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In this study, we compared the efficacy of geometric morphometric techniques, including outlines and landmark-based approaches, to support the differentiation of Trichodina bellottii from three co-occurring killifish species. Both methods were able to differentiate trichodinids from different host species. However, discriminat analyses and MANOVA results based on landmarks had greater accuracy possibly because these analyses only provide information on certain points defined by the researcher, while the analyses based on outlines take into account points with less taxonomic information., (© 2024. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Some parasites manipulate their host's phenotype to enhance predation rates by the next host in the parasite's life cycle. Our understanding of this parasite-increased trophic transmission is often stymied by study-design challenges. A recurring difficulty has been obtaining uninfected hosts with a coevolutionary history with the parasites, and conducting experimental infections that mimic natural processes. In 1996, Lafferty and Morris provided what has become a classic example of parasite-increased trophic transmission; they reported a positive association between the intensity of a brain-infecting trematode (Euhaplorchis californiensis) in naturally infected California killifish (Fundulus parvipinnis) and the frequency of conspicuous behaviors, which was thought to explain the documented 10-30× increase in predation by the final host birds. Here, we address the primary gap in that study by using experimental infections to assess the causality of E. californiensis infection for increased conspicuous behaviors in F. parvipinnis. We hatched and reared uninfected F. parvipinnis from a population co-occurring with E. californiensis, and infected them 1-2 times/week over half their life span with E. californiensis and a small cyathocotylid trematode (SMCY) that targets the host's muscle tissue. At 3 time points throughout the hosts' lives, we quantified several conspicuous behaviors: contorting, darting, scratching, surfacing, and vertical positioning relative to the water's surface. Euhaplorchis californiensis and SMCY infection caused 1.8- and 2.5-fold overall increases in conspicuous behaviors, respectively. Each parasite was also associated with increases in specific conspicuous behaviors, particularly 1.9- and 1.4-fold more darting. These experimental findings help solidify E. californiensis-F. parvipinnis as a classic example of behavioral manipulation. Yet our findings for E. californiensis infection-induced behavioral change were less consistent and strong than those previously documented. We discuss potential explanations for this discrepancy, particularly the idea that behavioral manipulation may be most apparent when fish are actively attacked by predators. Our findings concerning the other studied trematode species, SMCY, highlight that trophically transmitted parasites infecting various host tissues are known to be associated with conspicuous behaviors, reinforcing calls for research examining how communities of trophically transmitted parasites influence host behavior., (© American Society of Parasitologists 2023.)

Modulation of brain serotonin (5-HT) signalling is associated with parasite-induced changes in host behaviour, potentially increasing parasite transmission to predatory final hosts. Such alterations could have substantial impact on host physiology and behaviour, as 5-HT serves multiple roles in neuroendocrine regulation. These effects, however, remain insufficiently understood, as parasites have been associated with both increased and decreased serotonergic activity. Here, we investigated effects of trematode Euhaplorchis californiensis metacercariae on post-stress serotonergic activity in the intermediate host California killifish ( Fundulus parvipinnis ). This parasite is associated with conspicuous behaviour and increased predation of killifish by avian end-hosts, as well as inhibition of post-stress raphe 5-HT activity. Until now, laboratory studies have only been able to achieve parasite densities (parasites/unit host body mass) well below those occurring in nature. Using laboratory infections yielding ecologically relevant parasite loads, we show that serotonergic activity indeed decreased with increasing parasite density, an association likely indicating changes in 5-HT neurotransmission while available transmitter stores remain constant. Contrary to most observations in the literature, 5-HT activity increased with body mass in infected fish, indicating that relationships between parasite load and body mass may in many cases be a real underlying factor for physiological correlates of body size. Our results suggest that parasites are capable of influencing brain serotonergic activity, which could have far-reaching effects beyond the neurophysiological parameters investigated here., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2020. Published by The Company of Biologists Ltd.)

Some parasite species alter the behavior of intermediate hosts to promote transmission to the next host in the parasite's life cycle. This is the case for Euhaplorchis californiensis , a brain-encysting trematode parasite that causes behavioral changes in the California killifish ( Fundulus parvipinnis ). These manipulations increase predation by the parasite's final host, piscivorous marsh birds. The mechanisms by which E. californiensis achieves this manipulation remain poorly understood. As E. californiensis cysts reside on the surface of the killifish's brain, discerning regional differences in parasite distribution could indicate mechanisms for host control. In this study, we developed a method for repeated experimental infections. In addition, we measured brain-region specific density using a novel methodology to locate and quantify parasite infection. We show that E. californiensis cysts are non-randomly distributed on the fish brain, aggregating on the diencephalon/mesencephalon region (a brain area involved in controlling reproduction and stress coping) and the rhombencephalon (an area involved in controlling locomotion and basal physiology). Determining causal mechanisms behind this pattern of localization will guide future research examining the neurological mechanisms of parasite-induced host manipulation. These findings suggest that parasites are likely targeting the reproductive, monoaminergic, and locomotor systems to achieve host behavioral manipulation.

