Nitrification and the enumeration of marine nitrifying bacteria in a closed prawn-culture system

Abstract

Nitrification in a closed prawn-culture system was well established and followed the classical oxidation sequence of ammonia via nitrite to nitrate. Ammonia levels were in the range 4,8–68,7 μg-at N·ℓ−1 nitrite 0,15–891 μg-at N·ℓ−1 and nitrate approached a maximum of 9 898 μg-at N·ℓ−1 after 22 weeks. Marine nitrifying bacteria were enumerated by the most probable number (MPN) technique. The maximum MPN estimate of either group of nitrifying bacteria in the filter was 1,73 × 107·cm−3 while the maximum MPN estimate of their counterparts in the culture water was approximately 500 times lower. To establish mean incubation times for the accurate enumeration of nitrifying bacteria, incubations were carried out over a period of 130 days. Maximum estimates of MPN of ammonia-oxidizing bacteria were obtained after an incubation period of 20 days with a mean of 15 days. Nitrite-oxidizing bacteria required a maximum of 65 days with a mean incubation period of 30,3 days. © 1989 Taylor & Francis Group, LLC.