 farm-to-city water-redistribution deal with nearby San Diego.1 Environmentalists and policy makers predict that the sea will reach a critical turning point in 2017, when temporary agreements that have been diverting fresh water into the sea to sustain its levels expire, unless action is taken to find more water—a tall order in an already-parched state.2 Allowing the sea to evaporate is problematic for reasons that involve environmental conditions for humans and nonhumans alike. Exposing the massive expanse of dusty soil, much of it polluted from eight decades of agricultural runoff, would likely create dust storms and compound air pollution in a region that already has exceptionally poor air quality.3 Resulting dust storms would choke the air with microscopic particulate matter, which is linked to a range of respiratory diseases, including asthma, much of it contaminated with toxic chemicals and heavy metals.4 Moreover, the sea is currently a crucial water resource [End Page 211] for migrating birds along the Pacific Flyway, supporting more than four hundred bird species that have precious few remaining wetlands left on which to rely. As many as 3.5 million birds use the sea every day, including eared grebes, white and brown pelicans, terns, cormorants, herons, and egrets.5 It is no exaggeration to say that the loss of the Salton Sea would be devastating to an impressive list of bird species, many of them already imperiled, and to at least one species of fish (the endangered desert pupfish). Despite its importance to wildlife, however, dangerous levels of selenium, ddt, pcbs, toxaphene, and a smattering of other chemicals and heavy metals have contributed to massive fish and bird die-offs since the 1990s, including one that killed 150,000 eared grebes from January to April 1992 and one that killed 7.6 million fish in a single day in August 1999.6 Despite these alarming environmental conditions (what one writer called the sea’s “penchant for poisoning its inhabitants” and another called its “reputation for bad smells and . . . fish skeletons”), advocates for saving the Salton Sea—on behalf of birds and fish, the respiratory health of nearby human communities, or both—have had a difficult time mustering resources for action.7 Given the stakes of the case for environmentalists committed to wildlife conservation and environmental health concerns for Southern Californians, it would seem that the crisis at the Salton Sea would rise to the fore. It does, after all, bring together a range of issues crucial to environmental and public health stakeholders, from those concerned with bird conservation to pollution-triggered asthma rates. Inertia in the face of these daunting environmental problems has long been apparent, prompting observers to wonder, as one local news station put it, “Why Don’t Californians Care about Saving the Salton Sea?”8 The sea’s reputation seems to be shaped more by ambivalence about its environmental role than any sense of urgency for its environmental conditions. Newspapers frequently run stories about the sea alongside photographs of its frequent fish and bird die-offs, featuring images of its shores choked with fish carcasses or government employees piling pelican bodies in the backs of trucks, which invoke ideas of the sea as an environmental threat—a “fetid swamp not worth saving”—rather than a resource in need of conservation.9 State hearings on the future of the Salton Sea are sparsely attended. Funding for restoration projects is notoriously hard to come by. If other California [End Page 212] Click for larger view View full resolution Fig. 1. The Salton Sea is a crucial habitat for migrating birds on the Pacific Flyway. Photograph by Douglas Barnum, US...

Endocrine and metabolic impacts of warming aquatic habitats: differential responses between recently isolated populations of a eurythermal desert pupfish.

Temperatures of inland aquatic habitats are increasing with climate change, and understanding how fishes respond physiologically to thermal stress will be crucial for identifying species most susceptible to these changes. Desert fishes may be particularly vulnerable to rising temperatures because many species occupy only a fraction of their historical range and occur in habitats with already high temperatures. Here, we examined endocrine and metabolic responses to elevated temperature in Amargosa pupfish, Cyprinodon nevadensis amargosae. We studied C. n. amargosae from two habitats with distinct thermal conditions: the Amargosa River, which experiences diurnally and seasonally variable temperatures (0.2-40°C); and Tecopa Bore, a spring and marsh fed by hot groundwater (47.5°C) from an artesian borehole. These allopatric populations differ in morphology, and prior evidence suggests that temperature might contribute to these differences via altered thyroid hormone (TH) regulation of morphological development. Here, we document variation in hepatic iodothyronine deiodinase type 2 (dio2) and type 3 (dio3) and TH receptor β (trβ) gene transcript abundance between the Amargosa River and Tecopa Bore wild populations. Fish from these populations acclimated to 24 or 34°C retained differences in hepatic dio2, dio3 and trβ mRNAs and also varied in transcripts encoding the TH membrane transporters monocarboxylate transporter 8 (mct8) and organic anion-transporting protein 1c1 (oatp1c1). Tecopa Bore pupfish also exhibited higher dio2 and trβ mRNA levels in skeletal muscle relative to Amargosa River fish. Muscle citrate synthase activity was lower at 34°C for both populations, whereas lactate dehydrogenase activity and lactate dehydrogenase A-chain (ldhA) transcripts were both higher and 3,5,3'-triiodothryonine responsive in Tecopa Bore pupfish only. These findings reveal that local population variation and thermal experience interact to shape how pupfish respond to elevated temperatures, and point to the need to consider such interactions in management actions for desert fishes under a changing climate.

