Role of dietary Laurencia obtusa in enhancing growth, blood indices, and hypoxia resistance of red tilapia (Oreochromis niloticus x O. mossambicus)

In the current study the effects of the dietary seaweed Laurencia obtusa on growth performance, feed utilization, blood indices, and hypoxia stress resistance of red tilapia (Oreochromis niloticus x O. mossambicus) were investigated. Four diets were prepared to contain four levels of dried L. obtusa as follows: 0, 2, 4, and 8 g kg−1 diet and coded as LO0, LO2, LO4, and LO8, respectively. Red tilapia (4.49 g fish−1) were fed the diets for 70 days. The best growth performance was shown at LO2 followed by LO4, and LO8, with LO0 giving the lowest results. Polynomial regression of weight gain showed that the optimum level of LO was at 4.1 g kg−1 diet. LO0 and LO8 produced the highest feed conversion ratio followed by LO2 and LO4. Cortisol, alanine aminotransferase, and aspartate aminotransferase showed the best results in LO2 and LO4 followed by LO0, while LO8 showed the worst results. The highest values of glucose were shown in LO0 and LO8, followed by LO2 and LO4. Alkaline phosphatase and lactate did not differ significantly among fish groups. Hematological counts were affected by hypoxia only, rather than diets; the number of erythrocytes, hemoglobin, hematocrit, and lymphocytes decreased while platelets, leukocytes, and neutrophils elevated in all groups. Serum glucose tended to decrease after hypoxia stress in all treatments; however, blood lactate significantly multiplied in all groups. Thus, the inclusion of L. obtusa in red tilapia diets improved the growth performance and the resistance to hypoxia stress.