We studied the morphology and occurrence of splenic Langerhans-like (LL) cells in species represe... more We studied the morphology and occurrence of splenic Langerhans-like (LL) cells in species representing 11 orders of ray-finned fishes, Actinopterygii. LL cells were frequent in spleen tissue of species among Cypriniformes, Esociformes, Salmoniformes, and Pleuronectiformes. These cells contained granules which resembled Birbeck granules known to occur in mammalian Langerhans cells. The ultrastructure of LL cells in Northern pike, Esox lucius, and in Atlantic halibut, Hippoglossus hippoglossus were similar to those reported in salmonids. LL cells found in cyprinids shared some characteristics with the LL cells in other Actinopterygii species, although unique structures distinguished them from the latter. They contained dense bodies within the Birbeck-like (BL) granules, a characteristic that was never observed in species outside the Cypriniformes. Two types of BL granules were characterized in cyprinid LL cells. The ultrastructure of BL granules across the species is discussed. LL cells in all Actinopterygii species demonstrated close contacts with nearby cells, characterized by adherens-like junctions. Additionally, multivesicular bodies were present within the cytoplasm and large aggregates of exosomes were observed closely associated with the plasma membrane suggesting their release from the cells. These structures are discussed in relation to mammalian dendritic cells. Macrophages found in European perch, Perca fluviatilis, blue gourami, Trichogaster trichopterus, and Atlantic halibut, Hippoglossus hippoglossus contained lysosomes and residual bodies with structures resembling Birbeck granules. These granules and cells were clearly distinct from LL cells.
Contemporary topics in laboratory animal science, 1998
Loma salmonae is an economically important gill microsporidian pathogen of pen-reared chinook and... more Loma salmonae is an economically important gill microsporidian pathogen of pen-reared chinook and coho salmon. Chinook and coho salmon are generally poorly suited for use in laboratory studies because of their high mortality rates when infected with L. salmonae and their high-level of susceptibility to other infectious diseases. Using gill tissue from chinook salmon that contained mature xenomas laden with L. salmonae spores, we successfully transmitted the infection to rainbow trout. The infection developed in an identical manner and over a similar time course in trout as for chinook salmon. In contrast, we were unable to transmit the infection to other candidate salmonid species, including Atlantic salmon, brook trout, or arctic charr. Gill tissue from experimentally infected rainbow trout was then used to successfully transmit the parasite to other trout. Horizontal transmission was documented from infected to naive tankmates. Analysis of these results indicated that L. salmonae ...
Loma salmonae is an economically important gill microsporidian pathogen of pen-reared chinook and... more Loma salmonae is an economically important gill microsporidian pathogen of pen-reared chinook and coho salmon. Chinook and coho salmon are generally poorly suited for use in laboratory studies because of their high mortality rates when infected with L. salmonae and their high-level of susceptibility to other infectious diseases. Using gill tissue from chinook salmon that contained mature xenomas laden with L. salmonae spores, we successfully transmitted the infection to rainbow trout. The infection developed in an identical manner and over a similar time course in trout as for chinook salmon. In contrast, we were unable to transmit the infection to other candidate salmonid species, including Atlantic salmon, brook trout, or arctic charr. Gill tissue from experimentally infected rainbow trout was then used to successfully transmit the parasite to other trout. Horizontal transmission was documented from infected to naive tankmates. Analysis of these results indicated that L. salmonae ...