This study examined the relationship between urbanization and parasite community structure in the estuarine fish, Fundulus heteroclitus. We measured landscape and physicochemical factors associated with urbanization at 6 sites from 4 collection periods. Concurrently, we quantified the metazoan parasite community in F. heteroclitus collected at those sites, with 105 fish studied per site during the 4 collection periods. Parasite community composition differed among sites. Host size was the most important variable for direct life-cycle parasite assemblages and indirect life-cycle parasites at the individual fish level, while landscape and physicochemical factors determined the structure of indirect life-cycle parasite assemblages at the population scale. Variation in the prevalence and intensity of infection of two indirect life-cycle parasites, Lasiocotus minutus and Glossocercus caribaensis, were the primary parasites that drove differences across sites. Variation in the presence/absence of these indirect life-cycle parasite species was associated with sediment Ni concentrations, patch density, and marsh size. Our data support the hypothesis that urbanization, acting at both landscape and physicochemical scales, can have a significant impact on parasite community structure. This, however, varied by parasite life history: there was little effect of urbanization on the prevalence and intensity of direct life-cycle parasites, but significant variation was detected for indirect life-cycle parasites. This study demonstrates how anthropogenically driven landscape change influences fine-scale population dynamics of parasites., Competing Interests: The authors have declared that no competing interests exist.

Parasites often use external cues to identify and move toward environments where they are likely to encounter suitable hosts. The trematode parasite Euhaplorchis californiensis produces cercariae that emerge from California horn snails ( Cerithideopsis californica [= Cerithidea californica]) to infect California killifish ( Fundulus parvipinnis) as second intermediate hosts. Based upon work on a congeneric Euhaplorchis species from Florida, and based on the ecology of its killifish host, we hypothesized that E. californiensis cercariae in southern California estuaries are positively phototactic and negatively geotactic, using both sunlight and gravity to guide their movement to the upper water column. To distinguish positive phototaxis from negative geotaxis, we first quantified E. californiensis movement in response to light along a horizontal plane and determined they were positively phototactic. In a second experiment, we quantified E. californiensis movement along a vertical plane in response to an overhead light, a light from below, or no light. We found that E. californiensis exhibit negative geotaxis in the absence of light, but will swim in the direction of gravity to move toward a light source from below. Thus, E. californiensis are both positively phototactic and negatively geotactic, but cercariae prioritize phototactic cues. These results suggest that E. californiensis cercariae aggregate in the open water, indicating that the pelagic zone represents an area of high infection risk for California killifish hosts.

Two species of digeneans belonging in Homalometron are described from Nearctic freshwater fundulid fishes: Homalometron robisoni n. sp. is described from the Blackstripe Topminnow, Fundulus notatus, from Oklahoma and Homalometron frocioneae n. sp. is described from the Banded Killifish, Fundulus diaphanus, from New York. Homalometron robisoni n. sp. differs from all congeners by having vitelline follicles that extend into the forebody, a feature that necessitates altering the generic diagnosis for the genus. Homalometron frocioneae n. sp. may be distinguished from North and Middle American congeners by the position of the intestinal bifurcation (relatively more posterior in the forebody than in other species) and tegumental spine coverage on the body (spines are absent from the posterior body extremity and on most of the dorsal surface). Comparison of ribosomal DNA (ITS 1 and 2 regions, 5.8S gene, and partial fragment of 28S gene) from the 2 new species and some congeners from the Western Hemisphere provided evidence for the validity of the 2 new species and affirmed a close relationship between H. robisoni n. sp. and Homalometron pallidum. Comparison of ribosomal DNA from newly collected Homalometron spp. and larval stages of an apocreadiid from brackish water hydrobiid snails (cercariae in rediae in Littoridinops palustris and metacercariae in L. palustris and Amnicola limosa ) from a tidal river in Mississippi revealed that larval stages represented Homalometron cupuloris. A phylogeny based on Bayesian inference analysis using partial 28S rDNA gene fragments from 14 species of Homalometron (all from the Western Hemisphere) and 1 megaperine and rooted by a second megaperine was conducted and produced a strongly supported phylogram that estimates the interrelationships among species. The estimated phylogeny suggests that ecological factors such as salinity and food web interactions between species of Homalometron, intermediate hosts, and fishes drive coevolutionary forces influencing speciation within Homalometron.

