Impact of iron supplementation on media bed aquaponic system: Focusing on growth performance, fatty acid composition and health status of juvenile mirror carp (Cyprinus carpio var. specularis), production of lettuce (Lactuca sativa var. ramosa Hort), water quality and nitrogen utilization rate

Abstract

To evaluate the effects of iron supplementation on the growth performance, body composition and health status of mirror carp (Cyprinus carpio var. specularis) (10.34 ± 1.56 g), production of lettuce (Lactuca sativa var. ramosa Hort), and nitrogen utilization efficiency in media bed aquaponic system, a 60-day experiment was conducted. During the experiment, 0 (C), 1, 2, 3 and 4 mg/L iron chelate (ferrous glycinate) was added to fish tank of each system every 20 days. The results indicated as following: (1) Regarding the growth performance of mirror carp, the 1 mg/L group showed the highest weight gain (WG) and the lowest feed conversion ratio (FCR) when compared to the C group and the 4 mg/L group (P < 0.05). (2) In terms of body composition of mirror carp, the 1 mg/L group exhibited a significant increase in crude fat and iron content in the muscle (P < 0.05), and the ∑n-3 LCPUFA (C20:5n-3, EPA; C22:6n-3, DHA) was significantly higher in this group compared to the other groups (P < 0.05). (3) Regarding the health status of mirror carp, the 1 mg/L group had the highest liver catalase (CAT) activity, and the level of superoxide dismutase (SOD) activity was significantly higher than in the C, 3 mg/L, and 4 mg/L groups (P < 0.05). Liver malondialdehyde (MDA) content of mirror carp was significantly lower in 1 mg/L group compare to other groups (P < 0.05). (4) Concerning lettuce growth, the yield increased with rising iron content, and the group with 2 mg/L exhibited the highest chlorophyll content (P < 0.05). (5) Nitrogen utilization results showed that the 2 mg/L chelated iron group had the highest nitrogen utilization rate of 33.95%, while the C group had the lowest nitrogen utilization rate of 28.61%. Additionally, iron supplementation did not have a negative impact on the water quality of the aquaponic system. In summary, under the conditions of this study, adding 1 mg/L of chelate iron every 20 days in the aquaponic system is beneficial to the growth, body composition and health status of the mirror carp, the lettuce in the 2 mg/L group had better growth and yield. It is recommended to add 1–2 mg/L glycine chelated iron in the media bed aquaponic system every 20 days to promote the growth of fish and vegetables and improve the nitrogen utilization efficiency of the system.