Mast cell responses to Ergasilus (Copepoda), a gill ectoparasite of sea bream

Immunocytochemical, light microscopy and ultrastructural studies were conducted on gill of sea bream, Sparus aurata L., naturally parasitized with the important parasitic copepod Ergasilus sp. to assess pathology and cellular responses. Thirty-seven S. aurata were examined from a fish farm; 26 (70%) were parasitized, with infection intensity ranging from 3 to 55 parasites per fish. Hosts were divided into two groups, lightly infected fish (<15 parasites per fish) and heavily infected fish (>15 parasites per fish). In histological sections, the copepod encircled gill lamellae with its second antennae, compressed the epithelium, provoked hyperplasia and hemorrhage, occluded arteries and often caused lamellar disruption. Fusion of the secondary lamellae due to epithelial hyperplasia was common in all infected fish; heavily infected fish showed more intense branchial inflammation. In both healthy and infected fish, mast cells (MCs) were free within the connective tissue inside and outside the blood vessels of the primary lamellae and made close contact with vascular endothelial cells, mucous cells and rodlet cells (RCs). MCs were irregular in shape with a cytoplasm filled by numerous electron-dense, membrane-bound granules. Immunostaining of primary and secondary gill filaments with an antibody against the antimicrobial peptide (AMP) piscidin 3 (anti-piscidin 3 antibody, anti-HAGR) revealed a subpopulation of MCs that were positive. These MCs were more abundant in gills of heavily infected fish than in either lightly infected or uninfected fish (ANOVA, P<0.05). Our report documents the response of gill to ectoparasite infection and provides further evidence that mast cells and their AMPs may play a role in responding to branchial ectoparasite infections.     

Prevalence and intensity of Haemobaphes diceraus (Copepoda: Pennellidae) from shiner perch,Cymatogaster aggregata (Embiotocidae)

The prevalence and intensity of the hematophagous pennellid copepod Haemobaphes diceraus were monitored over a 10-mo period in shiner perch Cymatogaster aggregata at Pipers Lagoon, Nanaimo, British Columbia. The prevalence and mean intensity of metamorphosed adult female H. diceraus (n = 421) were 10.0% and 1.2 (+/-0.5 SD), respectively. The majority (97.9%) of infected fish had single infections, reflecting the possibility of intensity-dependent parasite-induced mortality, rejection of additional parasites, or both. Transforming females were detected throughout the year; however, there was no detectable seasonal pattern of colonization. Neither copepodids nor adult males of H. diceraus were observed on the gills of shiner perch, and this was consistent with the hypothesis that an intermediate host harbors these stages. Males of Haemobaphes sp. infected the gills of bay pipefish Syngnathus griseolineatus with a prevalence and mean intensity of 56.0% and 6.8 +/- 3.7, respectively. Transmission of H. diceraus to shiner perch probably occurs in inshore protected areas, where shiner perch ecologically overlap with the probable intermediate host of H. diceraus, the bay pipefish.     

Trichodina sp. (Ciliophora: Peritrichida) in eel Anguilla anguilla in recirculation systems in denmark: host-parasite relations

Farmed eel cultured in recirculation systems in Denmark were found infected by Trichodina jadranica Raabe, 1958. Associations between parasite abundance and fish size was examined in 2 different production systems. In one system, stocked with relatively well-nourished eels (3 to 31 g), most of the parasites (66%) were found on the dorsal part on the skin and relatively few were found on the gills (approx. 8%). The infection level was significantly positively correlated both with fish weight and length. In the other system, stocked with relatively malnourished small eels (0.5 to 4 g), significantly more parasites (0.06 +/- 0.02 [SD]) were present on fish with a low condition factor than on fish with a higher condition factor (0.13 +/- 0.01 [SD]). In this eel stock the vast majority of the trichodines were found on the gills.     

Effect of concurrent infections of Lernaeocera Branchialis (Copepoda) and Trypanosoma murmanensis (Protozoa) on Atlantic cod, Gadus morhua

A study was initiated to ascertain the prevalence, effect and interaction of the adult stages of the parasitic copepod, Lernaeocera branchialis, on Atlantic cod concurrently infected with a hematozoan, Trypanosoma murmanensis, by comparing condition (K) factor, organ somatic indices, hematological values and lipid concentrations of the liver from infected and uninfected fish of comparable length. Prevalence of the copepod varied from 9 to 21% and was highest in fish examined on the southern coast of Newfoundland. Body condition and blood values were significantly lower in young cod infected with two parasites whereas only K-factor was altered in two size classes parasitized by one copepod. Although lipid concentrations were similar in three length groups of fish without and infected with L. branchialis, the pooled values were significantly greater among the infected group. Mortality occurred only in juvenile cod infected with the copepod and T. murmanensis concurrently. Cod which survived dual infections had lower K-factor and blood values than controls or fish harboring single, parasitic infections. It is concluded that an infection with an adult L. branchialis does not impair the health of fish in this area of the northwestern Atlantic Ocean, but the presence of T. murmanensis concurrently can potentiate its effect.     

