The aim of this study was to investigate the effect of dietary supplementation (10 g/kg) of various herbs (such as fenugreek, rosemary, thyme, and fennel) in the formulated diets for mono-sex Nile tilapia fries. Fish with an average weight of 1.81 ± 0.1 g were randomly assigned to 5 treatments, 3 replicates per treatment, 20 fries and kept at 15 hapas (1.5 x 0.5 × 1.0 m 3 ) for 12 weeks. The results of the study showed that the fish that ate the thyme-containing diet had the highest body weight and followed by those which ate the fenugreek-fortified diet. Fish fed diet with rosemary had the lowest body weight. All treatments had significant differences in weight gain (P<0.05). In particular, fish fed on the thymecontaining diet gained more weight than fish fed on the control diet with the highest weight gain. Based on the findings, the study found that fish diets fortified with thyme powder resulted in the highest specific growth rate (%SGR) compared to other diets. There was a significant difference between the thyme added diet and all other groups (P<0.05). Fish fed the thyme supplement also increased their feed intake and had the best feed conversion ratio (FCR) compared to the other groups. There was a significant difference in FCR (P<0.05) among all other treatments. The study found no significant difference in dry matter of all treatments, except for fish fed the control diet, which recorded the lowest value (P>0.05). The protein content was significantly different (P<0.05), and fish fed diet supplemented with fennel had the lowest protein content. Fish fed diets supplemented with fenugreek and fennel had the highest lipid contents (13.95, 13.69 %, respectively), while fish fed a diet supplemented with rosemary had the lowest (11.26 %). There was no significant difference in ash content of all treatments and fish fed a diet supplemented with thyme had the highest ash content. The results showed that fish fed the diet supplemented with fennel had the highest survival rate of 100%, while fish fed the control diet had the lowest survival rate of 95%. According to the search results, all examined fish tissues did not show any histopathological changes related to their diet across all treatments. Based on the search results, it appears that adding certain herbal plants, especially thyme, to the diets for Nile tilapia fries at a rate of 10 g/kg can enhance their growth performance and feed utilization without causing any negative impacts.

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