THE REPRODUCTIVE HABIT AND EMBRYONIC DEVELOPMENT OF ELOPICHTHYS BAMBUSA IN CHANGJIANG (YANGTZE RIVER)

The reproductive habit of Elopichthys bambusa is rather similar to the famous Chinese "domestio fishes"——grass carp, black carp, silver carp and big-head. Its spawning sites are widely distributed in the mainstream of the Changjiang River and one of its large tributaries——Hanjiang River. Those sections with mingled whirlpool current and turbulent flow are characteristic regions fit for spawning. In the breeding season, the rise of the water level of 0.12—5.5m., accompanying with the increase of the current velocity of 0.01—0.29m./sec., is the main factor that stimulates the ripe fishes of both sexes to discharge their eggs and sperm simultaneously. As a rule, spawning takes place at the time following the increase of the water level at any magnitude within 1—3 days and it was occasionally observed that the spawning activity was either exactly corresponding to the beginning of the increase of water level or prolonged, though intermittently and in a less extent, during the fall of the water level.The water temperatures in the spawning time were in the range of 16.9—30.2℃, whereas 20.0—27.0℃ were the most favorable. The turbidity of the water showed no connection with spawning behaviour.The embryonic development is subdivided into 46 stages, where the pre-embryonic period covers 30 stages and the post-embryonic 16 respectively. Comparing with those of the "domestic fishes", which are also charactericed by laying drifting eggs, this fish is distinguished from them in the course of early development as follows:1. In the stages before the 16-celled, the contour of the dividing germinal cells of Elopichthys bambusa is more or less squarish instead of arched.2. The bulk of the cell mass from morula to early gastrulation stages is almost identical to that of the yolk.3. The differentiation of the eye is delayed to such extent that the optic bulge begins to come out when 13 body segments have already been formed.4. The embryo appears to be particularly slender after the otolith-formation stage.5. The body segments, counted 52 constantly for the fry, are obviously more numerous than those of others species.