Body Condition Peaks at Intermediate Parasite Loads in the Common Bully Gobiomorphus cotidianus

Components influencing parasitism by Dadaytrema oxycephala (Digenea: Cladorchiidae) in Neotropical fish

The components that mold the structure of parasitic fauna are used as objects of study in an attempt to find patterns in their distribution. It is known that phylogeny (represented by specificity), host ecological traits (for example, feeding habits, position of the water column, reproductive strategies, body size, and age), and the environment affect the distribution and occurrence of parasites. In tropical regions, digeneans show high diversity, and the species Dadaytrema oxycephala is known to parasitize a wide range of host species. In this context, the objective of the present study is to analyze the components that affect the occurrence of D. oxycephala in Neotropical fish. We used data from the literature that contained the abundance of this parasite, as well as the geographic location and host species, and evaluated the influence of ecological traits, specificity, and latitude on parasite abundance, using a generalized linear mixed model (GLMM). The abundance of D. oxycephala can be explained by trophic level and position in the water column and latitude. However, coevolutionary processes are also extremely important, and the distribution of this parasite was not equal, showing high abundance for the genus Piaractus, which are the preferred hosts, even if the parasite is considered generalist. In short, host ecological traits are the important components in the distribution and occurrence of D. oxycephala, as well as the latitude.

Host–Parasite Relationship—Nematode Communities in Populations of Small Mammals

Nematode burdens and variation in morphological characteristics were assessed in eighty-eight animals from three host species (Apodemus sylvaticus, Apodemus flavicollis, and Myodes glareolus) from eight localities in Serbia. In total, 15 species of nematodes were identified, and the overall mean parasite species richness (IndPSR) was 1.61 per animal (1.98 in A. flavicollis, 1.43 in M. glareolus, and 0.83 in A. sylvaticus). Furthermore, the studied host species significantly differed in individual parasite load (IndPL) and in the following morphological characters: spleen mass, body condition index (BCI), and body mass. We aimed to analyze the relationship between the burden of intestinal nematodes, on one hand, and the body conditions of the host and its capability to develop immune defends on the other. Spleen mass was considered as a measure of immune response. In all host species, larger animals with a better condition (higher BCI) were infected with more parasites species (IndPSR), while parasite load was not related to BCI. Only in A. flavicollis were males significantly larger, but females of the same sizes were infected with more parasite species. This female-biased parasitism is contrary to the theoretical expectation that males should be more parasitized, being larger, more active, with a wider home range. Although the spleen size was significantly correlated with body condition and body mass, IndPSR was not related to spleen mass in any studied species, but in M. galareolus, we found that a smaller spleen was related to higher infection intensity (IndPL).

Interactions of cranial helminths in the European polecat (Mustela putorius): Implications for host body condition

Multiple helminth species commonly co-occur within mammals and their interactions may negatively affect the survival and breeding success of their hosts. However, it has been difficult to prove competition or mutualism between co-infesting helminths in field studies of wild mammals. The sinus cavities of European polecats (Mustela putorius) can be parasitised by the trematode Troglotrema acutum and the nematode Skrjabingylus nasicola and both helminths can co-occur within hosts. While both parasites can damage the host's bone structure and cause severe pathologies, their impact on host body condition is unclear. It is also unknown whether both parasites interact and how this might affect cranial damage and host body condition. We examined 515 fresh polecat skulls for the presence of both helminths and measured the hosts' amount of kidney perirenal fat as a measure of body condition. Our results demonstrated that, in addition to a host-intrinsic fixed factor (sex) and random factors accounting for spatial and temporal stochasticity, the helminths influenced each other's presence. Infestation with T. acutum increased the probability of catching S. nasicola with increasing age of the host, while males already infested with S. nasicola were more likely to become infested with T. acutum than females infested with the nematode. While we speculate that both effects resulted from parasite-induced behavioural alterations (increased foot consumption), it is not clear why, in the latter case, this effect would be stronger in males than females. We showed that the abundances of both parasites had significant positive effect on the likely presence of skull damage and a significant negative effect on the predicted presence of kidney fat. Given the evolutionary arms race that both host-parasite systems have undergone, it appears unlikely that either helminth played a significant factor in the population decline of the polecat in Europe.

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We provide evidence for interactions between co-infesting helminths in a wild mammal.

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Troglotrema acutum and Skrjabingylus nasicola can co-occur in the skulls of polecats.

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Infestation with one parasite can increase the probability of infestation with the other one.

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Heavy infestation with either helminth may have a negative effect on host body condition.

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Co-infestation does not change the severity of the parasites' clinical impact.