In coastal waters, pesticides and parasites are widespread stressors that may separately and interactively affect the physiology, behavior, and survival of resident organisms. We investigated the effects of the organophosphate pesticide chlorpyrifos and the trematode parasite Euhaplorchis californiensis on three important traits of California killifish (Fundulus parvipinnis): neurotransmitter activity, release of the stress hormone cortisol, and behavior. Killifish were collected from a population without E. californiensis, and then half of the fish were experimentally infected. Following a 30 day period for parasite maturation, infected and uninfected groups were exposed to four concentrations of chlorpyrifos (solvent control, 1-3ppb) prior to behavior trials to quantify activity, feeding behavior, and anti-predator responses. Water-borne cortisol release rates were measured non-invasively from each fish prior to infection, one-month post-infection, and following pesticide exposure. Killifish exposed to 3ppb chlorpyrifos exhibited a 74.6±6.8% and 60.5±8.3% reduction in brain and muscle acetylcholinesterase (AChE) activity relative to controls. The rate of cortisol release was suppressed by each chlorpyrifos level relative to controls. Killifish exposed to the medium (2ppb) and high (3ppb) pesticide concentrations exhibited reduced activity and a decrease in mean swimming speed following a simulated predator attack. Muscle AChE was positively related to swimming activity while brain AChE was positively related to foraging behavior. ​No effects of the parasite were observed, possibly because of low metacercariae densities achieved through controlled infections. We found that sublethal pesticide exposure has the potential to modify several organismal endpoints with consequences for reduced fitness, including neurological, endocrine, and behavioral responses in an ecologically abundant fish., (Copyright © 2015 Elsevier B.V. All rights reserved.)

For trophically transmitted parasites that manipulate the phenotype of their hosts, whether the parasites do or do not experience resource competition depends on such factors as the size of the parasites relative to their hosts, the intensity of infection, the extent to which parasites share the cost of defending against the host's immune system or manipulating their host, and the extent to which parasites share transmission goals. Despite theoretical expectations for situations in which either no, or positive, or negative density-dependence should be observed, most studies document only negative density-dependence for trophically transmitted parasites. However, this trend may be an artifact of most studies having focused on systems in which parasites are large relative to their hosts. Yet, systems are common where parasites are small relative to their hosts, and these trophically transmitted parasites may be less likely to experience resource limitation. We looked for signs of density-dependence in Euhaplorchis californiensis (EUHA) and Renicola buchanani (RENB), two manipulative trematode parasites infecting wild-caught California killifish (Fundulus parvipinnis). These parasites are small relative to killifish (suggesting resources are not limiting), and are associated with changes in killifish behavior that are dependent on parasite-intensity and that increase predation rates by the parasites' shared final host (indicating the possibility for cost sharing). We did not observe negative density-dependence in either species, indicating that resources are not limiting. In fact, observed patterns indicate possible mild positive density-dependence for EUHA. Although experimental confirmation is required, our findings suggest that some behavior-manipulating parasites suffer no reduction in size, and may even benefit when "crowded" by conspecifics., (© The Author 2014. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oup.com.)

This study examined the relationship between the metazoan parasite community in a focal species, Fundulus heteroclitus , and the species richness of the free-living community. Four distinct salt marsh areas were selected in order to reflect a gradient in free-living species richness and time post-restoration (unrestored, 0, 10, and 20 yr post-restoration). A total of 960 fish was studied, with 30 collected per site in each of 8 consecutive seasons between 2005 and 2007. Species richness and abundance of birds, fish, and benthic macroinvertebrates varied significantly between sites. However, increasing richness in the free-living community was neither positively nor negatively correlated with richness in the parasite infracommunity in F. heteroclitus . These results demonstrate that the relationship between community species richness and parasite richness is not linear. The data suggest that the diversity of parasites may be more correlated with measures of community composition, such as the structure and cohesiveness of the food web, rather than with prevailing measures of biodiversity.

