Pathogenicity and host specificity of Labyrinthuloides haliotidis (Protozoa: Labyrinthomorpha), a parasite of juvenile abalone

Abstract

Infections with Labyrinthuloides haliotidis, an achlorophyllous, eucaryotic protist, were lethal to almost all juvenile abalone (Haliotis kamtschatkana and Haliotis rufescens) less than 6 months of age in an abalone mariculture facility in British Columbia, Canada. In laboratory experiments, L. haliotidis isolated from infected abalone or grown in axenic nutrient medium was infective for abalone (H. kamtschatkana) less than 4.0 mm in shell length and 140 days of age. Ten days after exposure to at least 104 parasites in 20 mL of sea water, about 90% of these abalone died with numerous parasites throughout the tissues of the head and foot. By about 190 days of age, regardless of shell size, abalone mortalities were reduced to less than 50% after exposure to about 105 parasites. Finally, by about 340 days of age, most juvenile abalone (4.0 to 10.5 mm in shell length) did not succumb after three consecutive exposures, 13 days apart, to between 2 × 105 and 5 × 106L. haliotidis. Larger abalone (15 to 25 mm in shell length) did not become infected following intramuscular injections of about 1.5 × 104L. haliotidis. Small juvenile scallops (Patinopecten yessoensis) and juvenile oysters (Crassostrea gigas), both less than 8 months of age, were also resistant to infection. However, two of the oysters with badly cracked shells became infected. This suggests that if L. haliotidis can gain access, it is capable of using living oyster tissue as a source of nutrients for growth and multiplication.