Effect of wood apple Aegle marmelos, Correa (Dicotyledons, Sapindales, Rutaceae) extract as an antibacterial agent on pathogens infecting prawn (Penaeus indicus) larviculture

Aegle marmelos, an antimicrobial plant was extracted with 100% methanol and the sensitivity of the extract was assessed against different fish diseases caused by pathogenic bacteria. For sensitivity test, the minimal bacterial population growth (10-20%) was observed in the 40 mg/100 ml concentration of the culture medium. Different concentrations (25,50,75 and 100%) of the extracts were enriched with Artemia franciscana nauplii/pre-adult. These were fed to the Penaeus indicus post-larvae (6.5 to 6.85 mg of average weight) for 25 days, which were reared with four different pathogens (Pseudomonas aeruginosa, Aeromonas hydrophila, Salmonella typhi and Vibrio sp.) inoculated seawater. Among the four pathogens, P.aeruginosa was very sensitive to A. marmelos extract. Penaeus indicus post larvae fed on the un-enriched Artemia exhibited the lowest survival, which averaged 21 %, and this increased to the maximum of 58 % (averaged) in the 75% extract enriched Anemia fed post larvae of P.indicus. Similarly, the weight gain and specific growth rate were also increased significantly (P< 0.01) in the enriched Artemia fed post-larvae of P.indicus. Among the four different pathogens inoculated, the post-larvae, which were reared in the P.aeruginosa inoculation, exhibited the maximum survival (37.35 mg) and better growth rate (12.03 %). Also the bacterial count (cfu/g) was significantly (P<0.01) differed from the un-enriched to enriched Artemia fed post-larvae. The extract helped to reduce the bacterial count of a maximum of 1.9, 2.45, 0.96 and 2.36 times in the P.aerugiosna, A.hydrophila, S.typhi and Vibrio sp. respectively in the 100 % extract enriched Anemia fed post-larvae of P.indicus. Among the different percentages of enrichment, 75 % was considered the best for survival and growth characteristics of the post larvae.