Homalometron palmeri n. sp. is described and reported from the following fishes in the northern Gulf of Mexico: Micropogonias undulatus, Sciaenops ocellatus, Bairdiella chrysoura, Pogonias cromis, Fundulus grandis, Fundulus similis, and Eucinostomus argenteus. This species historically has been misidentified as Homalometron pallidum by some, and treated as Homalometron sp. by others. The new species differs from H. manteri by having a smaller body size, relatively longer postcecal space ranging from 7 to 15% of body length compared with 6-8%, body spines from 12 to 17 μm long compared with 15-20 μm, and an oral-to-ventral sucker width ratio of 1:1.2-1.3 compared with 1:1.3-1.5. Ribosomal DNA sequences from H. palmeri n. sp., H. pallidum, Homalometron manteri, and Homalometron pseudopallidum are compared and the new species is found to be most similar to H. manteri, a sympatric species. Comparison between 2 mitochondrial genes from H. palmeri n. sp. and H. manteri provided further evidence for their status as distinct species. Pairwise comparison of 503 aligned bases from ND1 gene revealed 33 variable sites (6.5%) between the 2 species. Pairwise comparison of 1,152 aligned bases from COI gene revealed 73 variable sites (6.3%) between the 2 species. Interspecific variability in mitochondrial sequences between the 2 species was 3-16 times greater than intraspecific variability in either species.

This paper presents novel evidence to address mechanisms by which trematode parasites effect behavioural changes in naturally infected fish hosts. California killifish Fundulus parvipinnis infected with the brain-encysting trematode Euhaplorchis californiensis display conspicuous swimming behaviours that render them 30 times more likely to be eaten by birds, the parasite's final host. Prevalence of E. californiensis reaches nearly 100% in most F. parvipinnis populations, with parasite biomass constituting almost 2% of F. parvipinnis biomass in some locations. Despite having thousands of cysts on their brains, infected fish grow and mature at rates comparable to those of uninfected populations. The lack of general pathology combined with the specificity of the altered behaviours suggests that the behavioural changes are due to parasite manipulation. The monoamine neurotransmitters serotonin and dopamine, which control locomotion and social behaviour in fishes and other vertebrates, were examined to explore the underlying mechanisms of this behaviour modification. Whereas previous studies were similarly conducted with experimentally infected fish, in this study, brain dopaminergic and serotonergic activity were analysed in naturally infected fish to assess how E. californiensis may alter F. parvipinnis monoamines in a naturally occurring system. A parasite density-associated decrease in serotonergic activity occurred in the hippocampus of naturally infected fish, as well as a decrease in dopaminergic activity in the raphe nuclei, suggesting that E. californiensis inhibits serotonin and dopamine signaling in naturally infected F. parvipinnis. The neurochemical profile of infected fish is consistent with the hypothesis that E. californiensis affects brain monoaminergic systems in order to induce impulse-driven, active, and aggressive behaviour in its hosts., (© 2012 The Authors. Journal of Fish Biology © 2012 The Fisheries Society of the British Isles.)

Some parasites modify the behavior of intermediate hosts to increase the probability of transmission to the next host in their life cycle. In habitats where this is common, parasites play an important role in predator-prey links and food web dynamics. In this study we used laboratory observations to investigate the behavior of longnose killifish, Fundulus similis, that were naturally infected with metacercariae of the trematode, Euhaplorchis sp. A, from Laguna Madre, south Texas. In particular, we examined whether there was a relationship between the number of metacercariae lodged on the brain of the infected fish and behaviors that made the fish more conspicuous to avian final hosts. We also quantified the abundance and cercariae production of this parasite in its first intermediate snail host, Cerithidea pliculosa , and examined the seasonal variation of Euhaplorchis sp. A in F. similis . Our data demonstrated that Euhaplorchis sp. A affected the surfacing behavior of F. similis in an intensity-dependent manner. Fish with many infections spent longer time at the surface of the water than fish with few infections. Our data also show that Euhaplorchis sp. A is a common parasite in the first intermediate host and produces close to 4,000 cercariae m(-2) day(-1). Consequently 97% of all fish collected and necropsied were infected, with little seasonal variation in the mean abundance of the parasite. Based on our data, Euhaplorchis sp. A is likely important to predator-prey links in Gulf of Mexico estuary food webs, similar to the closely related Euhaplorchis californiensis in southern California. We expect that other closely related species elsewhere may have similar effects on other fish hosts, emphasizing the need for incorporating trophically transmitted parasites in estuarine food web studies.

