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PubMed1977

Chloride transport across isolated opercular epithelium of killifish: a membrane rich in chloride cells.

The opercular epithelium of Fundulus heteroclitus contains typical gill chloride-secreting cells at the high density of 4 X 10(5) cells per square centimeter. When isolated, mounted as a membrane, and short-circuited, it actively transports chloride ions from the blood side to the seawater side of the preparation. This preparation offers a useful approach to the study of osmoregulation in bony fishes.

Animals↗
PubMed1977

Active chloride transport in the in vitro opercular skin of a teleost (Fundulus heteroclitus), a gill-like epithelium rich in chloride cells.

1. The opercular epithelium lining the inside of the gill chamber of the killifish, Fundulus heteroclitus, contains Cl(-) cells, identical in fine structure to gill Cl(-) cells, at the high density of 4 x 10(5) cells/cm(2). This epithelium can be isolated, mounted in a Lucite chamber, and its ion transport properties studied with the short-circuit current technique.2. The isolated opercular epithelia of seawater-adapted fish, when bathed on both sides with Ringer and gassed with 100% O(2), displayed a mean short-circuit current of 136.5 +/- 11.1 muA/cm(2), a mean transepithelial potential difference of 18.7 +/- 1.2 mV (blood side positive), and a mean transepithelial d.c. resistance of 173.7 +/- 12.1 Omega.cm(2) (mean +/- S.E. of mean; n = 64).3. The transepithelial potential difference across the opercular epithelia of seawater-adapted fish was dependent on both Na(+) and Cl(-) in the bathing solutions and increased linearly with increasing Cl(-) concentrations with a slope of 28.3 +/- 2.1 mV/tenfold concentration change. The short-circuit current was Na(+) dependent and increased linearly with increasing Cl(-) concentrations with no evidence of saturation kinetics below 142.5 m-equiv/l.4. When the short-circuited epithelia of seawater-adapted fish, bathed on both sides with Ringer, was gassed with 100% O(2) the mean Cl(-) blood side to seawater side flux was 211.7 +/- 27.1 muA/cm(2) and the mean Cl(-) seawater side to blood side flux was 48.9 +/- 10.0 muA/cm(2). This resulted in a net Cl(-) blood side to seawater side flux of 162.8 muA/cm(2) which was not statistically different (P > 0.70) from the mean short-circuit current of 158.6 +/- 16.3 muA/cm(2) for these flux studies. The mean Na(+) blood side to seawater side flux was 32.2 +/- 3.3 muA/cm(2) and the mean Na(+) seawater side to blood side flux was 34.8 +/- 4.1 muA/cm(2), resulting in no significant (P > 0.20) net flux of this cation. Similar results were obtained with short-circuited epithelia of seawater-adapted fish when bathed on both sides with Ringer and gassed with 95% O(2)/5% CO(2).5. Ouabain (10(-5)M), furosemide (10(-3)M), thiocyanate (10(-2)M), adrenaline (10(-6)M), and anoxia (100% N(2)) decreased the short-circuit current 92.7, 85.0, 45.3, 62.6, and 83.3% respectively. Theophylline (10(-4)M) stimulated the short-circuit current 54.9%. Increasing the HCO(3) (-) concentration in the bathing solutions had a stimulatory effect on the short-circuit current and the potential difference across epithelia from seawater-adapted fish.6. The opercular epithelia of freshwater-adapted F. heteroclitus, when bathed on both sides with Ringer, displayed a mean short-circuit current of 94.1 +/- 10.4 muA/cm(2), a mean transepithelial potential difference of 14.8 +/- 1.9 mV (blood side positive), and a mean d.c. resistance of 169.0 +/- 14.0 Omega.cm(2) (mean +/- S.E. of mean; n = 20). Isotope flux studies across these short-circuited epithelia revealed a net Cl(-) blood side to freshwater side flux of 95.2 +/- 16.1 muA/cm(2) and no significant net flux of Na(+).7. The opercular epithelia of 200% seawater-adapted F. heteroclitus, when bathed on both sides with Ringer, displayed a mean short-circuit current of 33.5 +/- 8.5 muA/cm(2), a mean transepithelial potential difference of 10.5 +/- 2.5 mV (blood side positive), and a mean transepithelial d.c. resistance of 440.7 +/- 62.6 Omega.cm(2) (mean +/- S.E. of mean n = 18). Isotope flux studies across these short-circuited epithelia revealed a net Cl(-) blood side to seawater side flux of 96.2 +/- 51.5 muA/cm(2) and a net Na(+) blood side to seawater side flux of 65.3 +/- 28.6 muA/cm(2).

Adaptation, Physiological↗
PubMed1978

Effect of prehatching weightlessness on adult fish behavior in dynamic environments.

