鱼类寄生虫免疫学研究进展

随着集约化水产养殖的发展,由寄生虫引起的鱼类流行病的暴发越来越频繁。虽然对鱼类寄生虫的分类学和生物学进行了广泛的研究,但是鱼类的保护性免疫及寄生虫对鱼类免疫系统的影响仍知之甚少。本文概述了鱼类寄生虫免疫学研究的现状,就近年来国内外鱼类的特异性及非特异性免疫在抗寄生虫感染方面的研究进展,以及鱼类寄生虫免疫学在水产养殖上的应用等作简要介绍。     

Reprint of “Fish immunity to scuticociliate parasites”

Some species of scuticociliates (Ciliophora) behave as facultative parasites and produce severe mortalities in cultured fish. Pathogenic scuticociliates can cause surface lesions and can also penetrate inside the body, where they feed on tissue and proliferate in the blood and most internal organs, killing the host in a few days. In this review, we describe the current knowledge on the protective role of fish cellular and humoral immune responses against these parasites. Immune humoral factors, especially complement, are of particular importance in defending fish against these ciliates. However, knowledge about how the fish immune system responds to scuticociliates is scant, and the cellular and molecular events that occur during the response are not known. We also describe the possible mechanisms used by scuticociliates to avoid or resist the defensive reaction of the host. For example, the release of proteases can help parasites enter fish tissues and impair the fish cellular and humoral responses. Several vaccine formulations containing scuticociliates have induced a good antibody response and protection in fish immunized and challenged with homologous strains of particular species. However, protection was not achieved in fish immunized and challenged with heterologous strains, and the antigens involved in protection and the antigenic differences between heterologous strains have not yet been determined.     

Health problems associated with consumption of fish and the role of aquatic environments in the transmission of human diseases

The majority of the numerous fish parasites are harmless to man and many domestic animals because when eaten with their fish hosts, they are digested. However, some of the fish parasites with larval stages in freshwater or marine teleosts have zoonotic potential if eaten raw or partially cooked. These are usually parasites, which have a piscivorous mammalian carnivore as their normal final host and are able to infect man because of the low host specificity of the adult stage. The major groups of fish parasite that are known as potentially dangerous pathogens of man belong to the helminth groups cestoda, trematoda, nematoda and rarely acanthocephala. However, bacterial and viral disease of man transmitted through fish are not uncommon. Toxic substances, metals and insecticides used to control human diseases in aquatic environments may accumulate in fish in po1lluted waters at such levels as to constitute a health risk to the consumer. Other health problems associated with fish arise from its perishable nature for example, in adequate handling, processing and storage, which may lead to the accumulation of microbes enhancing the risk of food poisoning. The aquatic environment in Africa constitutes a breeding habitat to several vectors of human diseases such as mosquitoes, snails and black flies. This paper reviews the role played by fish in transmitting diseases to humans as well as the importance of the aquatic environments in the transmission of human diseases such as Malaria, Schistosomiasis and onchocerciasis.     

Parasite fauna of the mediterranean grenadier Coryphaenoides mediterraneus (Giglioli, 1893) from the Mid-Atlantic Ridge (MAR)

A total of 38 Coryphaenoides mediterraneus from the Charlie-Gibbs Fracture Zone (CGFZ), a part of the Mid-Atlantic Ridge (MAR), was studied for parasites and feeding ecology. Sixteen different parasite species were found, most of them belonging to the Digenea (6 species) and Nematoda (6). Twelve new host and 11 new locality records were established, and 8 deep-sea generalists and 5 deep-sea specialists were found. Twelve adult and 3 larval parasites occurred, with Allopodocotyle margolisi (Digenea), Tetraphyllidea indet. (Scolex pleuronectis, Cestoda) and Ascarophis longiovata (Nematoda) being the predominant species. These parasites reached a prevalence of 50.0%, 86.8% and 68.4% with an intensity of infection of 1–10, 1–91 and 1–74, respectively. The food consisted of crustaceans and cephalopods; no further prey items such as fish could be identified. Coryphaenoides mediterraneus demonstrates a parasite fauna similar to that of other deep-sea macrourids. No MAR-specific parasite species were found, and the collected helminths are common fish parasites of the North Atlantic deep-sea basin and the adjacent continental shelf regions. Only few larval epipelagic generalists such as ascaridoid nematodes were found, due to the deep origin of the studied fish between 1700–3500 m. The recorded species rich parasite fauna reflects the wide depth range and opportunistic feeding behaviour of C. mediterraneus on benthopelagic food. The recorded parasite species composition around the MAR appears to be similar to other deep-sea locations in the Atlantic Ocean, demonstrating the wide zoogeographical distribution of these deep-sea metazoans. Consequences of the MAR, the CGFZ and the homogeneous deep-sea environmental conditions for the parasite species distribution are discussed.     

