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.