Ectoparasites are one of the most important bottlenecks for sustainable aquaculture production of tropical marine finfish species. External parasitic infestations are commonly associated with secondary bacterial infections, and this multifactorial pathogen combination constrains survival, growth performance and profitability. Health promoting additives are commonly used in commercial feeds as preventive strategies to reduce the severity of ectoparasite infestations.
This research investigated the effect of an essential-oil based health additive (Apex®Prefend, Adisseo) on growth performance and on prevalence and infestation intensity of ectoparasites in brown marble grouper (Epinephelus fuscoguttatus). The trial was conducted in an earthen pond farm located the North of Vietnam (Hanoi province). The additive was supplemented in feed at 0% (control), 0.3% (medium-dose) and 0.7% (high-dose) during the first 3 months of grow-out. The experiment was designed with three replicates per treatment group. Each replicate was in a net pen within the same earthen pond. Four ectoparasite species, including Trichodina sp., Caligus sp., Zeylanicobdella sp., and Dactylogyrus sp., were naturally detected in fish.
Results showed a relatively high survival for all treatment groups, ranging between 91.6-92.9%. However, the additive effects were detected in growth performance. The medium and high inclusions of Apex®Prefend improved daily weight wain (DWG) by 10% and by 14%, respectively. Likewise, the feed conversion ratio (FCR) was reduced by 7% and 10% by the medium and high inclusions, respectively. The prevalence and infection intensity were significantly reduced by 80% and 70% respectively in the medium-dose additive group, and by 70% and 60% in the high-dose additive group.
This study confirms under real field conditions that the essential oil-based functional additive Apex ®Prefend is an effective strategy to support grouper fish in dealing with ectoparasite infestations and therefore, to improve growth performance and health.
Keywords: functional feed addictive, growth performance, fish condition, ectoparasites.