The effects of salinity on swimming performance of two estuarine fishes,Fundulus heteroclitus and Fundulus majalis

Prolonged and high‐speed swimming performance measurements were used to explore the swimming abilities of two species of estuarine fishes, the mummichog Fundulus heteroclitus and the striped killifish Fundulus majalis, under different salinities. Critical swimming performance was significantly higher for F. majalis in high salinity than in low salinity, but no difference was observed in brief constant acceleration swimming trials in this species; however, the swimming performance of F. heteroclitus was not significantly affected by salinity changes, indicating that this species is well adapted to regular estuarine salinity oscillations. Fundulus majalis displayed higher swimming speeds than F. heteroclitus in both high and low salinities, and while this cannot be explained by their respective salinity preferences, the specific habitat preferences of F. majalis for sandy subtidal habitats and F. heteroclitus for vegetated marshes could explain the better swimming performance of F. majalis.     

Behavioral interactions under multiple stressors: temperature and salinity mediate aggression between an invasive and a native fish

Interspecific aggression is a critical determinant of the success and competitive superiority of many invasive over native species. While single abiotic stressors can alter aggression levels, the manner in which multiple stressors may alter the strength and outcome of interspecific interactions and hence the invasion potential of a species is still poorly understood, even though multiple stressors are prevalent in many ecosystems. Furthermore, multiple stressors may interact to produce synergistic or antagonistic effects on individual level behaviors, thereby modulating invasive-native species interactions in unexpected ways. Here we examined the effect of two key abiotic stressors in freshwater ecosystems-temperature and salinity-on interspecific aggression between the invasive eastern mosquito fish (Gambusia holbrooki) and juveniles of the native Australian bass (Macquaria novemaculeata). Under controlled laboratory conditions, individuals were exposed to low or high salinity levels (15 and 35‰), and low or high temperatures (21 and 28 °C), and the frequency of interspecific aggressive behaviors was scored. The effect of temperature and salinity on interspecific aggression was antagonistic for both M. novemaculeata and G. holbrooki. While elevated temperature promoted aggression, elevated salinity partially or entirely negated this effect. Moreover, regardless of temperature, M. novemaculeata was more aggressive than G. holbrooki under elevated salinity. In addition to this, the native displayed more aggression to smaller than larger heterospecifics when exposed to elevated salinity alone, while G. holbrooki showed no such preference. These results highlight the importance of considering the interplay between multiple abiotic stressors and behavioral interactions between invasive and native species, combined with the modulating effect of species-specific and size based responses to those stressors.     

Fundulus heteroclitus: ovarian reproductive physiology and the impact of environmental contaminants

Fundulus heteroclitus, the mummichog or Atlantic killifish, is the dominant small-bodied fish species of the east coast estuaries and salt marshes of Canada and the USA, where it is present as two subspecies, the northern F. h. macrolepidotus and the southern F. h. heteroclitus. Recently identified as the premier teleost model in environmental biology, the species has long been of value in understanding evolved tolerance to toxicants and more lately in adding to our knowledge about reproductive effects of environmental endocrine disruptors. The body of literature on F. heteroclitus ovarian physiology and reproduction, from both field and laboratory studies, provides the foundation for present work focused on understanding the reproductive effects and modes of action of environmental toxicants. In this paper, we review the environmental and endocrine factors controlling ovarian and reproductive cycling in F. heteroclitus, noting specifics related to field and laboratory studies on the two subspecies as well as key research gaps compared to other fish species. We also summarize recent development of methodologies to study the effects of environmental contaminants on endocrine signalling and egg production in F. heteroclitus. Continued efforts to progress both our fundamental understanding of reproductive physiology in mummichog, coupled with studies focused on the modes of action of environmental contaminants, have high potential to further develop this teleost model. While the model may presently lag behind those based on other species of fish, the unique biochemical and physiological adaptations which allow F. heteroclitus to adapt to changing environmental and toxic conditions provide a valuable experimental system for comparative physiologists, ecotoxicologists and evolutionary biologists.     

