STUDIES ON THE NON-PARASITIC METAMORPHOSIS OF CRISTARIA PLICATA GLOCHIDIA AND THE DEVELOPMENT OF EARLY JUVENILES

In nature, the glochidia of Cristaria plicata must successfully parasitize a suitable host fish to metamorphose into juveniles. The current study investigated non-parasitic metamorphosis of the glochidia mainly focusing on the development of glochidia in external morphology and internal organs using microscope and scanning electron microscope, and analyzed the effects of sediment and light on the survival and growth rate of newly metamorphosed juve-niles. The results showed that the glochidia remained similar in external morphology and size during the transformation process, while the feet, gill filaments, mantles, visceral mass and other inner organs were gradually formed. On the 3^rd day of the in vitro culture, the rudiment of foot was firstly observed; on the 6^th day, the feet had generally took shape with cilia showing on the surface of foot and the edge of mantle, and gill filaments began to show; on the 9^th day, the cilia on feet and mantles increased and gill filaments became more dense; and after 30 days of tank culture, the morphology of juvenile mussel gills was clearly evident and was similar with adult mussels, and three typical different cilia were observed on the surface of branchial filament. The results demonstrated that the sediment has significant effects on the survival and growth of juveniles (P < 0.01), whereas the nature light has no effect (P>0.05). These results provide basic insight for researches on the non-parasitic metamorphosis of glochidia of Unionidae species, and confirme that in vitro culture is an effective method for the artificial breeding and conservation of freshwater mussels.