A mycosis of juvenile spiny rock lobster, Jasus edwardsii (Hutton, 1875) caused by Haliphthoros sp., and possible methods of chemical control

Abstract

Mortalities of puerulus and juvenile rock lobsters, Jasus edwardsii (Hutton, 1875), held in shore‐based ongrowing facilities at water temperatures between 10 and 18 °C were associated with infection by an invasive oomycete identified as Haliphthoros sp. Gross signs of disease included loss of appetite, lethargy and 1–3 brown/black focal necrotic lesions in the gills near insertion of the walking legs. Hyphae were observed in wet preparations of gill filaments excised from lesions. Histology of gill lesions showed hyphae inside the gill cuticle, invasion and lysis of the skeletal muscle and massive haemocyte infiltration and melanization at the base of walking legs adjacent to infected gill filaments. Lobsters over approximately 30 mm carapace length appeared resistant to infection. Death of affected lobsters usually occurred prior to or during the moult and in some cases may have been associated with secondary bacterial infection. Haliphthoros sp. was isolated in pure culture and marine agar 2216 was the medium that produced best growth in vitro. Two isolates were exposed in vitro to five chemicals to determine if an effective treatment could be found. Chemicals that interrupted the life cycle by killing zoospores or preventing sporulation included malachite green, trifuralin, formalin and copper sulphate. The appearance of the disease was associated with poor hygiene and its elimination may be achievable by improving husbandry practices.