Management of spionid mud worm infestations of Tasmanian cultured abalone

Stock losses in the range 50-90% were recorded at experimental and pilot scale sea-based abalone farms in southern Tasmania in the mid-1990's. These were associated with spionid polychaete \mud worm\" infestation especially Boccardia knoxi. The overall aim of the multi faceted research presented here was to minimise the effects of spionid infestation. Studies of reproductive biology indicated initial infestation with B. knoxi could be delayed by placement of stock after the spring planktotrophic dispersal phase. This would also reduce infestation by a second species Polydora hoplura. Fieldwork during 1998-2001 indicated that large settlements of spionids might be relatively uncommon. Testing of 16 chemical/drug agents and freshwater bathing as a treatment for mud worm infestation failed to yield a useful candidate. Agents lacked penetration into shell burrows or were harmful to abalone at levels sufficient to kill spionids in situ. Air exposure of abalone for 2-4 hours at humidity less than approximately 63% was highly effective as a spionid treatment especially in the first 6 months post infestation. Assessment of risk factors associated with spionid settlement found that elevated levels of spirorbid polychaetes enhanced mud worm colonisation. Stock size rearing vessel design and position in the water column also led to differential spionid settlement outcomes. Spionid infestation was associated with a reduction in: growth % flesh weight protein and carbohydrate reserves and with an increased respiration rate. Major histological changes were elevated levels of brown pigment in the right kidney and digestive gland consistent with mobilisation and consumption of energy reserves. The ranges in levels of sodium potassium calcium magnesium chloride copper glucose and protein in haemolymph were established for apparently healthy abalone and spionid infested animals."