At 16-17 months of age, three groups of fish from the embryonated eggs in the ASTP killifish experiment were subjected to postflight tests consisting of rapidly changing environments. It was found that the group of fish with the least amount of development at orbital insertion (A-32) had a decreased rheotropism for both the moving background and the rotating water current tests when compared to ground control fish. Exposure to parabolic aircraft flight conditions revealed that the A-32 fish were less disoriented during zero gravity periods and were hypersensitive to high-gravity periods. These results suggested a modified vestibular competency due to a 9-d prehatching weightlessness exposure.

Adaptation, Physiological↗
PubMed2026

Evolutionary Reorganization of Transcriptomic Architecture Across a UVB Tolerance Gradient in Fish.

Environmental stressors such as ultraviolet radiation impose strong selective pressures on organisms, yet how adaptation to such stressors shapes transcriptomic responses at the network level remains poorly understood. Although stratospheric ozone is recovering globally, substantial regional variation in UV exposure persists, particularly in high-altitude environments where extreme UV levels can occur. Here, we compared three fish models representing distinct biological responses to UVB exposure: wild-type zebrafish (Danio rerio), a melanin-deficient zebrafish mutant (nacre) lacking a major protective mechanism against UVB damage, and the high-altitude Andean killifish Orestias ascotanensis, a species naturally exposed to extreme UVB radiation. Together, these models define a gradient spanning physiological protection, impaired protection, and evolutionary adaptation to UVB stress. Using RNA-seq and protein-protein interaction networks, we show that transcriptomic responses differ markedly across this gradient. Wild-type and nacre zebrafish exhibited relatively limited transcriptomic changes (∼2%-2.4% of genes changing), whereas O. ascotanensis displayed a large-scale and highly coordinated response (∼21.6% of genes changing) characterized by functionally specialized networks enriched in DNA repair pathways. These differences involved not only transcriptomic magnitude but also marked reorganization of transcriptomic architecture. Integration with positive selection analyses revealed that positively selected genes were concentrated within highly interconnected regions of transcriptomic networks, consistent with adaptation involving network reorganization. Furthermore, ortholog-based analyses suggest that adaptive responses involve differential reorganization of a conserved functional background. Together, our results support a model in which adaptation to environmental stress is associated with the reorganization of conserved transcriptomic networks across physiological and evolutionary contexts, providing a systems-level perspective on the molecular basis of adaptation.

UVB radiation↗
PubMed1976

Effects of DDT in Fundulus: studies on toxicity, fate, and reproduction.

The toxicity, absorption, distribution, metabolism, and effects on reproduction of DDT was studied using the killifish (Fundulus heteroclitus), a species of economic importance because of its widespread abundance and its presence toward the lower end of the food chain. 14C-DDT was administered by exposure from the ambient water. There was a rapid removal of the radioactive pesticide from the water accompanied by uptake of radioactivity primarily by carcass (primarily muscle tissue) and eggs of the fish. Most (greater than 92%) of the radioactivity in the carcass was shown by TLC methods to be the parent pesticide. One day after a single 24-hr exposure to 14C-DDT, approximately 70% of the administered radioactivity was found in the carcass and the levels of the tissue decayed with a t 1/2 of three days. One day after a single 24-hr exposure to 0.1 ppm of 14C-DDT, the organs that contained the highest concentration of the pesticide (ca. 5 ppm) were intestine and liver. When the pesticide was administered by two 24-hr exposures from water, the intestine, liver and ovaries contained the major concentration of radioactivity (7 to 14 ppm). Untreated Fundulus contained less than 0.2 ppm of total DDT-like compounds. A variety of doses and schedules were tested in an effort to maximize the absorption of DDT, while minimizing the mortality to the fish. An intermittent schedule of 24 hr in 0.1 ppm DDT followed by 24 hr in DDT-free sea water, repeated two times, was found to be optimal. At the levels examined, DDT delayed the rate of normal development of fertilized eggs from Fundulus, but did not appear to cause any observable alterations in the hatched fry. Fertilization of Fundulus eggs was significantly diminished when insemination was carried out in DDT-containing sea water.

Animals↗
PubMed2025

Fins as a reliable surrogate tissue for age-related changes of telomeres and DNA methylation in gonads of a short-lived fish.

Senescence is a multifactorial and individualised process of age-related physiological decline. Cellular markers, such as telomere length and DNA methylation, can reveal subtle changes associated with chronological age or expected lifespan. In this study, we evaluated the utility of fin tissue as a surrogate for assessing telomere length and proportion of DNA methylation in the gonads of a small, short-lived laboratory fish, the turquoise killifish (Nothobranchius furzeri). We collected fin and gonadal tissues from both females and males at three different ages. We extracted DNA to measure telomere length via terminal restriction fragment (TRF) analysis and global DNA methylation levels using double-digest restriction-associated DNA sequencing (ddRADseq). Our results show a notable correspondence between telomere length and DNA methylation patterns in fin and gonadal tissues. These findings support the use of fin biopsies as a non-lethal method for assessing ageing biomarkers in the gonads of small freshwater fish.

