IDENTIFICATION OF THE CAUSAL AGENT OF SHRIMP BLACK GILL IN THE COASTAL SOUTHEAST USA

Penaeid shrimp including Litopenaeus setiferus (white shrimp), Farfantepenaeus aztecus (brown shrimp), and Farfantepenaeus duorarum (pink shrimp) support the most valuable commercial fisheries in the US Southeast Atlantic. However, since the mid 1990’s the fishery has experienced a significant decline in reported harvest, due in part to declines in fishing effort (both fishing trips and licensed vessels). Another primary cause for this decline, particularly for the fall white shrimp, has been hypothesized to be due to severe outbreaks of a gill infection causing tissue melanization (Black Gill), but the agent of Black Gill has not been identified. Histological and molecular studies indicate the presence of a large ciliate with evidence of gill tissue necrosis and the formation of melanized nodules. Sequencing of nearly the complete 18S rRNA gene of the shrimp Black Gill (sBG) ciliate indicates that it is closely related to the apostomate ciliate Hyalophysa chattoni (99.6% nucleotide similarity). However, electron microscopy studies suggest that the sBG ciliate is not H. chattoni and may not even be an apostome ciliate because it lacks many of the definitive ultra-structural characteristics of this group of ciliates including well-stacked kinetodesmal fibers anchoring their basal bodies (kinetosomes), food plaquettes, trichocysts or an epiplasm. Investigations are continuing to identify definitively the sBG ciliate but these results point to the possible discovery of a new species of ciliate.