Parasites of fish as biomarkers of environmental degradation: a field study

Fish parasites as proxy bioindicators of degraded water quality of River Saraswati, India

The nature and intensity of water pollution determine the effects on aquatic biota and aquatic ecosystem health. The present study aimed at assessing the impact of the degraded physicochemical regime of river Saraswati, a polluted river having a historical legacy, on the parasitic infection and the role of fish parasite as a bioindicator of water quality. Two Water Quality Indices (WQIs) were adopted as useful tools for assessing the overall water quality status of polluted river based on 10 physicochemical parameters. Total 394 fish (Channa punctata) were examined. Ectoparasite Trichodina sp., Gyrodactylus sp., and endoparasites Eustrongylides sp. were collected from the host fish. Prevalence, mean intensity and abundance for each sampling period were calculated for the determination of parasitic load. The parasitic load of Trichodina sp. and Gyrodactylus sp. was significantly (p < 0.001) higher in winter, whereas the parasitic load of Eustrongylides sp. showed no significant (p > 0.05) seasonal fluctuation. The parasitic load of ectoparasites was negatively correlated with temperature, free carbon dioxide, biochemical oxygen demand, and WAWQI but positively correlated with electrical conductivity and CCMEWQI. Fish health was found to be adversely affected by degrading water qualities and parasitic infection. A 'vicious cycle' develops as a result of the interplay among deteriorating water quality, withering fish immunological defence, and amplifying parasitic infection. Since parasitic load was strongly conditioned by the combined influence of a suite of water quality parameters the fish parasites can be used as a powerful indicator of deteriorating water quality.

Mucous cell responses to contaminants and parasites in shorthorn sculpins (Myoxocephalus scorpius) from a former lead‑zinc mine in West Greenland

Previous studies of sculpins from the former lead (Pb) - zinc (Zn) mine near Maarmorilik, West Greenland, have shown that these fish are affected by heavy metal exposure from the mine. In this study, we applied mucosal mapping (a stereological method for mucosal quantification in fish) to uncover interactions between the host, parasites and heavy metal exposure (Pb and Zn) in shorthorn sculpins from the Maarmorilik mining site at a gradient of 3 stations. Skin and gill mucosal epithelia of shorthorn sculpins were significantly affected and reflected the exposure to environmental heavy metals and parasites. Size of skin mucous cells was significantly smallest in the sculpin from the station 3 where heavy metal contamination was lowest and the skin parasite load was highest. Gill filament mucous cells were largest and densest in fish from station 1 which was the most contaminated site. In gill lamellae the density of mucous cell followed a toxicity gradient and was significantly highest at the most contaminated station and significantly lowest at the least contaminated station. The persistent presence of toxic Pb and Zn levels in the sediment at the most contaminated station may have induced a small but measurable reduction in the surface area available for respiration and may have affected diffusion distance. The strong correlation between size of filamentous mucous cells and Pb concentrations in liver suggests that these cells can play an active role in reducing the somatic load of Pb in sculpin. We suggest that mucosal mapping can be used to assess effects of contaminant and parasite exposure in future environmental field studies.

The metazoan parasite communities of the shoal flounder (Syacium gunteri) as bioindicators of chemical contamination in the southern Gulf of Mexico

BACKGROUND

Because agriculture and offshore oil extraction are significant economic activities in the southern Gulf of Mexico, high concentrations of nutrients and hydrocarbons are expected. As parasite communities are sensitive to environmental impacts, these contaminants should have an effect on metrics such as species richness, relative abundance and similarity. Consequently, these community metrics can be used as indicators of aquatic environmental health. Our objectives were to describe the parasite communities of the shoal flounder Syacium gunteri and to determine potential thresholds above which environmental contaminants become major controlling factors of parasite community metrics.

METHODS

The study area included 33 sampling sites in the southern Gulf of Mexico, where benthic sediments, water and shoal flounder individuals were collected. Data on ecto- and endo-parasites from flounder and nutrients, contaminants and physicochemical variables from the water and sediments were obtained. The statistical associations of the parasite community metrics at the component and infracommunity levels and the environmental data were analysed using redundancy analysis (RDA).

RESULTS

Overall, 203 shoal flounder were examined for parasites, recovering 13 metazoan parasite species, and 48 physicochemical (e.g. temperature, nutrients) and contaminant (e.g. hydrocarbons, heavy metals) variables were obtained. The larval stages of the cestode Oncomegas wageneri and the nematodes Pseudoterranova decipiens and Hysterothylacium sp. were numerically dominant at the component and infracommunity levels. The parasite community metrics had significant negative statistical associations with both nitrate and total PAHs. With the exception of these two chemicals, which exceeded the threshold effect levels (TELs), no other environmental variable exceeded the range considered safe for marine organisms.

