Abstract
(1) Many hybrids from the reciprocal crosses between L. echigonia (buddhr-loach) and M. anguillicaudatus (mud loach), and between the former and C. biwae (spinous loach) died in the gastrulation stage, with a few deformed larvae which died just after hatching. The larvae were intermediate between the parent forms in size of the nucleus as well as in number of the myotome.
(2) The hybrid larvae from C. biwae_??_×M. anguillicaudatus_??_ were identical in development to pure-bred larvae, showing the intermediate color pattern between parent forms. The hybrids from the reverse crossing showed deformation and died in earliar stages of development.
(3) As regard to the fertilization rate and mortality of the cross-bred eggs and the viability of hybrids produced, the following order was observed: C. biwae _??_×L. echigonia_??_<L. echigonia_??_×C. biwae_??_<L. echigonia_??_×M. anguillicaudatus_??_ <M. anguillicaudatus_??_×L. echigonia_??_<M. anguillicaudatus_??_×C. biwae_??_<C. biwae _??_×M. anguillicaudatus_??_.
(4) Based on the above results, the view is expressed that C. biwae and M. anguillicaudatus are most closely related that M. anguillicaudatus and L. echigonia are less closely related than the above, and C. biwae and L. echigonia are taxonomically furthest apart.
