Proliferation, colonization, and detrimental effects of vibrio parahaemolyticus and vibrio harveyi during brine shrimp hatching

Brine shrimps are a nutritious and easy to raise feed for aquaculture, however, are considered a main vector of pathogenic microbes because they carry opportunistic bacteria that proliferate during their production. Considering that brine shrimp is also susceptible to some of those bacteria, their yield during nauplii production could be reduced by those opportunistic pathogens. In this study we evaluated the effect of Vibrio parahaemolyticus and Vibrio harveyi during cyst incubation. Under gnotobiotic conditions, proliferation, colonization, and ability to kill brine shrimp cysts before, during or after hatching, were examined. We found that nutritional materials released during cyst hatching supported a strong growth of V. parahaemolyticus and V. harveyi, at growth rates comparable with those recorded in bacteriological media (between 0.197 and 0.307generations·h^-1). Cysts were colonized externally after 2h of exposure to bacteria, some bacteria crossed the corium barrier and colonized the embryo before hatching. In some cases, brine shrimp yield was reduced to 10% in the presence of vibrios, this reduction was dose- and strain-dependent and was accounted for by the sum of the number of killed cysts and dead organisms during "umbrella" or instar I stages. The effect of each Vibrio strain on brine shrimp cysts was directly correlated with the virulence recorded during a standard challenge test using brine shrimp nauplii, indicating that the hatching process can be used as an alternative to assess the virulence of different wild bacterial isolates.