Screening and characterization of antiviral compounds from Enteromorpha flexuosa against white spot syndrome virus (WSSV) and its in vivo influence on Indian white shrimp Fenneropenaeus indicus

In vitro antiviral activities of the organic solvent extracts of six species of seaweeds collected from the Kanyakumari Coast, India, were screened against shrimp white spot syndrome virus (WSSV). Based on the primary screening, ethyl acetate extract of Enteromorpha flexuosa effectively suppressed WSSV multiplication, and this extract was further purified through silica column chromatography and resulted in different fractions. After the secondary antiviral screening against WSSV, fraction III (FIII) effectively controlled WSSV multiplication at the 95 % level, which was detected by two-step PCR. Thin-layer chromatography and GCMS analysis revealed that the phenolic antiviral compound 2-(2-hydroxyphenoxy)-1-phenylethanol is present in the FIII fraction. Further, the active fraction FIII was incorporated into the artificial diets at different concentrations of 100 (D1), 200 (D2), 300 (D3) and 400 (D4) mg kg−1. A control diet, devoid of seaweed extract, was also prepared. The control and experimental diets were fed to the Indian white shrimp Fenneropenaeus indicus for 25 days; they were then challenged with virulent WSSV. The shrimp control group was 100 % PCR positive, whereas the D4 group was only 5 % positive after two-step PCR detection, and the value differed significantly (F = 7.31; P ≤ 0.05). The biochemical parameters of the shrimp groups fed with experimental diets significantly improved (P < 0.001) the coagualse activity to 94.54 s and increased the oxyhemocyanin level to 1.12 m mol l−1. The immunological parameters such as prophenoloxidase and lysozyme activity also appeared to be significantly increased (F = 164.88; P ≤ 0.001) in the experimental compared to control groups.