Toxicity study and inhibitory properties of Melaleuca cajuputi leaf extract against Ecytonucleospora hepatopenaei

The emergence of diseases is one of the main obstacles to the shrimp industry when it comes to intensive aquaculture practices. Ecytocnucleospora hepatopenaei (EHP) is one of the shrimp microsporidia known to cause growth retardation and white discoloration associated with musculature, thereby decreasing shrimp production yield. Prolonged use of chemotherapeutic agents in bulk quantities may result in drug-resistant pathogenic microbes, toxic, and residual sedimentation in aquatic ecosystems. In this present study, Melaleuca cajuputi leaf extract (MCLE) was extracted, and an acute toxicity test was carried out to determine a 96-h median lethality concentration (LC₅₀). The behavior of shrimp was also observed after exposure to MCLE to determine their responses. The microsporidian-infected Litopenaeus vannamei was obtained from the shrimp farm in Terengganu, Malaysia, and the isolation and identification of EHP were performed using the Percoll-gradient method and polymerase chain reaction (PCR), respectively. Subsequently, the MCLE at 10, 20, and 30% of 96-h LC₅₀ were exposed to the isolated EHP to determine their antimicrosporidian potential and the morphological changes were viewed under scanning electron microscopy (SEM). Results showed that the 96-h LC₅₀ of MCLE to L. vannamei was recorded to be 162.14 mg L⁻¹. Behavior responses were observed in L. vannamei after exposure to MCLE including agitation, swimming erratically, gasping at the water surface constantly, lethargy, and color changes in abdominal segments and carapace, and the severity was proportional with the MCLE concentrations. All MCLE concentrations cause inhibition to EHP, with 48.6 mg L⁻¹ causing severe impairment on the EHP cell membrane. The finding could be useful to find natural antimicrosporidian therapeutics as an alternative to combat EHP in shrimp farms.