Bacterial gill disease – Gross Pathology

Figure 1. Intensively-reared goldfish with sub-acute/chronic BGD. Note the pale areas of hyperplasia and fusion within the gills (arrow). Although salmonids are most commonly affected, other species are also susceptible.

Bacterial gill disease (BGD) occurs in several species, but it is an especially serious problem of intensive salmonid culture, and in some parts of the world it is the most common disease, especially in fry and fingerlings. BGD is characterized by explosive morbidity and mortality rates, attributable to bacterial colonization of gill surfaces. Despite such pronounced clinical signs and high mortality, pathological changes are surprisingly few and hard to find in the acute disease. It is only when (if) the fish survive for a few...

Jellyfish Lesions in Fish – Histopathology

Figure 5. Phialella quadrata attached to gill raker of Atlantic salmon and showing necrosis of epithelium, loss of basement membrane, and underlying dermal haemorrhage. A close inspection of the interface between the jellyfish and the gill epithelium shows tube-like extensions reaching down through the epithelium – nematocysts?

The negative interactions between jellyfish and fish in aquaculture appear to be an increasing problem. This is partly due to increased numbers of jellyfish, associated with global warming, reduced numbers of their predators, and to the intensification of aquaculture operations in many coastal areas worldwide. Most reported problems have occurred in marine-farmed salmonids in northwest Europe. Nevertheless, aquaculture operations in other regions such as Asia, North America, and Australia have also been affected. Jellyfish involved are primarily cnidarians i.e. those species with stinging cells –...