Effects of different levels of Yucca schidigera extract on growth performance, nonspecific immunity and culture water quality of rainbow trout (Oncorhynchus mykiss) in the recirculating system

The present study was aimed at determining the effects of dietary Yucca schidigera extract on growth, feed and water quality of rainbow trout (Oncorhynchus mykiss). Fish with an average weight of 18.89±1.65 g and 12.40±0.77 cm was tested in four treatments, each with three replicates for 60 days (First period: 50 days without ammonia stress) and (Second period: 10 days under ammonia stress of 0.024 mg /L). Different levels of plant extract 0% (control), 0.5% (Y1), 1% (Y2) and 1.5% (Y3) were spread on the commercial diet. The results showed that fish fed in Y3 experimental had significant difference in final weight, weight gain, daily growth rate and specific growth rate compared with control (P<0.05). The lowest feed conversion ratio (FCR) observed in group fed diet containing 1% plant extract (Y2). At the end of experiment, 24 hours water was not replaced and water sampled every 4 hours. Ammonia (TAN) increased from 16 to 24 hours. The results indicate that different concentrations of Yucca extract affect the growth performance and Ammonia water. Based on the results obtained from the measurement of non-specific immune factors can be stated that Yucca extract stimulates the immune but not statistically significant effect in some cases there is need for further studies.