Development Of Sense Organs During Dabry’s Sturgeon(Acipenser Dabryanus) Ontogeny

Dabry’s sturgeon (Acipenser dabryanus) is endemic to China, which is the pure freshwater settled fish. It is mainly distributed in the tributaries of the upper reaches and the middle reaches of the Yangtze River. It was used to be one of the upper reaches of the Yangtze River economic fish. But in the late20th century, due to overfishing, water conservancy, shipping and water pollution, and many other effects of human activities, the number of wild populations of Dabry’s sturgeon declined gradually. The population resource was downturn seriously. Acipenser dabryanus was nearly extinct in the Yangtze River basin. Therefore, Dabry’s sturgeon was listed as a First Class Protected Animal by the national government of China in1988. Therefore, we should pay more effort in the study of species protection and stock enhancement. Knowledge of the early ontogenesis, especially sense organs development has not been reported. We observed the development of larval fish during Acipenser dabryanus ontogeny to provide a theoretical basis for the breeding and larval rearing. Conclusions from the studies are as follows:1) Larvae exhibited an undifferentiated retina at hatching. The single cones appeared at36hour and the rods appeared at6day. At7day, the visual system was differentiated completely. The apparent retinomotor responses first occurred at13day. However, the minimum separable angle (a) decreased from13.26’ of8day to3.37’ of64day.Over the whole range of development the densityof single conesand ganglion cells decreased while the density of the rods increased correspondingly. The ratio of nuclei of the outer nuclear layer to ganglion cells per100μm increased, as well as the ratio of nuclei of the outer nuclear layer to single cones. The investigation showed that the retina structure and the visual characteristics changed rapidly from6to12day, and these changes were adapted to the ecological shift andthe changes of phototaxis and feeding behavior.2) There were taste buds in barbell, upper and lower lips, tongue, palate, gillrakers and pharynx. Taste buds first occurred in lower lip and then in barbell and gillrakers, and last in pharynx. Number of taste buds in tongue was most and few in gillrakers and pharynx. The taste buds distribution and abundance are closely related to feeding sites. It is fully reflected the adaptability and unity of the structure and function. The first primary olfactory lamellae developed at5day, and the number increased continually. Olfactory sacs were developed completely at29day. The developing stage of9-29day was greatly changed. So we speculated that Acipenser dabryanus might be more use the sense of smell to find food in the later stages of development.3) The rudiment of pit organ in rostral were developed at4day. They centralized in midsection of venter rostral. Several pit organs were collected into cluster in vernter rostral at9day. Then few pit organ appeared in lateral rostral and around the eyes. There are many pit organs in the Acipenser dabryanus’s rostral, it began to appear and develop even before the larvae’s opening feeding. Therefore, it will help the larvae to get through the difficulties in the opening feeding.