PRELIMINARY-RESULTS ON THE EFFECTS OF SALINITY AND SETTLING CONDITIONS ON MEGALOPAL METAMORPHOSIS OF FIDDLER-CRAB ILYOPLAX PUSILLA

Metamorphosis of fiddler crab Ilyoplax pusilla larvae from megalopal t o first crab stage was studied in laboratory experiments under various conditions of salinity and substratum. The hatched zoea metamorphose through five stages before reaching megalopal stage. The megalops were placed in a 20 ml Petri dishes (2-3 megalops/dish), with salinities o f 10, 20 or 30 parts per thousand. Each salinity level was tested eith er with or without sandy mud substratum. Thirty to 35 megalops were us ed in each of the six treatments. The experiment was carried out at a water temperature of 28+/-0.5 degrees C and with daily feeding of the diatom Chaetoceros gracilis. Treatment of 20 parts per thousand salini ty and sandy mud substratum revealed the highest metamorphic rate (87% ), while in contrast no metamorphosis was observed at 30 parts per tho usand salinity without sandy mud substratum. Duration of the metamorph osis was about 16 days. Numerous malformed juvenile crabs were observe d in treatments conducted without sandy mud substratum.