The infrequently reported allocreadiid digenean Creptotrema funduli Mueller, 1934 is documented from the blackstripe topminnow, Fundulus notatus (Cyprinodontiformes: Fundulidae), in the headwaters of the Biloxi River, Harrison County, Mississippi. Specimens from Mississippi were compared with the type material from Fundulus diaphanus menona from Oneida Lake, New York, and no substantial difference was found. A fragment of ribosomal DNA, comprising a short portion of the 3' end of 18S nuclear rDNA gene, internal transcribed spacer (ITS) genes (including ITS1, 5.8S, and ITS2), and the 5' end of the 28S gene including variable domains D1-D3 was sequenced for the species. A portion of the 28S rDNA gene from C. funduli, plus similar fragments from 8 other allocreadiids and the callodistomatid Prosthenhystera sp., were aligned and subjected to maximum likelihood and Bayesian inference analyses. Resulting phylogenetic trees were derived from the analyses and used to estimate the relationship of Creptotrema Travassos, Artigas, and Pereira, 1928 with other allocreadiids. Creptotrema was found to be closely related to Megalogonia Surber, 1928 and 3 Neotropical genera, i.e., Wallinia Pearse, 1920, Creptotrematina Yamaguti, 1954, and Auriculostoma Scholz, Aguirre-Macedo, and Choudhury, 2004. No molecular data were available for species in Creptotrema prior to this study, so the ITS1, 5.8S, and ITS2 genes have been made available for comparative studies involving neotropical species in the genus.

Roads, bridges, and dikes constructed across salt marshes can restrict tidal flow, degrade habitat quality for nekton, and facilitate invasion by non-native plants including Phragmites australis. Introduced P. australis contributes to marsh accretion and eliminates marsh surface pools thereby adversely affecting fish by reducing access to intertidal habitats essential for feeding, reproduction, and refuge. Our study assessed the condition of resident fish populations (Fundulus heteroclitus) at four tidally restricted and four tidally restored marshes in New England invaded by P. australis relative to adjacent reference salt marshes. We used physiological and morphological indicators of fish condition, including proximate body composition (% lipid, % lean dry, % water), recent daily growth rate, age class distributions, parasite prevalence, female gravidity status, length-weight regressions, and a common morphological indicator (Fulton's K) to assess impacts to fish health. We detected a significant increase in the quantity of parasites infecting fish in tidally restricted marshes but not in those where tidal flow was restored to reduce P. australis cover. Using fish length as a covariate, we found that unparasitized, non-gravid F. heteroclitus in tidally restricted marshes had significantly reduced lipid reserves and increased lean dry (structural) mass relative to fish residing in reference marshes. Fish in tidally restored marshes were equivalent across all metrics relative to those in reference marshes indicating that habitat quality was restored via increased tidal flushing. Reference marshes adjacent to tidally restored sites contained the highest abundance of young fish (ages 0-1) while tidally restricted marshes contained the lowest. Results indicate that F. heteroclitus residing in physically and hydrologically altered marshes are at a disadvantage relative to fish in reference marshes but the effects can be reversed through ecological restoration.

We describe the distribution and abundance of the brain-encysting trematode Euhaplorchis californiensis and its second intermediate host, the California killifish (Fundulus parvipinnis), in 3 estuaries in southern California and Baja California. We quantified the density of fish and metacercariae at 13-14 sites per estuary and dissected 375 killifish. Density (numbers and biomass) was examined at 3 spatial scales, i.e., small replicate sites, habitats, and entire estuaries. At those same scales, factors that might influence metacercaria prevalence, abundance, and aggregation in host individuals and populations were also examined. Metacercaria prevalence was 94-100% among the estuaries. Most fish were infected with 100s to 1,000s of E. californiensis metacercariae, with mean abundance generally increasing with host size. Although body condition of fish did not vary among sites or estuaries, the abundance of metacercariae varied significantly among sites, habitats, estuaries, and substantially with host size and gender. Metacercariae were modestly aggregated in killifish (k > 1), with aggregation decreasing in larger hosts. Across the 3 estuaries, the total populations of killifish ranged from 9,000-12,000 individuals/ha and from 7-43 kg/ha. The component populations of E. californiensis metacercariae ranged from 78-200 million individuals/ha and from 0.1-0.3 kg/ha. Biomass of E. californiensis metacercariae constituted 0.5-1.7% of the killifish biomass in the estuaries. Our findings, in conjunction with previously documented effects of E. californiensis, suggest a strong influence of this parasite on the size, distribution, biomass, and abundance of its killifish host.

