Mortality in tilapia (Oreochromis niloticus) caused by management failures and the diagnostic challenge for official veterinary services

Abstract

Management failures due to excess feed supply, fish overpopulation and dissolved oxygen deficit in water are among the leading causes of mortality in fish farming. Therefore, these failures are important differential diagnoses that should be considered during investigations of notifiable diseases by the official veterinary services. This article reports a case of estimated total mortality of 70% in a tilapia farm in Brasília/DF, Brazil, caused by the excess feed provided, fish overpopulation and absence of aeration systems. The deaths were caused by hypoxia found in 4 of the 5 existing fish pond after analyzing the dissolved oxygen concentration in each unit. This fact highlights the importance of water analysis kits when attending to suspected fish diseases, as it is an important differential diagnosis, especially in cases of high mortality. Another finding was the presence of hepatic steatosis in the eight necropsied tilapias, confirmed by the observation of fatty degeneration of hepatocytes in histopathological assays.