Bacteriological water quality changes and substratespecificity of isolates associated with <i>Clarias lazera</i> culture system

Abstract

This study was undertaken to ascertain the impact of seasonal changes on the bacteriological water quality and substrate specificity of isolates in a Clarias lazera culture system at Obirikom, Rivers State, Nigeria. Bacteriological changes and substrate specificity were determined using standard microbiological techniques. Stratification was observed in the bacterial distribution with the pond sediment habouring more aerobic and anaerobic bacterial genera than the pond water. Obvious seasonality in the occurrence of bacterial genera was also observed with higher occurrence obtained in the dry than wet (rainy) season. Identification test revealed the presence of Pseudomonas, Proteus, Micrococcus, Escherichia, Chromobacterium, Serratia, Klebsiella, Bacillus, Staphylococcus, Lactobacillus, Pediococcus, Norcadia, Vibro, Salmonella, Aeromonas, Cytophaga, Corynebacterium, Campylobacter and unidentified gram-positive cocci. About 50 – 55% and 80 – 90% of these bacteria genera were isolated from the pond water and sediment samples respectively, with the latter having a preponderance of Micrococcus, Cytophaga, and Bacillus. Substrate specificity test of these isolates revealed variation in the ability of the bacteria genera to hydrolyse gelatin casein, tributyrine, starch and cellulose. The ability of bacterial isolates to utilize these macromolecules occurred more in the sediment than in the water column. Majority of the bacterial population hydrolysed all the substrates while only a small percentage of the population was able to hydrolyse cellulose. This study revealed that seasonal variation affects the bacteriological quality of Clarias lazera culture systems and the substrate specificity by isolates.


Key words: Bacteriological, water quality, Clarias lazera, culture system


Journal of Aquatic Sciences Vol.18(2) 2003: 105-112