Effect of bacteria on survival and isozymes in Nile tilapia, Oreochromis niloticus fingerlings [electronic resource].

Includes references.

Citrobacter freundii, Badllus pumilus, and Bacillus firmus were isolated from apparently healthy Nile tilapia (Oreochromis niloticus) and these isolates were harmless to O. niloticus. Six hundred apparently healthy fish (average body weight 10 ±1 g) were divided into five equal groups (120 fish each). Fish of the 1st group served as a control and was fed unsupplemented feed during the entire period of the experiment. Fish of the 2nd, 3rd and 4th groups werp fed with feed containing 10 7 cells/g of C. freundii, B. pumilus and B. firmus, respectively. The 5th group was fed with a mixed feed containing an equal number (10 7/g) of the three tested bacteria. After 14 days of feeding, the fish were dlallenged inbaperitoneally (IP) by Aeromonas hydrophila. The survivai rate was recorded and fish samples were examined for the effects of pathogenic bacteria on some.ISOzymes expression in liver and muscle tissues. The starch gel electrophoresis was used to study the changes on relative mobility of isozymes as an expression of gene product. The survival rate was significantly high in the fish group that fed a diet containing B. pumiJus in contrast to the group fed diet containing B. firmus. The control fish showed the lowest survival rate. There were differences between the treated and control fish regarding the relative mobility of electrophoretic bands. An increase in the number of electrophoretic bands of the treated fish was observed compared to that of the control fish. This confirmed the effect of bacteria on genes expression represented by the presence of different forms of bands of liver tissue. Isozyme results agreed with those for the survival ratio, where a-esteraSE' in Aer. hydrophila and 8. finnus gave the lowest ratio of survival which were in the line with isozyme results that expressed a-esterase, at low electrophoretdc relative mobility. Positive and strong correlation coefficient was shown between survival rate and relative mobility for C. freundii in muscles lactic Dehydrogenase (LDH) and Malate Dehydrogenase (MDH) and liver general esterase, whereas it was weak -for muscles a-Esterase. 8. pumllus was demonstrated negative correlation coeffident between survival rate and relative mobility for all tested isozymes from liver and muscles. A. hydrophila revealed negative correlation coefIident with muscles LDH compared With, a low and moderate in the rest of tested isozymes.

Summary in Arabic.

1