Abstract
Ciliate protozoa of the genus Euplotes commonly appears contaminating mass cultures of rotifers but also with potential to be used as live food in the larviculture of marine fish. To obtain a monoculture of Euplotes sp., three diets were tested: 1) microalgae Nannochloropsis oculata, 2) commercial diet for rotifers Culture Selco 3000, and 3) baker's yeast (Saccharomyces cerevisiae). The ciliates were inoculated at 10 ind. mL - ¹. On day 5, protozoa densities in the groups fed the commercial diet (1,911.0 ± 248.7 ind. mL - ¹) and the baker's yeast (2,600.0 ± 195.3 ind. mL -1 ) did not differ, but were higher than the group fed microalgae (2.0 ± 1.4 ind. mL -1 ) (p < 0.05). On day 6, the density in the group fed baker's yeast was higher (15,484.0 ± 1,164.9 ind. mL - ¹) than in the groups fed microalgae (3.0 ± 1.4 ind. mL - ¹) or commercial diet (11,287.0 ± 1,468.0 ind. mL - ¹). An exponential growth curve was observed for the protozoa fed baker's yeast (R² = 0.992; p < 0.05) and commercial diet (R² = 0.979; p < 0.05). The microalgae diet did not result in satisfactory growth of the protozoan. Feeding baker's yeast or commercial rotifer's diet to a monoculture of Euplotes sp. can result in very high densities of this protozoan.
Highlights
Ciliate protozoa are ubiquitous in aquatic environments and one of main consumers of bacteria in eutrophic waters (KAMIYAMA, 1994)
Food for fish larvae is usually determined by fish mouth size, prey size and fish ability to prey, which suggests that small prey with slow swimming, such as ciliate and dinoflagellate protozoa would be more suited (HUNT VON HERBING; GALLAGER, 2000, HUNT VON HERBING et al, 2001)
On day 5, there was no significant difference between the growth of populations in groups fed Culture Selco (1,911.0 ± 248.7 ind. mL-1) and baker’s yeast (2,600.0 ± 195.3 ind. mL-1), but were statistically higher (p < 0.05) than the group fed microalgae (2.0 ± 1.4 ind. mL-1)
Summary
Ciliate protozoa are ubiquitous in aquatic environments and one of main consumers of bacteria in eutrophic waters (KAMIYAMA, 1994). Because of their abundance and size - similar or even smaller than nauplii of copepods, probably they occupy an important position on aquatic trophic food web. According to Holt and Holt (2000), marine fish larvae in the wild commonly feed on a large array of microzooplankton, including protozoa (tintinnid and ciliates), dinoflagellates, larvae of mollusks and, mainly, eggs and nauplii of copepods. In the majority of marine fish larvae, especially the ornamental ones, e.g. flame angelfish (Centropyge loricula) (Günther, 1835), barber goby
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