Application of Rosmery (Rosmarinus officinalis) Solution to Reduce Marine Leeches in “Cantang” Hybrid Grouper (Epinephelus fuscoguttatus x Epinephelus lanceolatus)

One common disease that attacks hybrid grouper is marine leech (Zeylanicobdella sp.). Therefore, it is necessary to take safe and environmentally friendly treatment steps, namely bathing fish infected with marine leeches with rosemary solution. This research examined the application of rosemary solution with different concentrations and bathing times to decrease the intensity of marine leech infections in “cantang” hybrid grouper (Epinephelus fuscoguttatus x Epinephelus lanceolatus). The experimental design of this research was a randomized factorial design (rosemary solution concentration factor and bathing time factor) with three replications. This experimental’s treatments were a combination of rosemary solution concentrations (0, 7.5, and 15 mL/L) and bathing times (20, 40, and 60 minutes). The experiment showed that the interaction of concentration and bathing time of rosemary significantly eliminate the number of leeches in “cantang” hybrid grouper. The rosemary solution at concentrations of 15 mL/L and 7.5 mL/L significantly differed from the control; 15 mL/L was the best concentration for reducing leeches intensity, with an average intensity reduction of 29.91%. The best duration of bathing rosemary to decrease the intensity of leeches in “cantang” hybrid grouper is 60 minutes, with an average reduction in intensity of 19.21%. However, the concentration and duration of bathing in rosemary solution could not decrease the prevalence of leeches in “cantang” hybrid grouper. Bathing grouper fish in rosemary solution at a dose of 15 mL/L for 60 minutes is the best treatment to decrease the intensity of leech attacks on grouper fish by 44.85%. Bathing hybrid grouper with rosemary solution is one solution to decrease the intensity of marine leech attacks on fish farming.