Blood chemistry of bacterial gill disease in brook trout Salvelinus fontinalis

Abstract

Blood chemistry was examined in brook trout Salvelinus fontinalis suffering from bacterial gdl disease (BGD) and compared to normal healthy fish under identical conditions. Infected fish showed a marked decrease in serum Na+, Cl-and in osmolality, and a concommitant haemoconcentration as indicated by the increased serum protein and increased packed cell volume. Fish with BGD exhibited an mcreased rate of respiration (tachybranchia) but were not hypoxemic, suggesting that compensatory mechanisms, such as tachybranchia and enhanced recruitment of lamellar reserves, were successful. Nevertheless, the cause of the tachybranchia in BGD-infected fish remains unexplained; it may not be a response to impaired oxygen exchange, although this seems the most likely explanation. The acid-base status did not differ between healthy and diseased fish. These findings suggest that changes in blood components other than acid-base ones constitute the critical, and sometimes fatal changes occurring as a result of BGD infection, rather than hypoxemia. It is suggested that circulatory disturbances resulted from the rapid drop of blood electrolytes, which in turn triggered a fluid shift from the extracellular to the intracellular compartments, leading to haemoconcentration and death. However caused, tachybranchia probably exacerbated the worsening blood chemistry changes resulting from damaged gill epithelium. The implications of these findings for treatment include reducing the rate of ion loss from the gills by raising the salt levels in the water, combined with other chemicals directed specifically at the bacteria.

Blood chemistry and acid-base balance in rainbow trout Oncorhynchus mykiss with experimentally-induced acute bacterial gill disease

“…Blood PaO 2 is the primary stimulus for respiration in trout, although elevated PaCO 2 , and/or acidemia, may also contribute towards stimulating respiration (Perry and Wood 1989). Thus, the most economical explanation for the commonly observed phenomenon of tachybranchia in BGDinfected fish, namely the existence of an hypoxemia (Wakabayashi and Iwado 1985a,b;Ferguson 1989;Byrne et al 1991;Speare et al 1991a), is further corroborated by these findings.…”

“…Byrne et al (1991) suggested that the drop in serum [Na + ] and [C1-] was the dominant event in the pathogenesis of subacute/chronic BGD. Findings in the present study can neither corroborate nor refute this claim, but the dramatic drop in PaO 2 suggests that hypoxemia may also be a major mechanism, at least during the acute stages of the disease.…”

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

“…Many parasitic infections, as well as chemical irritation, will result in gill mucus production that inhibits carbon dioxide excretion and causes respiratory acidosis (Powell & Perry 1996, Powell et al 1998, 2000. Byrne et al (1991) demonstrated that brook trout Salvelinus fontinalis challenged with Flavobacterium branchiophilum showed no significant change in blood pH 1 and 4 d postchallenge. In contrast, rainbow trout (Byrne et al 1995) showed a significant decrease in blood pH 24 h postchallenge.…”

Behavioural indicators of welfare in farmed fish

“…These include artificial lighting, loud or aversive sound, arousing odours, unsuitable temperatures or substrates, restricted movement, reduced retreat space, forced proximity to humans, reduced feeding opportunities, manipulation of fish groups, transportation (e.g. Barreto and Volpato 2006;Morgan and Tromborg 2007), handling (Brydges et al 2009), air exposure (White et al 2008), the presence of predators (Barreto et al 2003), presence of chemicals (Neely 1979;Israeli-Weinstein and Kimmel 1998;Pane et al 2004;Scott and Sloman 2004), diseases (Byrne et al 1991), nanotubes ), cyanobacteria (Ernst et al 2007) and poor water quality in general (ammonia (NH 4 )/nitrate (NO 3 ) excess, etc. ).…”