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Nile tilapia is one of the most widespread fish in Egypt and it is of great economic importance. This study aimed to know the effect of seasonal variations on the body, level of hormones and blood parameters. To conduct this study, Nile tilapia monosex and mixed sex were collected during breeding and nonbreeding seasons. Results revealed that seasonal variations on body parameters are more prominent in body weight, abdominal length, abdominal width, and abdominal circumference especially in female fishes. Reproductive hormones (FSH, LH, prolactin, testosterone, and Estradiol E2) are significantly increased during breeding season. The Erythrogram, total and differential leukocytic count increased significantly during breeding season, while thrombocytes are significantly declined during breeding season. The significant increase of Hepato-somatic index % and Gonado-somatic index % can be an indicator of breeding season in some fresh-water fish.