A review and meta‐analysis of the effects of multiple abiotic stressors on marine embryos and larvae

Marine organisms are simultaneously exposed to anthropogenic stressors with likely interactive effects, including synergisms in which the combined effects of multiple stressors are greater than the sum of individual effects. Early life stages of marine organisms are potentially vulnerable to the stressors associated with global change, but identifying general patterns across studies, species and response variables is challenging. This review represents the first meta‐analysis of multistressor studies to target early marine life stages (embryo to larvae), particularly between temperature, salinity and pH as these are the best studied. Knowledge gaps in research on multiple abiotic stressors and early life stages are also identified. The meta‐analysis yielded several key results: (1) Synergistic interactions (65% of individual tests) are more common than additive (17%) or antagonistic (17%) interactions. (2) Larvae are generally more vulnerable than embryos to thermal and pH stress. (3) Survival is more likely than sublethal responses to be affected by thermal, salinity and pH stress. (4) Interaction types vary among stressors, ontogenetic stages and biological responses, but they are more consistent among phyla. (5) Ocean acidification is a greater stressor for calcifying than noncalcifying larvae. Despite being more ecologically realistic than single‐factor studies, multifactorial studies may still oversimplify complex systems, and so meta‐analyses of the data from them must be cautiously interpreted with regard to extrapolation to field conditions. Nonetheless, our results identify taxa with early life stages that may be particularly vulnerable (e.g. molluscs, echinoderms) or robust (e.g. arthropods, cnidarians) to abiotic stress. We provide a list of recommendations for future multiple stressor studies, particularly those focussed on early marine life stages.     

Cellular responses of encapsulated gastropod embryos to multiple stressors associated with climate change

As a consequence of global warming, environmental conditions such as temperature and salinity are likely to change in near-shore waters. Early life history phases are expected to be particularly vulnerable to changes in these abiotic variables. To evaluate the effect of multiple stressors on the responses of invertebrate larvae, to conditions anticipated under scenarios of climate change, we examined the cellular responses of embryos of three common rocky intertidal gastropod species to temperature and salinity changes. Encapsulated embryos of each species were exposed for 72 h to six combinations of ecologically realistic temperature and salinity levels (22° and 30 °C and 25, 35 and 45 ppt). Embryonic mortality and the responses of two biomarkers: total antioxidant capacity and lipid peroxidation, were then determined. We predicted that those organisms exposed to physiologically stressful levels of the combined stressors would show the strongest responses. The general trend was that both extremes of salinity (25 and 45 ppt) and high temperature (30 °C) negatively affected the embryos studied inducing oxidative stress and increasing lipid peroxidation, leading to increased embryonic mortality. The intensity of the response remained species-specific, with no clear pattern established as to which species was the most sensitive to salinity and temperature changes. Consequently, climate change induced temperature and salinity changes do exert molecular and physiological effects on early life stages of rocky shore gastropods, however, response to these stressors is species-specific.     

Role of spatial and environmental factors in shaping the rotifer metacommunity in anthropogenic water bodies

In spatially heterogeneous habitats, local communities may be shaped by both local biotic and abiotic factors and by regional factors (dispersal of individuals among habitats). In recent years, ecologists have been increasingly interested in measuring how much the structure of local communities is explained by spatial variables and by non-spatial environmental variables. We analysed the effects of biotic and abiotic factors on rotifer communities in 12 anthropogenic water bodies in the Silesian Upland. The studies were conducted in two groups of water bodies which were of differing dimensions: group A — seven water bodies situated very close to each other (between 50 and 500 m), group B — the water bodies from group A as well as 5 other water bodies situated 2 km away, which were at greater distances from each other (about 1–3 km). Apart from this, genetic variation was assessed in 3 populations of Brachionus plicatilis Müller to estimate the level of gene flow between them. A characteristic feature of anthropogenic water bodies is a high variation in environmental conditions, so they are specific and difficult habitats for many organisms. Our study shows that environmental factors played a major role in shaping the local rotifer communities in heterogeneous anthropogenic water bodies with respect to salinity. Results of this study suggest, however, that in neighbouring water bodies, dispersal is very important for maintenance of local species diversity. A medium level of genetic variation between populations of B. plicatilis indicates that gene flow occurs irrespective of the distance between local populations.     

