Globally, the most common penaeid shrimps currently being cultured are Penaeus monodon. As per the FAO statistics, the world production of cultivated shrimp has increased since the early 1980’s. Over a period, the demand for shrimp is exponentially increased. It is estimated that more than 50% of the world production of penaeid shrimp is contributed by P. monodon. In India intensification of shrimp culture methods and improper management strategies caused the shrimps to face stress and injury as well as consequent diseases, which devastated the farming activities. Infectious diseases constitute a main barrier to the development and continuation of shrimp aquaculture in terms of quality, quantity and regularity and also continuity. According to Global Aquaculture Alliance (GAA) survey, in 2001 an overall loss to aquatic animal disease of approximately 22% in a single year, and with respect to disease agents, the majority of efforts on disease control 80% focused on viral and bacterial pathogens. Several studies have indicated that resistance may be increasing in developing countries and diarrheal disease is one of the most important cases of illness and death occurs in young children. Moreover, the control of infectious diseases in aquaculture is seriously threatened by the steady increase in the number of pathogenic microorganisms that are resistant to antimicrobial agents. Vibrio infection has been implicated as a major mortality factor in juvenile penaeid shrimp. Vibriosis caused by V. alginolyticus and V. harveyi is still serious disease problem in cultured black tiger shrimp in India. Despite, penaeid acute viremia (white spot syndrome virus WSSV) prevails in Asian countries; Vibrio is considered as members of the normal bacterial flora of shrimp and the culture environment. Often acting as an opportunistic pathogen or secondary invaders, they induce mortality ranging from slight to 100% in affected population under stress. Vibrio sp isolated from diseased penaeids include V. alginolyticus, V. harveyi, V.parahaemolyticus, V.vulnificus, V. damsela and V.anguillarum. Considering then, the present study was initiated to develop cost effective therapeutants from microalgae species i.e. Chlamydomonas reinhardtii, Chlorella vulgaris, Klebsormidium flaccidum, Cosmarium impressulum, Kirchneriella lunaris, and Spirulina platensis can be potential inhibitors of the bioactivity in Vibrio outbreak in penaeid shrimp. The work was carried out mainly isolation of secondary/pathogenic Vibrio sp. from the outbreak caused by devastating WSSV in penaeid shrimp. Finally, experimental transmission and evaluation of pathogenicity of the Vibrio isolates.
Muralidharan Velappan and Deecaraman Munusamy