least 6 years of age; all are mature by 8 years. Ma-
ture females generally weighat least 9 kg. In natural
populations. only 6.7% of individuals reached sex-
ual maturity (4. 8% of males and 1. 9% of females.
Zenet al. 1988). It is hard to identify the sex of the
fish from external characteristics. When the body
weight of female Dabry’s sturgeon reaches 2.5–5.0
kg, the ovary can reach deelopmental stageII:by 5
kg in weight, the ovary is at stage III (stages accord-
ing to classification of Conteet al. 1988). The ma-
ture ovary accounts for 2/3 of the volume ofabdom-
inal cavity and the ovary of gravid females may
comprise 10.0–18.8% of the body weight. Gravid fe-
males can contain from 57 000 to 102 000 eggs. Ma-
lure eggs are gray to black and range from 2.7–3.4
mm in diameter. Eggs are sticky, firmly adhere to
stones on the bottom ofthe river after breeding, and
are not readily eaten by other fishes. We have never
found that copperfish and yellow catfish eat Da-
bry’s sturgeon eggs although those species usually
eat many eggs of Chinese sturgeon during their
spawning period. Male Dabry’s sturgeon can spawn
annually, but most females cannot. The time re-
quired to develop mature eggs is unknown, but ap-
parently it is longer than one year.weight(BW)and length (L) before and after sexual
maturity are as follows:
1gBW=6. 005 + 2. 721gL1gBW = 6.175 + 2. 721gL1gBW = 6.219 + 2.721gL(males and females before sexual maturity);(males after sexual maturity):(females after sexual maturity).Movement
Dabry’s sturgeon generally behaves as a resident
fish and does not undertake long migrations. This
behavior resembles that of Amur sturgeon. A.
schrenckii,in the Amur River (Nikolski 1960). His-
torically, some individuals of Dabry’s sturgeon
reached the lower-middle section of the Yangtze
River below Yichang (Figure l), but this was before
the construction of the Gezhouba Dam, and such
migrations are now impossible. Most of the avail-
able information about movements is based upon
recapture of tagged fish. Zhang (1988) reported that
a tagged fish swain 97 km downstream for 6 days
before recapture, but this is the only report of
movement over such a long distance. Most tagged
individuals only moved several kilometers either up
or downstream before recapture in 2 days to 8
months after releasing.
Dabry’s sturgeon swim upstream for spawning
during spring floods. Spawning fishes do not aggre-
gate to swim upstream together as a group but in-
stead move individually. After spawning, the spent
fish move slowly back downstream to the sandy
shoals where they feed intensively. Sometime they
enter large lakes to feed. There is a record that Da-
bry’s sturgeon was historically found far down-
stream in Anhui Province, more than 2000 km from
the probable spawning areas (He 1990).
Natural and artificial spawningBased on the capture of ripe individuals, we con-
clude that spawning occurs in the spring. although
some individuals may spawn in the fall (Yang 1986,
Zen et al. 1990). Since the late 1950s. researchers
have searched for spawning sites, but they remain
unknown despite considerable effort. Mature fish
are unknown in the reaches below Yibin, Sichuan
Province, whereas young are often caught in the
reach below Yibin. Thus we infer that the spawning
areas are in upper mainstream of the Yangtze,
above Yibin (Figure 1). The spawning environment
probably has a rubble, cobble and gravel bottom.
clear water, water velocity of 1.2–1.5 m s–1,water
depth of 5–15 m
Xie (1979) reported on early development (see
Bemis & Grande I992 For SEM stages ofpaddlefish-
es. which arc very similar).At17–18°C. the first
cleavage occurs 3–4 hours after fertilization; theReproductive biologyMales start to mature at 4 years, and all arc mature
by 7 years ofage.At maturity, males weigh more
than 4.5 kg. Females usually do not mature until at