First record of a population of the exotic mummichog Fundulus heteroclitus (L., 1766) in the Mediterranean Sea basin (Ebro River delta)

Until now, mummichog Fundulus heteroclitus have been recorded only from the estuaries of the southernmost river basins of the Iberian Peninsula (Guadiana and Guadalquivir Rivers). Data reported here indicate the first record of F. heteroclitus in the Ebro River delta (north-east Spain), and hence also the first citation for F. heteroclitus as an invasive species present in any estuary of the Mediterranean Sea basin.     

Influence of egg size on embryos and larvae of Fundulus heteroclitus (L.)

Egg size for Fundulus heteroclitus (L.) populations is concordant with the distribution of the two F . heteroclitus subspecies, i.e. F. h. heteroclitus eggs are considerably larger than F. h. macrolepidotus eggs. The influence of egg size on survival of embryos during incubation and survival and growth of newly-hatched larvae was estimated for four populations representing both subspecies along the Atlantic coast of the United States and in Delaware Bay. Survival of embryos was determined for incubation periods of 14, 21 and 28 days. Greatest differences in survival were detected following the longest incubation period where less than 50 per cent of the smaller F. h. macrolepidotus eggs survived while little or no mortality was detected among the larger F. h. heteroclitus eggs . Influence of egg size on larval survival was also greatest among those larvae hatched after 28 days where F. h. macrolepidotus larvae survived without food, for an average of 6 days, while F. h. heteroclitus larvae survived 11–12 days. F. h. heteroclitus larvae were significantly larger at hatching than F. h. macrolepidotus larvae. Larval growth rates were the same (0.4 mm day⁻¹) in both subspecies. As a result, size differences at hatching were still maintained after 42 days of growth. The differences in egg size along with other morphological and reproductive characteristics of F. heteroclitus populations probably represent genetically based adaptations to environmental conditions, of which the length of the spawning season is one of the major components stimulating the coevolution of these traits.     

Environmental impact of mosquito pesticides: influence of temefos on the brain acetylcholinesterase of killifish.

Temefos and six of its metabolites were tested for their capacity to inhibit the in vitro activity of brain acetylcholinesterase (AChE) of Fundulus heteroclitus. While temefos was not inhibitory at levels up to 10.7 mM in brain homogenate samples, its metabolites were active within the range of 2 X 10(-4)mM to 1.26 mM in causing a 50% reduction in the enzyme activity. Exposure of F. heteroclitus to temefos under laboratory conditions caused a reduction in AChE activity, which was proportional to the pesticide concentration and the exposure period. Visible symptoms of organophosphate poisoning were apparent only after the AChE inhibition reached 80%. F. heteroclitus and Cyprinidon variegatus exposed to 10 biweekly applications of temefos granules in the field showed no inhibition of brain AChE. However, exposure of F. heteroclitus to biweekly applications (four) of temefos emulsion caused a reduction in the enzyme (50%), but only in the pre-third application samples. A gradual increase in brain AChE occurred both in F. heteroclitus and C. variegatus as the season progressed from April to October.     

Continuous laboratory production of fertile Fundulusheteroclitus (Walbaum) eggs lacking chorionic fibrils

A brood stock of Fundulus heteroclitus (Walbaum) minnows was established at theJohnson Space Center in Houston, Texas. By use of the aquarium maintenance systemdescribed in this report the fish were induced to produce fertile eggs throughout the year.Additional data is presented to confirm that F. heteroclitus found in the vicinity of Beaufort, North Carolina produce eggs which lack chorionic fibrils, making them especially suitablefor use in embryo development studies.     

Development of rhythmic melatonin secretion from the pineal gland of embryonic mummichog (Fundulus heteroclitus)

The pineal gland of vertebrates produces and secretes the hormone melatonin in response to changes in the light-dark cycle, with high production at night and low production during the day. Melatonin is thought to play an important role in synchronizing daily and/or seasonal physiological, behavioral, and developmental rhythms in vertebrates. In this study, the functional development of the pineal melatonin-generating system was examined in the mummichog, Fundulus heteroclitus, an euryhaline teleost. In this species, the pineal gland contains an endogenous oscillator, ultimately responsible for timing the melatonin rhythm. Oocytes from gravid females were collected and fertilized in vitro from sperm collected from mature males. Skull caps containing attached pineal glands were obtained from F. heteroclitus embryos at different embryonic stages and placed in static or perfusion culture under various photoperiodic regimes. Rhythmic melatonin secretion from pineal glands of embryonic F. heteroclitus embryos exposed to a 12L:12D cycle in static culture was observed at five days post-fertilization. The ontogeny of circadian-controlled melatonin production from F. heteroclitus pineal glands exposed to constant darkness for five days was also seen at day five post-fertilization. These data show that early development of the pineal melatonin-generating system in this teleost occurs prior to hatching. Pre-hatching development of the melatonin-generating system may confer some selective advantage in this species in its interactions with the environment.     