Journal of Aquatic Animal Health 8:64-69, 1996 O Copyright by Che American Fisheries Society 1 ..... more Journal of Aquatic Animal Health 8:64-69, 1996 O Copyright by Che American Fisheries Society 1 ... Effects of Intermittent Formalin Treatment of Atlantic Salmon Juveniles on Growth, Condition Factor, Plasma Electrolytes, and Hematocrit in Freshwater and after Transfer to Seawater
Chloramine-T is a commonly used therapeutic agent for the treatment of bacterial gill and skin di... more Chloramine-T is a commonly used therapeutic agent for the treatment of bacterial gill and skin diseases in the intensive aquaculture of salmonids; however, little is known about its effects on healthy fish. Juvenile rainbow trout (Oncorhynchus mykiss) were exposed weekly to 5, 10, and 20 mg active chloramine-T ingredient∙L−1 in a 20-tank replicate flow-through facility. Control fish were treated with tank water only. Growth parameters and haematocrits were taken twice weekly and serum biochemistry was measured on termination of the experiment. Absolute growth rates were suppressed but only statistically significantly in fish treated with 20 mg chloramine-T∙L−1 compared with controls. Fish exposed to 10 and 20 mg chloramine-T∙L−1 showed significant predisposition to an erosive dermatitis of the caudal fin which appeared to be caused by opportunistic pathogens of the genus Pseudomonas spp. and Flavobacter spp. Haematocrits decreased in controls and ail treatments. A significant concentration-dependent decrease in plasma sodium and chloride was observed. Plasma glucose levels did not vary and were similar to those reported for unstressed trout. We recommend that care be taken when using chloramine-T prophylactically and that concentrations of less than 10 mg∙L−1 be used.
Following a per os challenge of naive rainbow trout with live spores of Loma salmonae, head kidne... more Following a per os challenge of naive rainbow trout with live spores of Loma salmonae, head kidney mononuclear cells (MNC) in culture were able to proliferate in response to crude soluble parasite extract or intact dead spores. A significant response was seen by week 2 post-exposure and a maximum response developed by week 6 or 8, respectively. During this initial challenge, spore filled cysts developed on the gills of challenged fish, and the cysts ruptured by week 12 as is typical for microsporidial gill disease of salmonids (MGDS). Two weeks following this, fish were re-challenged with live spores, and in these fish an enhanced in vitro proliferative response of MNC was immediately apparent, and spore filled cysts did not develop. In contrast, when naive trout were given dead spores by intraperitoneal injection, the most pronounced proliferative responses of MNC developed earlier (week 2 PE) and the response was greater when cells were incubated in vitro with dead spores rather than with crude soluble extract. When these fish were re-challenged per os with live spores, a heightened proliferation in MNC was observed 4 weeks after this exposure and the fish likewise resisted development of xenomas. In fish infected orally or injected intraperitoneally with spores, a marked increase in the response to the mitogen concanavalin A was seen for 22 weeks post-exposure when compared to controls not receiving any spores.
ABSTRACT In two variants of Loma salmonae that have specificity for rainbow trout Oncorhynchus my... more ABSTRACT In two variants of Loma salmonae that have specificity for rainbow trout Oncorhynchus mykiss(OA variant) and specificity to brook trout Salvelinus fontinalis(SV variant), the parasitophorous vacuole forms at the onset of sporogony. In the OA variant the merogonial stage is bound by a single plasma membrane in direct contact with host cytoplasm. The parasitophorous vacuole formation is initiated by the host cell surrounding the merogonial stages with endoplasmic reticulum (ER) as occurs in autophagy. Of the two host ER membranes surrounding the parasite, one remains in close association with the plasma membrane of the meront, while the other forms the limiting membrane of the vacuole. The sporogonial stage is bounded by two closely apposed membranes, giving the appearance of a thick electron dense plasmalemma. The observations from this study support the novel hypothesis that this microsporidian uses the intracellular process of autophagy to aid formation of a parasitophorous vacuole. The morphology of the SV‐variant is consistent with that of the OA‐variant suggesting that it uses the same mechanism for development.
Members of an Ahousaht First Nations community of Vancouver Island, Canada have developed a marke... more Members of an Ahousaht First Nations community of Vancouver Island, Canada have developed a market for wild-caught species of indigenous rockfish (Sebastes spp.). The fish, which are caught by hook and line, are transported live to fish markets in Vancouver. Recently, market place downgrading of the fish has occurred due to a syndrome referred to as``black-mould'', characterized by linear black disfigurations, and erosions, of the skin. Samples from 14 wild-caught rockfish were examined to determine the cause. On the basis of sub-gross and histological examination, the black-mould syndrome was attributed to intraepithelial deposition of eggs from a trichuroid nematode of the genus Huffmanela, coupled with an inflammatory response. The eggs observed in the tissues of the rockfish differed in size and morphology from those described for other species of Huffmanela. This is the first report of Huffmanela spp. infection in rockfish, probably due to a previously undescribed species.
