Multifactorial causes of chronic mortality in juvenile sturgeons (Huso huso)

Sturgeons are species of biological and economic importance. Among them the "beluga" sturgeon (Huso huso, Linnaeus, 1758) is the largest freshwater fish, which can reach a maximum weight of 1,000 kg. Over 80% of the existing sturgeon species are endangered, vulnerable, or on the brink of extinction because of their late sexual maturity and long period between spawning in the wild. Many species of sturgeon are being cultured to increase natural populations or are produced for human food consumption. Despite considerable global interest in sturgeon aquaculture, there is still a paucity of information on nutrient requirements and utilizations, and even on their general nutrition. The development of sturgeon aquaculture activities has been accompanied by the increase of disease outbreaks representing a serious problem. This article represents an investigation of a chronic mortality outbreak. The clinical presentation, suggestive of a neurologic condition, was deepened with various laboratory analyses that excluded the presence of the main viral agents of sturgeons, while evidenced both bacteria and mycetes. The pathological findings pointed out a severe myopathy, a depletion of lymphohematopoietic tissue, and signs of degeneration, explainable with suboptimal environmental state. Chemical analyses suggested also a nutritional imbalance.