Transmission dynamics of a trematode parasite: exposure,acquired resistance and parasite aggregation

This paper examines the relative importance of exposure and susceptibility to the infection of rainbow trout (Oncorhynchus mykiss) with the trematode parasite Diplostomum spathaceum under natural conditions. A total of 93 individually marked, similarly aged fish were introduced into three cages at regular time intervals and the intensity of infection in individuals recorded by counting parasites in live fish using ophthalmic techniques. Fish introduced into the cages became infected faster than fish that were already in the cages, indicating that fish developed resistance to infection after repeated exposure. Fish kept in the cages experienced similar levels of exposure and the distribution of parasites between these fish was not significantly different from a random distribution. In contrast, parasites from 16 Finnish wild roach populations were highly aggregated. The differences between the caged fish and the wild fish indicate that the aggregated distribution in wild fish might be determined by variations in exposure rather than variations in susceptibility between fish. This is one of the few studies to demonstrate the development of resistance in fish against the parasite under natural conditions, and to attempt to separate exposure and susceptibility as causative agents of parasite aggregation.     

Effects of ethanol extract of Artemisia annua L. against monogenean parasites of Heterobranchus longifilis

Ethanol extract of Artemisia annua was effective in the dislodgement and mortality of monogenean parasites of juvenile Heterobranchus longifilis at concentrations ranging from 50 to 200 mg/l. Five hundred 1-week-old juvenile fish were stocked in hapa in earthen pond for 7 days to accumulate parasites. The approximate number of parasites per fish was confirmed by counting the number of parasites attached to body surfaces and the gills with a stereo-microscope before being exposed to the extract under in vivo conditions. The bioactivity of the extract was conducted in plastic Petri dishes with three replications and controls. The results obtained from A. annua extract were matched against those produced by pure artemisinin and artesunate powder, respectively, under similar experimental conditions. There was a faster effect of pure artemisinin crystals on the parasites as compared to A. annua extract and artesunate. Coagulation of parasite cells was observed with artemisinin treatment, whereas parasites were merely dislodged from their attachment organs and killed some hours later in the same concentration of A. annua. There were positive correlations between the number of parasites dislodged/killed and the concentration of A. annua extract, artemisinin, and artesunate powder, respectively, as well as the duration of exposure of affected fish to the substances. This led to the conclusion that A. annua contains substances that are effective against helminthes parasites of H. longifilis.     

Immunity to gastrointestinal microparasites of fish

Fish intestinal parasites cause direct mortalities and also morbidity, poor growth, higher susceptibility to opportunistic pathogens and lower resistance to stress. This review is focused on microscopic parasites (Protozoa and Metazoa) that invade the gastrointestinal tract of fish. Intracellular parasites (mainly Microsporidia and Apicomplexa) evoke almost no host immune reaction while they are concealed in the cytoplasmic and nuclear compartments, and can even use fish cells (macrophages) as Trojan horses to spread in the host. Inflammatory reaction only appears when the parasite bursts infected cells. Immunity against extracellular parasites is depicted for the myxozoans Ceratonova shasta and Enteromyxum spp. The cellular and humoral innate responses and the production of antibodies are crucial for resolving some of these myxozoonoses, but an excessive inflammatory reaction (concerted by cytokines) can become a fatal pathophysiological consequence. The local immune response plays a key role, with numerous genes more strongly regulated in the intestine than at lymphohaematopoietic organs.     