Loma salmonae is an intracellular obligate parasite of farmed chinook salmon (Oncorhynchus tshawt... more Loma salmonae is an intracellular obligate parasite of farmed chinook salmon (Oncorhynchus tshawtscha) and is the causative agent for microsporidial gill disease (MGD). The infection occurs mainly in secondary gill lamellae, with the formation of large white spore-laden xenomas within the endothelial and pillar cells. The overall objective of the study was to investigate the minimum exposure time required for disease transmission between naive rainbow trout (Oncorhynchus mykiss) (RBT) and L. salmonae-infected fish using the cohabitation challenge model. In trial I, low (1), medium (5) or high (10) numbers of infected RBT were added to tanks containing 45 naive fish for a cohabitation period of 21 days. Trial II limited the cohabitation period between five L. salmonae-infected fish in a tank of 45 naive RBT to 1, 12, 24 or 96 h. For both trials, each treatment level was completed in duplicate and an additional tank of 45 naive RBT served as the control and did not receive infected fish. Beginning on day 21 post exposure (PE) and continuing biweekly until day 83 PE and 105 PE for each trial, respectively, fish were evaluated for branchial xenomas to determine xenoma onset time and intensity. The effect of adding one infected fish produced similar median xenoma onset time and mean xenoma intensity compared with adding 5 or 10 infected fish (trial I). Significant differences were observed amongst the survivor curves for the fish exposed to infected RBT for 1, 12, 24 and 96 h, with the median onset time equal to 63 days for the lowest exposure period. This study demonstrated that L. salmonae transmission was possible with as little as 1-h exposure time between 5 cohabiting infected and 45 naive RBT. Adding five L. salmonae-infected fish (at week 7 PE) to a group of naive RBT for a period of 1 h resulted in over 94.5% disease prevalence in cohabiting fish.
Chloramine-T is a widely used prophylactic and therapeutic agent in freshwater aquaculture. This ... more Chloramine-T is a widely used prophylactic and therapeutic agent in freshwater aquaculture. This study examined the effects of repeated intermittent exposure of healthy rainbow trout (Oncorhynchus mykiss) fingerlings to sublethal concentrations of chloramine-T (0, 5, 10, or 20 mg/L) twice weekly in 1-h pulses at 11 °C for 4 weeks in a replicate-tank facility. Gills were excised from subsamples of fish prior to exposure and at the end of the 4-week experimental period. Tissue was fixed and processed for light microscopy and transmission and scanning electron microscopy. The gill epithelium from fish treated with 10 and 20 mg/L chloramine-T appeared swollen and vacuolated, with extensive intercellular edema. There was a significant reduction in the number of lamellar mucous cells and an apparent increase in the numbers of chloride cells. Chloride cells from both the base of the lamella and the lamellar surface of gills exposed to chloramine-T had a significant increase in the area of the apical plasmalemma after treatment with 10 and 20 mg/L, and a reduction in the thickness of the apical plasmalemma-associated glycocalyx. These morphological changes are consistent with a compensatory mechanism for the remedial uptake of ions, suggesting that chloramine-T increased epithelial ion permeability coincident with a possible influx of water leading to intercellular edema. Chloride cell proliferation and intercellular edema may also have affected gas exchange across the branchial epithelium.
