PhD student, the Hong Kong University of Science and Technology
study the nutritional requirement of larval fish
Successful rearing of marine larval fish has long become the bottleneck of marine fish aquaculture. Despite of considerable progresses in recent years, many questions still remained for larval fish nutritional requirements. The overall study provided a full picture of essential micro-elemental nutrition in the early life stage of marine fish. Fish at the early life stage tend to have high micro-elemental requirements, and the requirement changed dynamically with their growth. By using a modified fractional model, we successfully quantified Zn and Fe requirement in a model organism marine medaka. However, responses to different micro-elemental supplementary levels were elemental independent, with both fragile (low Zn) and resistant (low Fe) responses observed. Combined with elemental stoichiometry, sufficiency of each micro-element in typical live feeds (rotifer, artemia and copepod) to marine fish larvae was evaluated, with rotifer potentially deficient in Zn and Se. This can be solved by short-time or long-time Zn and Se enrichment in rotifer. However, the residue time of rotifer during real application should be minimized due to the rapid loss of these enriched micro-elements. Furthermore, zinc oxide nanoparticle presented as a potential novel micro-element source due to its high bioavailability and low toxicity to stomach-less fish, which can be adopted in future micro-feed production.
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.
Pub.: 25 May '16, Pinned: 27 Jul '17
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