Effects of partial substitution of fish meal with different levels of marine macroalgae species on growth indices and RNA/DNA ratio of hybrid red tilapia.

A 90-days experiment was conducted to determine the impact of partial replacement of dietary fish meal (FM) with different concentrations of ultra-fine powder of Ulva lactuca, Laurencia obtusa and Cystoseira myrica on growth performance, feed utilization and RNA/DNA ratio of the hybrid red tilapia "Florida strain". A total number of 600 fish of Oreochromis sp., with an average weight of 5.67 ± 0.89 g and an average length of 6.4 ± 0.41 cm, were randomly divided into 30 aquaria (20 fish/ aquarium in triplicates). Ten experimental diets were formulated as control (C) that contains FM as the major source of protein and other dietsin which the FM was partially substituted (on the protein basis). Substitution was achieved with 5% Ulva lactuca (U5), 10 % U. lactuca (U10), 15% U. lactuca (U15), 5% Laurencia obtusa (L5), 10% L. obtusa (L10), 15% L. obtusa (L15), 5% Cystoseira myrica (C5), 10% C. myrica (C10) and 15% C. myrica (C15). Results of survival rate (SR) in all treatments were not significantly different but the control treatment showed the best SR%, while the lowest SR% was shown in C15 treatment. In case of Ulva lactuca, all growth parameters were at its highest values in U5 and decreased with the increase of inclusion levels. The growth values,when FM was partially replaced with C. myrica, were at their maximum at C15%. In Laurencia groups, the growth improved gradually with the increase in concentration and reached the highest level in Laurencia 15%. Moreover, the percentage of RNA/DNA increased significantly in Laurencia treatment compared with other treatments. In general, the results revealed that marine macroalgae could be considered as an acceptable alternative which can replace dietary FM protein in diets of the hybrid red tilapia. In addition, results showed that, the most effective group to be used is Laurencia obtusa which induced better growth performance with replacement levels up to 15% compared to the control diet. [ABSTRACT FROM AUTHOR]