Low-temperature preservation (at 4 degrees C) of marine rotifer Brachionus

Mass production of rotifers is essential as live food during the larval rea ring season. but a major problem of rotifer culture is unpredictable cultur e collapse, If mass-produced rotifers could be kept alive at low temperatur e for an extended period of time. they could be supplied as live food to cu ltured marine fish larvae without interruption, Four experiments were perfo rmed to test this possibility in six strains of Brachionus plicatilis O, F, Muller and eight strains of Brachionus rotundiformis Tschugunoff. The resu lts showed that: (1) B. rotundiformis strains were less tolerant to 4 degre esC than B, plicatilis strains. Among the B. rotundiformis strains. the str ains known as SS type were the most susceptible and showed the lowest survi val. (2) Exchange of culture media during the incubation at 4 degreesC in B , plicatilis and B. rotundiformis resulted in higher survival than not chan ging the culture media. but there were no differences in the regression slo pe with or without changing the culture media. (3) Acclimation at 15 degree sC for 96 h for B, plicatilis and B, rotundiformis before transfer to 4 deg reesC resulted in higher survival rates than acclimation at 10 degreesC, (4 ) The combination of frequent exchange of culture media and acclimation sig nificantly improved the survival of B. plicatilis and B, rotundiformis comp ared with controls that were maintained at 4 degreesC without exchange of t he culture media. Large-scale trials using B, plicatilis (Kamiura strain) c ultured in 30-L tanks were conducted in a hatchery at a density of 2000-20 000 individuals mL(-1). Rotifers were transferred directly from 25 degreesC to 4 degreesC, About 50% of the rotifers at 20 000 individuals mL(-1) surv ived after 14 days at 4 degreesC. These preserved rotifers could be culture d at 20 degreesC. recovering within 4 days.