Ulva reticulata extract contains phytochemical components that have the potential to be utilized in the field of environmentally friendly aquaculture. U. reticulata extract acts as a growth agent and health status enhancer in fish. This study aimed to evaluate the effects of different doses of U. reticulata extract on the growth of the red tilapia (Oreochromis sp.) fry. This study used a completely randomized design consisting of five doses of U. reticulata extract (0; 50; 150; 150; 200mg kg^-1) feed with four replicates given to the red tilapia fry measuring 5,2±0.09cm total length and 3,65±0.17g total weight on average during 30 days of rearing. The parameters evaluated were the growth rate, feed conversion ratio, blood hematology, and growth gene expression of the red tilapia fry. The results showed that U. reticulata extract significantly improved growth performance, evidenced by the increased expression of GH and IGF-1 growth genes, the decreased feed conversion ratio, and the improved blood biochemical profile of red tilapia, especially at the treatment dose of 200mg kg^-1 feed (P<0.05). Feeding U. reticulata extract at 200mg kg^-1 significantly increased the final individual weight (21.07g) by increasing the gene expression of GH by 4-fold and IGF by 2.5-fold, and decreasing the feed conversion ratio (1.25%). In addition, fish fry had the highest hemoglobin (10.54%), phagocytic activity (50.75%), differential leukocytes with lymphocytes (73%), neutrophils (19%), and lower monocytes (14%) than the control. In conclusion, U. reticulata extract 200mg kg^-1 improved the growth and health of the red tilapia fry and could be an alternative to aquaculture fish hatchery productivity.