Renovated Breeding Habitat use in Wild & Captive-bred Populations of an Endangered Desert Pupfish

The Leon Springs pupfish (Cyprinodon bovinus) is an endangered fish endemic to Diamond Y Spring in west Texas. To mitigate the negative effects of habitat loss, Diamond Y Spring was renovated to maintain and provide additional breeding habitat. Monsanto Pool, an extant location where C. bovinus have become extirpated, was also renovated in order to increase breeding habitat. After Monsanto Pool was renovated, captive-bred C. bovinus were reintroduced to this location to both increase the range of this species, and evaluate whether captive release is a viable option. These conservation efforts have led to the unique opportunity to evaluate the efficacy of habitat renovations in wild and captivebred populations of C. bovinus, occurring in natural and renovated breeding habitats at two separate locations. The overarching question asked was, is it better to renovate an unoccupied site and introduce captive-bred individuals, or to expand an occupied site that would allow the current population to grow? Habitat use and spawning in three different breeding areas were compared, and specific ecological factors were measured at each site in order to determine if any coincided with observed C. bovinus location preferences. Wild C. bovinus in the natural breeding habitat spawned more, had more spawns per individual male, and had greater territorial stability than wild or captive-bred C. bovinus in renovated habitats. Differences in social system stability and reproductive success between sites may be due to variation in their ability to adapt to a renovated site as well as the ecological makeup of the habitat.

Paradoxical anaerobism in desert pupfish.

In order to estimate metabolic demands of desert pupfish for conservation purposes, we measured oxygen consumption in fish acclimated to the ecologically relevant temperatures of 28 or 33°C. For these experiments, we used fish derived from a refuge population of Devils Hole pupfish (Cyprinodon diabolis). Measurement of routine oxygen consumption (V̇O2,routine) revealed some 33°C-acclimated fish (10% of 295 assayed fish) periodically exhibited periods of no measurable oxygen consumption despite available ambient oxygen tensions that were above the critical PO2. We call this phenomenon paradoxical anaerobism. The longest observed continuous bout with no oxygen consumption was 149 min, although typical bouts were much shorter. Fish maintained normal posture and ventilation rate (>230 ventilations per minute) during paradoxical anaerobism. Fish rarely demonstrated a compensatory increase in oxygen use following a period of paradoxical anaerobism. In contrast, only one out of 262 sampled fish acclimated at 28°C spontaneously demonstrated paradoxical anaerobism. Muscle lactate concentration was not elevated during periods of paradoxical anaerobism. However, the amount of ethanol released by the 33°C-acclimated fish was 7.3 times greater than that released by the 28°C acclimation group, suggesting ethanol may be used as an alternative end product of anaerobic metabolism. Exposure to exogenous ethanol, in concentrations as low as 0.1%, produced periods of paradoxical anaerobism even in 28°C-acclimated fish.

A review of the Leon springs pupfish (Cyprinodon bovinus) long‐term conservation strategy and response to habitat restoration

Abstract Choosing an optimal strategy to sustain imperilled wild populations is challenging, and many methods may be implemented before reaching an effective strategy. A review of previous conservation efforts used to maintain an endangered desert pupfish (Cyprinidon bovinus) are presented here. Conservation strategies for C. bovinus have included removal of fish hybridizing with a non‐native species, reintroduction of captive‐bred C. bovinus into their historic range, and habitat restoration and expansion. In general, these methods have successfully increased the C. bovinus population over a 15‐year period, with habitat expansion appearing to be the most critical intervention method. Habitat restorations that increased the available breeding habitat for C. bovinus and the total number of breeding males were also associated with a downward trend in individual male reproductive behaviour. Since habitat expansion resulted in unexpected consequences for reproductive ecology, it emphasizes the importance not only of monitoring species abundance but also of evaluating individual reproductive behaviour when implementing conservation strategies. Copyright © 2015 John Wiley & Sons, Ltd.