Field preservation of monogenean parasites for molecular and morphological analyses

In the present work we examined the efficacy of three different chemical solutions (EtOH 70%, DMSO-NaCl solution, and Longmire buffer) in field preservation of fish gills to be subsequently screened for monogenean specimens destined to morphological and molecular analyses. Degree of difficulty in collecting monogeneans from gills, morphological state of parasites, integrity of their DNA and reliability of sequence reading were observed and qualitatively compared to those of gills and parasites stored in 5% formalin and 99% ethanol. Data were collected over a period of 2 months. Storage in Longmire buffer resulted in dissociation of gills and parasites, while both DMSO and 70% ethanol provided a fine physical and molecular preservation of gills and monogeneans, allowing rapid collection of parasites from lamellae, and easy extraction, amplification and sequencing of parasitic DNA.     

Ultrastructural study of the early development and localization of Loma salmonae in the gills of experimentally infected rainbow trout

The early ultrastructural stages of Loma salmonae were studied in the gills of experimentally infected rainbow trout. No parasitic stages were identified during the first 2 wk of the infection. By week 3 postexposure (PE), uninucleate and binucleate meronts were recognized within host cells (no xenomas) associated with the capillary channels of secondary lamellae and lamellar arteries. An inflammatory reaction was absent. In secondary lamellae, infected cells were isolated from the capillary lumen, and some were recognized as pillar cells. In lamellar arteries, infected cells were localized beneath the endothelium and not in the lumen. Inflammatory reaction and destruction of parasites inside blood cells in the lumen of secondary lamellae were observed by week 4 PE. Three hypotheses, i.e., isolation, internalization, and evasion, are proposed to explain the localization of the infected cells in the gills. It is concluded that meronts are the earliest parasitic stage observed by week 3 PE, pillar cells are secondarily infected by phagocytosis of infected cells in the blood, endothelial cells of gills are not infected, and inflammatory response to the parasite starts by week 4 PE.     

Immunohistochemistry,ultrastructure and pathology of gills of Abramis brama from Lake Mondsee,Austria, infected with Ergasilus sieboldi (Copepoda)

Immunohistochemical, ultrastructural and pathological studies were carried out on the gills of bream Abramis brama (L.) from Lake Mondsee, Austria, that were naturally infected with Ergasilus sieboldi Nordmann, 1832. Of a total of 14 specimens of bream examined, the gills of 7 (50%) were parasitized with this copepod and the intensity of infection ranged from 1 to 23 crustaceans per host. Histopathological investigations of infected gill showed extensive tissue damage due to attachment and feeding of the crustacean. Parasites attached close to the base of filaments near the gill arch. Pressure exerted by the ectoparasite attached to the lateral margin of the gill filaments induced atrophy of the secondary lamellae. Tissue reactions included hyperplasia and mucous cell proliferation of the respiratory epithelium. Mucous cells displayed an intense immunohistochemical reactivity with the anti-nitric oxide synthase antibody. In parasitized primary and secondary lamellae, a high number of eosinophilic granular cells and rodlet cells were noticed. Rodlet cells represent an inflammatory cell type closely linked to other piscine inflammatory cells. Presence of a high number of inflammatory cells at the site of E. sieboldi attachment is related to intense host cellular reaction.     

