Paramoeba pemaquidensis (Sarcomastigophora: Paramoebidae) infestation of the gills of coho salmon Oncorhynchus kisutch reared in sea water

Abstract

Gill disease associated with Paramoeba pemaquidensis Page 1970 (Sarcomastigophora: Paramoebidae) infestations was observed in coho salmon Oncorhynchus lasutch reared in sea water Fish reared in net pens in Washington and in land-based tanks in California were affected. Approximately 25 O/ O mortality was observed in the net pens in 1985, and the disease recurred in 1986 and 1987. Amoeba infesting the gill surfaces elicited prominent epithelia1 hyperplasia. Typical of Paramoeba spp., the parasite had a Feulgen positive parasome (Nebenkorper) adjacent to the nucleus and floatlng and transitional forms had digitiform pseudopodia. We have established cultures of the organism from coho gills; it grows rapidly on Malt-yeast extract sea water medium supplemented with Klebsiella bacteria. Ultrastructural characteristics and nuclear, parasome and overall size of the organism in study indicated it is most closely related to the free-living paramoeba P. pemaquidensis. The plasmalemma of the amoeba from coho gills has surface filaments. Measurements (in pm) of the amoeba under various conditions are as follows: transitional forms directly from gills 28 (24 to 30), locomotive forms from liquid culture 21 X 17 (15 to 35 X 11 to 25), and locomotive forms from agar culture 25 X 20 (15 to 38 X 15 to 25). Nuclei and parasomes from liquid cultures were 5 to 7 and 3 to 5 X 2 to 3, respectively. The disease was not induced by laboratory exposure of coho salmon to amoeba cultures, but the amoeba was consistently isolated from exposed fish and aquarium detritus for 4 wk after exposure. This suggests that the organism is an opportunistic pathogen which only proliferates on fish gills and causes disease under certain situations yet to be clearly defined. In vitro studies indicated that the optimal salinity for growth of the amoeba was between 15 and 20 ppt, while growth was greatly dminished below 10 ppt. This concurs with field observations where the amoeba was eradicated from fish held in sea water tanks following a reduction in salinity.

Influence of salmonid gill bacteria on development and severity of amoebic gill disease

“…can infect gills and cause AGD in salmonids (Group 1) after KMnO 4 disinfection and with very low levels of culturable bacteria. Therefore, in agreement with other authors we have shown that the amoeba can be a primary pathogen and cause AGD in salmon (Kent et al 1988, Roubal et al 1989, Munday et al 1990, Dyková et al 1995, Adams & Nowak 2003. …”

“…survival and growth, once it has gained access to salmon gills, has not been clearly identified. Previous researchers suggest that other infectious amoebae may feed on gill bacteria (Noble et al 1997) and perhaps attain bloom populations in the presence of abundant food organisms (Kent et al 1988). In vitro growth of trophozoites of a Platyamoeba strain isolated from the diseased gill tissues of cultured turbot increased considerably in the presence of Aeromonas hydrophila, Vibrio natriegens, Pseudomonas nautica and Escherichia coli (Paniagua et al 2001).…”

“…Until now AGD infection has always been established by cohabiting naïve fish with infected fish (Howard et al 1993, Akhlaghi et al 1996, or by exposing fish to isolated, gill-associated Neoparamoeba sp. , Morrison et al 2004, Morrison et al 2005 as the disease cannot be reproduced using cultured organisms (Kent et al 1988, Howard et al 1993, Findlay et al 2000, Morrison et al 2005.…”

Epizootic mortality in the pilchard Sardinops sagax neopilchardus in Australia and New Zealand in 1995. I. Pathology and epizootiology

“…The amoebae present in the epithelium in very small numbers. Bacappeared as round, crescentic to irregularly shaped, teria were not seen on gills of the majority of affected pale, amphophilic organisms with a few cytoplasmic fish but a few small colonies of robust Gram-positive granules (Kent et al 1988, Roubal et al 1989) and were coccobacilli were found in the interlamellar spaces of present on the superficial epithelium, on the epithefish regardless of disease status. Small colonies of lium of the interlamellar spaces and in intraepithelial Gram-negative, fine, short to filamentous rods were cystic spaces.…”

Tropical reef-fish disease outbreaks and mass mortalities in Florida, USA:what is the role of dietary biological toxins

“…In recent years, the association of amoebiasis with epizootics and mortalities of aquatic organisms has emphasized our relative lack of knowledge about the pathogenesis, epizootiology, and ecology of these amoebae (Jones 1985, Kent et al 1988). Of some concern is the potential transmission of normally freeliving amoebae to marine organisms and their apparent switch to pathogenic forms in stressed hosts.…”