Contemporary Topics in Laboratory Animal Science American Association For Laboratory Animal Science, Apr 1, 1998
Gill disease associated with the microsporidian parasite Loma salmonae is an emerging problem aff... more Gill disease associated with the microsporidian parasite Loma salmonae is an emerging problem affecting the marine aquaculture production of Pacific salmon, most notably chinook salmon (Oncorhynchus tshawytscha) and, to a lesser extent, coho salmon (O. kisutch) (1-6). Parasites develop in the vasculature of the gills to form large spore-laden xenomas (2-6). Loma salmonae also infect rainbow trout (O. mykiss) (7-9); however, in contrast to the Pacific salmon, the clinical effects on these fish vary considerably (9). Furthermore, on the basis of unpublished observations from diagnostic materials sent to the Fish Health Unit of the Atlantic Veterinary College, L. salmonae is often detected in groups of trout that do not have a history of clinical disease, whereas this is not the clinical history for chinook salmon. Because of the restrictive nature of current regulations pertaining to the use of therapeutic agents in aquaculture, licenced therapeutic agents are not available for treating fish infected with L. salmonae. Accordingly, there is a need to study the pathobiologic characteristics of L. salmonae in an effort to uncover management factors that could limit the economic effects of infection. Laboratory studies of this disease would benefit by the availability of a species other than chinook salmon, even though they are the principal aquaculture species affected by L. salmonae. Chinook salmon have proven to be difficult to work with in laboratory studies (10) and often become diseased or die because of a range of other endemic infectious diseases, particularly when the fish are stressed. Rainbow trout, in contrast, are a relatively hardy fish that are frequently used in laboratory studies (11). They have been the salmonid species used as a model for many studies, and their requirements and physiologic responses are well documented (11). Our purpose was to evaluate the suitability of rainbow trout as an animal model for L. salmonae infections with particular emphasis on the ability of this parasite to complete its life cycle in a manner similar to that seen in naturally and experimentally infected chinook salmon. Materials and Methods Source of Loma salmonae spores: In the initial studies on trans-Abstract _ Loma salmonae is an economically important gill microsporidian pathogen of pen-reared chinook and coho salmon. Chinook and coho salmon are generally poorly suited for use in laboratory studies because of their high mortality rates when infected with L. salmonae and their high-level of susceptibility to other infectious diseases. Using gill tissue from chinook salmon that contained mature xenomas laden with L. salmonae spores, we successfully transmitted the infection to rainbow trout. The infection developed in an identical manner and over a similar time course in trout as for chinook salmon. In contrast, we were unable to transmit the infection to other candidate salmonid species, including Atlantic salmon, brook trout, or arctic charr. Gill tissue from experimentally infected rainbow trout was then used to successfully transmit the parasite to other trout. Horizontal transmission was documented from infected to naive tankmates. Analysis of these results indicated that L. salmonae can have a complete life cycle in trout and produce viable spores. Although abundant xenomas developed in the gills of infected trout, the fish did not have clinical signs and there were no fatalities. We concluded that use of rainbow trout offers several key advantages for study of the pathobiologic characteristics of L. salmonae.
We studied the morphology and occurrence of splenic Langerhans-like (LL) cells in species represe... more We studied the morphology and occurrence of splenic Langerhans-like (LL) cells in species representing 11 orders of ray-finned fishes, Actinopterygii. LL cells were frequent in spleen tissue of species among Cypriniformes, Esociformes, Salmoniformes, and Pleuronectiformes. These cells contained granules which resembled Birbeck granules known to occur in mammalian Langerhans cells. The ultrastructure of LL cells in Northern pike, Esox lucius, and in Atlantic halibut, Hippoglossus hippoglossus were similar to those reported in salmonids. LL cells found in cyprinids shared some characteristics with the LL cells in other Actinopterygii species, although unique structures distinguished them from the latter. They contained dense bodies within the Birbeck-like (BL) granules, a characteristic that was never observed in species outside the Cypriniformes. Two types of BL granules were characterized in cyprinid LL cells. The ultrastructure of BL granules across the species is discussed. LL cells in all Actinopterygii species demonstrated close contacts with nearby cells, characterized by adherens-like junctions. Additionally, multivesicular bodies were present within the cytoplasm and large aggregates of exosomes were observed closely associated with the plasma membrane suggesting their release from the cells. These structures are discussed in relation to mammalian dendritic cells. Macrophages found in European perch, Perca fluviatilis, blue gourami, Trichogaster trichopterus, and Atlantic halibut, Hippoglossus hippoglossus contained lysosomes and residual bodies with structures resembling Birbeck granules. These granules and cells were clearly distinct from LL cells.
Contemporary topics in laboratory animal science, 1998
Loma salmonae is an economically important gill microsporidian pathogen of pen-reared chinook and... more Loma salmonae is an economically important gill microsporidian pathogen of pen-reared chinook and coho salmon. Chinook and coho salmon are generally poorly suited for use in laboratory studies because of their high mortality rates when infected with L. salmonae and their high-level of susceptibility to other infectious diseases. Using gill tissue from chinook salmon that contained mature xenomas laden with L. salmonae spores, we successfully transmitted the infection to rainbow trout. The infection developed in an identical manner and over a similar time course in trout as for chinook salmon. In contrast, we were unable to transmit the infection to other candidate salmonid species, including Atlantic salmon, brook trout, or arctic charr. Gill tissue from experimentally infected rainbow trout was then used to successfully transmit the parasite to other trout. Horizontal transmission was documented from infected to naive tankmates. Analysis of these results indicated that L. salmonae ...