Paradoxical Anaerobism in Desert Pupfish

Oxidation of glucose through aerobic pathways is ~15X more efficient than is anaerobic metabolism. Pupfish of the genus Cyprinodon experience variable periods of up to nearly 5h of virtually no oxygen consumption. This paradoxical anaerobism occurs in the presence of oxygen. The longest continuous bout was 149 min although more typical bouts are only a few minutes in length. Fish randomly cycle between periods of paradoxical anaerobism and stable oxygen consumption patterns suggesting no long‐term damage or alternations to mitochondria. There is no evidence for compensatory oxygen use. Fish produce ethanol as an apparent alternate end product of anaerobic metabolism. Exposure to exogenous ethanol induces rapid onset of paradoxical anaerobism.

Entire mitochondrion genome sequence of the Desert Pupfish, Cyprinodon macularius Baird & Girard, 1853

The complete mitochondrial genome sequence of the Desert Pupfish, Cyprinodon macularius (Gene accession number KM985373) has a length of 16,940 bp, and the arrangement consisted of 13 protein-coding genes, 2 ribosomal RNA (rRNA) genes and 22 transfer RNA, which are similar to other known mitogenomes for the family Cyprinodontidae.

Estatus actual de conservación de seis especies de peces dulceacuícolas de la península de Baja California, México

The current distribution and conservation status of six native freshwater fishes of the Baja California peninsula (Entosphenus tridentatus, Oncorhynchus mykiss nelsoni, Fundulus lima, Cyprinodon macularius, Gasterosteus aculeatus and Gobiesox juniperoserrai), included in the Norma Oficial Mexicana-059-2010, were assessed on the basis of information generated during the study period of 2000–2014. Except for E. tridentatus in the Santo Domingo river drainage and G. juniperoserrai in the Las Pocitas-San Hilario drainage, most of the species were recorded in the hydrological basins sampled. Oncorhynchus mykiss nelsoni showed a significant population fluctuation in the San Rafael river in relation to the dynamics of the base flow and the forest fire events. Fundulus lima presented the probable extirpation from four drainages (San Javier, Bebelamas, San Luis, and Las Pocitas-San Hilario) that is contrasting with the finding of a new population in the Santa Cruz stream. Cyprinodon macularius in the most important remnant population in Baja California (cerro Prieto geothermal ponds) showed interannual fluctuations related with the level of flooding and availability of marginal habitats. Gasterosteus aculeatus showed a progressive population reduction in the southernmost distributional locality (mouth of El Rosario river), as well as the extirpation in the lower Santo Domingo river basin and its recent presence in the mouth of the Cantamar river. Gobiesox juniperoserrai, known only from the type locality is determined as extirpated.

From accident to management: The Cienega de Santa Clara ecosystem

The 1977 creation of the Cienega de Santa Clara, an 18,000ha wetland (6500ha cattail marsh with 11,500ha of open water lagoons and mudflats) in Sonora, Mexico, was the unintended consequence of the solution to reduce the salinity of the U.S. water deliveries to Mexico. Under the 1944 Water Treaty, the U.S. was obliged to deliver water to Mexico. But the water that was delivered from the U.S. harmed crops in Mexico because it included brackish agricultural runoff from fields in the Lower Colorado River basin. In 1972, Minute 242 to the Treaty called for a reduction in the salinity of U.S. deliveries. As a result, the U.S. diverted the agricultural runoff to a desiccated Colorado Delta floodplain in Sonora, Mexico, inadvertently creating the Cienega de Santa Clara, a wetland that now provides habitat for protected species (Desert Pupfish and the Yuma Clapper Rail), and wintering grounds for more than 200,000 migratory waterbirds. In June 1993, the wetland became part of Mexico's Upper Gulf of California and Colorado River Delta Biosphere Reserve. The Yuma Desalting Plant, completed in 1992, was constructed by the U.S. to desalinate the agricultural runoff that flows to the Cienega. The high cost of operation and abundant Colorado River flow have kept the plant idle. However, the past decade of drought in the Colorado Basin has now made the agricultural runoff a valuable resource to meet growing U.S. water demands, but operating the plant could risk damage to the Cienega wetlands. In response, a binational collaboration of government agencies, environmental groups and university scientists began working together to protect and study this wetland. Replacement flows and environmental monitoring during the 2010–2011 trial run of the Yuma Desalting Plant are prompting a shift from passive to active management of this binational ecosystem. The purpose of this paper is to identify management practices that could help maximize the ecological benefits of water flows. The suggested management practices are based on historical variations in quantity, timing and quality of inflows, occasional dredgings and wildfires. The most important management recommendation is a formal allocation of water of adequate volume and quality. The agreement reached in 2010s Minute 316 to the Treaty is a precedent for successful efforts to protect shared ecosystems along the U.S.–Mexico border.

