Atypical bacterial gill disease: a new form of bacterial gill disease affecting intensively reared salmonids

Abstract

An unusual form of bacterial gill disease (BGD) was identified which affected five species of cultured salmonids from Canada (i.e. rainbow trout, chinook salmon and Atlantic salmon), Norway (i.e. brown trout) and Chile (i.e. coho salmon). All outbreaks occurred at low water temperatures (< 10 °C) and with clinical presentations distinct from classical BGD, which is caused by Flavobacterium branchiophilum. In contrast to classical BGD, fish did not show marked respiratory distress with flaring of the opercula, the animals did not orientate at the surface of the water column near inflow water or at the margins of the tanks, and the feed response of the fish was varied. While mortality was increased, it was not precipitous as in classical BGD. Eight outbreaks were examined in greater detail using histopathology, scanning electron microscopy, bacteriology and immunohistochemistry. Large numbers of small bacterial rods were seen adhering to the lamellar epithelium of affected gills from all outbreaks. Histologically, the lamellar epithelium appeared swollen, often with evidence of single cell degeneration and exfoliation. In more severe instances, the formation of lamellar synechiae was seen, usually associated with sequestration of bacteria between fused lamellae. By contrast with typical BGD, overt epithelial hyperplasia, lamellar fusion and filamental clubbing were not common sequelae to infection; instead, the end result was shortened and somewhat stubby lamellae covered with swollen epithelial cells. The predominant bacterium recovered from affected gills was a small, Gram‐negative, motile, fluorescent pigment‐producing rod that shared phenotypic characteristics with Pseudomonas fluorescens. Polyclonal antisera prepared against three representative isolates indicated a weak antigenic similarity among them. Immunohistochemistry corroborated this finding, in that the antisera reacted strongly with gill sections containing the homologous bacteria, but not against morphologically similar bacteria in heterologous sections. A Gram‐negative, yellow pigmented bacterium (YPB), identified as Flavobacterium psychrophilum, was also recovered, but only from the gills in the Ontario outbreaks. Antiserum prepared against this YPB indicated an antigenic similarity among isolates recovered from the Ontario outbreaks, but immunohistochemistry failed to recognize antigenically related bacteria on the gills of fish from the other outbreaks. Based on the unusual clinical presentation and the histopathological appearance of the gills, in conjunction with the absence of filamentous bacteria associated with and recovered from affected gills, the present authors have called this condition ‘atypical bacterial gill disease’ or ABGD.

A Review of Flavobacterium Psychrophilum Biology, Clinical Signs, and Bacterial Cold Water Disease Prevention and Treat

“…However, F. psychrophilum infections have been reported in a wide range of both anadromous and non-anadromous salmonids of various sizes [34][35][36][37][38][39][40][41][42]. In addition, F. psychrophilum has either caused disease or been detected in Japanese eel Anguilla japonica [43], European eel Anguilla anguilla [44], common carp Cyrpinus carpio [44], crucian carp Carassius carassius [44], tench Tinca tinca [44], ayu Plecoglossus altivelis [27,29], pale chub Zaco platypus [28], perch Perca fluviatilis [45], and roach Rutilis rutilis [45].…”

Transcriptional Responses of Resistant and Susceptible Fish Clones to the Bacterial Pathogen Flavobacterium psychrophilum

“…In the so-called “peduncle disease” and “bacterial cold-water disease”, ulcerative lesions occur in the area surrounding the adipose fin and progressively extend to the whole caudal peduncle [5]. Gill lesions and nervous forms of the disease were also reported [7], [8]. In Europe, F. psychrophilum infection mostly manifests itself as a septicemic form with high mortality known as the “rainbow trout fry syndrome” as it usually concerns rainbow trout fry and fingerlings [2], [6].…”

Flavobacterium psychrophilum y su patología en alevines de Onchorhynchus mykiss del centro piscícola El Ingenio, Huancayo

“…La enfermedad fue posteriormente descrita en alevines de salmón coho (O. kisuth) por Borg (1960), quien la denominó como enfermedad de baja temperatura o enfermedad bacteriana del agua fría y propuso a Cytophaga psychrophila como el agente causal. En los últimos 20 años han sido descritas en diferentes partes del mundo patologías similares en alevinos, juveniles y adultos de "trucha arcoiris", todas bajo el nombre genérico de síndrome del alevin de trucha arcoiris ("Raibow Trout Fry Sindrome" o RTFS) (Bernardet et al 1988;Sarti et al 1992;Toranzo & Barja 1993;Bustos et al 1995;Ostland et al 1999;Madetoja et al 2001;Lorenzen et al 1991;Wakabayashi et al 1991;Wiklund et al 1994;Rangdale 1999;Nematollahi et al 2003).…”