Praziquantel form, dietary application method and dietary inclusion level affect palatability and efficacy against monogenean parasites in yellowtail kingfish.

The bitterness of racemic praziquantel (PZQ) currently constrains its use as an in-feed treatment against monogenean flukes in finfish aquaculture. In an effort to increase the palatability of diets containing racemic PZQ for yellowtail kingfish, the palatability and efficacy of 2 forms of racemic PZQ (powder or powder within microcapsules) against natural infestations of skin and gill flukes were compared using 2 different dietary application methods (incorporated within the pellet mash prior to extrusion or surface-coated after extrusion) at active dietary inclusion levels of 8, 16 and 25 g kg-1 in large (3.5-4 kg) yellowtail kingfish. There was no clear benefit of incorporating PZQ into diets prior to extrusion. PZQ microcapsules improved the palatability of PZQ-containing diets but did not completely mask the bitter flavour. At the lowest active dietary inclusion level of 8 g kg-1, ingestion of the diet containing PZQ microcapsules was equal to the control and significantly better than that containing PZQ powder. At an inclusion level of 16 g kg-1, ingestion of the PZQ microcapsule diet was significantly better than that containing the same inclusion of PZQ powder but significantly lower than the control. Consumption of the diet containing 25 g kg-1 of PZQ microcapsules was poor. All fish consuming medicated feeds had a significant reduction in flukes relative to control fish; however, efficacy data and blood serum analysis suggested that diets containing PZQ microcapsules had lower bioavailability than those containing PZQ powder.