Effects of gill abrasion and experimental infection with Tenacibaculum maritimum on the respiratory physiology of Atlantic salmon Salmo salar affected by amoebic gill disease

Abstract

The effects of gill abrasion and experimental infection with Tenacibaculum maritimum were assessed in Atlantic salmon Salmo salar with underlying amoebic gill disease. The respiratory and acid-base parameters arterial oxygen tension (P a O 2 ), arterial whole blood oxygen content (C a O 2 ), arterial pH (pH a ), haematocrit and haemoglobin concentrations were measured at intervals over a 48 h recovery period following surgical cannulation of the dorsal aorta. Mortality rates over the recovery period were variable, with gill abrasion and inoculation with T. maritimum causing the highest initial mortality rate and unabraded, uninoculated controls showing the lowest overall mortality rate. Fish with abraded gills tended to show reduced P a O 2 and lower C a O 2 compared with unabraded fish. Infection with T. maritimum had no effect on P a O 2 or C a O 2 . All fish showed an initial alkalosis at 24 h post-surgery/inoculation which was more pronounced in fish inoculated with T. maritimum. There were no significant effects of gill abrasion or infection upon the ratio of oxygen specifically bound to haemoglobin or mean cellular haemoglobin concentration. Histologically, 48 h following surgery, abraded gills showed multifocal hyperplastic lesions with pronounced branchial congestion and telangiectasis, and those inoculated with T. maritimum exhibited focal areas of branchial necrosis and erosion associated with filamentous bacterial mats. All fish examined showed signs of amoebic gill disease with multifocal hyperplastic and spongious lesions with parasome-containing amoeba associated with the gill epithelium. The results suggest that respiratory compromise occurred as a consequence of gill abrasion rather than infection with T. maritimum.

Tenacibaculosis infection in marine fish caused by Tenacibaculum maritimum: a review

“…Powell et al (2004Powell et al ( , 2005) inoculated a high concentration of bacteria (10 11 to 10 12 cells per fish) on salmon gills, producing variable mortalities of fish, and they noted that respiratory damage occurred as a consequence of gill abrasion rather than infection with the bacterium. These findings indicate that the gills might not be an especially important route of infection for Tenacibaculum maritimum.…”

Effect of an acute necrotic bacterial gill infection and feed deprivation on the metabolic rate of Atlantic salmon Salmo salar

“…The 00/3280 strain of T. maritimum has been shown to be highly pathogenic to Atlantic salmon at high concentrations in a previous study (Powell et al 2004). Furthermore, in Powell et al (2004Powell et al ( , 2005b) the infection remained primarily as a gill disease and did not manifest as a skin lesion. As the aim of this particular trial was to use an acute necrotic gill infection as a model for examining the effects on M O 2 , it was deemed appropriate to use a high bacterial concentration similar to that previously described (Powell et al 2004).…”

“…As the aim of this particular trial was to use an acute necrotic gill infection as a model for examining the effects on M O 2 , it was deemed appropriate to use a high bacterial concentration similar to that previously described (Powell et al 2004). Furthermore, this allowed for a relative comparison with regard to the physiological effect of infection on the fish with previous studies conducted (Powell et al 2004(Powell et al , 2005b. Control fish received a saline solution and all fish were returned to their respective tanks.…”

“…Briefly, 200 ml of Shieh's medium formulated with seawater mineral salts buffer (MSB) was inoculated with T. maritimum and gently agitated at 20°C for 48 h. The suspension was centrifuged at 2500 relative centrifugal force (RCF), the pellet washed twice and resuspended in 15 ml of sterile seawater, and the bacterial concentration determined by serial dilution. Following the pre-inoculation M O 2max measurement, a 200 μl suspension of T. maritimum (5 × 10 12 cells ml -1 ) was applied evenly over all of the 8 gill arches of the anaesthetised Atlantic salmon (Powell et al 2004(Powell et al , 2005b. The 00/3280 strain of T. maritimum has been shown to be highly pathogenic to Atlantic salmon at high concentrations in a previous study (Powell et al 2004).…”

“…Cultures were incubated at 20°C for 36 h and colonies were confirmed as T. maritimum by colony colour and shape (Wakabayashi et al 1986, Powell et al 2005b). This was considered sufficient as the experiment was following protocols used in Powell et al (2005b), in which colony colour and shape were used primarily as a means of identifying T. maritimum.…”