The presence or absence of parasites within host populations is the result of a complex of factors, both biotic and abiotic. This study uses a non-parametric classification tree approach to evaluate the relative importance of key abiotic and biotic drivers controlling the presence/absence of parasites with complex life cycles in a sentinel, the common killifish Fundulus heteroclitus. Parasite communities were classified from 480 individuals representing 15 fish from 4 distinct marsh sites in each of 4 consecutive seasons between 2006 and 2007. Abiotic parameters were recorded at continuous water monitoring stations located at each of the 4 sites. Classification trees identified the presence of benthic invertebrate species (Gammarus sp. and Littorina sp.) as the most important variables in determining parasite presence: secondary splitters were dominated by abiotic variables including conductance, pH and temperature. Seventy percent of hosts were successfully classified into the correct category (infected/uninfected) based on only these criteria. The presence of competent definitive hosts was not considered to be an important explanatory variable. These data suggest that the most important determinant of the presence of these parasite populations in the common killifish is the availability of diverse communities of benthic invertebrates.

Fundulotrema porterensis n. sp. (Monogenea: Gyrodactylidae) is described from the mummichog, Fundulus heteroclitus (L.; Cyprinodontidae), inhabiting Porters Lake, Nova Scotia, Canada. The new parasite species is characterized by having a ventral bar with small anterolateral processes and linguiform membrane, differentiating it from all other known species of Fundulotrema. The morphological description of F. porterensis is supplemented with 1011 sequenced base pairs (bp) of ribosomal DNA (rDNA) spanning both internal transcribed spacers (ITS-1 and ITS-2) and 5.8S regions of the genome. A BLAST (basic local alignment search tool) search revealed that the 5.8S (157 bp) region varied by 1 bp from Gyrodactylus turnbulli Harris, 1986 and G. pictae Cable, Oosterhout, Barson and Harris, 2005, which also infect cyprinodontids. Morphometrically, F. porterensis most closely resembles Fundulotremafoxi (Rawson, 1973), but the 2 species are easily separated by length of hamuli (50.7 vs. 42.2 microm, respectively), length of anterolateral process of the ventral bar (4.9 vs. 8.9 microm), shape of marginal hooks, and shape of the ventral bar membrane. A morphological and molecular supplemental diagnosis of Gyrodactylus stephanus Mueller, 1937, from the mummichog, is also presented. This new material provides previously unrecorded information on the attributes of the ventral bar, marginal hooks, and also clarifies the structure of the male copulatory organ (MCO).

Heterospecific grouping behavior of mummichogs (Fundulus heteroclitus) and banded killifish (Fundulus diaphanus) was analyzed in the laboratory and in a freshwater tidal marsh in Cremona, Maryland. Several parameters of wild, intact shoals were measured, including species composition, body length, parasite load, gender, and any physical abnormalities. Fish collected were used for laboratory analysis of shoaling preferences. When size was equal, banded killifish and mummichogs preferred conspecific shoals to heterospecific shoals, consisting of mummichogs, banded killifish, and sheepshead minnows (Cyprinodon variegates). Shoal collection from the field resulted in mixed species shoals with individuals predominantly unaffected by parasites or other physical abnormalities. Size appeared to be a sorting mechanism. A temporal shift in lengths was evident. Initial shoals caught contained significantly smaller fish compared to the final shoals caught. Results are compared with previous studies on heterospecific shoaling in killifish and new characteristics of heterospecific shoals inhabiting freshwater tidal marshes are discussed.

California killifish (Fundulus parvipinnis) infected with the brain-encysting trematode Euhaplorchis californiensis display conspicuous swimming behaviours rendering them more susceptible to predation by avian final hosts. Heavily infected killifish grow and reproduce normally, despite having thousands of cysts inside their braincases. This suggests that E. californiensis affects only specific locomotory behaviours. We hypothesised that changes in the serotonin and dopamine metabolism, essential for controlling locomotion and arousal may underlie this behaviour modification. We employed micropunch dissection and HPLC to analyse monoamine and monoamine metabolite concentrations in the brain regions of uninfected and experimentally infected fish. The parasites exerted density-dependent changes in monoaminergic activity distinct from those exhibited by fish subjected to stress. Specifically, E. californiensis inhibited a normally occurring, stress-induced elevation of serotonergic metabolism in the raphae nuclei. This effect was particularly evident in the experimentally infected fish, whose low-density infections were concentrated on the brainstem. Furthermore, high E. californiensis density was associated with increased dopaminergic activity in the hypothalamus and decreased serotonergic activity in the hippocampus. In conclusion, the altered monoaminergic metabolism may explain behavioural differences leading to increased predation of the infected killifish by their final host predators.

