| | In general, the health status of farmed abalone in Australia has been relatively high. In the wild, the shell of an abalone can be the host to a variety of organisms including boring sponges, clams and polychaetes. These organisms generally do not harm the animal since they do not bore completely through the shell but they could affect appearance and hence marketability. Filtration of incoming water inhibits biofouling, in pipes and tanks and on abalone in land-based systems, but increases costs. Infectious diseases are currently not a major problem in abalone culture; however, there are several bacterial pathogens including Vibrio spp that can occasionally cause death or reduced growth. | |
MortalityMortalities in abalone systems are often caused by opportunistic, secondary, bacterial infections due to the individual being weakened by stress from, for example, high water temperatures or poor water quality, or through mantle or foot injury during removal from a tank (the mantle is the frill of tissue, between the foot and the shell which lays down the new shell material). Improvements in husbandry techniques and management procedures have reduced the rate of mortality due to these factors although high summer water temperatures can still increase risks. A protozoan parasite ( Perkinsus olseni ) has been found to cause death of stressed abalone in culture facilities. Also, this parasite has caused mortalities in wild populations of Blacklip abalone in South Australia. Perkinsus enters a culture facility through the use of wild animals infested with this parasite, so it is essential that growers inspect and quarantine any new animals brought into the culture operation (Hone and Fleming, 1998). Mudworms have caused major problems in sea-based facilities or growout operations located in less oceanic sites. Wild Roe's abalone seem particularly prone to mortality associated with mudworm. Polydora spp. and, more seriously, Boccardia knoxi cause most of the problems by boring into the shell, which the abalone must repair by laying down nacreous layers over the cavity in the shell. The mudworms do not eat the abalone, but cause the animals to be stressed from the added activity. If the worm infestation is severe, a sea-based operation can have a mortality rate over 50 per cent (Lleonart in Fleming and Roberts 2000, pp. 115-126). Operators of land-based abalone culture facilities can quickly remove individuals with mudworms, so they do not cause a problem for this culture method (Hone and Fleming, 1998). Within Australia, Boccardia knoxi is only known to occur in Tasmanian subtidal Pacific oyster and abalone farms. If any of these oysters are brought into Western Australia for use by restaurants, vigilance will be needed to ensure that seawater, coming in contact with the oysters, or the oyster shells, is not disposed into the marine environment. While survival rates of abalone in growout systems have been remarkably high, given their low tolerance to environmental stresses (Burke et al ., 1999), vigilance will be required as disease problems usually emerge in more mature aquaculture industries (see Handlinger, 2000 in AB-brief, 4(2): 7-8). Unexplained mortality or stress symptoms should be discussed with Fish Health Unit staff. Informtation courtesy of the WA Department of Fisheries |