Development Of Sense Organs And The Behaviour Function During Chinese Sturgeon (Acipenser Sinensis) Ontogeny

The Chinese sturgeon (Acipenser sinensis Gray) is among the large anadromous species that involves riverine spawning migration. It lives mainly in the East China Sea, Yellow Sea, Pearl River and Yangtze. Spawning timing of the Pearl River population is in the spring and in the fall of the Yangtze River population. The Pearl River population is likely extirpated due to overfishing and habitat modification. The spawning run of the Yangtze River population was blocked and the population greatly reduced by the construction of Gezhouba Dam in 1981. Because of the overfishing and other environmental stressor, the Chinese sturgeon has become endangered. The artificial spawning below the Gezhouba Dam was successed in 1983 for the first time and has been continued since then. The fish was listed in the National Class I Protected Animals in 1988. In 1997, the aquaculture on large scale began in China and since then the offspring at different ages have been grown. By the beginning of this century, great progress had been made in the fields of morphology, reproductive biology and, especially, reproductive ecology and stock assessment of the spawning population below the Gezhouba Dam. Knowledge of the early ontogenesis, especially sense organs development and their behaviour function remains rare yet. The author studied the development of sense organs and the behaviour functions of Chinese sturgeon. Conclusions from the studies are as follows:1. The eyeball of 2 d.p.h. (days post hatch) had iris and vision nerve appeared at 3 d.p.h.. At 40 d.p.h., the eyeball was developed completely. At hatching, larvae exhibited an undifferentiated retina. The retina of 3 d.p.h. had cones (C) at high density. The rods appeared at 9 d.p.h., and it is assumed that at this time the visual system was developed completely. The density of cones (C) and ganglion cells (G) decreased with proceeding development, while the density of the rods (R) gradually increased. The ratio of nuclei of the outer nuclear layer to ganglion cells (ON/G) per 100μm increased, and so did the ratio of nuclei of the outer nuclear layer to cones (ON/C). The minimum separable angle (a) decreased from 64.2' of 4 d.p.h. to 11.3' of 91 d.p.h.. Retinomotor responses first occurred at 16 d.p.h. and became remarkable at 25 d.p.h.. All of the larvae preferred illumination from 0 to 8 d.p.h.. The phototactic ratio decreased to 45 percent at 10 d.p.h.. and began to increase to 51 percent at 12 d.p.h.. Till 17 d.p.h., the ratio came back to 100 percent and remained it. The investigation showed that the structure of the retina changes rapidly from 9 to 17 d.p.h., which is a transitional period of the...