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...

Epitheliocystis in Cobia – Histopathology

Cobia, gill: abundant lamellar basophilic inclusions are observed, consistent with severe epitheliocystis infection H&E

Aquaculture of cobia (Rachycentrum canadum) has gained popularity in the last decade, and this species is now farmed in several countries in Latin America and Asia. Epitheliocystis is a chlamydia or rickettsia-like organism infecting the gills and skin of a variety of species in both fresh and saltwater. The disease has been reported in at least 90 species of marine and freshwater fish in both the southern and northern hemispheres. At least four bacterial species may be involved in this condition: Candidatus Piscichlamydia salmonis (Salvelinus...

Proliferative Gill Disease (PGD) – Gross Pathology

PGD in Atlantic salmon showing white spots (clubbing), distal third of filaments.

PGD is a multifactorial worldwide disease with both infectious and non-infectious causes.  PGD leads to significant problems in Atlantic salmon (Salmo salar) and many other species. Among the infectious causes are viruses (Atlantic salmon paramyxovirus-ASPV, Salmon gill poxvirus-SGPV), bacteria (Tenacibaculum maritimus, Piscichlamydia salmones, Candidatus Clavochlamydia salmonis), parasites (Neoparamoeba perurans, Loma salmonae, Ichthyobodo spp., Trichodina sp.). Non-infectious causes include phytoplankton and zooplankton. Gross pathological changes include “clubbing”, in which thickened white areas of hyperplastic epithelium can be easily seen, mainly at the ends or distal third...

Pseudochattonella cf. verruculosa – Phytoflagellate

Pseudochattonella cf. verruculosa - Phytoflagellate

Pseudochattonella cf. verruculosa is a phytoflagellate, Dictyochophyceae class that has abundant golden chloroplasts. It has two flagella, one of which, is directed forward, thereby allowing cell movement. The cell size varies between 12 – 45 microns depending on the stage of its life cycle. Its surface, the cell is covered by specialized structures that resemble papillae or warts, hence the name “verrucous”. These structures are mucocysts through which mucus is discharged. It is distributed in water bodies that fluctuate between 10 – 18 oC, salinities...

Freshwater Amoebiasis – Histopathology

Freshwater Amoebiasis - Histopathology

Fish affected with branchial amoebiasis, have marked epithelial fusion and hyperplasia, leading often to loss of normal gill architecture, with obliteration of interlamellar spaces. Several species are involved, some of which invade the lamellar epithelium. Trophozoites can therefore be seen in small groups within the branchial epithelium as well as on the surface. Several diagnostic methods can be used for the detection of amoebae, including whole mounts of fresh gills, histopathology, isolation and culture, in situ hybridization (ISH), electron microscopy and indirect immunofluorescence. Differential diagnoses...

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