The effects of Lepeophtheirus salmonis infections on the stress response and immunological status of Atlantic salmon (Salmo salar)

This study was conducted to determine the effects of a high level of infection of the parasitic copepod L. salmonis on the stress response and immunological status of Atlantic salmon. An initial low-level initial infection was carried out 14d prior to a second infection in which twice as many parasites were introduced. Plasma cortisol and prostaglandin E(2) (PGE(2)) levels were monitored concurrent to the expression of six immune-related genes over five sample times (9, 21, 26, 33 and 40days post initial infection, dpii). The mean lice counts on the infected fish increased significantly from the first infection (16.3+/-1.89 at 9dpii) to the second (142.8+/-12.8 at 26dpii). Plasma cortisol levels increased significantly at 26, 33 and 40dpii in infected fish compared to controls. Plasma PGE(2) levels were significantly higher in infected fish at 9, 33 and 40dpii, when compared to controls. At 9dpii, expression of interleukin-1beta (IL-1beta), tumour necrosis factor-alpha (TNFalpha)-like cytokine, major histocompatibility class II (MH II), transforming growth factor-beta (TGFbeta)-like cytokine and cyclooxygenase-2 genes were increased in infected fish compared to controls. The expression of most of these genes returned to control levels at 21dpii when the highest expression of the MH class I gene was observed in infected fish (significantly higher than controls). Major histocompatibility class I gene expression remained higher in infected fish at 26 and 33dpii compared to controls and this was observed for the TNFalpha-like gene. By 33dpii, MH class II and TGFbeta-like genes had higher expression in infected fish compared to controls. Interleukin-1beta and TNFalpha-like gene were the only genes that showed significantly higher expression in infected fish compared to controls at 40dpii, while MH class I gene expression was significantly depressed in infected fish at this time. The expression of nearly all immune-related genes studied here increased following initial infection with L. salmonis, however, immunological stimulation did not reduce parasite numbers or protect against re-infection.     

Effects of dexamethasone on host innate and adaptive immune responses and parasite development in rainbow trout Oncorhynchus mykiss infected with Loma salmonae

The effects of dexamethasone (dex) treatment on infections with the microsporidian parasite, Loma salmonae and the effects of dex on initiation of the adaptive immune response were investigated in rainbow trout, Oncorhynchus mykiss experimentally infected with the parasite. Dex treatment resulted in significantly higher infections with the parasite in the gills and other internal organs, suggesting that dex inhibits aspects of the innate immune response to L. salmonae; the heavier infections in the gills and organs of rainbow trout resembled infections seen in Chinook salmon. Mean xenoma counts per microscope field in the gills of fish infected with L. salmonae treated with dex or left untreated were 169 and 30, respectively. Although higher numbers of xenomas were observed in dex treated fish, the xenomas were generally smaller in size than in infected control fish. The xenomas in dex treated fish showed morphological signs of degeneration including loss and degeneration of early parasite stages, accumulation of amorphous material in xenomas, and infiltration with phagocytic cells containing degenerated parasites. The xenomas in infected untreated fish had larger xenomas with a more uniform size and contained identifiable parasite stages in the cytoplasm. According to this study, once fish have developed an adaptive immune response to the parasite by previous exposure, then fish have 100% protection to reinfection even when treated with heavy doses of dex. L. salmonae immune fish treated or untreated with dex during reinfection with the parasite developed no xenomas in the gills 6 weeks post reinfection. These results indicate that once the cellular response is primed to L. salmonae, then dex related immunosuppression does not reduce the effectiveness of the adaptive immune response.     

Metazoan parasites on the gills of the skipjack tuna Katsuwonus pelamis (Osteichthyes: Scombridae) from the Alboran Sea (western Mediterranean Sea)

The gills of 31 skipjack tuna Katsuwonus pelamis (L.) caught in the Alboran Sea (western Mediterranean Sea) were examined for metazoan parasites, and the gills of 4 specimens from the Balearic Sea (also western Mediterranean Sea) were analysed for comparative purposes. Nine -species of parasites were found, including 8 didymozoid trematodes (Atalostrophion cf. bio-varium, Didymocylindrus filiformis, Didymocylindrus simplex, Didymocystis reniformis, Didymoproblema fusiforme, Didymozoon longicolle, Koellikeria sp. and Lobatozoum multisacculatum) and 1 caligid copepod (Caligus bonito). Koellikeria sp. and L. multisacculatum were not recorded in the Balearic Sea. Most of the parasites (79.2% of all specimens) were didymozoids. Didymozoon longicolle was the dominant species; A. cf. biovarium, D. simplex, D. fusiforme and L. multisacculatum are reported from the Mediterranean Sea for the first time. No correlation was found between the intensity of infection of any parasite species and host size or sex. Most of the parasites, particularly didymozoids, showed a high site-specificity. Significant differences were found between the parasite assemblages of K. pelamis from the Alboran Sea and from the Atlantic Ocean. D. fusiforme, D. longicolle and L. multisacculatum are suggested as potential tags to follow skipjack tuna migrations between the Atlantic Ocean and Mediterranean Sea.     

