Effects of substituting different percentages of Azolla and duckweed as a partial substitute for soybean meal in feeding common carp fish (Cyprinus carpio L.)

The Azolla and duckweed and their mixture are one of the most important alternatives to feed in fish diets because they contain high levels of proteins and other nutrients and their role in improving production efficiency (2.5 and 5%, respectively), as well as their effects on the growth parameters of common carp during the experimental period (49 days). The experiment included feeding carp using seven experimental diets containing Azolla, duckweed and the mixture. The results of the statistical analysis indicated a significant superiority (P ≤ 0.05) for the seventh treatment (the mixture 5%) for each of the characteristics of final weight, total increase, daily increase, the relative growth, and the specific growth rate compared to the control diet and the rest of the other treatments. A significant superiority of the same seventh treatment (5% mixture) was observed on the amount of feed intake and the food efficiency ratio compared to the control group and the rest of the treatments. The seventh treatment also recorded a significant increase in the rate of protein intake and the percentage of protein efficiency compared to the control and the rest of the treatments. The protein deposited rate and the protein produced value in the second treatment (Azolla 2.5%) were significantly superior (P ≤ 0.05) in fish compared with the control and the rest of the treatments. It reached 7.25 g fish^-1 and 58.70% respectively. The results of the statistical analysis of the chemical composition of the fish body after being fed on different experimental diets in the proportion of protein showed that there were significant differences (P ≤ 0.05) between the treatments, where the proportion of protein in the seventh treatment (the mixture 5%) increased significantly over the control and the rest of the treatments and amounted to 19.87%. There were no significant differences in the percentages of fat and ash among all treatments except for the control in the percentage of ash, which recorded a significant decrease compared to the rest of the treatments, amounted 1.89%. It is concluded that the mixture (Azolla and duckweed) can be used at a rate of 5% as a substitute for soybeans as the best growth criterion.