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Iron supplementation in plant-based aquafeed: Effects on growth performance, tissue composition, iron-related serum parameters and gene expression in rainbow trout (Oncorhynchus mykiss)

Ece Evliyaoğlu, Serdar Kilercioğlu, Hatice Asuman Yılmaz, Giovanni M. Turchini, Marina Paolucci, Timothy D. Clark, İbrahim Demirkale, Orhan Tufan Eroldoğan
Aquaculture 2022 v.550 pp. 737884
Oncorhynchus mykiss, aquaculture, aquaculture feeds, blood serum, condition factor, digestibility, feed conversion, feed intake, ferritin, ferrous sulfate, fish, gene expression, growth performance, hepcidin, intestines, iron, juveniles, leptin, lipids, liver, nutrient content, specific growth rate, transferrin, villi, weight gain
This study evaluated the effects of iron supplementation in plant-based aquafeed on growth performances, feed intake, nutrient composition, digestibility, iron-related serum parameters and gene expression in juvenile rainbow trout (Oncorhynchus mykiss). Triplicate groups of fish were fed for 60 days using incremental levels of iron in a ferrous sulphate heptahydrate form, as follows: 0 (group Fe0); 150 (group Fe150); 300 (group Fe300); 600 (group Fe600) mg iron/kg feed, corresponding to actual iron levels of 132, 273, 403, 741 mg iron/kg feed, respectively. As a further control, a fifth group was fed a commercial feed (CMF; 253 mg iron/kg feed). Growth performances showed that the highest specific growth rate (SGR), condition factor (CF), protein efficacy ratio (PER), feed intake (FI) and lowest feed conversion rate (FCR) were found in Fe150, Fe300 and CMF groups. Final weight and weight gain (WG) were significantly higher in CMF and Fe150 groups, followed by the Fe300, Fe600 and Fe0 groups (P < 0.05). Apparent digestibility coefficients (ADCs) of protein, lipid, ash and iron were over 90% in Fe150 and Fe300 groups, while significantly lower ADCs were observed in Fe0 and Fe600 groups. Intestinal histomorphological measurements of muscular thickness (muscularis externa; ME, inner circular layer; ICL, outer longitudinal layer; OLL) were higher in CMF and Fe150 groups, while villus length was generally similar among groups, with the exception of the Fe0 group. Serum iron levels were significantly higher in Fe150 and Fe300 groups, while total iron-binding capacity (TIBC) was highest in the Fe150 group. No significant differences were observed in either serum ferritin or liver ferritin gene expression among groups, although hepcidin gene expression was highest in the Fe300 group followed by the Fe150 group. Transferrin gene expression was the lowest in the Fe0 group. Appetite-related Leptin A1 gene expression was not affected by iron addition, but Leptin A2 was up-regulated in all groups except for the Fe0 group. In summary, the study showed that the addition of 150 mg/kg feed of iron (equivalent to ~270 mg/kg feed total) improved growth performances and feed utilization in rainbow trout, which aligns well with the iron levels in current commercial feeds.