Praziquantel form, dietary application method and dietary inclusion level affect palatability and efficacy against...

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.