An epizootic bacterial infection in the giant freshwater prawn Macrobranchium rosenbergii occurred in Taiwan from May to June 1999. The cumulative mortality was approximately 30 to 75%. The diseased prawns showed opaque and whitish muscles and were approximately 2 mo old with total lengths from 5 to 6 cm. Histopathologically, they showed marked edema and necrotic lesions with inflammation in the muscles and hepatopancreas. Bacteria isolated using brain heart infusion medium or tryptic soy agar were Gram-positive and ovoid. Three isolates from diseased prawns at different farms were tested using the API 20 Strepsystem and conventional tests and identified as Lactococcus garvieae. Experimental infections with these isolates gave gross signs and histopathological changes similar to those seen in the naturally infected prawns. The LD 50 value of isolate MR1 was 6.6 × 10 5 colony forming units/prawn. Identification of MR1 was confirmed by a PCR assay for L. garvieae that gave the expected amplicon of 1100 bp. In addition, its 16S rDNA sequence (GenBank accession number AF283499) gave 99% sequence identity to Enterococcus seriolicida (synonym L. garvieae; GenBank accession number AF061005). This is the first report of confirmed L. garvieae infection in prawn aquaculture. KEY WORDS: Lactococcus garvieae · Giant freshwater prawn · Macrobranchium rosenbergii · PCR · 16S rDNA sequencing Resale or republication not permitted without written consent of the publisherDis Aquat Org 45: [45][46][47][48][49][50][51][52] 2001 ola quinqueradiata in Japan was named Enterococcus seriolicida (Kusuda et al. 1991) after previously being classified as Streptococcus (Kusuda et al. 1976). However, taxonomic studies based on DNA-DNA hybridization (Eldar et al. 1996) and sequence analysis of 16S rRNA (Domenech et al. 1993) indicated E. seriolicida (Kusuda et al. 1991) was synonymous with L. garvieae (Eldar et al. 1996). In Spain, a serious septicemic disease of Scopthalmus maximus or large turbot (100 g to 3 kg) was accredited to an Enterococcus-like bacterium (Nieto et al. 1995) that was also found to match with L. garvieae (Eldar et al. 1996). Zlotkin et al. (1998) subsequently developed a polymerase chain reaction (PCR) assay based on unique regions of the L. garvieae 16S rRNA gene that allow for its specific identification.The giant freshwater prawn Macrobranchium rosenbergii is commercially cultured throughout the world and intensively so in Taiwan, where production, however, decreased by 47 to 52% from 1992 to 1995 (New 1995, Taiwan Fisheries Bureau 1996 due to disease problems. Two diseases have been linked to production decline. One is a yeast infection that occurs mostly in the cool season (October to March), with symptoms including a yellow exoskeleton, a swollen hepatopancreas (HP), milky hemolymph and opaque and whitish muscles (Shu 1993, Cheng & Chen 1998a. The other is an Enteroccoccus-like infection that occurs mostly in the hot season (June to September, especially during phytoplankton blooms) and causes muscle ...

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The diseased cage‐cultured cobia (Rachycentron canadum) displayed clinical signs, haemorrhagic eyes, dorsal darkness and gross pathological lesions, enlargement of spleen and liver. Haemorrhages were found in brain, heart and liver with cumulative mortality rates ranging from 20% to 50%. Extensive congestion in the heart, liver, spleen, kidney and brain was observed histopathologically. Epicarditis and meningitis were also revealed in diseased cobia. All isolates recovered from the organs (liver, spleen, head kidney, posterior kidney, brain and muscle) of cobia were found to be gram‐positive, non‐motile, ovoid cocci, short‐chain–forming (diplococci) and α‐haemolytic. The API 32 strep system together with the polymerase chain reaction assay for species‐specific primers (pLG1 and pLG2) and the internal transcribed spacer (ITS) region (G1 and L1 primers) confirmed all four selected isolates as Lactococcus garvieae. Partial 16S rDNA nucleotide sequence (~1,100 bp) of one representative L. garvieae isolate AOD109191 (GenBank accession number, MW328528.1) shared 99.9% identities with the 16S rDNA nucleotide sequence of L. garvieae (GenBank accession numbers: MT604790.1). Transmission electron microscopy (TEM) evaluation of one representative L. garvieae isolate (AOD109191) and the results of multiplex PCR did not reveal the presence of the capsular gene cluster (CGC), thus categorizing the isolate as the KG+ phenotype. Capsule staining and TEM observations confirmed the presence of a hyaluronic acid‐like capsule, a possible virulence factor in KG+ phenotype L. garvieae isolates. The pathogenic potential of the representative isolate (AOD109191) was assessed through intraperitoneal injection challenges in cobia. The gross lesions and histopathological changes found in experimentally infected cobia were similar to those seen in naturally infected fish. This is the first report that confirms L. garvieae‐induced ‘warm water lactococcsis’ can cause outbreaks of diseases in cage‐cultured cobia.

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