Euryhaline rotifer Proales similis as initial live food for rearing fish with small mouth

17 The SS-type rotifer Brachionus rotundiformis is a common initial food for rearing fish 18 larvae with small mouth. However, there are commercially important fish species whose mouth 19 sizes are too small to feed on SS-type rotifers. In 2004, we isolated a small (body length= 82.7 20 ±10.9 μm; body width 40.5±6.4 μm), flexible, and iloricate rotifer, Proales similis from an 21 estuary in Okinawa, Japan. Under laboratory conditions (25 o C, 2-25 ppt) P. similis produced its 22 first offspring on 2.5 to 2.8 days after hatching, and produced 4.3 to 7.8 offspring within 4.0 to 23 4.7 days life span. Batch cultured P. similis fed Nannochloropsis oculata suspension at 28.8 μg 24 dry weight ml -1 and cultured at 25 o C, 25 ppt filtered seawater, increased exponentially from 25 to 25 2400 ind ml -1 after 11 days of culture with an overall intrinsic rate of natural increase (r) of 0.42 26 day -1 . Growth rate of P. similis was not significantly different when fed fresh N. oculata and 27 super fresh Chlorella vulgaris-V12®. Total lipid per wet weight of P. similis fed by N. oculata 28 and C. vulgaris were 2.4 and 2.6%, respectively. The compositions of eicosapentaenoic acid 29 (EPA), docosahexaenoic acid (DHA), and arachidonic acid (ARA) of P. similis fed N. oculata 30 were 23.2, 0.0 and 5.3%, respectively, while these were 11.0, 17.5 and 0.5% respectively, when 31 fed C. vulgaris. The use of P. similis to feed small mouth fish including seven-band grouper 32 Epinephelus septemfasciatus, rusty angelfish Centropyge ferrugata, and humphead wrasse 33 Cheilinus undulatus showed that it is an excellent starter food for these species because of their 34 high selectivity index and improved survival. In addition, P. similis was ingested by Japanese 35 eel Anguilla japonica larvae with complicated digestive system. The use of P. similis as starter 36 feed for small mouth fish larvae is highly recommended. 37