Copper toxicity in fish

Liver from Atlantic salmon fingerling showing positive copper reaction in hepatocyte cytoplasm. Rhodamine stain. Note the intracytoplasmic granules (bright red or rust-red) that correspond to lysosomes with sequestered excess copper (arrow).

Copper is a significant trace element necessary for the normal growth and metabolism of living organisms. However, if there is overexposure, it can be toxic. Levels of dissolved copper are often increased from anthropogenic origins such as mine washings and direct applications of algicides, molluscicides or antifouling agents. The most toxic form of copper is the cupric ion (Cu2+). Fish and crustacea are 10 to 100 times more sensitive to the toxicity of copper than mammals. For salmonids, the upper recommended limit is < 0.03...

Tenacibaculosis in Fish – Gross Pathology

Figure 1. Rainbow trout displaying tail and peduncle lesions.

Tenacibaculosis is primarily a skin infection causing ulcerative dermatitis in a range of commercially important species worldwide. Three species belonging to the genus Tenacibaculum have been associated with the disease: T. dicentrarchi, T. finnmarkense, and T. maritimum.   These bacteria are all Gram-negative and filamentous.  In marine fish, the most common isolate is T. maritimum. There is variation in the external pathological signs of the disease, depending on the species and age of the fish involved. Different names have been used for this usually ulcerative dermatitis; they include salt water columnaris...

Short operculum – Gross Pathology

Figure 1. Severe opercular erosion in farmed rainbow trout.

Bone deformities occur regularly in fish farms around the world. The operculum is one of the earliest craniofacial bones to form embryologically and is subject to a range of developmental and acquired abnormalities. Opercular shortening is one of the most prevalent diseases in larval and juvenile salmonids (and other species), sometimes affecting up to 80% of fish in a population. In those species that rely on the operculum to help move water over the gills, loss of efficiency in this part of the pumping mechanism...

Blue sac disease (BSD) – Gross Pathology

Blue sac disease in Atlantic salmon yolk-sac fry. Note a gill haemorrhage.

Blue-sac disease (BSD) or dropsy (hydrocoele embryonalis) is an abnormal condition that affects the egg and sac fry stages, typically of trout and salmon, but also of other freshwater fishes whose young emerge with a relatively large yolk sac.  It is characterized by abnormal accumulation of fluid with bluish tint between the yolk-sac and the outer membranes of the fry. It may also involve the pericardium and lymphatic spaces. BSD can be observed shortly after hatching and become more apparent within a few days. Blue-sac...

Nephrocalcinosis in Fish – Gross pathology

Figure 1. Gross appearance of nephrocalcinosis. The kidney is swollen and grey with an irregular surface and white mineral deposits in the ureters.

Nephrocalcinosis (or urolithiasis) in fish is a chronic inflammatory condition of unknown aetiology in which calcium and other minerals precipitate as hydroxyapatite within the distal renal tubules and collecting ducts. The disease usually records low mortality and although food conversion efficiency is probably impaired, the major concern about the condition centres round a reduction in carcase quality at slaughter. In severe cases, the muscle dorsal to the kidney may also be affected. There are some predisposing factors for this condition like high levels of carbon...

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