Animals↗
PubMed1976

High-resolution autoradiography of 3H-ouabain binding in salt transporting epithelia.

The distribution of salt transporting sites in epithelia is a problem of special interest to electrolyte metabolism. Autoradiography of freeze-dried plastic embedded tissue was used to localize 3H-ouabain in rabbit small intestine and renal medulla and gills of killifish. Resolution approaching theoretical limits for tritium at the light microscope level was achieved. The results of several tests are presented which demonstrate the resolution of the method and the specificity of the observed ouabain binding patterns. A large uptake of ouabain was found along the basolateral membranes of the enterocyte, thick ascending tubules and chloride cells (fish gill).

Animals↗
PubMed2026

MKMC enables reference-free transcriptomic analysis using k-mer representations.

Traditional RNA-seq analysis depends heavily on genome alignment and gene annotation, limiting its utility in non-model organisms and introducing biases that can obscure regulatory complexity. We present MKMC (Multi-sample Kmer Counter), a scalable, reference-free toolkit for RNA-seq analysis that leverages k-mer-based statistics to detect biological variation without requiring alignment. MKMC integrates fast k-mer counting, abundance matrix generation, normalization, dimensionality reduction, and differential analysis into a unified workflow. Across diverse datasets, MKMC recapitulates key biological signals-including sex differences in killifish liver-and matches alignment-based pipelines in differential expression analysis and transcriptomic age prediction. Notably, MKMC detects isoform-specific events missed by traditional methods, one of which we validated using in situ hybridization. These results reveal previously hidden isoform-level regulatory events that contribute to sex- and age-associated transcriptional programs. MKMC offers a robust, extensible alternative to alignment-based approaches, enabling transcriptomic discovery across both model and non-model systems. While we focus here on RNA-seq as a primary application, MKMC is broadly applicable to any k-mer-based analysis of next-generation sequencing data.

MKMC↗
PubMed1979

Laboratory assessment of the molluscicidal activity of B-2, a new chemical against Oncomelania nosophora.

Laboratory trials of sodium 2.5 dichloro-4-bromophenol named B-2 for the molluscicidal effect against Oncomelania nasophora were carried out by Komiya's immersion technique. The values of LC50 of B-2 varied from 0.38 ppm to 0.54 ppm depending on the collection time of the snail. They were almost equal to those of NaPCP, but lower than those of Niclosamide. In the tests of toxicity to carp, rainbow trout and killifish, B-2 showed lower toxicity than NaPCP. Some aspects of mollusciciding application of the chemical were discussed.

Animals↗
PubMed1977

Organochlorine pesticide and polychlorinated biphenyl residues in selected fauna from a New Jersey salt marsh--1967 vs. 1973.

More than a half million pounds of DDT were applied to control mosquitoes in salt marsh estuaries of Cape May County, New Jersey, from 1946 to 1966. The use of DDT was discontinued in the County after 1966. In 1967, mean concentrations of DDT and metabolites ranged from 0.63 to 9.05 ppm in aquatic fauna, but by 1973 mean residue levels had decreased 84 to 99 percent among nine species. DDE was still present at reduced levels in nearly all samples in 1973, but other DDT isomers had mostly disappeared. Dieldrin was detected only in clapper rails, and residue levels decreased during the period. Mean concentrations of PCB's increased in the clapper rail, remained the same in the fiddler crab and mud snail, and decreased in the sheepshead minnow, mummichog, striped killifish, and salt marsh snail. Small amounts of mirex, toxaphene, cis-chlordane (and/or trans-nonachlor), oxychlordane, and HCB were detected in a few specimens.

Animal Population Groups↗
PubMed1977

Myxosoma funduli Kudo 1918 (Protozoa: Myxosporida) in Fundulus kansae: summer epizootiology.

The occurrence and distribution of the myxosporida Myxosoma funduli on the gills of the plains killifish (Fundulus kansae) were investigated; Fundulus kansae is reported as a new host. Host samples from various sites on the South Platte River, Nebraska, were collected during the summer months of 1975 and 1976. The protozoan parasite population was shown to be overdispersed within the host population, and this distribution was similar to that described by the negative binomial equation. Demographic characteristics of the infected fish subpopulation were virtually identical to those of the whole fish population. Infection intensity was independent of gill bar number or side. The frequency of bilateral infections was 0.54, of left only infections was 0.23, and of right only infections was 0.22. Distribution of immature and mature plasmodia indicated that a pre-existing infection did not preclude a new infection, and suggested a prepatent period of less than two months.

Animals↗