EMERGING LARVAL HEALTH ISSUES IN Litopenaeus vannamei (BOONE, 1931) – A CASE STUDY

The increasing trend in intensification and commercialization of shrimp seed production has exacerbated the epizootics of several larval and post larval infections and diseases in shrimp hatcheries in Indian context. Towards this end, an extensive survey was made to study the emerging larval health issues in Litopenaeus vannamei (Boone, 1931) by organizing surveys in major shrimp hatcheries located in Tamil Nadu, Southeast coast of India. Collection of primary and secondary data was done based on the following factors: status of brood stock, samples of shrimp larvae from respective hatcheries, information on occurrence and history of larval infections and diseases, data on major water quality parameters, information on the broodstock and larval feed. The survey revealed that several bacterial infections are found to predominant. The shell degrading bacteria like Vibrio spp., Pseudomonas spp., Aeromonas spp., Flavobacterium spp. etc. are known to cause necrosis of body and appendages among the shrimp larvae. Bacterial septicemia in shrimp larvae, caused by Vibrio spp., was also reported to occur. Apart from these bacterial infections, in recent time, the prevalence of Zoea-2 Syndrome in shrimp hatcheries is known to occur in various hatcheries causing impairment in the nutrient absorption leading to delayed molting and mortality of larvae at Zoea 2 stage.  Larval and post larval shrimps are commonly affected by fungal species Lagenidium spp. and Serolpidium spp. Besides, protozoan parasites like Zoothamnium sp. (ecto-commensals) and Voritcella sp. (microsporidia) and gregarines (endo-commensals) had also been reported to cause infection.  Added to the above, incidence of Larval Deformities Syndrome (LDS) has also become a major problem in shrimp hatcheries, occurring from Nauplius to Post Larval stages. The specific causative agent is still unknown behind this syndrome. Another nutritional problem, known as Swollen Hindgut Syndrome (SHG) had been reported to cause digestive problems in post larvae. Among the various larval diseases and infections listed above, it was found that the most dominant are Zoea-2 Syndrome and Larval Deformities Syndrome followed by bacterial necrosis in shrimp hatcheries disrupting the normal seed production activities and further studies are on.