Prevalence of Streptococcus agalactiae in tilapia in flowing water, ponds, rivers and reservoirs.

摘要

Streptococcus agalactiae was isolated from 713 Tilapia from irrigation canal, 708 from ponds, 633 from ex-mining pool, 2,610 from river and 1,729 from reservoirs in a floating net cage-culture system for 24-months. Fish were dissected before brain, eye and kidney swabs were streaked onto blood agar, and pure isolates were subjected to Gram stain, API 20 STREP kit, Slidex Strepto-kit and PCR evaluation.Streptococcus agalactiae was isolated from all water bodies and a significant difference (p<0.05) was found in the mean prevalence from Tilapia kept in reservoirs (12.50%) with very low water flow (0.006+or-0.003 cm/seconds) and moderate-sized rivers with moderate water flow (0.25+or-0.24 cm/seconds) compared to small-sized pond (0.70%), irrigation canal (0.28%) and ex-mining pool (0.17%). Significantly (p<0.05) high mortality was observed in tilapias kept in reservoirs when water temperature was high (>29.51 degrees C), affecting tilapias between 10 cm to 30 cm (100 g-350 g) in size. There was a highly significant correlation (r=0.9312, P=0.0008) between isolations of S. agalactiae and mortalities of tilapias in reservoirs in the presence of Staphylococcus spp. These results indicated that water temperature, rate of water flow and size of fish influenced the prevalence of S. agalactiae in tilapia.