In this study, the experimental set-up was based on fed Clarias lazera commercial diet with probiotic for 45 days either 1 time/week (W1) all over the experiment or 3 times/week for the 1st two weeks then 1 time/week till the end of the
experiment (W3). Bacteriological and biochemical examinations were done on intestinal tract and serum respectively.
Bacteriological investigation revealed the presence of Escherichia coli and Klebsiella spp. in all groups and Pseudomonas aeruginosa failed to be isolated from W1 and W3. Bacterial isolates proved to be pathogenic for mice, positive for Congo
red binding activity and toxigenic in infant mice. The intestinal total aerobic bacterial count; Enterobactereacae count and coliform count in males and females of both W1 and W3 fish groups were significantly lower than the respective values in control group. Significant low values were detected in W3 group compared to W1 group.
Significant sex differences in the three counts were detected in the three groups of fish except the Enterobactereacae count in W3 group. Concentrations of serum ammonia and urea were significantly decreased in both treated groups compared to the control group. Both serum items were significantly lower in W3 group than that in W1 group. Significant sex difference was recorded in serum creatinine of the three groups (females lower than males).
The activities of serum alkaline phosphatase; alanine aminotransferase and aspartate aminotransferase enzymes significantly differed according to sex with a general trend that these enzymes were significantly higher in W3 group than that ofW1 group.Serum  total protein, albumin, globulin and A/G ratio in fish of W1 group weremore affected by  probiotic administration than that in W3 group. These serum protein items in all groups were significantly affected by sex. Serum IgM level in both sexes of W1 group was significantly higher than that in both control and W3 groups.
A correlation analysis was conducted to determine the strength of the association between serum biochemical parameters and viable total bacterial count;Enterobactereacae and coliform counts in the guts of fish. Male fish showed
similarity of the correlations analysis between the three bacterial counts and the
different serum biochemical parameters, while female fish detected some variations
according to the type of bacterial count.