## 3 Results and Discussion  
The present study describes the first attempt to evaluate the efficacy of PZQ against _Z. serialae_ in Mediterranean greater amberjack, inspired by the fact that the drug has been a promising parasitic to confront helminths of _Seriola_ spp. [9] in field and experimental studies. Our trial was carried out with the use of small cages installed in situ and harboring naturally infected fish. This infection model proved ideal for the purpose of the study, where the use of commercial cages as replicates was not economically feasible. Such an experimental set up lacks any technical complexities and can be easily adopted in forthcoming studies using different combination of fish species and ectoparasites. Acceptance of the medicated diet by experimental fish is one of the main challenges of any PZQ trial. Low inappetence signs were observed herein, which did not affect the overall consumption of the medicated diet. The inclusion of dietary attractants, such as krill meal, was perhaps beneficial to overcome the bitterness of PZQ, as recently demonstrated [15], although previous masking attempts to feed dietary PZQ treatments to various farmed fish species revealed mixed results [12; 18; 19; 20]. Prior to the study, the total parasitic load from sampled fish was measured to be 21 \(\pm\) 6.4 parasites that was considered acceptable for the initiation of the medication. No mortalities of greater amberjack were noticed during the trial, although the environmental temperature was ideal for the development of the disease and the age of fish used is considered the most susceptible to _Z. serialae_, possibly due to the acquired protection of older stages, as seen against other pathogens of _Seriola_[21]. Prevalence of _Z. serialae_ on the other hand was 100% in all examined fish. Although PZQ administration failed to fully eliminate _Z. serialae_ from the medicated group, there were significant differences (_p_ = 0.001) in parasitic load between PZQ-treated and Control greater amberjack (Table 2). Moreover, the estimated efficacy in the medicated fish reached a remarkable value exceeding 80%, approaching thus, the corresponding values (81-100%) calculated in previous studies where PZQ was dietary delivered to fight monogeneans of other farmed fish species [14; 22; 23; 24]. Dietary PZQ treatments have been previously evaluated in other monogenean-infected _Seriola_ spp. For example, the delivery of PZQ at 50-150 mg/kg fish for 3-6 days against _Benedenia seriolae_ and _Z. serialae_ infections in yellowtail kingfish (_S. lalandi_) [14] revealed that lower daily doses of PZQ were associated with fewer parasites compared with fish fed higher daily doses for fewer days. This was attributed to the increased palatability issues emerging from the surface-coating of higher PZQ dosages. Dietary administration of PZQ was promising against _Nebebebeleania girelae_ infection in spotted halbit (_Verasper variegatus_), where a long-term, low-dose treatment (40 mg/kg for 11 days) was the most effective measure [12]. Using intubation of PZQ [22], a dosing of 70-120 mg/kg for 3 days was very effective against _Z. serialae_ in yellowtail kingfish, while _B. serialae_ appeared more resistant to the drug, necessitating a timed repeat therapy. Full efficacy of PZQ was observed against _Heterobothrium okamoti_ affecting tiger puffer (_Takifugu rubripes_) when 40 mg/kg were delivered for 20 days [23]. Sadly, antiparasitic use of PZQ in fresh water formed fish suffering from helminths, has been mainly evaluated via baths or dips (reviewed by [PERSON] et al. [9]) thereby rendering weak any further comparisons with dietary PZQ applications in other environments. Comparably, baths with formalin, a widely used therapeutic application for various ectoparasites, seems ineffective against _Z. serialae_[13], as opposed to hydrogen peroxide baths. The latter can be remarkably effective [7] since in most cases single applications