Black gill disease, also known as black spot disease or black death, is a bacterial disease affecting various species of fish, including shellfish and crustaceans, across the Atlantic and Pacific oceans. The disease is characterized by the visibly noticeable black melanated gills, speculated to be caused by a fungus bacterium called Fusarium solani or a similarly shaped ciliate. Human consumption of fish affected by black gill disease is harmless. A significant portion of the aquaculture communities and fishing businesses have scientifically observed a steady decline in healthy fish capture since 1996, contributing to a shortage of shrimp and fish in the food industry. The origin of the fungus agent causing black gill disease is unknown and unlikely to dissipate. Researchers have also observed a causal relationship between the disease and environmental factors, such as waste spill contamination, ocean pollution, and climate change. Studies to determine the prevalence of the disease have been largely conducted by methodically collecting batches of healthy and infected shrimp across regional coastlines. Two main species of shrimp used for research include Litopenaeus setiferus (white shrimp) and Farfantepenaeus aztecus (brown shrimp). Characteristics Black gill disease is visible to the human eye. Affected gills may exhibit crusted, surface-corroding, scattered light brown to black spots or a large black patch on one or both sides of the fish. Discoloration at the gill area will be distinct from the rest of the body. These symptoms are separate from gill fouling or fin rot. Normal colored shrimp do not necessarily mean a lack of infection. Scientists have microscopically observed the ciliate fungus in shrimp that had not reached the discoloration phase. Seen under an electron microscope, the foreign circular ciliates (30–38 µm) attach to the gill nodules, creating cystic imprints on the tissue. More rarely, the ciliate may penetrate the tissue and house invasively. The fungus is contagious among fish species. Upon capture, an infected head placed near an entirely healthy fish can infect the latter. Causes Research in the Persian Gulf, China, and India has resulted in an initial determination that a fungus bacteria exactly or related to Fusarium solani is responsible for black gill disease. Extensive research ongoing since 2010 and funded by the University of Georgia has determined that an invasive ciliate strain, possibly Hyalophysa chattoni, attaches itself to gill nodules. The presumed ciliate propagates while activating oxygenation of phenols within the organic makeup of the sea creature.