CONCLUSIONS

The community metrics chosen generally had robust statistically significant associations with both physicochemical and contaminant variables, which supports the ecological relevance of these parameters as indicators of aquatic environmental health. Within the study area, the shoal flounder and their parasites live in a polluted environment with relatively high levels of hydrocarbons and nitrate. Regarding nitrate, we emphasise that if uncontrolled sewage discharge continues in the southern Gulf of Mexico, hypoxic conditions similar to those caused by the Mississippi river can be expected in the near future.

Acetylcholinesterase activity in the host-parasite system of the cod Gadus morhua and acanthocephalan Echinorhynchus gadi from the southern Baltic Sea

Acetylcholinesterase (AChE) activity measurement is widely used as a specific biomarker of neurotoxic effects. The aim of this study was to evaluate AChE activity in a host fish (the cod) and its acanthocephalan parasite Echinorhynchus gadi from the southern Baltic. AChE activity in hosts and parasites was inversely related: the highest cod AChE activity corresponded to the lowest E. gadi enzymatic activity and vice versa ("mirror effect"). This is the first report on the simultaneous application of this biomarker in cod and its acanthocephalan parasites. Results obtained for the host-parasite system are complementary and provide comprehensive information about the response of this biomarker. Analysis of the system allows for detection of a greater number of factors influencing AChE activity in the marine environment than separate analysis of the host and parasites. Thus, AChE activity measurement in a host-parasite system may be considered to be a promising tool for biomonitoring.

Influence of sediment contaminated with untreated pulp and paper mill effluent on winter flounder, Pleuronectes americanus

This study was conducted to ascertain the influence of sediment contaminated with pulp and paper mill effluent in a fjord on winter flounder, Pleuronectes americanus, based on a laboratory study. Flounder, captured from a pristine site, were exposed in a flow-through system for 16 weeks to sediment collected at 2, 5, 7, and 10 km from the outfall. A group of controls was placed in uncontaminated sediment. Mortality occurred almost exclusively in fish exposed to sediment taken from 2 km than from more distant sites. Additionally, the condition factor was lower, the liver was enlarged, and toxicopathic lesions in the liver and spleen were significantly greater in fish submerged in the sediment than in fish from the more distant locations or the controls. Two ectoparasites including a ciliate, Trichodina jadranica, and a monogenean, Gyrodactylus pleuronecti, were observed only in the control group, while a digenean in the digestive tract, Steringophorus furciger, was more abundant in fish exposed to sediment from sites more distant from the outfall and the controls than at 2 km. Comparison of these results with data from a previous gradient field study on biological variables in winter flounder, captured at 2, 5, 7, and 10 km down-current from the outfall, revealed an enlarged liver that was associated with elevated levels of detoxification of hepatic enzymes and prevalence of toxicopathic lesions in both the liver and the spleen; these were significantly greater in samples taken nearest to the outfall from the mill than at more distant sites. Moreover, two metazoan parasites, S. furciger (Digenea) and Echinorhynchus gadi (Acanthocephala), in the digestive were more abundant in samples taken at farther locations and also from the reference sites. These results, based on a laboratory study, are in agreement with previous observations that winter flounder exposed to sediment at the site nearest to the outfall, where high concentrations of toxic contaminants persisted, was greater than in the fish from the other locations.

Influence of a thermal discharge on parasites of a cold-water flatfish, Pleuronectes americanus, as a bioindicator of subtle environmental change

A study was conducted to ascertain the influence of a thermal discharge on the health and parasites of a coastal cold-water flatfish, the winter flounder (Pleuronectes americanus), a species sensitive to environmental change. Flounder were sampled in spring 1998 and 1999 beneath the plume and at reference sites north and south up to 1 km from the discharge. Species diversity and estimates of abundance of macroscopic algae, invertebrates, and fish were also recorded. After capture by scuba divers, a comparison of condition factor, organ indices, blood values, histology, and parasites was made between groups of fish from the discharge and reference sites. Diversity and abundance of algae, invertebrates, and fish were considerably greater beneath the plume than at the reference sites. The thermal water had no apparent effect on flounder taken beneath the plume, but it affected both its ecto- and endoparasites. Prevalence and mean abundance of Cryptocotyle lingua metacercariae were significantly greater, whereas Trichodina jadranica and Gyrodactylus pleuronecti were less on the gills of fish sampled beneath the plume than at the reference sites. Four endoparasites, i.e., Ceratomyxa drepanopsettae, Steringophorus furciger, Macvicarius soleae, and Lecithaster gibbosus were significantly more abundant in the reference samples. These results suggest that environmental change affected transmission of the parasites of winter flounder exposed to the thermal effluent.

