A comparison of the palatability of racemic praziquantel and its two enantioseparated isomers in yellowtail kingfish Seriola lalandi (Valenciennes, 1833)

The bitterness of racemic praziquantel (Rac‐PZQ) constrains its use as an in‐feed treatment against monogenean flukes in finfish aquaculture. Evidence exists in mammals that the R‐(?) enantiomer of PZQ is less bitter than the S‐(+) enantiomer. If fish exhibit this same response, then the recently described techniques for the large‐scale resolution of R‐(?)‐PZQ from Rac‐PZQ could facilitate the wide‐spread application of this effective anthelmintic compound via feed. The hypothesis that yellowtail kingfish Seriola lalandi would find R‐(?)‐PZQ more palatable than Rac‐PZQ and S‐(+)‐PZQ was tested in four trials. During the first three trials, the palatability of diets top‐coated with 10 g kg^?1 of Rac‐PZQ or its two enantioseparated isomers were compared in small (85–160 g) and large (1.2 kg) yellowtail kingfish. A fourth trial compared the palatability of R‐(?)‐PZQ and Rac‐PZQ at dietary inclusion levels of 2.5, 5.0 and 10.0 g kg^?1 in small yellowtail kingfish (170 g). Ingestion data showed that R‐(?)‐PZQ to be no more palatable than either Rac‐PZQ or S‐(+)‐PZQ to yellowtail kingfish, regardless of size. Indeed, evidence suggested that the S‐(+)‐PZQ to be slightly more palatable than both R‐(?)‐PZQ and Rac‐PZQ. From these data, we hypothesize that the strong smell of R‐(?)‐PZQ (which was not present in S‐(+)‐PZQ) is an equally important determinant to palatability as taste in yellowtail kingfish. Results demonstrate that dietary inclusion level is a more important determinant to palatability than PZQ chirality; however, administration of R‐(?)‐PZQ may still be advantageous if it is demonstrated to be the only enantiomer efficacious against monogeneans.