Halioticida noduliformans isolated from cultured abalone (Haliotis midae) in South Africa

A recent outbreak of mycosis has been discovered in abalone culture facilities in South Africa. Infected abalone are characterised by multifocal areas of necrosis of the epithelium, underlying muscle fibres and connective tissues of the foot, epipodium and mantle. The lesions are typically 2-3 mm in diameter and contain numerous hyphae. Affected aquaculture facilities have suffered significant production losses, with up to 90% mortality among spat and up to 30% mortality among older animals. The pathogen has been identified as Halioticida noduliformans Muraosa, Morimoto, Sano, Nishimura and Hatai, 2009 from the morphological characteristics, the physiological characteristics that were investigated and molecular analysis of the large subunit ribosomal RNA (LSU rRNA) gene. Although the optimum temperature for growth of the fungus was 20-25 degrees C. it grew at a wide range of temperatures (10-25 degrees C). No growth occurred at 5 and 30 degrees C. The fungus grew well in peptone yeast glucose saline (PYGS) agar containing 50-100% seawater, with optimum growth occurring in full strength seawater (-35 ppt salinity). No vegetative growth was observed on PYG agar without seawater or supplemented exclusively with varying concentrations (0-5%) of NaCl. The isolate grew at a wide range of pH (4.0-10.0) with the optimum pH value of 7.0-8.0. The disease was reproduced in juvenile abalone (30-50 mm shell length) by artificial infection and the fungus was re-isolated from moribund abalone, demonstrating that the isolated H. noduliformans fungus is the cause of abalone tubercle mycosis disease that has been occurring in South Africa since 2006. (C) 2011 Elsevier B.V. All rights reserved.