To investigate the effect of Bacillus subtilus probiotics on fish fecundity, 160 Oreochromis niloticus females were fed incorporated with basal diets for 30 days. After microscopic examinations of their ova, fish were classified into prespawning or spawning eight groups: two control fed basal diet only (one prespawning + one spawning), two fed basal diet + B. subtilus for one month, two challenged with dose of 0.3 I/P V. anguillarum for one week and two fed B. subtilus + challenged with dose of 0.3 I/P V.anguillarum for one week. The results indicate that fecundity was improved among prespawning fish fed B. subtilus compared to those of the control group. From the immunological point of view, B.subtilus increased total globulins and decreased mortality among prespawning fish fed B.subtilus only or fed B.subtilus + V. anguillarum compared to the control ones or those challenged V. anguillarum only. In contrast, spawning fish fed B.subtilus + V. anguillarum appeared to be more stressed than those fed B. subtilus as indicated from the highly significant decrease in their total globulins. It is recommended that B. subtilus could be supplemented to prespawning fish diets only while it's unprofitable within spawning periods. In addition full care and concern should be given to fish during spawning period to avoid fecundity decline by any virulent pathogen as V.anguillarum which cause damage to ovaries during prespawning and spawning periods.
Key words: fecundity, prespsawning, spawning, total ripening eggs number, globulins, Bacillus subtilus, V. anguillarum.
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