tailieunhanh - Streptococcus In Tilapia part 1

Published by Intervet - The theory that tilapia is a hardy and disease-resistant fish species is no longer correct. Producers, scientists and processors have now become aware that diseases may well be the number one threat for the future of this industry. Introduction Several diseases have been identified in tilapia farming (see Intervet AAH Newsletter no. 11). | Streptococcus In Tilapia Published by Intervet - The theory that tilapia is a hardy and disease-resistant fish species is no longer correct. Producers scientists and processors have now become aware that diseases may well be the number one threat for the future of this industry. Introduction Several diseases have been identified in tilapia farming see Intervet AAH Newsletter no. 11 . Streptococcosis is considered to be the most devastating disease as it can cause massive kills of large size fish and is responsible for heavy economic losses. In this article we discuss Streptococcosis in tilapia including the various clinical signs observed during Streptococcus outbreaks. Causative agent Streptococcus agalactiae including the previously-described S. difflcilis difficile now reclassified as S. agalactiae is the major cause of streptococcosis in farmed tilapia. S. iniae also causes mortality but to a lesser extent. Streptococcus spp. are Gram positive non-acid fast non-motile oxidase-positive catalase-negative cocci. There is no obvious difference in the clinical signs induced by one or other of the Streptococcus species. Clinical signs External signs Abnormal behaviour Due to the tropism of the bacteria for the central nervous system swirling behaviour lethargy bent bodies and disorientated fish are commonly observed. Eye lesions Sick fish often have eye lesions such as endophthalmia or exophthalmia. Unilateral or bilateral opacification of the eye can also be associated with the previous signs and eye haemorrhages are common. However not all fish affected with streptococcus necessarily have eye lesions. Abscesses In Streptococcus-infected fish it is common to find 2- to 3-mm abscesses symmetrically positioned on the inferior jaw. In general these abscesses quickly burst and become haemorrhagic ulcers which do not heal. Bigger abscesses of approximately 5 mm can also be observed at the base of the pectoral fins. The base of the tail is a common site for large .