Melatonin feeds promoted the growth of Elodea nuttallii by chlorophyll, devoid of the adverse effects on water quality

In the ecological culture of the Eriocheir sinensis in China, the coexistence of feeds fed for crabs and Elodea nuttallii is a common pattern in ponds. The objective of this study, for the first time, was to evaluate the effects of feeds (Melatonin added) on E. nuttallii growth and water quality under the artificial cultivation condition and avoid the influence of complex ecological factors. According to the characteristics of E. nuttallii growth, the optimum culture conditions (light intensity, branch type and culture time) were firstly explored in the laboratory and then chosen as culture conditions for feed experiment. The results showed that the 4500lux, Branch I (with about 1 cm visible branch), and 14-day culture were selected as the optimum E. nuttallii culture conditions in the laboratory. Fresh weight, weight growth rate, relative growth rate and height in MT feeds group were significantly higher than those in the basic feeds and no feeds groups (p < 0.05). Chlorophyll b contents in the MT feeds group were significantly higher than that in the basic feeds group (p < 0.05). Total nitrogen, total phosphorus, ammonia nitrogen and nitrite nitrogen contents in MT feeds group were not significantly higher than that in the basic feeds group (p > 0.05). The results indicated that residual feeds containing melatonin in crab ponds boost the growth of E. nuttallii to some extent and without negative effects on water quality. The results will help to lay a foundation for clarifying the relationship between feeds and aquatic plants and water quality in E. sinensis aquaculture.