Characterization of Na(+) uptake in the endangered desert pupfish, Cyprinodon macularius (Baird and Girard).

This study provided an initial characterization of Na(+) uptake in saline freshwater by the endangered pupfish, Cyprinodon macularius. This species occurs only in several saline water systems in the southwestern USA and northern Mexico, where salinity is largely controlled by water-management practices. Consequently, understanding the osmoregulatory capacity of this species is important for their conservation. The lower acclimation limit of C. macularius in freshwater was found to be 2 mM Na(+). Fish acclimated to 2 or 7 mM Na(+) displayed similar Na(+) uptake kinetics, with K m values of 4321 and 3672 μM and V max values of 4771 and 3602 nmol g(-1) h(-1), respectively. A series of experiments using pharmacological inhibitors indicated that Na(+) uptake in C. macularius was not sensitive to bumetanide, metolazone, or phenamil. These results indicate the Na(+)-K(+)-2Cl(-) cotransporter, Na(+)-Cl(-) cotransporter, and the Na(+) channel-H(+)-ATPase system are likely not to be involved in Na(+) uptake at the apical membrane of fish gill ionocytes in fish acclimated to 2 or 7 mM Na(+). However, Na(+) uptake was sensitive to 1 × 10(-3) M amiloride (not 1 × 10(-4) or 1 × 10(-5) M), 5-(N-ethyl-N-isopropyl)-amiloride (EIPA), and ethoxzolamide. These data suggest that C. macularius relies on a low-affinity Na(+)-H(+) exchanger for apical Na(+) uptake and that H(+) ions generated via carbonic anhydrase-mediated CO2 hydration are important for the function of this protein.

Paradoxical anaerobism in desert pupfish

Pupfish in the genus Cyprinodon migrated into the Mojave Desert when the region contained a network of large lakes and interconnecting streams. Climate change over the past ten thousand years has resulted in isolated populations in remaining warm springs and pools. Devils Hole is such a pool with stable temperatures between 33 and 34° C and a small population of C. diabolis whose population fell to 38 adult fish counted in 2006. Reproduction occurs on a shallow ledge where temperatures range from 26° C in the winter to 39° C in the summer. We hypothesized that the warm temperatures of the pool were detrimental to the fish. We used a refuge population of C. diabolis to measure oxygen consumption (VO2) of fish acclimated to 28 and 33° C. The 28° C acclimated group (Control) showed a consistent pattern of VO2 over a 2–4 hour experimental period. The 33° C acclimated group showed three patterns: 1) Predictable, i.e. like the 28° C group. 2) Variable, fluctuated between depressed VO2 and values near that of the Predictable group. 3) Intermittent, characterized by periods where VO2 virtually ceased for as long as 67 minutes. Fish showing intermittent VO2 were actively ventilating. Fish acclimated to 33° C produced 7.3X more ethanol than fish acclimated to 28° C indicating use of anaerobic metabolism despite the availability of oxygen.

Condition status of the endangered desert pupfish, Cyprinodon macularius Baird and Girard, 1853, in the Lower Colorado River Basin (Mexico)

The length-weight relationship (LWR) was used to test differences in the fish somatic condition factor among four populations of the endangered desert pupfish, Cyprinodon macularius, from the Lower Colorado River Basin, Mexico. Bimonthly fish sampling and habitat assessments were carried out from September 1996 to August 1997 for four sites in Baja California and Sonora. Slope b of the WLR varied from 3.238 (Cerro Prieto population) to 3.613 (Welton-Mohawk population), showing in all populations a positive allometric growth. Male b values were higher than those of females for Cerro Prieto (3.303 vs 3.071), Welton-Mohawk (3.866 vs 3.579), and Flor del Desierto (3.357 vs 3.169) populations. The Cerro Prieto population showed the highest somatic condition (y-intercept, a = −11.759). Water depth and salinity were the ecological variables that better accounted for most of the variation in the somatic condition of this pupfish, with a negative and a positive effect, respectively.