Atwelve week experiment was conducted to evaluate the suitability of gambusia {Gambusia afflnis) fish meal (GFM) as a partial or complete substitute for the protein supplied by herring fish meal (HFM) in diets for the growth of common carp fingerlings (mean weight of 0.35g/fish). Seven isonitrogenous (35% crude protein), isolipidic (9%) and isocaloric {3.7 kcal DE/g) diets were formulated in which GFM replaced 0.0%, 10%, 25% 50%, 75%, 90% and 100% of the protein supplied by HFM. Results demonstrated that GFM has good potential as a substitute for up to 50% of the protein supplied by HFM in common carp diets with no significant (P < 0.05) adverse effects on growth, feed efficiency, body composition and apparent digestibility of dry matter, protein and gross energy compared to fish fed the HFM-based diet (control diet). Survival rates in fish fed all the experimental diets were high and were statistically comparable to that offish fed the control diet and ranged from 93.3% to 95.6%. The percentages of apparent protein digestibility showed variation between diets, ranging from 81.1 to 86.6 with no significant differences among treatment means compared to the control diet. At the end of the study, substituting HFM-protein with GFM-protein in diets for common carp resulted in insignificant differences in final body composition of protein and ash, whereas dry matter and fat were significantly reduced (F > 0.05) compared to fish fed the control diet. Hematological characteristics of common carp were examined at the end of the study and the results showed that values of hemoglobin, RBC, hematocrit and serum protein in fish groups of all the treatments were statistically equal or even better than those offish fed the control diet. An economic analysis suggested the possibility of using GFM as an alternative source of protein in common carp feed, Diets containing 50% of the protein from HFM and 50% from GFM provided the best economic efficiency offish weight gain among all other test diets.