Loma salmonae is an economically important gill microsporidian pathogen of pen-reared chinook and... more Loma salmonae is an economically important gill microsporidian pathogen of pen-reared chinook and coho salmon. Chinook and coho salmon are generally poorly suited for use in laboratory studies because of their high mortality rates when infected with L. salmonae and their high-level of susceptibility to other infectious diseases. Using gill tissue from chinook salmon that contained mature xenomas laden with L. salmonae spores, we successfully transmitted the infection to rainbow trout. The infection developed in an identical manner and over a similar time course in trout as for chinook salmon. In contrast, we were unable to transmit the infection to other candidate salmonid species, including Atlantic salmon, brook trout, or arctic charr. Gill tissue from experimentally infected rainbow trout was then used to successfully transmit the parasite to other trout. Horizontal transmission was documented from infected to naive tankmates. Analysis of these results indicated that L. salmonae ...
Journal of Aquatic Animal Health 8:64-69, 1996 O Copyright by Che American Fisheries Society 1 ..... more Journal of Aquatic Animal Health 8:64-69, 1996 O Copyright by Che American Fisheries Society 1 ... Effects of Intermittent Formalin Treatment of Atlantic Salmon Juveniles on Growth, Condition Factor, Plasma Electrolytes, and Hematocrit in Freshwater and after Transfer to Seawater
Chloramine-T is a commonly used therapeutic agent for the treatment of bacterial gill and skin di... more Chloramine-T is a commonly used therapeutic agent for the treatment of bacterial gill and skin diseases in the intensive aquaculture of salmonids; however, little is known about its effects on healthy fish. Juvenile rainbow trout (Oncorhynchus mykiss) were exposed weekly to 5, 10, and 20 mg active chloramine-T ingredient∙L−1 in a 20-tank replicate flow-through facility. Control fish were treated with tank water only. Growth parameters and haematocrits were taken twice weekly and serum biochemistry was measured on termination of the experiment. Absolute growth rates were suppressed but only statistically significantly in fish treated with 20 mg chloramine-T∙L−1 compared with controls. Fish exposed to 10 and 20 mg chloramine-T∙L−1 showed significant predisposition to an erosive dermatitis of the caudal fin which appeared to be caused by opportunistic pathogens of the genus Pseudomonas spp. and Flavobacter spp. Haematocrits decreased in controls and ail treatments. A significant concentration-dependent decrease in plasma sodium and chloride was observed. Plasma glucose levels did not vary and were similar to those reported for unstressed trout. We recommend that care be taken when using chloramine-T prophylactically and that concentrations of less than 10 mg∙L−1 be used.
Following a per os challenge of naive rainbow trout with live spores of Loma salmonae, head kidne... more Following a per os challenge of naive rainbow trout with live spores of Loma salmonae, head kidney mononuclear cells (MNC) in culture were able to proliferate in response to crude soluble parasite extract or intact dead spores. A significant response was seen by week 2 post-exposure and a maximum response developed by week 6 or 8, respectively. During this initial challenge, spore filled cysts developed on the gills of challenged fish, and the cysts ruptured by week 12 as is typical for microsporidial gill disease of salmonids (MGDS). Two weeks following this, fish were re-challenged with live spores, and in these fish an enhanced in vitro proliferative response of MNC was immediately apparent, and spore filled cysts did not develop. In contrast, when naive trout were given dead spores by intraperitoneal injection, the most pronounced proliferative responses of MNC developed earlier (week 2 PE) and the response was greater when cells were incubated in vitro with dead spores rather than with crude soluble extract. When these fish were re-challenged per os with live spores, a heightened proliferation in MNC was observed 4 weeks after this exposure and the fish likewise resisted development of xenomas. In fish infected orally or injected intraperitoneally with spores, a marked increase in the response to the mitogen concanavalin A was seen for 22 weeks post-exposure when compared to controls not receiving any spores.