Fundulus heteroclitus from six sites throughout the Hackensack Meadowlands District in northern NJ, U.S.A., were examined. Differences in behaviour (surfacing, conspicuousness and activity) were compared to gill infection intensity. Fish from populations infected with >1500 digenean metacercariae of Ascocotyle phagicola diminuta and Echinochasmus schwartzi, spent significantly more time at the water surface and exhibited significantly more conspicuous behaviour (e.g. jerking) than fish from less parasitized populations. This more conspicuous behaviour has the potential to increase trophic transmission of the parasite to its definitive wading-bird host.

Plagiocirrus loboides n. sp. (Digenea: Opecoelidae) is described from Fundulus nottii, F. dispar blairae, F. chrysotus, and Notemigonus crysoleucas from the Pascagoula River in Mississippi. Plagiocirrus loboides differs from P. primus Van Cleave and Mueller, 1932, by having a longer postcecal space (14-25% of body length vs. about 7%); a more anterior vitellarium (extending at least to the middle of the ventral sucker vs. to its posterior margin); and larger eggs (51-71 microm long by 23-34 microm wide vs. 40-55 microm long by 30-35 microm wide). Plagiocirrus loboides differs from P. testeus Fritts, 1959, by having a long postcecal space (vs. < 5% of body length); irregular, oblique, contiguous testes (vs. strongly lobed, well separated, tandem testes); and a more extensive vitellarium. Plagiocirrus loboides differs from both congeners by having an ovary comprised of 3 or 4 distinct lobes rather than having an entire ovary. Plagiocirrus wuyienensis Wang, 1981, from Hemimyzon zebroidus in Fujian Province, China, is herein considered a species inquirenda because it has a Y-shaped excretory bladder. Molecular phylogenetic analysis of 28S rDNA gene fragments from P. loboides and 17 digenean species demonstrates that Plagiocirrus belongs in Opecoelidae.

Membership and richness of infracommunities and component communities of myxozoan fauna of the banded killifish (Fundulus diaphanus) from freshwater localities in Ontario, Quebec, New York State, New Brunswick, Nova Scotia, and Maryland were studied. Five species of parasites were found: Myxobolus diaphanus (Fantham, Porter, and Richardson, 1940) (connective tissue throughout the body and head), Myxobolus funduli (Kudo, 1918) (interlamellar), Myxobolus neurophilus (Guilford, 1963) (optic tectum of the brain), Myxobolus sp. (connective tissue, typically adjacent to vertebrae), and Sphaerospora sp. (kidney tubules). The most abundant species locally and regionally was M. diaphanus, occurring at prevalences of 14.2 to 93.3% at 6 of 9 localities. Myxobolus funduli and Myxobolus sp. were at 3 and 2 localities respectively, while M. neurophilus and Sphaerospora each occurred at single localities. Four of the 5 myxozoans appear to be specific to fundulids, the exception being M. neurophilus, which is typically a parasite of Perca flavescens. Mean infracommunity richness was 0-1.2. Component community richness was 0-3 species. The fauna is similar in composition to that described from the spottail shiner (Notropis hudsonius) in the Great Lakes in being dominated by histozoic myxobolids and in having maximum prevalence at any single locality correlate positively with geographical distribution. Moreover, mean infracommunity richness was correlated with percentage of hosts infected with any species at a locality, and maximum infracommunity richness was correlated with component community richness. Probably because fewer species of myxozoans of fundulids occur in the regional pool, myxozoan communities encountered in the present study are generally less rich than those described from N. hudsonius. It appears that dispersal of relatively resilient myxospores through such a mechanism as piscivory effectively distributes these parasites over the landscape, while the more delicate actinospores serve to ensure colonization by amplifying species' prevalence at a specific locality and thereby contributing to initial establishment. As such, these types of myxozoans, though they are autogenic, having their entire life cycle normally completed within the aquatic environment, behave more like allogenic parasites that rely on birds and mammals as definitive hosts.

Accurate estimates of population-level parameters of parasites, such as prevalence and mean intensity, require large sample sizes. The processing of such samples becomes an overwhelming task when parasites are abundant, as with trematode metacercariae in fishes. In the present study, a subsampling method reduced processing time while maintaining an accurate estimation of metacercariae prevalence and intensity across 3 trematode species and 2 fish species. By double sampling, we generated regression models to predict total intensity from a combination of subsamples. The key to this approach lies in choosing the best strategy from a large number of potential subsampling routines. We selected the most efficient routine by weighing the costs and benefits of each. This approach, however, could not provide an estimate of parasite abundance when no parasites occurred in the initial subsample. To estimate prevalence accurately, our subsampling algorithm prescribed an additional sampling sequence using a new, optimal regression model. In addition, we optimized the technique to measure three parasite species infecting a single host simultaneously. This efficient subsampling procedure decreased the overall processing time per host by up to 91% while obtaining accurate (R2 > 0.8) estimates for both prevalence and intensity.