Immunocytochemical localization of piscidin in mast cells of infected seabass gill

Annual losses of ～5–10% of the juvenile stock of European seabass, Dicentrarchus labrax (L.) in the northern coast of the Adriatic Sea has been attributed to heavy infections of the gill monogenean Diplectanum aequans. Immunocytochemical, light and ultrastructural studies were carried out on seabass naturally parasitized with this monogenean. The site of the worm's attachment was marked by the common presence of haemorrhages and white mucoid exudate. In histological sections, infected gills showed hyperplasia, as well as proliferation of mucous cells and rodlet cells. Disruption and fusion of the secondary lamellae were common in all infected seabass, with several specimens also showing marked inflammation and erosion of the primary and secondary lamellar epithelium. Immunostaining of primary and secondary gill filaments with an antibody against the antimicrobial peptide piscidin 3 (anti-piscidin 3 antibody, anti-HAGR) revealed a subpopulation of mast cells that were positive. Mast cells were both within and outside the blood vessels of the primary and secondary lamellae, and often made intimate contact with vascular endothelial cells. Mast cells were irregular in shape with a cytoplasm filled by numerous electron-dense, membrane-bound granules. Our data provide evidence showing the presence of piscidin 3 in the cytoplasmic granules of an important group of fish inflammatory cells, the mast cells resident in seabass gill tissue. There was no significant difference in the number of HAGR-positive mast cells between infected and uninfected fish (ANOVA, p > 0.05). However, mast cells in parasitized gills usually showed much stronger immunostaining intensity compared to those in unparasitized gills. These data are the first to document a response of piscidins or any other antimicrobial peptide of fish to parasite infection and suggest that mast cells may play a role in certain inflammatory responses without a detectable increase in their numbers.     

Morphometric analysis of the gills of the European eel, Anguilla anguilla

The gills of the European eel, Anguilla unguilla L. were analysed morphometrically. Fresh (unfixed) gills and resin-replica casts of the branchial vascular system were examined. The total gill surface area was found to be proportional to (body mas) 0-715 for fish of between 60 and 1 160 g. This relationship between gill surfxe area and body mass was maintained irrespective of a reduction in body mass produced by fasting. Vessel dimensions were obtained from the vascular casts. Calculations made using these values suggest that the major sites of gill vascular resistance lie at the level of the afferent lamellar arterioles and the secondary lamellae.     

对鲇鱼鳃部寄生的固着鳋的生态研究

作者研究了江西江口水库鲇鳃部寄生固着鳋的种群生态学及其对寄生部位的选择性。固着鳋的感染率和丰盛度表现出明显的季节变化,以夏初最高;其繁殖也具有季节性,怀卵个体的比例同样有夏初最高。固着鳋对寄生部位的选择性似乎与种群的数量有关,当种群数量高时更多的固着鳋分布于中间的鳃片上,对多种寄生虫同时寄生条件下固着鳋寄生部位选择性的研究,将有助于进一步了解固着鳋和寄生鲇鳃部其它种类的寄生虫之间的关系。     

瓦氏雅罗鱼生殖洄游过程中离子调节相关生理变化研究

为了解达里湖瓦氏雅罗鱼(Leuciscus waleckii)生殖洄游过程中血清离子调节相关生理变化, 对比了达里湖和贡格尔河瓦氏雅罗鱼血清离子(Na+、K+、Cl?、Ca2+和Mg2+)水平, 鳃、肠和肾组织Na+/K+-ATPase和鳃Ca2+/Mg2+-ATPase活性、血清催乳素(PRL)、生长激素(GH)和类胰岛素生长因子-1(IGF-1)水平及鳃组织结构差异; 并利用实验生态学方法, 研究达里湖中瓦氏雅罗鱼转入贡格尔河水24h后上述生理参数的响应。研究结果显示, 与达里湖未洄游的瓦氏雅罗鱼相比, 洄游到贡格尔河后其血清Na+含量显著降低(P<0.05), Cl?含量显著升高(P<0.05), 肾脏和肠组织中Na+/K+-ATPase活性显著升高(P<0.05), 而鳃组织中Na+/K+-ATPase活性无显著变化; 血清K+、Ca2+、Mg2+水平和GH、IGF-1、PRL含量无显著变化。将达里湖瓦氏雅罗鱼转入河水中24h后, 其血清Cl?含量显著升高(P<0.05)、K+含量显著降低(P<0.05), 且在鳃、肠和肾组织中Na+/K+-ATPase及鳃Ca2+/Mg2+-ATPase活性均显著升高(P<0.05), 血清PRL和IGF-1水平显著升高(P<0.05); 比较湖中和河中瓦氏雅罗鱼鳃组织形态结构, 显示湖中瓦氏雅罗鱼鳃基底膜分布着大量黏液细胞, 洄游到河水中后黏液细胞数量明显减少, 鳃基底膜上氯细胞体积增大而数量未见明显变化。本研究结果表明: 瓦氏雅罗鱼从达里湖洄游到贡格尔河后通过提高血清PRL和IGF-1水平, 进而介导鳃、肠和肾组织中Na+/K+-ATPase活性增加, 从而维持鱼体较高或稳定的血清离子水平。     

