Variation in the antiviral and antibacterial activity of abalone Haliotis laevigata, H. rubra and their hybrid in South Australia

Abalone (Haliotidae), well-known commercial gastropods, have experienced large scale disease outbreaks such as abalone viral ganglioneuritis caused by a herpesvirus and summer mortality typically caused by bacteria such as Vibrio harveyi. Identification of the factors that influence antimicrobial activity could assist future management of disease in the abalone industry. A proportion of abalone naturally survive these outbreaks (5–40%) raising the possibility that some abalone are relatively resistant. Identifying such abalone could enable breeding of resistant populations. This study applied in vitro assays to investigate antiviral and antibacterial activity of abalone haemolymph. Comparisons were made among Haliotis laevigata (greenlip), H. rubra (blacklip) and their hybrid. Intraspecific variation was examined at the individual scale, as well as between commercial aquaculture family lines and natural populations. Abalone sourced from the wild showed higher antiviral and antibacterial activities than those from a land-based farm. We found no significant difference in antiviral activity between greenlip, blacklip and hybrid abalone (p > 0.05). The antibacterial activity of greenlip abalone was also similar to the blacklip, but significantly lower than the hybrid (p = 0.001). There was substantial individual variation among abalone (maximum range of 31–69% for antiviral activity and 4–46% for antibacterial activity) within the same family line or geographic location. Antiviral and antibacterial activity increased slightly with an increase in shell length, and a 2 yr old family line had lower activity than 3 yr old family lines. There was no significant effect of gender or reproductive activity on antiviral or antibacterial status (p > 0.05). Further investigation is required to establish whether the individual variability in antimicrobial activity is inheritable in breeding programs and whether higher activity confers greater resistance to disease.