ABSTRACT In two variants of Loma salmonae that have specificity for rainbow trout Oncorhynchus my... more ABSTRACT In two variants of Loma salmonae that have specificity for rainbow trout Oncorhynchus mykiss(OA variant) and specificity to brook trout Salvelinus fontinalis(SV variant), the parasitophorous vacuole forms at the onset of sporogony. In the OA variant the merogonial stage is bound by a single plasma membrane in direct contact with host cytoplasm. The parasitophorous vacuole formation is initiated by the host cell surrounding the merogonial stages with endoplasmic reticulum (ER) as occurs in autophagy. Of the two host ER membranes surrounding the parasite, one remains in close association with the plasma membrane of the meront, while the other forms the limiting membrane of the vacuole. The sporogonial stage is bounded by two closely apposed membranes, giving the appearance of a thick electron dense plasmalemma. The observations from this study support the novel hypothesis that this microsporidian uses the intracellular process of autophagy to aid formation of a parasitophorous vacuole. The morphology of the SV‐variant is consistent with that of the OA‐variant suggesting that it uses the same mechanism for development.
Members of an Ahousaht First Nations community of Vancouver Island, Canada have developed a marke... more Members of an Ahousaht First Nations community of Vancouver Island, Canada have developed a market for wild-caught species of indigenous rockfish (Sebastes spp.). The fish, which are caught by hook and line, are transported live to fish markets in Vancouver. Recently, market place downgrading of the fish has occurred due to a syndrome referred to as``black-mould'', characterized by linear black disfigurations, and erosions, of the skin. Samples from 14 wild-caught rockfish were examined to determine the cause. On the basis of sub-gross and histological examination, the black-mould syndrome was attributed to intraepithelial deposition of eggs from a trichuroid nematode of the genus Huffmanela, coupled with an inflammatory response. The eggs observed in the tissues of the rockfish differed in size and morphology from those described for other species of Huffmanela. This is the first report of Huffmanela spp. infection in rockfish, probably due to a previously undescribed species.
Loma salmonae is an intracellular obligate parasite of farmed chinook salmon (Oncorhynchus tshawt... more Loma salmonae is an intracellular obligate parasite of farmed chinook salmon (Oncorhynchus tshawtscha) and is the causative agent for microsporidial gill disease (MGD). The infection occurs mainly in secondary gill lamellae, with the formation of large white spore-laden xenomas within the endothelial and pillar cells. The overall objective of the study was to investigate the minimum exposure time required for disease transmission between naive rainbow trout (Oncorhynchus mykiss) (RBT) and L. salmonae-infected fish using the cohabitation challenge model. In trial I, low (1), medium (5) or high (10) numbers of infected RBT were added to tanks containing 45 naive fish for a cohabitation period of 21 days. Trial II limited the cohabitation period between five L. salmonae-infected fish in a tank of 45 naive RBT to 1, 12, 24 or 96 h. For both trials, each treatment level was completed in duplicate and an additional tank of 45 naive RBT served as the control and did not receive infected fish. Beginning on day 21 post exposure (PE) and continuing biweekly until day 83 PE and 105 PE for each trial, respectively, fish were evaluated for branchial xenomas to determine xenoma onset time and intensity. The effect of adding one infected fish produced similar median xenoma onset time and mean xenoma intensity compared with adding 5 or 10 infected fish (trial I). Significant differences were observed amongst the survivor curves for the fish exposed to infected RBT for 1, 12, 24 and 96 h, with the median onset time equal to 63 days for the lowest exposure period. This study demonstrated that L. salmonae transmission was possible with as little as 1-h exposure time between 5 cohabiting infected and 45 naive RBT. Adding five L. salmonae-infected fish (at week 7 PE) to a group of naive RBT for a period of 1 h resulted in over 94.5% disease prevalence in cohabiting fish.