Analysis of a parasite supra community from the Flensburg fjord

Parasites from Flensburg fjord, northern German Baltic coast, were investigated under regard of the component, guild, and supra community level. At least, 28 host species of the guilds snails, planktonic and benthic crustaceans, and fish (exclusively small-sized species) were infected by 53 parasite species (28 autogenic and 19 allogenic ones, six of uncertain status). The sampling location was a shallow water with muddy sand bottom and rich vegetation, which is influenced by brackish conditions and strong eutrophication. The density of hosts was high but corresponds to values from other locations in the western Baltic. Prevalence and parasite density was low in snails and planktonic copepods but moderate in benthic crustaceans and often high in the fish guild due to the peculiarities of the single parasite species. Diversity of parasites was high in snails and most crustaceans on the component level, but mostly low in fish. In contrast, only snails attained high diversity on the guild level. Species identity of parasites in mud snail hosts (three Hydrobia spp.) was high, and therefore, they can substitute each other, whereas fish hosts present predominantly their own parasite fauna. At least, 17 developmental cycles of helminths were pursued in the guilds. The supra community is decisively influenced by the host species richness which render possible the diversity of guild communities. The characteristics of the parasite supra community from Flensburg fjord are marked by a random agglomeration of helminth species and their larval stages and some species of other parasite groups.     

Transmission of fish parasites into grouper mariculture (Serranidae: <Emphasis Type="Italic">Epinephelus coioides</Emphasis> (Hamilton, 1822)) in Lampung Bay,Indonesia

Differently fed groupers Epinephelus coioides from an Indonesian finfish mariculture farm were studied for ecto- and endohelminth parasites. Pellet-fed E. coioides were infested with 13 parasite species/taxa of which six had a monoxenous and seven a heteroxenous life cycle. A total of 14 parasite species/taxa were found in the fish that were fed with different trash fish species, four of them with a monoxenous and ten with a heteroxenous life cycle. The use of pellet food significantly reduced the transfer of endohelminths and the number of parasites with a heteroxenous life cycle. Out of ten studied trash fish species, 62 parasite species were isolated (39% ectoparasitic and 61% endoparasitic), four of them also occurring in the cultured E. coioides and 14 in different groupers from Balai Budidaya Laut Lampung. The trash fish is held responsible for the transmission of these parasites into the mariculture fish. Endohelminth infestation of pellet fed fish demonstrates that parasite transfer also occurs via organisms that naturally live in, on, and in the surroundings of the net cages. Seventeen recorded invertebrates from the net cages might play an important role as intermediate hosts and hence parasite transmitters. The risk of parasite transfer can be considerably reduced by feeding selected trash fish species with a lower parasite burden, using only trash fish musculature or minimizing the abundance of invertebrates (fouling) on the net cages. These methods can control the endoparasite burden of cultivated fish without medication. The control of ectoparasites requires more elaborate techniques. Once they have succeeded in entering a mariculture farm, it is almost impossible to eliminate them from the system.     

Fish Allergy: In Review

Globally, the rising consumption of fish and its derivatives, due to its nutritional value and divergence of international cuisines, has led to an increase in reports of adverse reactions to fish. Reactions to fish are not only mediated by the immune system causing allergies, but are often caused by various toxins and parasites including ciguatera and Anisakis. Allergic reactions to fish can be serious and life threatening and children usually do not outgrow this type of food allergy. The route of exposure is not only restricted to ingestion but include manual handling and inhalation of cooking vapors in the domestic and occupational environment. Prevalence rates of self-reported fish allergy range from 0.2 to 2.29 % in the general population, but can reach up to 8 % among fish processing workers. Fish allergy seems to vary with geographical eating habits, type of fish processing, and fish species exposure. The major fish allergen characterized is parvalbumin in addition to several less well-known allergens. This contemporary review discusses interesting and new findings in the area of fish allergy including demographics, novel allergens identified, immunological mechanisms of sensitization, and innovative approaches in diagnosing and managing this life-long disease.     