Karyotypic analysis of 2 sympatric species of fish, Fundulus heteroclitus L. and F. majalis

A chromosome study was performed on 2 sympatric species of marine fish, Fundulus heteroclitus L. and F. majalis . A modification of techniques which included the combination of the procedures of McPhail & Jones (1966) with those more recently developed by Ohnuki (1968), for demonstrating the spiral structure of cultured human leukocytes, resulted in clear and distinct chromosome spreads from gill epithelial cells of these 2 species. Optimum chromosome spreading and accumulation of metaphase figures resulted when specimens of F. heteroclitus received either a 0·28 ml or a 0·4 ml injection of a 0·1 % colcemid solution for 45 h and 48 h respectively. Best results in F. majalis occurred when specimens received a 0·1 ml dose of the 0·1 % colcemid solution for 22 1/2 h. Studies of the karyotypes of 18 specimens of F. heteroclitus and 9 specimens of F. majalis indicated that the 2 N chromosome number for each species was 48.     

Increased prevalence of larval Eustronglylides (Nematoda) in the mummichog, Fundulus heteroclitus (L.), from the discharge canal of a power plant in the Chesapeake Bay

The prevalence of larval Eustrongylides sp. in the mummichog, Fundulus heteroclitus , was compared for two populations, one in the vicinity of the intake and one in the discharge canal of a power plant at Chalk Point on the Patuxent River, Maryland. The parasite was four times as prevalent in female F. heteroclitus collected from the discharge canal as in those collected from the intake area. Almost all infected fish were 70 mm or greater in total length. The larvae occurred in capsules and free in the mesentery, or associated with the gut, liver, or gonad of the host; multiple infections were common. Infection by Eustrongylides resulted in pronounced negative effects on F. heteroclitus . The dry weight of somatic tissue was reduced 5% and ovary dry weight was reduced 50% in infected individuals, compared to uninfected individuals of the same length. The proportion of infected females carrying ripe eggs during the breeding season was less than half the value for uninfected females. It is hypothesized that the greater prevalence of the parasite in the discharge canal results from increased abundances of oligochaetes (suspected first intermediate hosts of the parasite), presumably as a consequence of elevated temperatures and organic enrichment from the power plant.     

Microsatellite analysis of the phylogeography, Pleistocene history and secondary contact hypotheses for the killifish, Fundulus heteroclitus

The mummichog, Fundulus heteroclitus, exhibits extensive latitudinal clinal variation in a number of physiological and biochemical traits, coupled with phylogeographical patterns at mitochondrial and nuclear DNA loci that suggest a complicated history of spatially variable selection and secondary intergradation. This species continues to serve as a model for understanding local and regional adaptation to variable environments. Resolving the influences of historical processes on the distribution of genetic variation within and among extant populations of F. heteroclitus is crucial to a better understanding of how populations evolve in the context of contemporary environments. In this study, we analysed geographical patterns of genetic variation at eight microsatellite loci among 15 populations of F. heteroclitus distributed throughout the North American range of the species from Nova Scotia to Georgia. Genetic variation in Northern populations was lower than in Southern populations and was strongly correlated with latitude throughout the species range. The most common Northern alleles at all eight loci exhibited concordant latitudinal clinal patterns, and the existence of an abrupt transition zone in allele frequencies between Northern and Southern populations was similar to that observed for mitochondrial DNA and allozyme loci. A significant pattern of isolation by distance was observed both within and between northern and southern regions. This pattern was unexpected, particularly for northern populations, given the recent colonization history of post-Pleistocene habitats, and was inconsistent with either a recent northward population expansion or a geographically restricted northern Pleistocene refugium. The data provided no evidence for recent population bottlenecks, and estimates of historical effective population sizes suggest that post-Pleistocene populations have been large throughout the species distribution. These results suggest that F. heteroclitus was broadly distributed throughout most of its current range during the last glacial event and that the abrupt transition in allele frequencies that separate Northern and Southern populations may reflect regional disequilibrium conditions associated with the post-Pleistocene colonization history of habitats in that region.     

Use of multiple endpoints to assess the impact of captivity on gut flora diversity in Long Island Sound Fundulus heteroclitus

Environmental Biology of Fishes - We evaluated the impact of short-term captive housing on gut flora diversity in Fundulus heteroclitus by characterizing culturable gut bacteria immediately after...     

Evidence from mtDNA RFLP analysis for the introduction of Fundulus heteroclitus to southwestern Spain

Restriction analysis of mitochondrial DNA confirmed the taxonomic status of a southwestern Iberian Peninsula population of Fundulus heteroclitus and its probable origin in North America.     

