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United States Department of Agriculture

Agricultural Research Service


item Pasnik, David
item Evans, Joyce
item Klesius, Phillip

Submitted to: Annual Eastern Fish Health Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 2/22/2006
Publication Date: 3/28/2006
Citation: Pasnik, D.J., Evans, J.J., Klesius, P.H. 2006. Atypical clinical signs of streptococcus agalactiae in nile tilapia (oreochromis niloticus). 31st Annual Eastern Fish Health Workshop. Charleston, SC. March 28-30, 2006. page 66.

Interpretive Summary:

Technical Abstract: After injection challenge with Streptococcus agalactiae, a male Nile tilapia, Oreochromis niloticus, exhibited an erratic corkscrew swimming pattern and assumed a “C”-shaped body posture. The fish did not die after challenge but developed a grossly-observable “hunchback” at the level of the cervical spine. Radiographs revealed multiple spinal curvatures along the length of the spinal column with vertebral lordosis and kyphosis. The male fish also developed a cranial cavitation on the dorsal aspect of the head, forming a depression between the eyes. The fish subsequently mated and helped produce fry that initially appeared normal. The fry population soon experienced high mortalities, and moribund fish exhibited reddened gills, presumptively over-inflated bladders, and spun on their longitudinal axis, often with their head pointed down (tail-up swimming). Surviving fry had stunted or absent fins, deformed gill opercula, and/or cranial cavitation, but did not show vertebral deformities. Gram-positive bacteria identified as S. agalactiae were isolated from the fry. Streptococcus agalactiae appears to be the causative agent of these skeletal anomalies among the male broodfish and the fry, and this is the first report of hunchback skeletal abnormalities in S. agalactiae-infected fish. Furthermore, the results demonstrate the vertical transmission of S. agalactiae to the fry.

Last Modified: 10/19/2017
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