Bacterial gill disease – Gross Pathology

This rainbow trout fingerling with BGD shows the typical flared opercula of respiratory distress. Note that the edge of the flared operculum is eroded. This erosion is typical of intensively-reared fish; its cause is unknown, but might be the result of higher-than-optimal bacterial enzymes in and around the branchial cavity. Whatever the cause, the consequence is a huge reduction in the ability of the animal to pump water due to elimination of the water-tight seal between the trailing edge of the operculum and the body of the fish (the cleithrum). Thus the negative pressure of the opercular pump is greatly reduced. And this in an animal that is trying to pump larger-than-normal volumes of water over its gills due to the hypoxaemia of BGD!

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 –...