Abstract
Iron (Fe) is an essential trace element for marine fish. However, our knowledge of Fe requirements at different development stages of marine fish is still limited. Here, we reported the efficient Fe absorption strategies adopted by larval fish under different dietary Fe supplementary levels (i.e., 0–640 mg/kg). Biokinetically, the larval fish controlled their dietary Fe assimilation efficiency (AE, 1.6–18.5%), and enhanced their waterborne Fe uptake (ca. 2.5 fold change of uptake rate constant) once the dietary Fe was deficient (i.e., 27.4 mg Fe/kg feed). Transcriptionally, the expression of hepcidin1 (hep1; Fe regulator; i.e., 2.3–15.7 fold change) in larval fish was positively correlated with the Fe supplementary levels. Comparatively, the female adult fish were poor in assimilating the added Fe source (i.e., ferric form) with similar life-sustainable levels of Fe (i.e., 0.046–0.12 μg/g/d assimilated for Fe supplementary levels of 27.4, 162 and 657 mg Fe/kg feed). The overall feeding experiments suggested that dietary net Fe flux sufficient for the normal growth of larval medaka was 0.71–1.75 μg/g/d (i.e., 83.9 mg Fe/kg feed), consistent with the modeled value (i.e., 1.09–2.16 μg/g/d). In female adults, the estimated essential net Fe flux was 0.88–0.90 μg/g/d.
Highlights
During the development of a single embryo, iron (Fe) is actively involved in various biological processes
Ferrous ions could be more efficiently transported across the intestinal barrier than ferric ions in the European flounder (Platichthys flesus)[9]. This was further supported by the evidence that diet supplemented with ferrous sulfate was able to meet the Fe requirements of tilapia (Oreochromis niloticus×O. aureus), whereas diets supplemented with ferric citrate was not[7]
The hep is actively involved in Fe regulation in fish, but the relative importance is still unknown compared to other Fe absorption related genes
Summary
During the development of a single embryo, iron (Fe) is actively involved in various biological processes (e.g., oxygen transfer, DNA synthesis and immune function). Previous study on Zn requirement in fish suggested that higher Zn flux was needed in juvenile stage than in post-juvenile stage[12], and similar stage-dependent Fe requirement may occur. Concerning these factors, our knowledge of the basic biological Fe requirements in fish is still lacking, not to mention its underlying regulation. The hep is actively involved in Fe regulation in fish, but the relative importance is still unknown compared to other Fe absorption related genes (e.g., dmt[1], fpn[1] and dcytb; see Table 1 for full name). A modified fractional model developed by Wang and Wang[12] was applied to estimate the essential daily net Fe flux in medaka as well as some other fish species at different life stages
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