I think one of the killies would be the most suitable - there are dozens of
species with hatching times of differing durations e.g. 6 weeks to 6 months
or more that could be confidently expected to hatch out "on cue".
Bruce Hansen, ANGFA, caring for our aquatic ecosystems.
Please visit us at http://www.ozemail.com.au/~fisher/angfa.htm