The pink shrimp Farfantepenaeus duorarum, its symbionts and helminths as bioindicators of chemical pollution in Campeche Sound, Mexico

The pink shrimp Farfantepenaeus duorarum may acquire pollutants, helminths and symbionts from their environment. Statistical associations were studied between the symbionts and helminths of F. duorarum and pollutants in sediments, water and shrimps in Campeche Sound, Mexico. The study area spatially overlapped between offshore oil platforms and natural shrimp mating grounds. Spatial autocorrelation of data was controlled with spatial analysis using distance indices (SADIE) which identifies parasite or pollutant patches (high levels) and gaps (low levels), expressing them as clustering indices compared at each point to produce a measure of spatial association. Symbionts included the peritrich ciliates Epistylis sp. and Zoothamnium penaei and all symbionts were pooled. Helminths included Hysterothylacium sp., Opecoeloides fimbriatus, Prochristianella penaei and an unidentified cestode. Thirty-five pollutants were identified, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), pesticides and heavy metals. The PAHs (2-3 ring) in water, unresolved complex mixture (UCM), Ni and V in sediments, and Zn, Cr and heptachlor in shrimps were significantly clustered. The remaining pollutants were randomly distributed in the study area. Juvenile shrimps acquired pesticides, PAHs (2-3 rings) and Zn, while adults acquired PAHs (4-5 rings), Cu and V. Results suggest natural PAH spillovers, and continental runoff of dichlorodiphenyltrichloroethane (DDT), PCBs and PAHs (2-3 ring). There were no significant associations between pollutants and helminths. However, there were significant negative associations of pesticides, UCM and PCBs with symbiont numbers after controlling shrimp size and spatial autocorrelation. Shrimps and their symbionts appear to be promising bioindicators of organic chemical pollution in Campeche Sound.

Parasites of winter flounder (Pleuronectes americanus) as an additional bioindicator of stress-related exposure to untreated pulp and paper mill effluent: a 5-year field study

A study was conducted in a marine inlet to assess the effects of untreated discharges from a pulp and paper mill, a municipality, and industries in western Newfoundland on winter flounder (Pleuronectes americanus), a fish species shown previously to be sensitive to environmental contaminants in sediment. The fish were captured by SCUBA divers about 2 km down-current from the mill discharging effluent containing resin acids, and at three reference sites 2 to 11 km away near the opposite shore, each spring in five consecutive years and the fish were necropsied on site. A total of 360 and 339 flounder were examined near the mill and references sites, respectively. Several bioindicators were used to assess fish health including parasites. More fish exhibiting external and microscopic lesions in several tissues, lower condition factors, elevated hepatosomatic index, and delayed reproductive development were observed in samples taken near the paper mill than at the reference sites. A higher prevalence of an ectoparasite, Cryptocotyle lingua, but a significantly lower mean abundance of three metazoans infecting the digestive tract was noted in fish near the mill than in the reference samples. These results, comprising abnormal fish size distribution, low body condition factor, external and internal lesions, enlarged liver, delayed gonadal development, and changes in parasitism, were stress-related, indicative of impaired health, and associated primarily with untreated discharges from the pulp and paper mill. This integrated and multidisciplinary study also provides further evidence on the use of fish parasites as a valid and an additional bioindicator in programs monitoring environmental contaminants.

Assessment of stress-related bioindicators in winter flounder (Pleuronectes americanus) exposed to discharges from a pulp and paper mill in Newfoundland: a 5-year field study

This study assessed the effects of discharges from a sulphite-bleaching paper mill on winter flounder (Pleuronectes americanus) sampled each spring over a 5-year period in St. George's Bay, Newfoundland, prior to foraging activity. The fish were captured by SCUBA divers near the mill and at a reference site 10 km up current. Several bioindicators were used to assess fish health. Larger and older flounder exhibiting gross and microscopic tissue lesions, lower condition factor, and elevated hepatosomatic index but lower gonadosomatic index that was associated with delayed development, were observed in samples caught near the mill compared to those at the reference site. Additionally, fish examined near the mill were infested with an ectoparasite, Cryptocotyle lingua, that causes black spot disease but harbored fewer numbers of a digene, Steringophorus furciger, in the digestive tract than samples taken at the reference site. These results suggest that abnormal size distribution, interruption of growth, high prevalence of lesions, lower condition factor, enlarged liver, delayed gonadal development, and differences in parasitic levels were indicative of stress in winter flounder caused by discharges from the mill compared to samples from a reference site. There was no evidence of a population decline in the inlet because of annual recruitment possibly from St. George's Bay into which it opens.