Gills of the medaka (Oryzias latipes): A scanning electron microscopy study

The general morphology and surface ultrastructure of the gills of adult and larvae medaka (Oryzias latipes) were studied in freshwater and seawater using scanning electron microscopy. The gills of all examined fish were structurally similar to those of other teleosts and consisted of four pairs of arches supporting (i) filaments bearing lamellae and (ii) rakers containing taste buds. Three cell types, specifically pavement cells, mitochondria‐rich cells (MRCs), and mucous cells, constituted the surface layer of the gill epithelium. Several distinctive characteristics of medaka gills were noted, including the presence of regularly distributed outgrowth on the lamellae, enlarged filament tips, the absence of microridges in most pavement cells in the filament and lamellae and the presence of MRCs in the arch at the filament base. A rapid mode of development was recorded in the gills of larval fish. At hatching, the larvae already had four arches with rudimentary filaments, rakers, and taste buds. The rudimentary lamellae appeared within 2 days after hatching. These results suggest the early involvement of larval gills in respiratory and osmoregulation activities. The responses of the macrostructures and microstructures of gills to seawater acclimation were similar in larvae and adult fish and included modification of the apical surface of MRCs, confirming the importance of these cells in osmoregulation. The potential roles of these peculiarities of the macrostructures and microstructures of medaka gills in the major functions of this organ, such as respiration and osmoregulation, are discussed.     

Acidophilic granulocytes in the gills of gilthead seabream Sparus aurata: evidence for their responses to a natural infection by a copepod ectoparasite

Immunohistochemical and ultrastructural studies were conducted on the gills of gilthead seabream, Sparus aurata L., naturally infected with the copepod ectoparasite Ergasilus lizae (Krøyer, 1863) in order to assess pathology and the host immune cell response. Gills of 56 gilthead seabream were screened for ectoparasites; 36 specimens (64.3%) harbored E. lizae. Intensity of infection was 32.7±8.7 (mean ± SE). Pathological alterations to the gills of the host were more pronounced in close proximity to the copepod site of attachment. The parasite attached to the gills by means of its modified second antennae, occluded the arteries, provoked epithelial hyperplasia and hemorrhages and most often caused lamellar disruption. Numerous granular cells were encountered near the site of E. lizae attachment. In both infected and uninfected gills, the granular cells lay within the filaments and frequently occurred within the connective tissue inside and outside the blood vessels of the filaments. The type of granular cell was identified by immunohistochemical staining by using the monoclonal antibody G7 (mAb G7), which specifically recognizes acidophilic granulocytes (AGs) of S. aurata and with an anti-histamine antibody (as a marker for mast cells, MCs) on sections from 13 uninfected gills and 21 parasitized gills. The use of mAb G7 revealed that, in gills harboring copepods, the number of G7-positive cells (i.e., AGs; 32.9±3.9, mean number of cells per 45,000 μm² ± SE) was significantly higher than the density of the same cells in uninfected gills (15.3±3.8; ANOVA, P<0.05). Few histamine-positive granular cells (i.e., MCs) were found in the uninfected and parasitized gills. Here, we show, for the first time in S. aurata infected gills, that AGs rather than MCs are recruited and involved in the response to E. lizae infection in seabream.     

