Effects of aquaponics mode on growth and digestive enzyme activities of GIFT tilapia

GIFT tilapia（ Oreochromis niloticus） was used as animal model，and three aquaculture modes， including herba houttuyniae（ Houttuynia cordata Thunb.）-tilapia intensive aquaponics mode（ IAM），herba houttuynia-tilapia-yellow catfish（ Pelteobagrus fulvidraco） polyculture aquaponics mode（ PAM） and conventional intensive aquaculture mode（ CIAM），were selected to investigate the effects of aquaponics on growth and digestive enzyme activities of GIFT tilapia. Results showed that on the level of growth performances，the hepatosomatic index of tilapia in IAM was the lowest. However，there was no significant difference on average weight and relative fatness indices among the tilapia under three modes. For digestive enzyme activities，the stomach protease activity of tilapia in CIAM was significantly lower than that in other two modes. While the protease activity of tilapia hepatopancreas in IAM and protease activity of tilapia foregut in PAM were the highest，respectively，during most of experimental months. Moreover，both in July and October，the lipase activity of tilapia hepatopancreas and foregut in IAM were the highest. The amylase activity of tilapia foregut in IAM was the highest. The lowest amylase activity of hepatopancreas was observed in IAM in August，and the amylase activity of hepatopancreas in IAM was significantly higher than that in CIAM in September，while the other groups showed no significant difference. Herba houttuynia ecological floating flats can improve the water quality for aquacultural environment，thus，intensive aquaponics mode showed higher digestive ability. The stocking density of fish in polyculture aquaponics mode was too intensive，which led to the crowding stress，damaged the growth and health of tilapia.