Expression of aquaporin 3 in gills of the Atlantic killifish (Fundulus heteroclitus): Effects of seawater acclimation

Estuarine fish, such as the Atlantic killifish (Fundulus heteroclitus), are constantly and rapidly exposed to changes in salinity. Although ion transport in killifish gills during acclimation to increased salinity has been studied extensively, no studies have examined the role of aquaglyceroporin 3 (AQP3), a water, glycerol, urea, and ammonia transporter, during acclimation to increased salinity in this sentinel environmental model organism. The goal of this study was to test the hypothesis that transfer from freshwater to seawater decreases AQP3 gene and protein expression in the gill of killifish. Transfer from freshwater to seawater decreased AQP3 mRNA in the gill after 1 day, but had no effect on total gill AQP3 protein abundance as determined by western blot. Quantitative confocal immunocytochemistry confirmed western blot studies that transfer from freshwater to seawater did not change total AQP3 abundance in the gill; however, immunocytochemistry revealed that the amount of AQP3 in pillar cells of secondary lamellae decreased in seawater fish, whereas the amount of AQP3 in mitochondrion rich cells (MRC) in primary filaments of the gill increased in seawater fish. This response of AQP3 expression is unique to killifish compared to other teleosts. Although the role of AQP3 in the gill of killifish has not been completely elucidated, these results suggest that AQP3 may play an important role in the ability of killifish to acclimate to increased salinity.     

Interactive effects of three pervasive marine stressors in a post-disturbance coral reef

Ecosystems are commonly affected by natural, episodic disturbances that can abruptly and drastically alter communities. Although it has been shown that resilient ecosystems can eventually recover to pre-disturbed states, the extent to which communities in early stages of recovery could be affected by multiple anthropogenic stressors is poorly understood. Pervasive and rising anthropogenic stressors in coastal marine systems that could interactively affect the recovery of these systems following natural disturbances include high sedimentation, nutrient enrichment, and overfishing. Using a 6-month field experiment, we examined the effects of all combinations of these three stressors on key functional groups in the benthic community growing on simulated, post-disturbance reef patches within a system recovering from large-scale natural disturbances (corallivorous seastar outbreak and cyclone). Our study revealed that sedimentation, nutrient enrichment, and overfishing (simulated using exclusion cages) interactively affected coral survival and algal growth, with taxon-specific effects at multiple scales. First, our treatments affected corals and algae differently, with sedimentation being more detrimental to macroalgal growth but less detrimental to coral (Porites rus) survival in caged plots, driving significant interactions between sedimentation and caging for both taxa. We also observed distinct responses between coral species and between algal functional groups, with the most extensive responses from algal turf biomass, for which sedimentation suppressed the synergistic (positive) combined effect of nutrient enrichment and caging. Our findings suggest that different combinations of ubiquitous anthropogenic stressors, related to either sea- or land-based activities, interactively influence community recovery from disturbance and may alter species compositions in the resulting community. Our findings further suggest that anthropogenic stressors could promote further degradation of coral reefs following natural disturbances by inhibiting recovery to coral-dominated states that provide vital ecosystem services to coastal populations worldwide.     

Weak response of saltmarsh infauna to ecosystem-wide nutrient enrichment and fish predator reduction: A four-year study

We examined the effect of whole-ecosystem manipulations of predator removal and nutrient enrichment on saltmarsh macroinfauna in the Plum Island Estuary, Massachusetts. Nitrate and phosphate loading rates were increased 10× above background levels in experimental creeks, and we significantly reduced (by 60%) the abundance of the killifish, Fundulus heteroclitus, a key predator in this system. Two creek pairs were manipulated; Creek Pair 1 for three growing seasons and Creek Pair 2 for one. Infaunal responses were examined in four habitats along the inundation gradient: mudflat, creek wall, Spartina alterniflora, and S. patens habitats. Although benthic microalgae increased synergistically in our treatments, we detected no long-term, population-level numerical response by any taxon. Similarly, no long-term species diversity or community responses were observed. However, nutrient enrichment increased the population biomass of the polychaete Manayunkia aestuarina in the creek wall habitat and the oligochaete Cernosvitoviella immota in the S. alterniflora habitat. No numerical or biomass responses of infauna were detected in predator removal treatments although indirect effects associated with killifish reduction may have contributed to an ephemeral interaction between nutrient addition and predator reduction in S. patens habitat. Our data suggest that population and community responses between benthic microalgae and macroinfauna are not tightly coupled even though some species benefit from increased benthic algae biomass by achieving larger body size.     

