INFLUENCE OF ABIOTIC FACTORS AND FOOD CONCENTRATION ON POPULATION GROWTH OF THE CILIATE Euplotes sp.  

Live food organisms used for feeding larval marine fish have received significant research in the past decade. Most of this research and development has focused on rotifer enrichments and feeds, and mass scale production methods for several species of copepods. However, there is a need to investigate other small live food organisms to potentially improve survival and growth of larval fish during the hatchery phase of culture. One potential live food organism is a ciliate. However, there is a dearth of information on optimal production parameters for ciliates. The objectives of this study were to evaluate the influence of abiotic factors including salinity, photoperiod, temperature, aeration, and food concentration on the growth of Euplotes sp. populations. Five replicated small scale experiments were designed and conducted. First, food concentrations of 50, 100, 250, and 500 mg of Protein Selco (INVE) per million ciliates were investigated. Second, salinities of 15, 20, 25, 30, and 35 g/L were investigated. Third, four levels of aeration were investigated. Fourth, temperatures of 17, 20, 23, 26, 29, and 32°C were investigated. Fifth, four photoperiods were investigated.

Results indicated that the optimal range of conditions for production of the ciliate Euplotes sp. to be a feed concentration of Protein Selco (INVE) of 250 mg per million ciliates, salinity from 20-35 g/L, low or no aeration, temperatures between 26 and 32°C, and a photoperiod between 0L:24D and 16L:8D. Based on the results and observations during this study, we conclude that the ciliate Euplotes sp. has characteristics favorable to mass production including resistance to adverse conditions such as high concentrations of ammonia and very low dissolved oxygen concentrations, they experience high growth and reproduction rates, can grow to very high densities, received nutrition either directly or indirectly from an inert diet, and adapted well to a wide range of salinities and temperatures.