Understanding the micro-elemental nutrition in the larval stage of marine fish: A multi-elemental stoichiometry approach

In the present study, we for the first time systematically investigated the multi-elemental stoichiometric changes in three marine fish larvae (marine medaka, gilthead seabream and golden pompano). These larvae were raised up to 4-week post-hatching using live feeds (i.e., rotifer and Artemia), and micro-elemental (i.e., Zn, Cu, Fe, Mn, Co and Se) requirements in the brood stock and early larval stage were evaluated from the very basic elemental levels. Different micro-elements levels were found in the newly hatched larvae, especially in pompano with a comparatively high Zn (210 mg/kg dry wt.) and Se (3.4 mg/kg) concentration. Diverse micro-elemental concentrations and changes were also observed in the three fish during development, especially around the mix-feeding stage. By using micro-element/P ratios, we found that seabream and pompano required more microelements than medaka. Furthermore, literature available data on micro-element/P ratios in some other marine fish larvae (e.g., Atlantic cod, red seabream and amberjack) and different live feeds (e.g., rotifer, Artemia and copepods) were calculated. By comparing these ratios, the importance of copepods in micro-elements supply to marine fish larvae was demonstrated. Due to the potential high demand of fish at the very early life stage, Zn and Se were likely to be limited when supplied with rotifers, while Fe, Cu, Co and Mn should generally meet the fish requirements. Potential shortage of Fe, Mn and Co from non-enriched Artemia may occur due to the increasing demands at late larval stage, which could be relieved by co-feeding with rotifer or enrichment. This study shows the diverse micro-element concentrations and changes during early fish ontogeny. More future multi-elemental stoichiometry studies are required to have a deep understanding of the micro-elemental requirements in the early life stage of fish.