Clinical observations of black disease in fairy shrimps, Streptocephalus sirindhornae and Branchinella thailandensis, from Thailand and pathogen verification C Saejung 1 , K Hatai 2 , S Wada 2 , O Kurata 2 and L Sanoamuang 1,3 1 Applied Taxonomic Research Center, Department of Biology, Faculty of Science, Khon Kaen University, Khon Kaen, Thailand 2 Laboratory of Fish Diseases, Nippon Veterinary and Life Science University, Tokyo, Japan 3 Faculty of Science, Mahasarakham University, Mahasarakham, Thailand Abstract In this study, black disease infecting fairy shrimps, Streptocephalus sirindhornae Sanoamuang, Mur- ugan, Weekers & Dumont, and Branchinella thai- landensis Sanoamuang, Saengphan & Murugan, in Thailand, was investigated. The typical signs of the disease are the appearance of black spots on the cuticle, located mainly on the dorsal side and thoracopods. A number of rod-shaped bacteria aggregated in the black spots and were visualized by scanning electron microscopy. The histopathologi- cal results showed that a haemocytic response to the infection resulted in a dense melanized core of bacteria. In addition, generalized septicaemia by rod-shaped bacteria was also observed in the in- fected tissue. Of the 31 isolates, Aeromonas spp. were predominantly isolated and six strains were selected for the experimental infections. The most pathogenic strain was identified molecularly as A. hydrophila. When fairy shrimp were infected at bacterial concentrations of 10 4 and 10 6 cfu mL )1 , the overall infection levels were 73.33  6.67% and 93.33  6.67%, respectively. The experimen- tally infected fairy shrimp showed abnormal swimming and died within 24–48 h after the appearance of the dark pigment. Keywords: Aeromonas spp., black spot, Branchinella thailandensis, fairy shrimp, haemocytic encapsula- tion, Streptocephalus sirindhornae. Introduction Fairy shrimp are freshwater anostracans, which are sources of carotenoid pigments including astaxanthin, canthaxanthin, antheraxanthin, lutein, b-cryptoxan- thin, violaxanthin (Velu & Munuswamy 2003; Sriputhorn & Sanoamuang 2011) and fatty acids (Mura, Ferrana, Fabietti, Delise & Bocca 1997; Mura, Zarattini, Delise, Fabietti & Bocca 1999; Mura, Zarattini, Delise, Fabietti & Bocca 2000). Recently, the fairy shrimps, Streptocephalus sirindhornae Sano- amuang, Murugan, Weekers & Dumont and Branchinella thailandensis Sanoamuang, Saengphan & Murugan, have been discovered from temporary ponds in Thailand (Sanoamuang, Murugan, Wee- kers & Dumont 2000; Sanoamuang, Saengphan & Murugan 2002). They have been reared as a source of live food for ornamental fish within Thailand (Dararat, Starkweather & Sanoamuang 2011) and have been exported to Hong Kong. Although the cultivation of fairy shrimp has been developed, the productivity is still limited. The presence of black spots on the infected cuticle, i.e. black disease, is a major factor limiting their cultivation. The appear- ance of the disease found on fairy shrimp in Thailand is similar to that found in other countries including Spain, Algeria, Germany, America, Belgium (Dierc- kens, Vandenberghe, Beladjal, Huys, Mertens & Swings 1998) and Japan (Nambu, Tanaka & Nambu 2007). The disease is considered to be a cause of mortality in fairy shrimp and also has an adverse effect on commercial cultivation. However, there is little reference to black disease affecting fairy shrimp in the literature and the cause remains unclear. Journal of Fish Diseases 2011, 34, 911–920 doi:10.1111/j.1365-2761.2011.01314.x Correspondence Dr L Sanoamuang, Applied Taxonomic Research Center, Khon Kaen University, Khon Kaen, Thailand (e-mail: la_orsri@kku.ac.th) 911 Ó 2011 Blackwell Publishing Ltd