Streptococcus agalactiae infection in Nile tilapia (Oreochromis niloticus) and its transmission potential to cohabitated sheepshead minnows (Cyprinodon variegatus)

Authors: Garcia, Julio; Shoemaker, Craig; Lafrentz, Benjamin

Submitted to: Annual Eastern Fish Health Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 3/25/2018
Publication Date: 4/9/2018
Citation: Garcia, J.C., Shoemaker, C.A., Lafrentz, B.R. 2018. Streptococcus agalactiae infection in Nile tilapia (Oreochromis niloticus) and its transmission potential to cohabitated sheepshead minnows (Cyprinodon variegatus)[abstract]. Annual Eastern Fish Health Workshop. p. 34.

Interpretive Summary:

Technical Abstract: Streptococcus agalactiae has emerged as an economically important bacterial pathogen affecting global aquaculture. Worldwide aquaculture losses due to S. agalactiae are estimated around U.S. $1 billion, annually. Streptococcus agalactiae also known as a Lancefield Group B Streptococcus (GBS) is a Gram-positive, cocci shaped, ß-hemolytic or non-hemolytic, catalase negative, oxidase positive bacteria. The present study examined the possibility of horizontal transmission of S. agalactiae isolate ARS-11-MU-BR (capsular serotype Ia) from Nile tilapia (Oreochromis niloticus) to sheepshead minnows (Cyprinodon variegatus) in experimental cohabitation challenges at 15 ppt salinity and 32°C. Results from our experiments demonstrated that Nile tilapia infected with S. agalactiae by either intraperitoneal injection or bath immersion were infectious to healthy cohabitated sheepshead minnows. Mortality in cohabitated sheepshead minnows due to S. agalactiae was attained when both species were cohabitated in the same tank and when cohabitated in the same tank but separated by a barrier. Mortality of sheepshead minnows in direct cohabitation with Nile tilapia infected by intraperitoneal injection was higher than cohabitated fish separated by a screen barrier with cumulative percent mortalities of 47% and 33%, respectively. An additional experiment in which S. agalactiae bacteria was added directly into the aquarium water and maintained static for 14 days demonstrated that healthy cohabitated tilapia and sheepshead minnows can get Streptococcosis from waterborne exposure to S. agalactiae. This research demonstrated horizontal transmission of S. agalactiae, and the results suggest that transmission of the bacteria is probable between susceptible fish in aquaculture or the environment.