Actinobacteria are prolific sources of secondary metabolites and the
vast majority of these compounds are derived from the single genus
Streptomyces. Streptomyces is a Gram-positive aerobic genus in the
order Actinomycetales, suborder Streptomycineae and family Streptomycetaceae
(Stackebrandt et al., 1997) and has a DNA G+C content of
69–78 mol%. Marine-derived Streptomyces have been studied for
isolation of several novel secondary metabolites (Fenical and Jensen,
2006; Das et al., 2006a). However, to date there have only been a few
studies that have considered Actinobacteria for their application as
probiotics in aquaculture.