Isolation of a fungus from shell lesions of New Zealand abalone, Haliotis iris Martyn and H. australis Gmelin

Abstract

Shell irregularities characterized by deposition of conchiolin on the inner shell surface of abalone, Haliotis spp., have been reported in populations along the South Island of New Zealand for over 50 years. A previously reported, but unidentified, fungus associated with these shell lesions is isolated for the first time from Haliotis iris, the black footed paua, and H. australis, the yellow footed paua, both obtained from Jacks Bay, South East Otago. Fungal hyphae measured 1.20 – 2.38 μm (=1.83 μm) in diameter. Occasionally, wider hyphae that measured 2.38 – 3.60 μm (= 2.60 μm) in diameter with an apical swelling that measured 4.80 – 7.20 × 7.20 – 15.00 μm (= 6.20 × 11.80 μm) were observed within lesions. Visible growth of aerial hyphae was observed on plates within 12 d at 16 °C on several media. Three morphologically indistinguishable isolates were obtained: two originated from H. iris shells and one from an H. australis shell. We examined 8 fungal and/or bacterial media and determined that the fungus grew best on a dilute medium (yeast extract, glucose, shell extract (+/-peptone agar) at 15 °C. Fungal growth was observed between 7 – 20 °C but not at room temperature (24 °C). Sporulation has not been induced , therefore the fungus is provisionally identified as a member of the Class Deuteromycotina.

No significant relationship between animal length and incidence of shell mycosis was observed. Abalone condition was not influenced by the shell mycosis in either species. The number of circulating haemocytes was significantly elevated in infected H. australis (1.19 × 10⁷ cells ml⁻¹) relative to uninfected individuals (6.72 × 10⁶ cells ml⁻¹) but not between infected and uninfected H. iris. No significant relationships were observed between the degree of fungal infection and protein levels of whole haemolymph, serum or sex (immature, male or female; p<0.050; N=34). We are currently attempting to determine the taxonomic placement of the fungus and further characterize its growth physiology and pathogenicity.