Black gill is a common manifestation of a number of disease syndromes (Vibriosis, fouling organisms, mycosis, mycobacterium infection, ascorbic acid deficiency). In addition to an infectious or nutritional etiology, a number of heavy metals (e.g. cadmium or copper used in shrimp ponds as algaecides) and certain other chemicals (e.g., ammonia, nitrite, chlorine, potassium permanganate) may cause malaise lesions. This etiology must be differentiated from black gills that arise from the accumulation of organic matter, which can easily occur in highly turbid water.