Abstract
The study herein evaluated the effects of dietary supplementation with different yucca (Yucca schidigera) extract levels on rearing water quality, growth performance, protein utilization, hematological and immunological status, and economic benefits of cultured European seabass (Dicentrarchus labrax) juveniles. Yucca extract (YE) was incorporated in an experimental diet at levels of 0, 0.25, 0.50, and 1 g YE kg−1, and offered to fish reared in 70-L glass aquaria (15 fish per aquarium; three replicates each). Dietary YE supplementation significantly (P<0.05) decreased ammonia-nitrogen levels in water. Compared with the control, groups fed 0.50 and 1 g YE kg−1 diets showed improved growth performance (by 26.02% and 36.98%, respectively) and protein efficiency ratio (by 31.39% and 37.29%, respectively). In addition, hematological parameters (red blood cells, hemoglobin, hematocrit, white blood cells and neutrophil) and innate immune parameters (globulin fractions and lysozyme activity) improved with increasing dietary YE levels. Growth, hematological, and immunological parameters increased with a polynomial second-order regression models, with curves peak close to 1 g YE kg−1 diet. The cortisol level decreased significantly (P<0.05) with increasing dietary YE levels. The groups fed the 0.50 and 1 g YE kg−1 diets generated significantly (P<0.05) higher revenue than groups fed the 0.25 g YE kg−1 and the control diets. The using of YE is recommended as a dietary feed additive at a level of 1 g kg−1 for reducing the environmental footprint of fish protein production, accelerating growth, and improving health status of cultured seabass in a short-term feeding period.