Effect of the herbal Houttuynia cordata floating bed on the Nile tilapia pond culturing system

This study investigated the effects of Houttuynia cordata floating beds with different cover ratios on fish growth, water quality, and the bacterial microbiota of tilapia and pond water. The experiment included four cover ratio treatments: C5 (5 %), C10 (10 %), C15 (15 %), and the control C0 (0 %). The peak relative removal rates of total phosphorus (TP), total nitrogen (TN), ammonia nitrogen (NH4+-N), and nitrate nitrogen (NO3- -N) in treatment C10 were higher than those in C5 and C15. Prior to the 30th day, the relative removal rates of NH4+-N, NO3- -N, TN, TP, and PO43--P had risen along with the plant cover ratios. The rank order of the relative removal rates was C10 C5 > C15 for NH4+-N and TN (after the 45th day) and TP and PO43--P (after the 60th day). The body weights of fish in treatments C10 and C15 were higher than those in C5 and C0 (p < 0.05). The relative expression levels of fish immune-related genes (TLR1, TLR2, TLR3, TLR9, TNF-a, and IFN) and the serum NO (nitric oxide), AKP (alkaline phosphatase) and SOD (superoxide dismutase) activities in treatment C10 were also significantly higher than those in C5, C15 and C0 (p < 0.05). On the 45th day, the observed OTUs as well as the Chao, ACE, Shannon, and Simpson indices in treatment C10 were higher than in all other treatments for both water and gut samples. The results demonstrated that using H. cordata floating beds in aquaponics could improve the pond water quality and increase the richness and diversity of the bacterial community in tilapia ponds and in fish guts. A 10 % cover ratio of H. cordata floating bed was superior to ratios of 15 % and 5 %.