The Influence of Contracaecum larvae (Nematoda, Anisakidae) Parasitism on the Population of Prussian carp (Carassius gibelio) in Lake Sakadaš, Croatia

Contracaecum larvae are geographically widely distributed, utilizing many animal species as hosts; and fish represent an important paratenic host in their life cycle. Their presence in Prussian carp (Carassius gibelio) was studied in Lake Sakadaš (Croatia) in 2017 and 2018. Two gill nets of different sizes submerged during a 12-h period were used to collect the fish. Contracaecum larvae were recorded in the stomach, slightly coiled or elongated on the intestine serosa or encapsulated in a gut wall of 20 individuals. The effect of Contracaecum sp. on the health of their host was determined by estimating the effect of the parasites’ presence, number, and biomass on fish length, weight, and the Fulton’s condition factor (CF). Infected fish showed negative (b < 3; p < 0.05) and uninfected fish positive allometric growth (b > 3; p < 0.05). Fish weight and CF in infected individuals were significantly low in comparison to the uninfected ones (Mann−Whitney U test: U = 1078.00, U = 423.50, respectively; p < 0.004). These results emphasize the importance of evaluating parasitic nematode presence in economically important fish species. Even more, if this endoparasite has a detectable negative impact on a resilient species such as the Prussian carp, it is important to monitor its occurrence in other fish species.

Logging effects on parasitic infections in a swamp rat (Malacomys edwardsi) in West Africa

Habitat disturbance can have negative impacts on biodiversity, such as reducing species richness. The effects of habitat disturbances on parasite infections of host species, potentially altering their survival rate and thus abundance, are less well known. We examined the influence of forest logging in combination with seasonality, host abundance, host body condition, and host sex, on the community composition of gastrointestinal parasites infecting Edward’s swamp rat, Malacomys edwardsi. Community composition of parasites did not differ between logged and undisturbed sites, but the abundance of some nematodes (i.e., Ascaris and hookworm) was higher in undisturbed than logged sites. The higher abundance of these nematode species implies a changed host-parasite relationship, thus potentially influencing host persistence.

Helminth communities in amphibians from Latvia, with an emphasis on their connection to host ecology

Helminth infracommunities were studied at 174 sites of Latvia in seven hosts from six amphibian taxa of different taxonomical, ontogenic and ecological groups. They were described using a standard set of parasitological parameters, compared by ecological indices and linear discriminant analysis. Their species associations were identified by Kendall's rank correlation, but relationships with host size and waterbody area were analysed by zero-inflated Poisson and zero-inflated negative binomial regressions. The richest communities (25 species) were found in post-metamorphic semi-aquatic Pelophylax spp. frogs, which were dominated by trematode species of both adult and larval stages. Both larval and terrestrial hosts yielded depauperate trematode communities with accession of aquatic and soil-transmitted nematode species, respectively. Nematode loads peaked in terrestrial Bufo bufo. Helminth infracommunities suggested some differences in host microhabitat or food object selection not detected by their ecology studies. Associations were present in 96% of helminth species (on average, 7.3 associations per species) and dominated positive ones. Species richness and abundances, in most cases, were positively correlated with host size, which could be explained by increasing parasite intake rates over host ontogeny (trematode adult stages) or parasite accumulation (larval Alaria alata). Two larval diplostomid species (Strigea strigis, Tylodelphys excavata) had a negative relationship with host size, which could be caused by parasite-induced host mortality. The adult trematode abundances were higher in larger waterbodies, most likely due to their ecosystem richness, while higher larval abundances in smaller waterbodies could be caused by elevated infection rates under high host densities.

Parasitism reduces oxidative stress of fish host experimentally exposed to PAHs

Some parasites are known to bioaccumulate some environmental pollutants within their host. We hypothesized that these parasites may be beneficial for their hosts in polluted environments. We experimentally increased long-term (five weeks) exposure to polycyclic aromatic hydrocarbons (PAHs, three levels: 0.1X, 1X, 10X environmental exposure) in European chubs (Squalius cephalus) that were naturally infected or uninfected with acanthocephalan parasites. We monitored PAHs levels in fish tissues, as well as oxidative stress, telomere length and condition indices. Although parasite infection did not significantly reduce the levels of PAHs and PAH metabolites in host tissues, host oxidative status was explained by parasitism and pollution levels. Oxidative damage increased with parasitism in fish exposed to low PAH levels (0.1X) but decreased in infected fish at higher PAH exposure (10X), thus corroborating our hypothesis. Meanwhile, antioxidant capacity did not differ in response to parasite infection nor PAHs exposure. Despite this imbalance in oxidative status, experimental increase in PAH levels did not compromise telomere length, body condition, or survival in infected and uninfected fish. This study provides the first experimental evidence that the outcome of host-parasite interactions can shift from negative to positive as pollutant exposure increases.

