SInfluences of Cultivation Conditions on Microbial Profiles of Pacific White Shrimp (Litopenaeus vannamei) Harvested from Eastern and Central Thailand

Abstract

This study investigated influences of cultivation conditions on microbial profiles of Pacific White Shrimp (Litopenaeus vannamei) from three different cultivation environments: location, season and cultivation system (sanitation control farm and semi-natural farm). The first shrimp samples were collected from a sanitation control farm in Rayong (Eastern Thailand) in January 2011 (S1). Average temperature of water in the ponds was 27.1±0.2 °C with salinity 22.8±2.5 ‰ and pH 8.50±0.16. After harvesting, the samples were immediately shocked by ice before subjecting to microbiological analysis. Under these conditions, total plate counts (TPCs) of shrimps were generally below 4.00 Log CFU/g. Vibrio spp. was observed in 25 g of all samples. Vibrio parahaemolyticus was observed in terms of most probable number (MPN) values ranging from 3.6 to 11 MPN/g. The second shrimp samples were collected from the same farm in June 2011 (S2). Average temperature and salinity of waters were significantly higher than S1 (30.6±2.1°C and 30.4±0.4 ‰, respectively), whereas pH value was not significantly different (8.37±0.17). The TPCs and occurrence of Vibrio spp. of this batch were also similar to S1, whereas MPN values of V. parahaemolyticus were significantly higher (240 to >1100 MPN/g). The third shrimp samples were collected from a semi-natural farm in Samut Songkram (Central Thailand) in August 2011 (S3). In this farm, salinity was dramatically lower than the sanitation control farms (0.6±0.5 ‰), whereas the temperature and pH value were relatively similar (29.1±0.3°C and 8.27±0.27, respectively). TPCs observed were significantly higher than the control system farms (5.14 to 5.86 Log CFU/g). Vibrio spp. was detected in all samples. Interestingly, MPN values of Vibrio parahaemolyticus were significantly lower than the first two samples (<0.3 to 3.6). According to the results, microbial load on shrimp could be influenced by salinity and farming operation systems. The V. parahaemolyticus populations correlated positively with increasing temperature. In addition, salinity increase seems to be a key factor influencing contamination levels of V. parahaemolyticus on shrimps.