mid-gastrula stage occurs 28–30 hours after fertil- Aquaculture, fisheries, and conservation
ization, neurulation is complete 43–45 hours after
fertilization, and hatching occurs 115–117 hours af- Domestication of Dabry’s sturgeon started in the
ter fertilization. Newly hatched embryos, about 4 early 1970s (Xie 1979). Because it matures rapidly, it
mm long, swim erratically and vertically due to their was expected that the species had potential both for
large yolksac. Three days after hatching, the larvae intensive aquaculture in ponds and for extensive
can balance themselves. Four days after hatching, aquaculture in lakes and reservoirs by artificial
the pectoral fin appears, with dorsal fin appearance stocking (Jia et al. 1981, Yang 1986, He 1990). How -
on day 5 and anal fin appearance on day6.In10–11 ever, limited experience with production tech-
days, most of the yolk is absorbed and the mouth niques and poorly developed markets prevented
parts are developed so the young are ready to feed. early success in this industry. Only in the last 10–15
Yolk is depleted 12 days after hatching. Young fish years with the improvement of propagation tech-
immediately swim downstream. They can be found niques has commercial culture of Dabry’s sturgeon
in reaches at Luxian, Hejiang and Jiangjing, about been possible (Xie 1992).
100–200 km below the supposed spawning areas. Dabry’s sturgeon was an important commercial
Artificial stripping of Dabry’s sturgeon was re- species in the upper Yangtze River, near Yibin, Si-
ported by Xie et al. (1976) using mature fish caught chuan Province (Figure 1). In the 1960’s, landings of
in the Jingsha River. Subsequently, Tian et al. (I986) Dabry’s sturgeon reached 10% of the total harvest
reported artificial stripping of Dabry’s sturgeon do- of Hejiang Fishing Squad (He 1990). In the 1970s, up
mesticated in ponds from juvenile to adult. Early to 5000 kg of Dabry’s sturgeon could be caught in a
workers used injections of pituitary glands of Chi- spring season from the Yibin reach. Because adult
nese or Dabry’s sturgeon to induce ovulation. In- Dabry’s sturgeon are uncommon and do not like to
duction included two injections, with the initial (or aggregate, young individuals, weighing several
primary) injection separated from the second (or hundred grams, made up most of the harvest. Since
resolving) injection by 8 hours. Ovulation occurred the 1970s, however, total landings of Dabry’s stur-
within 14–24 hours after administration of the sec- geon sharply declined, and it now seldom occurs be-
ond injection. More recently, luteinizing hormone low Gezhouba Dam.
releasing hormone analog (LHRH-A) has been Possible causes of decline in Dabry’s sturgeon
used to induce ovulation of Dabry’s sturgeon. populations are: (1) Unsuitable fishing methods.
Artificially propagated interspecific hybrids of Fishermen repeatedly have decreased the mesh size
Dabry’s sturgeon (male) and Chinese sturgeon (le- of nets, so that they take many small fish. This meth-
male) exhibit significant hybrid vigor, prove to be od is harmful to the small fish, especially during the
fertile, and seem to be a promising candidate for flood season, when many young Dabry’s sturgeon
commercial production. Hybrid progeny add concentrate to feed. As a result, the sturgeon taken
weight much faster than do Dabry’s sturgeon, and from the Luzhou reach usually weigh less than 50 g.
about as fast as Chinese sturgeon, before 3 years of (2)Overfishing.For example, in the Neijiang reach
age. At 6 years of age, female hybrids weigh more of the Tuo River there were only 500 fishing boats in
than^40 kg, much larger than Dabry’s sturgeon. Fur- 1950s, but this number increased to about^2000 by
thermore, female hybrids reach maturity at 6 years 1985. In the Leshan Reach of the Ming River, drift
of age, 2 years earlier than most female Dabry’s gill nets are crowded together from day to night. (3)
sturgeon, and male hybrids reach maturity at 3 Unsuitable fishing season.The traditional busy fish-
years of age, which is also earlier than male Dabry’s ing season in the main stream of Jingsha River is
sturgeon. Some of the hybrids arc hermaphrodites between March and August, with more than 30% of
(D.J. Xie personal communication). the catch processed in April and May. However, this
is also spawning season of Dabry’s sturgeon in the
main stream, so it threatens the spawning stock.
(4)Pollution from factories and pesticides. With ec-
martin jones
(Martin Jones)
#1