Bacteria attached to suspended particles in Northern White Shrimp (Penaeus vannamei L.) ponds

Epibacteria, i.e. bacteria attached to suspended particles, were studied in ponds, used for the cultivation of Northern White Shrimp (Penaeus vannamei L.), at Hai-yan Farm (Zhejiang Province, China). Four ponds with different surface area and age were used. The water temperature ranged from 24 to 32 °C on the sampling days. Salinity and pH values of all shrimp ponds ranged 10-20‰ and 7.8-8.4, respectively, during the experimental period, from 20 May to 20 August 2004. In this study, the numbers of suspended particles (SP), particles with bacteria attached (BP), epibacteria, i.e. bacteria attached to suspended particles only (EB), and total plate count (TPC) were determined and the concentration of particulate organic carbon (POC) measured. In addition, the correlation between particles, epibacteria and POC was analyzed. Results showed that the average number of SP in four shrimp ponds was 5.41 × 104 ml− 1, with a BP of 3.00 × 104 ml− 1, while the percentage of particles with bacteria attached was 55.41% of the total number of suspended particles. The EB and TPC of the four ponds were 6.33 × 104 per ml and 3.59 × 106 per ml, respectively, while the percentage of EB to TPC was only 1.76%. There were highly significantly lower counts (P < 0.01) of BP, EB and TPC for the first year culture ponds during all phases. However, there was no significant difference (P > 0.01) for POC between the four shrimp ponds. The number of particles to which one, two, three or four bacteria were attached was 46%, 22%, 14% and 9%, respectively, of the total number of particles with bacteria attached. However, the percentage of particles with more than four bacteria attach was only 9%. There was a significant correlation between the number of epibacteria and particles with bacteria attached (r = 0.9920, n = 36; P < 0.01). The number of epibacteria was also correlated with the number of suspended particles (SP) (r = 0.9558, n = 36; P < 0.01) and the total number of bacteria (TPC) (r = 0.8657, n = 36; P < 0.01), but was not correlated with POC (r = 0.1340, n = 36; P > 0.05).