Preliminary study on hatching of rotifers (Brachionus plicatilis) and copepods (Cyclopoida): response to flooding and organic fertilisation
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The effect of water flooding, organic fertiliser application and salinity manipulation in stimulating the hatching of rotifer resting eggs was investigated during the dry season (in August/September 1999) in simulation tanks and earthen ponds at Makoba, Zanzibar. The majority of hatched zooplankton included rotifers, identified as Brachionus plicatilis, and other zooplankton such as copepods and protozoa were present in small numbers. The number of rotifers hatched in simulation treatments with low salinity was higher than the values in treatments containing undiluted seawater. Up to 22 ± 1.5 (mean ± SE) rotifers/ml were counted in treatments with low salinity, whereas only a maximum of 13 ± 1. rotifers/ml were found in high-salinity treatments. On the other hand, although salinity in earthen ponds was similar (32–33‰), the ponds flooded and fertilised with chicken manure yielded significantly more rotifers (26 ± 1 /ml), compared to a maximum of only 8 ± 0.5 rotifers/ml counted in the control unfertilized pond. These results suggest that it is possible to induce hatching and production of rotifers by manipulating salinity and fertility of ponds. The reared rotifers can be harvested and used to feed finfish larvae elsewhere.