Chloramine-T is a widely used prophylactic and therapeutic agent in freshwater aquaculture. This ... more Chloramine-T is a widely used prophylactic and therapeutic agent in freshwater aquaculture. This study examined the effects of repeated intermittent exposure of healthy rainbow trout (Oncorhynchus mykiss) fingerlings to sublethal concentrations of chloramine-T (0, 5, 10, or 20 mg/L) twice weekly in 1-h pulses at 11 °C for 4 weeks in a replicate-tank facility. Gills were excised from subsamples of fish prior to exposure and at the end of the 4-week experimental period. Tissue was fixed and processed for light microscopy and transmission and scanning electron microscopy. The gill epithelium from fish treated with 10 and 20 mg/L chloramine-T appeared swollen and vacuolated, with extensive intercellular edema. There was a significant reduction in the number of lamellar mucous cells and an apparent increase in the numbers of chloride cells. Chloride cells from both the base of the lamella and the lamellar surface of gills exposed to chloramine-T had a significant increase in the area of the apical plasmalemma after treatment with 10 and 20 mg/L, and a reduction in the thickness of the apical plasmalemma-associated glycocalyx. These morphological changes are consistent with a compensatory mechanism for the remedial uptake of ions, suggesting that chloramine-T increased epithelial ion permeability coincident with a possible influx of water leading to intercellular edema. Chloride cell proliferation and intercellular edema may also have affected gas exchange across the branchial epithelium.
Contemporary Topics in Laboratory Animal Science American Association For Laboratory Animal Science, Apr 1, 1998
Gill disease associated with the microsporidian parasite Loma salmonae is an emerging problem aff... more Gill disease associated with the microsporidian parasite Loma salmonae is an emerging problem affecting the marine aquaculture production of Pacific salmon, most notably chinook salmon (Oncorhynchus tshawytscha) and, to a lesser extent, coho salmon (O. kisutch) (1-6). Parasites develop in the vasculature of the gills to form large spore-laden xenomas (2-6). Loma salmonae also infect rainbow trout (O. mykiss) (7-9); however, in contrast to the Pacific salmon, the clinical effects on these fish vary considerably (9). Furthermore, on the basis of unpublished observations from diagnostic materials sent to the Fish Health Unit of the Atlantic Veterinary College, L. salmonae is often detected in groups of trout that do not have a history of clinical disease, whereas this is not the clinical history for chinook salmon. Because of the restrictive nature of current regulations pertaining to the use of therapeutic agents in aquaculture, licenced therapeutic agents are not available for treating fish infected with L. salmonae. Accordingly, there is a need to study the pathobiologic characteristics of L. salmonae in an effort to uncover management factors that could limit the economic effects of infection. Laboratory studies of this disease would benefit by the availability of a species other than chinook salmon, even though they are the principal aquaculture species affected by L. salmonae. Chinook salmon have proven to be difficult to work with in laboratory studies (10) and often become diseased or die because of a range of other endemic infectious diseases, particularly when the fish are stressed. Rainbow trout, in contrast, are a relatively hardy fish that are frequently used in laboratory studies (11). They have been the salmonid species used as a model for many studies, and their requirements and physiologic responses are well documented (11). Our purpose was to evaluate the suitability of rainbow trout as an animal model for L. salmonae infections with particular emphasis on the ability of this parasite to complete its life cycle in a manner similar to that seen in naturally and experimentally infected chinook salmon. Materials and Methods Source of Loma salmonae spores: In the initial studies on trans-Abstract _ Loma salmonae is an economically important gill microsporidian pathogen of pen-reared chinook and coho salmon. Chinook and coho salmon are generally poorly suited for use in laboratory studies because of their high mortality rates when infected with L. salmonae and their high-level of susceptibility to other infectious diseases. Using gill tissue from chinook salmon that contained mature xenomas laden with L. salmonae spores, we successfully transmitted the infection to rainbow trout. The infection developed in an identical manner and over a similar time course in trout as for chinook salmon. In contrast, we were unable to transmit the infection to other candidate salmonid species, including Atlantic salmon, brook trout, or arctic charr. Gill tissue from experimentally infected rainbow trout was then used to successfully transmit the parasite to other trout. Horizontal transmission was documented from infected to naive tankmates. Analysis of these results indicated that L. salmonae can have a complete life cycle in trout and produce viable spores. Although abundant xenomas developed in the gills of infected trout, the fish did not have clinical signs and there were no fatalities. We concluded that use of rainbow trout offers several key advantages for study of the pathobiologic characteristics of L. salmonae.
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