Why ignoring parasites in fish ecology is a mistake

Parasites are ubiquitous components of biological systems that have evolved in multiple independent lineages during the history of life, resulting in a diversity of taxa greater than that of their free-living counterparts. Extant host-parasite associations are the result of tight reciprocal adaptations that allow parasites to exploit specific biological features of their hosts to ensure their transmission, survival, and maintenance of viable populations. As a result, parasites may affect host physiology, morphology, reproduction or behaviour, and they are increasingly recognized as having significant impacts on host individuals, populations, communities and even ecosystems. Although this is usually acknowledged by parasite ecologists, fish ecologists often ignore parasitism in their studies, often acting as though their systems are free of parasites. However, the effects of parasites on their hosts can alter variables routinely used in fish ecology, ranging from the level of individual fish (e.g. condition factors) to populations (e.g. estimates of mortality and reproductive success) or communities (e.g. measures of interspecific competition or the structure and functioning of food webs). By affecting fish physiology, parasites can also interfere with measurements of trophic levels by means of stable isotope composition, or have antagonistic or synergistic effects with host parameters normally used as indicators of different sources of pollution. Changes in host behaviour induced by parasites can also modify host distribution patterns, habitat selection, diet composition, sexual behaviour, etc., with implications for the ecology of fish and of their predators and prey. In this review, we summarise and illustrate the likely biases and erroneous conclusions that one may expect from studies of fish ecology that ignore parasites, from the individual to the community level. Given the impact of parasites across all levels of biological organisation, we show that their omission from the design and analyses of ecological studies poses real risks of flawed interpretations for those patterns and processes that ecologists seek to uncover.

Potential Benefits of Acanthocephalan Parasites for Chub Hosts in Polluted Environments

Some parasites are expected to have beneficial impacts on wild populations in polluted environments because of their bioaccumulation potential of pollutants from their hosts. The fate of organic micropollutants in host-parasite systems and the combined effect of parasitism and pollution were investigated in chub Squalius cephalus, a freshwater fish, infected (n = 73) or uninfected (n = 45) by acanthocephalan parasites Pomphorhynchus sp. from differently contaminated riverine sites. Several ubiquitous pollutants (polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), polybrominated diphenyl-ethers (PBDEs), polycyclic aromatic hydrocarbons (PAHs), phthalates, insecticides, pyrethroids, and N,N-diethyl-meta-toluamide (DEET)) and some of their metabolites were characterized for the first time in parasites and various fish matrices (muscle, liver, and stomach content). Most organic pollutants reached higher levels in parasites than in chub matrices. In contrast, metabolite levels were lower in parasite tissues compared to fish matrices. Infected and uninfected chub exhibited no significant differences in their pollutant load. Body condition, organo-somatic indices, and immunity were not affected by parasitism, and few correlations were found with chemical pollution. Interestingly, infected chub exhibited lower oxidative damage compared to uninfected fish, irrespective of their pollutant load. In light of these results, this correlative study supports the hypothesis that acanthocephalan parasites could bring benefits to their hosts to cope with organic pollution.

Carryover effects of larval environment on individual variation in a facultatively diadromous fish

Intraspecific trait variation may result from "carryover effects" of variability of environments experienced at an earlier life stage. This phenomenon is particularly relevant in partially migrating populations composed of individuals with divergent early life histories. While many studies have addressed the causes of partial migration, few have investigated the consequences for between-individual variability later in life.We studied carryover effects of larval environment in a facultatively diadromous New Zealand fish, Gobiomorphus cotidianus, along an estuarine salinity gradient. We investigated the implications of varying environmental conditions during this critical stage of ontogeny for adult phenotype.We inferred past environmental history of wild-caught adult fish using otolith microchemistry (Sr/Ca) as a proxy for salinity. We tested for main and interactive effects of larval and adult environment on a suite of traits, including growth rates, behavior (exploration and activity), parasite load, and diet (stable isotopes and gut contents).We found a Sr/Ca consistent with a continuum from freshwater to brackish environments, and with different trajectories from juvenile to adult habitat. Fish with Sr/Ca indicating upstream migration were more vulnerable to trematode infection, suggesting a mismatch to freshwater habitat. Diet analysis suggested an interactive effect of larval and adult environments on trophic position and diet preference, while behavioral traits were unrelated to environment at any life stage. Growth rates did not seem to be affected by past environment.Overall, we show that early life environment can have multiple effects on adult performance and ecology, with the potential for lifetime fitness trade-offs associated with life history. Our study highlights that even relatively minor variation in rearing conditions may be enough to generate individual variation in natural populations.

