Developing New Vaccines to Prevent Fish Kills

Agricultural Research Service scientists in Auburn, Ala., are closing in on a vaccine that protects fish from a streptococcus bacterium. ARS is the U.S. Department of Agriculture’s chief research agency.

Streptococcus iniae is an emerging bacterial pathogen in cultivated tilapia, hybrid striped bass, rainbow trout, yellowtail, eel and turbot. Worldwide, streptococcal infections are reported in 22 species, both cultured and wild.

S. iniae is recognized as one of the most problematic bacterial pathogens in intensively cultured tilapia and hybrid striped bass in the United States. The combination of development of good health management practices and a vaccine to control this bacterium is a superior approach to using antibiotics or chemicals, according to researchers at ARS’ Aquatic Animal Health Research Laboratory.

Antibiotics are currently used to control the streptococcal disease, which causes $150 million a year in losses worldwide.

The streptococcus bacterium possibly enters the nares (noses) of hybrid striped bass and tilapia from the water. The higher the density of cultured fish, the more easily streptococcus is transmitted and the higher the mortality rate.

Signs of the disease in fish are abnormal behavior, like erratic swimming, whirling motion at the surface of the water, darkening of the skin, blindness, pop-eyes and small lesions on the fish’s body, fins and anus.

ARS scientists are also researching fish behavior and health problems related to fungal, algal, bacterial and chemical toxins that have been implicated in fish kills in U.S. coastal waters.

An in-depth article appears in the October issue of Agricultural Research magazine. The story is also on the World Wide Web:

http://www.ars.usda.gov/is/AR/archive/oct99/fish1099.htm

Scientific contact: Philip H. Klesius, ARS Aquatic Animal Health Research Laboratory, Auburn, Ala., phone (334) 887-3741, fax (334) 887-2983, [email protected].