Mating rendezvous in monogenean gill parasites of the humbug Dascyllus aruanus (Pisces: Pomacentridae)

The gills of the humbug, Dascyllus aruanus (Pomacentridae), were infected by a monogenean genus Haliotrema at a high prevalence (83%) but with a low mean intensity (5.6 worms/fish). All the gill arches of 365 fish, caught on the fringing reef of Moorea Island (French Polynesia), were examined for parasites. Each hemibranch was divided into 12 subequal sections. Monogeneans showing microhabitat overlap were defined as couples. Hosts with low intensity of infection (fewer than 5 monogeneans per gill) were selected and couples were recorded. Among the 37 hosts harboring 2 worms on their gills, 18 fish were infected with these 2 monogeneans on the same gill side of the body; 50% (n = 9) of these harbored monogeneans within the same gill arch and 55% (n = 5) of these last fish showed individual parasites within the same section of the gill. In the case of hosts with few monogeneans (3 and 4 individuals; n = 37) on the same arch, more than 40% (n = 16) harbored worms in couples. There may be some chemical communication that allowed these monogeneans to migrate toward each other and thus enhance mating success. Mating rendezvous appears to be a more important factor than site location for these gill monogeneans.     

The intestinal parasite Pomphorhynchus laevis (Acanthocephala) interferes with the uptake and accumulation of lead (210Pb) in its fish host chub (Leuciscus cephalus)

Uninfected chub as well as fish experimentally infected with the acanthocephalan parasite Pomphorhynchus laevis were exposed to ²¹⁰Pb²⁺ for up to 38 days and the uptake and distribution of lead within different fish organs and the parasites was determined at various time points. Highest metal concentrations were detected in the acanthocephalans, followed by intestine, bile, liver, gill and muscle of the fish host. Infected chub had significantly lower ²¹⁰Pb levels in the gills on day 17 (P≤0.01), in the bile on day 24 (P≤0.05) and in the gills as well as in the intestine on day 38 compared with uninfected fish. A subsequent polynomial regression revealed that lead levels for the infected fish ranged below the levels determined for uninfected fish during most of the exposure period. This is the first proof that P. laevis reduces lead levels in the bile thereby diminishing or even impeding the hepatic intestinal cycling of lead, which may reduce the amount of metals available for the fish organs. This is especially important for ecotoxicological research. For example, organisms used as accumulation indicators may erroneously indicate low levels of pollution if they are infected with parasites which alter their pollutant uptake mechanisms. Additionally, the results gave further experimental evidence for acanthocephalans as accumulation indicators for metals.     

Assessment of the State of Flounders from Sivuch'ya Bight (Peter the Great Bay, Sea of Japan) Based on Histopathological Parameters

The liver and gills of five flounder species (Pleuronectes obscurus, P. punctatissimus, P. yokahamae, P. herzensteini, and Platichthys stellatus) from Sivuch'ya Bight were histologically studied. Specimens of all species were characterized by a wide spectrum of histomorphological changes. The proportions of most specific pathologies in P. obscurusfrom Sivuch'ya Bight were estimated. The pathologies comprised two major groups: those of the gills (edema and fusion of the respiratory lamellae; lifting and hyperplasia of the respiratory epithelium; vacuolization of the epithelium cells; and the presence of clavate lamellae, aneurysmal areas, and parasites) and those of the liver (vacuolization of the hepatocytes, aneurysms, necrosis of the parenchyma tissue, pathologies of the hepatocyte nuclei, pigment accumulation, and an increase in the number and size of melanomacrophage centers). The estimated proportions of pathological changes were compared with those observed in P. obscurusspecimens from the most contaminated area of Amurskii Bay. In both Sivuch'ya Bight and Amurskii Bay, the proportion of fish with various pathologies was high. The comparison of pathological changes in the gills and liver of P. obscurusand P. stellatusfrom Sivuch'ya Bight showed that, in terms of many parameters, the former species is more sensitive to pollution of the marine environment than the latter. Pathomorphological changes in the organs of the flounders studied are apparently caused by chronic pollutant action and suggest that the fish of both areas are in a damaged state.     

Ichthyophthirius multifiliis (Fouquet) in the mirror carp, Cyprinus carpio L.

Mirror carp were infected with Ichthyophthirius multifiliis (Fouquet) under standardized conditions. The size and number of parasites at selected sites on the body were recorded during the course of the infection. Initial exposure to 40 mature parasites resulted in a mild infection with 100% recovery after 18 days. Recovered fish did not appear to be carriers of the parasite. Exposure to 400 parasites resulted in 100% mortality between 22–25 days. The growth rate of the parasite was linear. Parasites were more numerous in the dorsal surface of the fish than in the lateral or ventral surface. The increase in parasite numbers during the disease was greater in the gills than in the skin.