Parasites of Urophycis brasiliensis (Gadiformes: Phycidae) as indicators of marine ecoregions in coastal areas of the South American Atlantic

The potential value of parasites as ecosystem markers was tested by analyzing the metazoan assemblages of Urophycis brasiliensis caught in four locations distributed in three ecoregions of the Warm Temperate Southwestern Atlantic. A total of 5,001 metazoan parasites belonging to 33 species were found. The identified parasites varied across locations in terms of presence, prevalence, and abundance, and their multivariate analyses resulted in clear similarity patterns. No differences were observed between two locations of the same ecoregion, whereas an evident separation of samples was observed across ecoregions in support of the existing hypotheses regarding the ecoregional division of the southwestern Atlantic. We proposed that parasite assemblages, which are composed of several metazoan phyla, are potentially useful as ecosystem indicators. This suggestion is derived from the combined evidence of the evolutionary history and biogeography of multiple lineages, which is expected to be more efficient in capturing recurrent patterns in overall biodiversity than individual lineages. Furthermore, as many parasites have complex life cycles, their distribution patterns are dependent not only on environmental conditions but also on the distribution and population density of all hosts involved in their life cycles, adding further sources of distributional variability that act synergistically to define robust geographical patterns. The selection of long-lived parasites and their comparative analysis provided evidence supporting the existence of three different stocks in the four sampled areas. The best parasite tags were those with low specificity in fish hosts, constituting promising biological tags for the stock discrimination of other fish species in the region.     

Parasite fauna of farmed Nile tilapia (<Emphasis Type="Italic">Oreochromis niloticus</Emphasis>) and African catfish (<Emphasis Type="Italic">Clarias gariepinus</Emphasis>) in Uganda

An intensive parasite survey was conducted in 2008 to better understand the parasite fauna occurrence, distribution and diversity in the commercial aquaculture fish species in Uganda. A total of 265 fish collected from hatcheries and grow-out systems were examined for parasites using routine parasitological techniques. The survey yielded 17 parasite species: 11 from Oreochromis niloticus and ten from Clarias gariepinus. Four parasites—Amirthalingamia macracantha, Monobothrioides sp., Zoogonoides sp. and a member of the family Amphilinidae—were recorded for the first time in the country. The parasite diversity was similar between hosts; however, O. niloticus was dominated by free-living stage-transmitted parasites in lower numbers, whereas both trophically and free-living stage-transmitted parasites were equally represented in C. gariepinus in relatively high intensities. The patterns in parasite numbers and composition in the two hosts reflect differences in fish habitat use and diet. A shift in parasite composition from monoxenous species-dominated communities in small-sized fish to heteroxenous in large fishes was recorded in both hosts. This was linked to ontogenetic feeding changes and prolonged exposure to parasites. Polyculture systems showed no effect on parasite intensity and composition. The gills were highly parasitized, mainly by protozoans and monogeneans. Generally, the occurrence and diversity of parasites in these fish species highlight the likelihood of disease outbreak in the proposed intensive aquaculture systems. This calls for raising awareness in fish health management among potential farmers, service providers and researchers.     

First record of anisakid juveniles (Nematoda) in the European seabass <Emphasis Type="Italic">Dicentrarchus labrax</Emphasis> (family: Moronidae), and their role as bio-indicators of heavy metal pollution

This study assessed the anisakid nematode distribution pattern in the fish collected from coasts of Mediterranean Sea, Egypt, during the period September 2010–April 2011. Two hundred thirty out of 300 (76.7%) Dicentrarchus labrax (European seabass) marine fishes belonging to family Moronidae were dissected and found to be infected with larva three nematodes. The larvae had been studied by light and scanning electron microscopy. The present work represents the first record of the presence of the parasite in this fish in the Mediterranean Sea. The concentrations of some heavy metals (Pb, Zn, Fe, Cd, Cu, Mn, Ni) in parasites as well as in tissues of fish were measured. The presented results showed that the nematode parasites are able to accumulate heavy metals in their tissues and in some cases that they are able to accumulate large amounts of heavy metals in a higher amount than host tissues. This demonstrated their sustainability as bioindicators of environmental pollution by removing heavy metals and help in the survival of fish.     

