Mass production of Euplotes sp. in static culture using commercial inert diets and a practical fixed-feeding strategy

Abstract Ciliates are promising first-feed organism for marine fish larvae because of their small size, nutritional value, and ease of culture. They can bridge the feeding gap until larvae are able to consume larger live prey. Intensive cultivation of ciliated protozoa under controlled conditions remains limited due to difficulties in maintaining high densities in steady cultures. This study evaluated the efficiency of different diets (BY – baker’s yeast Saccharomyces cerevisiae ; RD – commercial rotifer diet; and RE – commercial rotifer enrichment product) and tested practical methods for supplying baker’s yeast and improve Euplotes sp. biomass production. Population density, specific growth rate (μ), and total ammonia nitrogen (TAN) were analysed using linear mixed models. Higher population densities growth were achieved with RD (31,386.0 cil mL⁻ 1 ) and BY (21,346.6 cil mL⁻ 1 ) than with RE (9142.3 cil mL⁻ 1 ) after seven consecutive days of cultivation. The RD supported continued population growth during 24-h feed-withdrawal, reaching the highest density (43,727 cil mL⁻ 1 ) on day 8. Feeding a fixed daily amount of baker’s yeast (0.4 g L⁻ 1 day⁻ 1 ) proved to be an effective alternative to density-based feeding. Specific growth rate was not affected by treatment in either experiment, although a significant temporal effect was detected in Experiment 2. Although high ammonia levels were observed during cultivation (33–60 mg L⁻ 1 NH 3 /NH 4 + ), ciliate populations continued to increase without water renewal. These results demonstrate that short production cycles and simplified feeding strategies can support efficient Euplotes sp. cultivation. Further studies should investigate the effect of prolonged ammonia accumulation, the composition of the culture microbiota, and the nutritional profile of ciliates fed culture and enriched with different food sources.