The effects of hypophysectomy on the retinomotor responses of the killifish, Fundulus heteroclitus

This paper presents the results of an investigation concerned with the effects of long-term hypophysectomy on the retinomotor responses of the euryhaline killifish, Fundulus heteroclitus: 1. The eye of hypophysectomised Fundulus heteroclitus responds to light and dark in the same manner as that of intact controls: the retina is not in a state of permanent light-adaptation as claimed by Vilter (1942) for the hypophysectomised eel. 2. There is no evidence of a persistent circadian rhythm during continous darkness. 3. Unilateral illumination of the eye of intact fish results in dispersion of retinal pigment in both illuminated and unilluminated eyes, as in the goldfish (Ali, 1964), but no such contralateral response was evident after hypophysectomy. The cones are unresponsive.     

Allosteric modifiers of fish hemoglobins: in vitro and in vivo studies of the effect of ambient oxygen and pH on erythrocyte ATP concentrations.

Fundulus heteroclitus decreases erythrocyte adenosine triphosphate and increases blood hematocrit when acclimated to hypoxic conditions. A defined medium has been developed which allows isolated F. heteroclitus erythrocytes to be maintained for several hours without an appreciable loss of cellular ATP. The effect of oxygen tension, pH and metabolic inhibitors on the cellular concentration of ATP of fish red cells has been investigated as an in vitro model to explain in vivo responses to environmental changes. The isolated red cells significantly decrease their ATP/Hb molar ratio when exposed either to anaerobiosis or metabolic inhibitors. It is concluded that the in vivo response is mediated at the red cell level via decreased oxidative phosphorylation in the presence of low environmental oxygen. The length of time necessary to elicit the responce both in vivo and in vitro is also discussed.     

Copper uptake by two sympatric species of Killifish Fundulus heteroclitus (L.) and F. majalis (Walbaum)

Differential copper uptake within brain, visceral, gill, somatic and residual tissue was examined in the two sympatric species of killifishes Fundulus heteroclitus and F. majalis . Various salinities and copper concentrations were tested on both juvenile and adult stages to examine their effects on copper uptake. Salinity played a significant role in copper uptake in both species of killifishes. However, the effect of salinity was specific for each species and life history stage. Copper content of various tissues was directly related to the uptake pattern exhibited by whole adult fishes. Fundulus majalis brain tissue and F. heteroclitus muscle tissue were exceptions. Severe body lesions and subcutaneous haemorrhaging were observed after 2–3 day exposure to both 2 and 8 ppm copper.     

The effects of species manipulation on growth and survival of an assemblage of juvenile estuarine fish

Growth and survival of Cyprinodon variegatus, Fundulus heteroclitus, Menidia beryllina , and Lucania parva , held in combination with an omnivorous grass shrimp– Palaemonetes pugio , and a predatory diving beetle Tropisternus lateralis , were measured at 12–60% in outdoor static microcosms that simulate salt marsh ponds. We predicted that the low species richness of this abiotically harsh but highly productive habitat would lead to a high degree of interaction among species. The presence of the beetle had no effect on the fish or the shrimp. Removal of the shrimp similarly had no detectable effect on the fish. There was a trend in proportions of survival among three fish: C. variegatus>F. heteroclitus>M. beryllina . Survival of M. beryllina was greater when it was alone at low densities of its own species (333 v. 667 fish m ⁻³), and less when it was paired with F. heteroclitus . Interactions with other species diminished the growth of M. beryllina . Survival of F. heteroclitus was greater when it was alone at low density (333 m ⁻³), than when the same number were placed together with Menidia and Cyprinodon at a total fish density of 999 m ⁻³. There were no effects of removal of other species on survival or growth of C. variegatus at either 12'5 or 24%. This study showed that a complex array of interactions occurred among six common members of a salt marsh food web, but the degree of interaction Was less than We predicted.     

Further consideration of phenobarbital effects on cytochrome P-450 activity in the killifish, Fundulus heteroclitus

1. Ethoxyresorufin O-deethylase (EROD) activity, aldrin epoxidase (AE) activity, cytochrome P-450 content, and levels of cytochrome P-450E (the major BNF-inducible P-450 form and primary EROD catalyst in scup) or its homologues were measured in hepatic microsomes isolated from Fundulus heteroclitus, scup (Stenotomus chrysops) and brook trout (Salvelinus fontinalis) treated with beta-naphthoflavone (BNF) or phenobarbital (PB). 2. In all three teleost species, BNF treatment caused expected increases in P-450 content, EROD activity and P-450E level; but either no change or a slight decrease in AE turnover rate (nmol/min/nmol P-450). 3. Polyclonal antibodies to P-450E did not inhibit AE activity in microsomes from BNF-treated scup, confirming that this major BNF-inducible P-450 form does not catalyze AE activity in fish. 4. In contrast, PB treatment did not affect hepatic AE activity, P-450 content or levels of "P-450E" in F. heteroclitus, but did variably affect EROD activity which was suppressed in one experiment and elevated in another. 5. The results indicate that (i) contrary to previous reports, neither PB nor MC-type inducers increase AE activity in F. heteroclitus, (ii) MC-type inducers do not affect AE activity in the other teleost species examined, and (iii) AE activity is not a reliable indicator of P-450 induction by environmental chemicals. 6. We emphasize the need to establish the mechanism of PB action, and the nature of any fish P-450 forms analogous to PB-inducible forms in mammals in order to conclusively evaluate PB-responses in fish.     