The diagnosis of Kudoa funduli (Hahn, 1915) Meglitsch, 1948 (Myxozoa), is supplemented through study of new material collected from Fundulus heteroclitus (Cyprinodontidae) in coastal waters of Nova Scotia, Canada, and Connecticut. Plasmodia normally develop intracellularly in striated muscle of the flank and head, eventually rupturing and releasing spores. Spores disperse along adjacent epimysium, sometimes as far as the skin surface. Some plasmodia develop extracellularly within the bony cavities of vertebrae. Formalin-fixed spores viewed with a light microscope possess rounded edges, an inconspicuous apical region, thin sutural ridges, measure 6.6-7.4 microm wide, 4.3-5 microm thick, and 5.1-5.4 microm long, and have 4 equally sized polar capsules, 1.7-2.3 microm length by 1.4-1.7 microm width. Scanning electron microscopy revealed that spores are almost stellate, with inconspicuous uplifted tips, and that, within intracellular plasmodia, are embedded in an extensive honeycomb-like matrix. Prevalence of infection of K. funduli was 100% in host populations sampled in both Nova Scotia and Connecticut. Molecular sequence data of the 18S ribosomal DNA (737 base pairs) reveal that K. funduli is a valid species and a member of a clade that includes Kudoa dianae Dyková, Avila, and Fiala, 2002, Kudoa miniauriculata Whitaker, Kent, and Sakanari, 1996, and Kudoa paniformis Kabata and Whitaker, 1981.

Phyllodistomum funduli n. sp. is described from the urinary bladder and ureters of the plains topminnow, Fundulus sciadicus, from Cedar Creek in Keith County, Nebraska (41 degrees 11.18'N, 101 degrees 21.77'W). Phyllodistomum funduli differs from most other Phyllodistomum species reported in possessing an oral sucker that is larger than the acetabulum. Currently, 7 other species of Phyllodistomum have been reported to possess this trait. A comparison of P. funduli with these 7 other species indicates that P. funduli is a distinct species, lacking notches, posterior body folds, caudal projections, or cephalic glands found in some congeners. There is no published report on parasites other than monogeneans inhabiting the plains topminnow, and there is no other report of members from the Gorgoderidae inhabiting any members of the Fundulidae.

When exposed to methylmercury in the laboratory, grass shrimp, Palaemonetes pugio, parasitized by the isopod Probopyrus pandalicola, accumulated lower concentrations of mercury than their unparasitized counterparts. The parasitic isopod accumulated far less mercury than the grass shrimp. When exposed to mercury in a contaminated field site, mummichogs, Fundulus heteroclitus, parasitized with the nematode Eustrongylides, similarly accumulated lower concentrations of mercury than unparasitized fish, and the parasite similarly accumulated less than the host. The lower uptake by the parasites compared to their hosts is counter to the general view of biomagnification of methylmercury, since parasites are a trophic level above their hosts. The mechanism whereby parasitized animals accumulate less toxicant than unparasitized ones is unknown, but may be partially due to lower metabolic rate.

The pollution-tolerant mummichog, Fundulus heteroclitus, inhabits a heavily contaminated estuary, Piles Creek (PC), in Linden, NJ. PC contaminants include PAHs, PCBs and many metals, including high Hg and Pb. PC mummichog livers and kidneys were compared with those from a pristine estuary in Tuckerton (TK), NJ, by standard histopathological methods, with quantification by computerized image analysis. PC livers had > 2 x the lipid ratios of TK livers. Cell sizes and shapes were not different between populations. TK livers had a 25% incidence of basophilic areas and an age-related 30% incidence of macrophage aggregates; PC livers had none of these lesions. PC livers had a 100% incidence of necrotic foci, compared with 55% of TK livers. Inflammation was noted in 50% of TK livers but only 27% of PC livers. Curiously, the TK livers had a 45% incidence of metacercarial cysts of a digenetic trematode, while none were found in the PC livers. The TK focal necrosis and macrophage aggregates coincided with parasite infestation. There were no observed kidney lesions in either population. Positive biomarkers in this species thus included high hepatic lipid content, possibly necrosis, but no other lesions. The lack of trematode cysts in PC livers may reflect the lack of an intermediate host in this low biodiversity estuary.