Resistance against eye flukes: naïve versus previously infected fish

A central issue in fish production is the influence of parasitic infections on fish health in fish farms and on survival prospects after fish-stocking into the wild. Is it preferable to produce fish in infection-free conditions or to allow some infection to elicit resistance in fish? We explored the infection of totally naïve and previously infected rainbow trout (Oncorhynchus mykiss) by the trematode parasite Diplostomum spathaceum in laboratory conditions. We found that up to 86.1% of the presented cercariae became established in the lenses of naïve fish, which indicated that these fish were highly susceptible to infection and that innate resistance served little or no protection against the parasite. However, acquired resistance after initial infection decreased parasite establishment by 85.0–89.1%. Parasite establishment was also affected by fish host density as fewer parasites were found in fish in higher densities. The implications of these results for the fish-farming industry and fish-stocking protocols are discussed.     

Parasites of commercially important fish from Lake Naivasha,Rift Valley,Kenya

In Lake Naivasha, the common carp Cyprinus carpio L. 1758 was accidentally introduced from fish farms adjacent to River Malewa in 1999 and now forms the bulk of the total fish caught. Since its introduction, no study has been made on its parasitic community nor are there any reports on ectoparasites from other fish species in this lake to the best of our knowledge. Therefore, the aim of this study was to describe the parasitic community of C. carpio and two other commercially important fish species: Oreochromis leucostictus and Tilapia zillii. Additionally, the abundant Barbus paludinosus was included in the study. A total of 286 fish (145C. carpio, 56 O. leucostictus, 18?T. zillii, and 67 B. paludinosus) were collected during the year 2011 and examined. Ten taxa of parasites were recovered from C. carpio dominated by the monogenean Dactylogyrus minutus, occurring with a prevalence (p) of 99.3 %. Thirteen taxa of parasites were identified from O. leucostictus dominated by monogeneans Cichlidogyrus spp. (p?=?91.1 %). T. zillii harbored nine taxa of parasites with the digenean Tylodelphys sp. (p?=?83.3 %) being dominant and B. paludinosus harbored 11 taxa of parasites dominated by an unidentified monogenean of the genus Dactylogyrus (p?=?83.6 %). C. carpio had the lowest helminth species diversity and richness while monogenetic trematodes, which have never been reported from fish in Lake Naivasha, were the most prevalent parasites recovered.     

Helminth parasites of the Atlantic chub mackerel, <Emphasis Type="Italic">Scomber colias</Emphasis> Gmelin, 1789 from Canary Islands,Central North Atlantic,with comments on their relations with other Atlantic regions

Eleven parasite taxa were found infecting 68 Atlantic chub mackerel, Scomber colias Gmelin, 1789 from the Canary Islands, Central North Atlantic. The most abundant parasites were the gill monogenean Pseudokuhnia minor (P = 54.4%), larval anisakid nematodes (P = 11.8%) in the body cavity, a larval tetraphyllidean infecting bile ducts (P = 8.8%) and didymozoid digeneans infecting the gills (P = 7.4%). No correlation between fish length and abundance of infection with these parasites was found. Within the Atlantic, the comparison of present results with previous reports on the occurrence of parasites in this fish host, might suggest that there is more than one population unit of Atlantic chub mackerel in the Eastern Atlantic.     

Parasite communities in three sympatric flounder species (Pleuronectiformes: Paralichthyidae): similar ecological filters driving toward repeatable assemblages

