Vibriosis is a common disease problem in mariculture or coastal aquaculture which is generally controlled by using antibiotics. However, many fish bacterial pathogens have now developed resistance to many of these antibiotics and hence alternative methods of treatment is encouraged these days. Medicinal plants (Aloe vera) are considered new resources for producing agents that could act as alternatives to antibiotics. The aim of this work was to investigate the antibacterial effect of Aloe vera gel against the commonly occurring species of Vibrio which cause disease outbreak in sea cage farming, viz; Vibrio parahaemolyticus and Vibrio alginolyticus. The Aloe vera gel was extracted using different solvent viz., Ethanol, Methanol, N-Butanol and distilled water. The antibacterial activity was tested by the agar well diffusion method.
Crude N-Butanol extract of Aloe vera exhibited highest zone of antibacterial activity which was 18 mm against V. parahaemolyticus and 14 mm against V. alginolyticus. The methanol extract showed moderate activity against tested pathogens, where as there was no antibacterial activity for the extract using distilled water. It was also found that, the tested pathogens were highly susceptible to the broad spectrum antibiotics such as Gentamycin (10µg/disc), Cefotaxime (30 µg /disc), Amikacin (30 µg /disc), Ofloxacin (5µg/disc), Nalidixic acid (30 µg /disc), Cefixime (5µg/disc) and Tetracycline (30 µg /disc). The present study revealed that N-butanol and methanol extract of the Aloe vera showed remarkable antibacterial activity against tested bacterial strains. However, these plant based chemicals are required to go through a toxicity analyses before they can be safely applied to aquaculture animals.