Biomarker/bioindicator response profiles of organisms can help differentiate between sources of anthropogenic stressors in aquatic ecosystems

Aquatic ecosystems can be chronically stressed by multiple environmental factors which originate from a variety of point and non-point sources. In addition, these stressors may vary both spatially and temporally, and, combined with synergestic and cumulative interactions of these stressors, complicate the interpretation and evaluation of stress responses in organisms. To help identify and differentiate between sources of anthropogenic stressors in aquatic systems, a diagnostic approach based on exposure-response profiles in sentinel organisms was developed from the known effects of various anthropogenic activities on biological systems. To generate these exposure-effects profiles, biomarkers of exposure were plotted against bioindicators of corresponding effects for several major anthropogenic activities including petrochemical, pulp and paper, domestic sewage, mining operations, land-development, and agricultural activities. Biomarkers of exposure to environmental stressors varied widely depending on the type of anthropogenic activity involved. Bioindicator effects, however, including histopathological lesions, bioenergetic status, growth, reproductive impairment, and community-level endpoints were similar among several of the major anthropogenic activities because responses at these higher levels are less specific to stressors than are biomarkers. This approach appears useful for helping to identify and diagnose sources of stress in environments impacted by multiple stressors. By identifying the types and sources of environmental stressors impacting key components of biological systems, aquatic ecosystems can be more effectively protected, regulated, and managed to help improve and maintain environmental quality and ecosystem fitness.     

Management of Local Stressors Can Improve the Resilience of Marine Canopy Algae to Global Stressors

Coastal systems are increasingly threatened by multiple local anthropogenic and global climatic stressors. With the difficulties in remediating global stressors, management requires alternative approaches that focus on local scales. We used manipulative experiments to test whether reducing local stressors (sediment load and nutrient concentrations) can improve the resilience of foundation species (canopy algae along temperate rocky coastlines) to future projected global climate stressors (high wave exposure, increasing sea surface temperature), which are less amenable to management actions. We focused on Fucoids (Cystoseira barbata) along the north-western Adriatic coast in the Mediterranean Sea because of their ecological relevance, sensitivity to a variety of human impacts, and declared conservation priority. At current levels of sediment and nutrients, C. barbata showed negative responses to the simulated future scenarios of high wave exposure and increased sea surface temperature. However, reducing the sediment load increased the survival of C. barbata recruits by 90.24% at high wave exposure while reducing nutrient concentrations resulted in a 20.14% increase in the survival and enhanced the growth of recruited juveniles at high temperature. We conclude that improving water quality by reducing nutrient concentrations, and particularly the sediment load, would significantly increase the resilience of C. barbata populations to projected increases in climate stressors. Developing and applying appropriate targets for specific local anthropogenic stressors could be an effective management action to halt the severe and ongoing loss of key marine habitats.     

A new look towards BAC-based array CGH through a comprehensive comparison with oligo-based array CGH

Background

Natural populations of the teleost fish Fundulus heteroclitus tolerate a broad range of environmental conditions including temperature, salinity, hypoxia and chemical pollutants. Strikingly, populations of Fundulus inhabit and have adapted to highly polluted Superfund sites that are contaminated with persistent toxic chemicals. These natural populations provide a foundation to discover critical gene pathways that have evolved in a complex natural environment in response to environmental stressors.

Results

We used Fundulus cDNA arrays to compare metabolic gene expression patterns in the brains of individuals among nine populations: three independent, polluted Superfund populations and two genetically similar, reference populations for each Superfund population. We found that up to 17% of metabolic genes have evolved adaptive changes in gene expression in these Superfund populations. Among these genes, two (1.2%) show a conserved response among three polluted populations, suggesting common, independently evolved mechanisms for adaptation to environmental pollution in these natural populations.

Conclusion

Significant differences among individuals between polluted and reference populations, statistical analyses indicating shared adaptive changes among the Superfund populations, and lack of reduction in gene expression variation suggest that common mechanisms of adaptive resistance to anthropogenic pollutants have evolved independently in multiple Fundulus populations. Among three independent, Superfund populations, two genes have a common response indicating that high selective pressures may favor specific responses.     

