Long-term incorporation of Selenium and Zinc in microalgae Isochrysis galbana and Nannochloropsis oculata and its effects on rotifer

Abstract

Rotifers are widely used in hatcheries to feed small-sized aquatic larvae although one of their disadvantages is the lack of zinc and selenium 5- and 30-fold lower than in copepods, respectively. To improve the rotifers quality, different concentrations of zinc and selenium (2, 4, 5 and 10 mg L−1 of each mineral) were added to the medium of the microalgae Isochrysis aff. galbana and Nannochloropsis oculata for 4 days, and then the microalgae were harvested and concentrated to feed the rotifers. N. oculata accumulated a greater amount of Zn and Se into cells than I. galbana. The cell size of algae given 0, 2, and 4 mg L−1 of minerals did not change in both microalgae, but enrichment of the microalgae with the 5 and 10 mg L−1 decreased the sizes and paled the colour of cells and increased cell division. The 2 mg L−1 was the best group for rotifers in terms of growth (population density, number of eggs, egg ratio, Specific growth rate, the maximum number and doubling time), and contained the second-highest level of Zn (69.26 ± 0.60) and Se (103.5 ± 5.0) content within a safe limit. Thus, rotifers enriched with Se and Zn can be used as a mineral delivery method to cover the nutritional requirements of marine larvae.