Gas Bubble Disease

Figure 1. Rainbow trout with several gas bubbles in the anterior chamber. Note the haemorrhage both dorsally and ventrally, the latter “coning” through the ventral iris pore

Gas bubble disease (GBD) is the fish equivalent of the “bends” in human scuba divers. It is the result of gas coming out of solution in the bloodstream, thereby leading to the formation of emboli, especially in smaller blood vessels, including rete. Thus, lesions are common in gills, and the choroid gland of the eye. In water that is supersaturated, fish equilibriate with that supersaturated gas, just as human scuba divers equilibriate with gas at high pressures. It is not known precisely what prompts the...

Flavobacterium psychrophilum in salmonids – Gross Pathology

Figure 2. F. psychrophilum infection in rainbow trout. Note the classical “peduncle disease” with necrosis and darkening of tissues distal to the anal fin.

Flavobacterium psychrophilum is a ubiquitous Gram-negative filamentous and yellow-pigmented bacterium, and as the name suggests, it thrives in cooler water temperatures, causing disease in freshwater fish at 4-12°C. It likes connective tissues, especially those in younger fish in which it causes diseases such as bacterial cold-water disease (BCWD or peduncle disease) and rainbow trout fry syndrome (RTFS). As fish get older and the proportions/chemistry/locations of connective tissue change, the types of lesions also change. F. psychrophilum is responsible for significant economic losses in salmonid aquaculture...