Effects of adding spermidine carbon quantum dots in feed on growth, intestinal morphology, immunity and disease resistance of Anguilla japonica and Anguilla marmorata

Japanese eel (Anguilla japonica) and giant mottled eel (Anguilla marmorata) are the main eel species reared in recirculating aquaculture system (RAS) in Taiwan. RAS increases the rearing density of eel. On the other hand, it spreads pathogens and diseases more efficiently and uncontrollably. Currently, eel farmers use antibiotics to control disease in RAS, but their misuse can lead to resistance and food-safety issues. Spermidine carbon quantum dots (CQDSpds), a newly developed carbon nanomaterial with positive charges on the surface, can bind to the negatively charged bacterial cell membrane to destroy bacteria and not cause drug resistance. This research investigated the effects of different concentrations of CQDSpds as paste feed additives on the growth performance, intestinal morphology, immune-related gene expression, and disease resistance of Japanese and giant marble eels. The results showed the highest final body weight, weight gain, and specific growth rate of Japanese eel and giant mottled eel fed with 1 ppm and 0.5 ppm CQDSpds added. Compared with the control group, 1 ppm CQDSpds group showed higher lysozyme expression in Japanese eels. In the part of intestinal morphology, there was not a significant difference in intestinal villus height and intestinal morphology between the CQDSpds groups and the control group in both eel species. The survival rate of each group supplemented with CQDSpds was higher than the control group after the E. tarda challenge test, among which the highest were found at 1 ppm group in Japanese eel and 0.5 ppm group in giant mottled eel. By this research, the additive of CQDSpds in eel culturing could improve the growth and immune performance with not caused an impact on the intestine of both eels, which can be a potential feed additive in intensive eel farming.