The present study investigated the effect on growth performance and ectoparasites prevalence in grouper (Epinephelus fuscoguttatus) after being fed with 0%, 0.3% and 0.7% essential oil-based functional additive supplementation (control group; medium-dose group and high-dose group). The experiment was designed with three replicates of each treatment group, each replicate located in a net pen within the same earthen pond.
Final survival rates were 91.6-92.9% and no significant differences were detected between groups. However, the functional feed addictive improved the DWG from 0.93 to1.02 and 1.06 g/day and the FCR was reduced from 1.56 to 1.45 and 1.40 for control (0%) to medium-dose (0.3%) and high-dose (0.7%) supplementation, respectively. Regarding morphometric indexes, the total length, body thickness and condition factor were significantly increased in treatment groups, while for the hepatosomatic index and the visceral somatic index no significant differences between group were detected.
Fish were naturally infected to four ectoparasites including Trichodina sp., Caligus sp., Zeylanicobdella sp., and Dactylogyrus sp. The prevalence and infection intensity of the aforementioned parasites in control group was significant higher compared to treatment groups. Red blood cell count (RBC), white blood cell count (WBC), hemoglobin level, lymphocyte count, and monocyte count were significantly increased in grouper fed with the functional additive compared with control group, while the mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean corpuscular hemoglobin concentration (MCHC), and thrombocytes did not show any statistically significant difference between groups. This study validates in the field that the essential oil-based functional additive has a strong positive impact on growth performance, flesh quality, immune response and significantly reduces the prevalence and impact of ectoparasites in grouper culture.
Keywords: functional feed addictive, growth performance, fish condition, ectoparasites.