BLACK DEATH, A DISEASE SYENDROME OF PENAEID SHRIMP RELATED TO A DIETARY DEFICIENCY OF ASCORBIC ACID

California brown shrimp (Penaeus californiensis) fed a diet low in or without added L-ascorbic acid, developed blackened lesions (after 6 to 8 weeks in the subcuticular tissues of the general body surface, in the walls of the esophagus, stomach and hindgut, and in the gills and gill cavity. The condition has been previously observed in tank and raceway-reared P. californiensis and P. aztecus, often in epizootic proportions, and has been named black death disease. The disease has only been observed in postlarval and juvenile shrimp fed alginate-bound artificial diets in tanks or raceways that received no sunlight and contained no plant material. Handling and other stress factors often precipitated epizootics in apparently healthy groups of shrimp. Once clinical signs of the disease became apparent, affected shrimp ceased feeding, and death usually followed within 24 to 72 hours. Opportunistic bacteria such as Vibrio spp. and Pseudomonas spp. often, But. not always, produced a terminal septicemia in affected shrimp. Mortalities of 1 to 5% per day due to this disease were observed on several occasions in tank and raceway-reared P. californiensis in 1974 and 1975 at Puerto Penasco, Mexico. Histopathology showed the blackened lesions to be, composed of masses of hemocytes and necrotic tissue. The black pigmentation of the lesions was due to melanin deposited in areas of heavy hemocyte infiltration, particularly near the centers of developing hemocyte nodules. No parasites or bacteria could be demonstrated in the centers of these nodules.