Phenotypic plasticity and divergence in gene expression

The extent to which phenotypic plasticity, or the ability of a single genotype to produce different phenotypes in different environments, impedes or promotes genetic divergence has been a matter of debate within evolutionary biology for many decades (see, for example, Ghalambor et al. 2007 ; Pfennig et al. 2010 ). Similarly, the role of evolution in shaping phenotypic plasticity remains poorly understood (Pigliucci 2005 ). In this issue of Molecular Ecology, Dayan et al. ( 2015 ) provide empirical data relevant to these questions by assessing the extent of plasticity and divergence in the expression levels of 2272 genes in muscle tissue from killifish (genus Fundulus) exposed to different temperatures. F. heteroclitus (Fig.  1 A) and F. grandis are minnows that inhabit estuarine marshes (Fig.  1 B) along the coasts of the Atlantic Ocean and Gulf of Mexico in North America. These habitats undergo large variations in temperature both daily and seasonally, and these fish are known to demonstrate substantial phenotypic plasticity in response to temperature change (e.g. Fangue et al. 2006 ). Furthermore, the range of F. heteroclitus spans a large latitudinal gradient of temperatures, such that northern populations experience temperatures that are on average ~10°C colder than do southern populations (Schulte 2007 ). By comparing gene expression patterns between populations of these fish from different thermal habitats held in the laboratory at three different temperatures, Dayan et al. ( 2015 ) address two important questions regarding the interacting effects of plasticity and evolution: (i) How does phenotypic plasticity affect adaptive divergence? and (ii) How does adaptive divergence affect plasticity?     

Effects of Environmental Stressors and Immunosuppressants on Immunity in Fundulus heteroclitus

Environmental stressors have been shown to alter immunocompetencein mammals. Similar effects have been reported in fish. Thepurpose of this paper is to review the literature concerningthe white blood cells and immunity in Fundulus heteroclitus.Evidence for immunosuppression following prolonged captivity,handling, hypophysectomy, radiation, changes in temperatureand salinity, and exposure to chemicals including environmentalpollutants is discussed. New evidence for immunosuppressionfollowing exposure to benzo-a-pyrene, pentachlorophenol, andhexachlorobenzene is presented. Possible mechanisms of immunealteration and the consequences to F. heteroclitus are discussed.     

Herbivore Impacts on Marsh Production Depend upon a Compensatory Continuum Mediated by Salinity Stress

Plant communities are disturbed by several stressors and they are expected to be further impacted by increasing anthropogenic stress. The consequences of these stressors will depend, in part, upon the ability of plants to compensate for herbivory. Previous studies found that herbivore impacts on plants can vary from negative to positive because of environmental control of plant compensatory responses, a.k.a. the Compensatory Continuum Hypothesis. While these influential studies enhanced our appreciation of the dynamic nature of plant-herbivore interactions, they largely focused on the impact of resource limitation. This bias limits our ability to predict how other environmental factors will shape the impact of herbivory. We examined the role of salinity stress on herbivory of salt marsh cordgrass, Spartina foliosa, by an herbivore previously hypothesized to influence the success of restoration projects (the scale insect, Haliaspis spartinae). Using a combination of field and mesocosm manipulations of scales and salinity, we measured how these factors affected Spartina growth and timing of senescence. In mesocosm studies, Spartina overcompensated for herbivory by growing taller shoots at low salinities but the impact of scales on plants switched from positive to neutral with increasing salinity stress. In field studies of intermediate salinities, scales reduced Spartina growth and increased the rate of senescence. Experimental salinity additions at this field site returned the impact of scales to neutral. Because salinity decreased scale densities, the switch in impact of scales on Spartina with increasing salinity was not simply a linear function of scale abundance. Thus, the impact of scales on primary production depended strongly upon environmental context because intermediate salinity stress prevented plant compensatory responses to herbivory. Understanding this context-dependency will be required if we are going to successfully predict the success of restoration efforts and the ecological consequences of anthropogenic disturbances.     

High tolerance to abiotic stressors and invasion success of the slow growing freshwater snail, Melanoides tuberculatus

Considerable research has been conducted to determine traits common to invasive species with the goal of predicting, preventing, or managing invasions. The importance of physiological tolerance to abiotic stressors in the ability of invasive species to establish and displace native species has been hypothesized to be important although there are few actual tests of the hypothesis in the literature. In freshwater molluscs it has been suggested that high fecundity is the most important trait for invasion success and that physiological tolerance to abiotic conditions is unlikely to play a significant role. We examined the tolerance to abiotic stressors using a known invasive snail species (Melanoides tuberculatus) that has a much slower growth rate and fecundity than a native species it has displaced (Biomphalaria glabrata). We tested the hypothesis that M. tuberculatus would have significantly greater tolerance to natural and anthropogenic abiotic stressors (cadmium, malathion, temperature extremes, and desiccation) which may provide a mechanism for displacement of B. glabrata. A time-to-event analysis was used to determine relative tolerance between species. M. tuberculatus was significantly more tolerant to the tested abiotic stressors than B. glabrata with the exception of low temperature (5°C). Stress tolerance may partly explain the ability of M. tuberculatus to displace B. glabrata despite having a much lower growth rate and fecundity. These results also suggest that M. tuberculatus is likely to have a strong advantage in disturbed or polluted habitats. Identifying those traits most important for the invasion success of particular species could be used to better inform removal strategies and may allow for improved predictions of invasion potential.     