The relative role of host phylogeny and ecology on parasite community structure is analyzed in three sympatric paralichthyids from Argentine waters: the carcinophagous Xystreurys rasile and the piscivorous Paralichthys isosceles and P. patagonicus. Their relatedness, inherited ecological and physiological traits and shared past histories should result in certain similarities in their parasite assemblages. With this as our null hypothesis, we focused on the effects of measurable traits (size, age and diet) across fish species, with departures from a general pattern being interpreted as a consequence of ecological filters preventing homogeneous infections. The percentage of individuals/species that host-specific parasites contributed to each component community, as well as their effect on similarity of assemblages within/across host species, showed that they were not important contributors to abundance, richness and similarity, being irrelevant for the repeatability within component communities and across fish species as a phylogenetically related group. To minimize the effect of variables other than diet or trophic level only trophically transmitted nonspecific parasites were included in further analyses. After controlling for fish size, the congeneric host species harboured assemblages significantly different from those found in X. rasile, but were similar to each other because of their shared high trophic levels. Assemblages of equivalent structure harboured by fish with different age-size relationships showed that these variables seem to act at dissimilar rates on different features of the parasites assemblages. Indeed, age affected mainly the parasite abundance, whereas body size influenced mostly species richness. In conclusion, similar ecological filters produce analogous infections across host species driving towards homogeneous parasite communities.     

Diet assimilation trends and host-parasite relationships in two species of sunfish (<Emphasis Type="Italic">Lepomis</Emphasis>) revealed by stable isotope analyses of multiple tissues

White grub flukes, Posthodiplostomum minimum centrarchi (Trematoda), and hookworms Pomphorhynchus bulbocolli (Acanthocephala) are common internal parasites for many North American freshwater fishes. P. minimum are found as cysts in internal organ tissues, while P. bulbocolli are found as sexually mature adults in gastrointestinal (GI) tracts. Stable isotopes of carbon and nitrogen (δ¹³C and δ¹⁵N) are commonly used to infer food web relationships in freshwater lakes. To see if δ¹³C and δ¹⁵N could be used to analyze parasite-host relationships, we analyzed the stable isotopes of the two species of parasites and various tissue types of their fish hosts (bluegill and pumpkinseed sunfish) from different host tissues. The samples δ¹³C and δ¹⁵N demonstrated that P. minimum and P. bulbocolli fed on the fish hosts livers and intestines, respectively. It is also corroborated by correlations in C/N ratios of those fish parasites and their fish host tissues. This study highlights the importance of identifying the specific host tissues parasites feed on in stable isotope analysis.     

Parasite communities of the Salzhaff (Northwest Mecklenburg, Baltic Sea) II. Guild communities, with special regard to snails, benthic crustaceans, and small-sized fish

Metazoan parasites of guilds of benthic snails and crustaceans and of four fish families – Gobiidae, Gasterosteidae, Syngnathidae, and Zoarcidae – were investigated off the brackish Salzhaff area (Southwest Baltic) in the semienclosed Salzhaff and the near Rerik Riff in the free Baltic. Comparisons revealed greater similarities in parasite populations and communities within the fish guilds than between them. According to an evaluation of the core-/satellite-species concept using abundance values, the most important parasites of fish were some generalists, such as Cryptocotyle spp., Podocotyle atomon, and Diplostomum spathaceum, as well as some specialists, such as Acanthostomum balthicum, Thersitina gasterostei, and Aphalloides timmi. These specialists revealed high degrees of prevalence in their main hosts and lower degrees in one or two by-hosts. Additional importance is assigned to parasites that cause harm to their hosts due to their large size, e.g., Schistocephalus spp., or via massive infestation, e.g., several digenean metacercariae. Because specialists were more prominent in snails and fish from the Rerik Riff, the correlation of host numbers with prevalence resulted in only a slight increase instead of a more rapid rise in regression among crustaceans and fish from the entire Salzhaff, where the generalists were more prevalent. The selected host guilds demonstrated the entire life cycles of three digeneans (P. atomon, A. balthicum, A. timmi), one acanthocephalan (Echinorhynchus gadi), and one nematode (Hysterothylacium sp.). The prevalence increased in these cycles from host level to host level and attained relatively high values in all guilds. The parasite fauna of the Salzhaff area is influenced by eutrophication stress, which leads to a high level of productivity and, consequently, to great densities in primary consumers such as snails and crustaceans. These are attractive for several secondary consumers such as fish and birds, which is the reason for the existence of at least 24 autogenic and 20 allogenic parasite species at this locality. The slight surplus of the first category indicates a yet-balanced environment in the investigation area. Received: 5 September 1999 / Accepted: 21 October 1999