Description of Tylodelphys darbyi n. sp. (Trematoda: Diplostomidae) from the threatened Australasian crested grebe (Podiceps cristatus australis, Gould 1844) and linking of its life-cycle stages

Species of the genus Tylodelphys (Diplostomidae) have a cosmopolitan distribution. Metacercariae of these species infect the eye, brain, pericardial sac or body cavity of fish second intermediate hosts, and the adults are found in piscivorous birds of many orders. An unnamed species of Tylodelphys from the eyes of bullies (Gobiomorphus cotidianus) was characterized molecularly and morphologically as a metacercaria in a previous study, in which it was predicted that the adult of this species would be found in the Australasian crested grebe. Two specimens of this bird became available and specimens of the unnamed Tylodelphys species were, indeed, found in them, confirmed by identity of genetic sequence data. Found to differ morphologically from its congeners, the new species is here described as Tylodelphys darbyi n. sp. Three species are closest to the new species in morphology: Tylodelphys glossoides, T. immer and T. podicipina robrauschi. Compared with T. darbyi n. sp. these three species are slightly larger and possess longer eggs. Tylodelphys glossoides also differs in having a wider oral sucker and T. podicipina robrauschi in having comma- or kidney-shaped pseudosuckers and an ovary that reaches a larger size, along with higher upper limits for body width, hind body and sucker width, holdfast and oesophagus length, and pharynx, pseudosucker and testes length and width. Tylodelphys immer also differs from T. darbyi n. sp. in having a shorter ventral sucker and the largest pseudosuckers of any Tylodelphys species.

Water-quality impacts in semi-arid regions: can natural 'green filters' mitigate adverse effects on fish assemblages?

The effective aridity in riparian areas is increasing from climate change and from human water consumption, which exacerbates the impacts of effluents from wastewater-treatment plants and from catchment run-off in rivers. The potential of natural riparian areas to act as 'green filters' has long been recognized, but the possible ecological benefits of natural riparian areas over large-scale environmental gradients on fish have not been explored in detail. Using an extensive data-set from northeastern Spain (99,700 km², 15 catchments, 530 sites), ours is the first study to ask whether natural riparian vegetation can mitigate the effects of pollution on fish in rivers experiencing water scarcity. We used multimodel inference to explore the additive and interactive effects of riparian vegetation with nutrient pollution and water conductivity, which are among the world's worst river stressors, on multiple fish guilds, including widely distributed species and highly invasive alien fish species. Most models (54%) supported the additive effects of water-quality factors on fish, after having accounted for the influence of geography and hydrological alterations. Although many fewer models (7%) included riparian vegetation as an important predictor, riparian vegetation modulated the forms of the associations between fish and pollution. The relationship of nutrient pollution with native and alien fish richness changed from negative to positive with greater riparian structure or species richness. However, we found the opposite effect for the mean body size of sedentary fish, and only positive additive effects of riparian richness for the probability of occurrence of pelagic fish. Ammonium and nitrite concentrations adversely affected fish in these rivers up to 10 years after the enforcement of the implementation of the Water Framework Directive by the European Union. High conductivity also much affects fish, having negatives associations with migratory, pelagic, invertivorous and native fish, and positive associations with sedentary, benthic, omnivorous and alien fish. Therefore, the current status of natural riparian areas is unlikely to fully mitigate water-quality impacts on fish. The conservation of freshwater resources in semi-arid regions, such as north-eastern Spain, requires improved waste-water treatments and better agriculture practices.

In situ monitoring of the Sinos River, southern Brazil: water quality parameters, biomarkers, and metal bioaccumulation in fish

The Sinos River is an important water supply in Southern Brazil and receives industrial, agricultural, and domestic effluents which may affect aquatic biota. Water physicochemical and microbiological analyses, biomarker responses (scaled mass index (SMI), gill histopathology, and micronucleus and nuclear abnormality (MN and NA) frequencies), and metal bioaccumulation in muscle were assessed in the fish species Bryconamericus iheringii (Characidae) captured at three sampling sites (S1, S2, and S3) in four sampling periods. The mean values of five parameters (total phosphorus, thermotolerant coliforms, aluminum, iron, and lead) exceeded the limits established by the Brazilian legislation at the three sampling sites. Although physicochemical analysis indicated higher impacts at S3, in some samples, significantly higher MN frequencies and bioaccumulation of manganese in fish muscle were observed at S1, whereas low SMI and higher concentrations of aluminum and zinc in fish muscle were found at S2. Histopathological alterations in gills were observed in fish collected at the three sampling sites; however, no spatial differences were observed, indicating similar environmental conditions with respect to this biomarker. Moreover, temporal variation of biomarker responses and metal bioaccumulation were found at all sampling sites. Furthermore, the consumption of fish from the Sinos River should be avoided given the concentrations of chromium (all samples), cadmium, and lead in fish muscle above the threshold for safe human consumption.