Rotifers are considered to be an excellent food source for newly hatched fish larvae. Availability of adequate number of rotifer with enriched nutrients, especially polyunsaturated fatty acids determines and helps the initial success in marine finfish hatcheries. Rotifers must be cultured at relatively high densities to provide an adequate supply of food for producing large numbers of fingerlings. An adequate supply of these rotifers relies on mass cultures practices standardised in a hatchery and on the reproductive performances of rotifer. The reproductive rate of rotifers in cultures depends on the type and quality of feed used. Rotifers have to be enriched with polyunsaturated fatty acids since the marine finfish requires 2:1 ratio of DHA and EPA as their initial feed. Therefore, optimum feed needs to be identified to enhance population growth and nutritional value of rotifer with economical benefit.
The present study was conducted to observe the growth, reproductive and nutritional performance of rotifer fed with different feeds. The live microalgae: Nannochloropsis oculata, Isochrysis galbana and baker's yeast and then three in combinations were used in the experiments. The study was conducted with purified strains of Brachionus plicatilis in 125 lit capacities FRP tank. Initially, tanks were inoculated with 1 million of adult rotifers (100-150µ in size) at the concentration of 50 numbers/ml. The experimental rotifers were fed with respective feeds thrice in a day and optimum concentration of 4 to5 lakhs cells/ml were maintained at the time of feeding. In experiment with yeast, it was added at 0.5g-1.0g /1million of rotifer/day. In combination feed, the equal concentrations of rations were maintained. All the experiments were conducted in triplicates for seven days till the rotifer population reached the declining growth phase and repeated for four different times. Rotifer growth with respect to numbers and presence of eggs were daily monitored in microscope. The result showed that in all the treatments, the growth was high at the fourth day with maximum growth count of 11.202 millions in Nannochloropsis sp fed group, minimum with yeast (3.33 millions). The maximum numbers of egg production was observed on third day in all treatments with high in Nannochloropsis sp (1.54 milions) and lease for yeast (0.11 millions). A maximum of 3 eggs were observed per female in treatment with Nannochloropsis sp. Rotifers were harvested and analysed to understand fatty acid profile by Gas Chromatography Flame Ionising Detector (GCFID) method. The result showed that a total of 35 different fatty acids were found in rotifers and the rotifer fed with Nannochloropsis sp showed maximum content (9.05%) of EPA (C20:5) and rotifer fed with Isochrysis sp showed the maximum content (14.09%) of DHA (C22:6). However, the rotifers fed with a combination of these two algae and yeast showed comparatively lesser content of EPA and DHA than the rotifers fed with individual species of algae. The study infers that Nannochloropsis oculata is the suitable feed with respect to growth and reproduction and Isochrysis galbana is the suitable feed for increasing the nutritional (DHA) content.