Studies on the causative organism of Sarotherodon niloticus (Linnaeus) fry mortalities - 2. Identification and characterization of the physiological properties of Pseudomonas fluorescens

Abstract

Identification and examination of the physiological characteristics of Pseudomonas sp. isolated from fry of Sarotherodon niloticus (L.) was conducted. Based on morphological and biochemical tests, the bacterium was identified to be a strain closest to Pseudomonas fluorescens. In vitro physiological growth patterns at varying temperatures, NaCl concentrations, and pH were observed for a maximum of eleven days incubation while growth of the test bacterium into various water media were observed for a maximum of 148 days. Bacterial growth occurred between 10° to 41°C with optimum growth at 25° to 30°C. The bacterium tolerated NaCl concentrations of 0 to 50 ppt. Optimum growth, however, was obtained from 0 to 15 ppt. It was found that growth was possible only at pH 5.0 to 9.7. Optimum growth occurred at pH ranging from 5.7 to 8.4. Inoculation of the test bacterium into different freshwater media obtained from various sources resulted in growth and rapid multiplication. Viability was maintained throughout the 148 day incubation period. Growth in the brackishwater medium was observed only until 50 days. No growth was observed in the seawater medium.