Diversity and distribution of gynogenetic hybrids between Fundulus diaphanus and Fundulus heteroclitus in Porter's Lake (Nova Scotia) in relation to salinity

Unisexual hybrids between Fundulus diaphanus and Fundulus heteroclitus were found in low proportions at intermediate salinity in Porter's Lake, Nova Scotia. One clone accounted for 72% of the hybrids, with most other hybrids being different at a single microsatellite allele. This clone thrives over a wide range of salinities, suggesting a general-purpose genotype.     

Nucleotide sequence of the 18S ribosomal ribonucleic acid gene from two teleosts and two sharks and their molecular phylogeny.

The 18S rRNA sequence was determined for two teleostean fish species, Fundulus heteroclitus and Sebastolobus altivelis, and two sharks, Squalus acanthias and Echinorhinus cookei. To study the molecular phylogeny of these taxa, the sequences were compared with 18S rRNA sequences of the Coelacanth Latimeria chalumnae, the frog Xenopus laevis, and humans. Maximum parsimony analysis of the sequences resulted in a single most parsimonious tree that is in agreement with the expected phylogeny. The correct phylogenetic tree was also found when using S. altivelis alone as the teleost representative. In contrast, the most parsimonious tree found by using F. heteroclitus as the teleost representative presented anomalous groupings (the teleost branch being grouped with humans), matching results previously obtained. However, a bootstrap analysis showed that some branches containing anomalous relationships were not significantly supported. An explanation for this peculiarity, the differences between our tree and previously identified ones, and their phylogenetic implications are discussed.     

Oogenesis in Fundulus heteroclitus. VI. Establishment and verification of conditions for vitellogenin incorporation by oocytes in vitro

A procedure was developed for studying vitellogenin (VTG) incorporation by vitellogenic oocytes of Fundulus heteroclitus in vitro. Since homologous VTG can be obtained from this animal only with great difficulty, the use of [32P]VTG from Xenopus laevis was explored as an alternative. Vitellogenic as well as maturational-stage oocytes were found to sequester X. laevis [32P]VTG from the medium, and incorporation was found to be linear with time for at least up to 12 hr. Once incorporated into the oocyte, [32P]VTG did not appear to undergo turnover. The effect of different [32P]VTG concentrations on incorporation indicated that the uptake mechanism was saturable. Unlabeled F. heteroclitus VTG and X. laevis VTG were also found to compete effectively with X. laevis [32P]VTG, whereas bovine serum albumin did not. These results represent the first documentation of a successful culture system for receptor-mediated VTG incorporation by teleost oocytes.     

Temporal dynamics in growth and white skeletal muscle composition of the mummichog Fundulus heteroclitus during chronic hypoxia and hyperoxia

Specific growth rate (G(S) ) and white skeletal muscle composition were measured in the mummichog Fundulus heteroclitus over a period of 28 days at four levels of dissolved oxygen (DO): severe hypoxia (c. 1.2 mg O(2) l(-1) ), moderate hypoxia (3.0 mg O(2) l(-1) ), normoxia (7.1 mg O(2) l(-1) ) and hyperoxia (10.6 mg O(2) l(-1) ). The G(S) was calculated over 0-8, 0-14, 0-28 and 14-28 days, and muscle protein, lactate dehydrogenase (LDH), DNA, RNA and water were measured at 0, 8, 14 and 28 days. Exposure of fish to severe hypoxia was associated with significantly reduced G(S) , lower muscle protein content and lower RNA:DNA compared with other DO treatments. When calculated over the first and second half of the 28 day exposure, however, G(S) of fish in severe hypoxia increased significantly during the second two-week interval, to the same rate as that of normoxic fish. Muscle LDH activity and water content were not significantly affected by DO level. Neither moderate hypoxia nor hyperoxia significantly affected G(S) or any biochemical variable. The results demonstrate that F. heteroclitus can tolerate wide variation in ambient oxygen concentration and, during prolonged exposure to severe hypoxia, shows significant compensation for the initial negative effects on growth. The capacity of F. heteroclitus to grow over a wide range of DO probably contributes to its ability to exploit habitats characterized by marked variation in oxygen availability.