Reproductive isolating mechanisms contributing to asymmetric hybridization in Killifishes (Fundulus spp.)

When species hybridize, one F1 hybrid cross type often predominates. Such asymmetry can arise from differences in a variety of reproductive barriers, but the relative roles and concordance of pre-mating, post-mating prezygotic, and post-zygotic barriers in producing these biases in natural animal populations have not been widely investigated. Here, we study a population of predominantly F1 hybrids between two killifish species (Fundulus heteroclitus and F. diaphanus) in which >95% of F1 hybrids have F. diaphanus mothers and F. heteroclitus fathers (D♀ × H♂). To determine why F. heteroclitus × F. diaphanus F1 hybrids (H♀ × D♂) are so rare, we tested for asymmetry in pre-mating reproductive barriers (female preference and male aggression) at a common salinity (10 ppt) and post-mating, pre-zygotic (fertilization success) and post-zygotic (embryonic development time and hatching success) reproductive barriers at a range of ecologically relevant salinities (0, 5, 10, and 15 ppt). We found that F. heteroclitus females preferred conspecific males, whereas F. diaphanus females did not, matching the observed cross bias in the wild. Naturally rare H♀ × D♂ crosses also had lower fertilization success than all other cross types, and a lower hatching success than the prevalent D♀ × H♂ crosses at the salinity found in the hybrid zone centre (10 ppt). Furthermore, the naturally predominant D♀ × H♂ crosses had a higher hatching success than F. diaphanus crosses at 10 ppt, which may further increase their relative abundance. The present study suggests that a combination of incomplete mating, post-mating pre-zygotic and post-zygotic reproductive isolating mechanisms act in concert to produce hybrid asymmetry in this system.     

Characteristics and Main Trends of Anthropogenic Florogenesis in the Southern Volga Uplands

The entire range of aspects of anthropogenic florogenesis in the southern part of the Volga Uplands is addressed. Trends in the anthropogenic dynamics of local flora in the last 100 years have been identified. A shift 50–100 km northward of the southern border of natural habitats of some boreal species (Antennaria dioica (L.) Gaertn., Maianthemum bifolium (L.) F.W. Schmidt, Pyrola rotundifolia L., etc.) has been noted. Data on the adventive flora and modern migration paths of the plants within the study area are provided. The adaptive activity of aboriginal species in relation to the entire range of anthropogenic habitats of the region is characterized. Information on findings of protected plant species in anthropogenic biotopes is provided. Overall, flora aridization and xerophytization have been noted, as has an increased role of tree and shrub life forms in the anthropogenic florogenesis. It is proposed to use a method based on the identification of anthropochorophilic elements in the aboriginal flora to forecast the adaptation of flora to the conditions of anthropogenic habitats.     

A divergent CFTR homologue: highly regulated salt transport in the euryhaline teleost F.heteroclitus

The killifish,Fundulus heteroclitus, is a euryhalineteleost fish capable of adapting rapidly to transfer from freshwater (FW) to four times seawater (SW). To investigate osmoregulation at amolecular level, a 5.7-kilobase cDNA homologous to human cysticfibrosis transmembrane conductance regulator (hCFTR) was isolated froma gill cDNA library from SW-adapted killifish. This cDNA encodes aprotein product (kfCFTR) that is 59% identical to hCFTR,the most divergent form of CFTR characterized to date. Expression ofkfCFTR in Xenopus oocytes generatedadenosine 3',5'-cyclic monophosphate-activated,Cl-selective currentssimilar to those generated by hCFTR. In SW-adapted killifish,kfCFTR was expressed at high levels in the gill, opercular epithelium, and intestine. After abrupt exposure of FW-adapted killifish to SW, kfCFTR expression in the gill increasedseveralfold, suggesting a role for kfCFTR in salinity adaptation. Undersimilar conditions, plasma Na⁺levels rose significantly after 8 h and then fell, although it is notknown whether these changes are directly responsible for the changes inkfCFTR expression. The killifish provides a unique opportunity to understand teleost osmoregulation and the role of CFTR.