Effects of low and medium levels of red alga Nori (Porphyra yezoensis Ueda) in the diets on growth, feed utilization and metabolism in intensively fed Nile tilapia, Oreochromis niloticus (L.)

A 10-week feeding experiment was conducted in a respirometric system to evaluate the suitability of red alga Nori (Porphyra yezoensis) as a partial replacement for fish meal in intensively fed Nile tilapia. Diets were formulated to be iso-nitrogenous and iso-energetic and to replace 0%, 15% and 30% fish meal with Nori, P. yezoensis. No statistically significant differences in growth or feed utilization between the control diet and either Nori diet were found. Tilapia fed on Nori 15 increased their body mass by 415%, those fed the control diet by 341% and fish fed Nori 30 by 317% over the experimental period. Nori 15 fed fish showed the best feed utilization, highest metabolic growth rate and significantly lower oxygen consumption rates than the control. Both Nori supplemented groups (Nori 15: 4.1 g O2 g-1 protein gain and Nori 30: 3.9 g O2 g-1 protein gain) used less oxygen per gram of protein gain compared to fish fed the control diet (5.4 g O2 g-1 protein gain). Our results show that a low replacement level (15%) of fish meal with Nori improves growth and feed utilization while oxygen consumption and amount of oxygen consumed per gram protein gain are significantly decreased.