The aim of this study was to assess the impact of using rapeseed meal as a partial replacement for fish meal in the diet of
farmed tilapia. We evaluated the effect of this replacement on growth performance, profitability, serum biomarkers, antioxidant
status, gut morphology, and water quality. A total of 960 apparently healthy Oreochromis niloticus (O. niloticus) and
Sarotherodon galilaeus (S. galilaeus) fingerlings were randomly distributed into four dietary treatment groups for each tilapia
species (triplicate design, 120 fish/group, and 40 fish/replicate). The diets consumed by these groups were formulated to
replace fish meal (FM) with rapeseed meal (RM) at 0%, 10%, 20%, and 30%, respectively, for 12 consecutive weeks. Results
indicated that replacing RM in the diet of S. galilaeus (up to 20%) and O. niloticus (up to 10%) resulted in increased growth
performance parameters, including final weight, weight gain, length, length gain, weight gain rate, and specific growth rate
(SGR), and return parameters such as a total return and relative return compared to the control group. Moreover, an increase
in RM up to 30% improved net profit and increased the mucosal length, intestinal villi length, and the number of goblet
cells compared with results in its relative control groups. Additionally, we observed a significant increase in serum and liver
AST and ALT with increased RM replacement. With respect to water parameters, we observed a significant difference in
the ammonia levels, turbidity, and conductivity with the changes to the percentage of RM in the diets. As for the effect on
each species, O. niloticus showed a more significant increase in all examined parameters compared to results in S. galilaeus.
In summary, up to 10% RM can be used to replace FM without any adverse effects on the growth performance, profitability
measures, intestinal morphometric analysis, or water quality.