same generation mature and spawn a year earlier 22° C (Svirskii 1971). Free embryos and larvae of the
than they would during cold years. Males spawn estuary drift downstream from the spawning
once every three to four years, and females, every grounds to the lower reaches of the Amur River and
four to five years (Svirskii 1971, Krykhtin 1986). To- estuary. Some juveniles from the estuary popula-
tal degeneration of previtellogenic oocytes (40–470 tion remain in the lower reaches until age two to
μm in diameter) was observed in a few adult fe- five years, where they feed together with juveniles
males at age 18–24years (Svirskii 1979). Maturation from the population of the lower Amur.
in these females can be delayed for two years and Kaluga from the lower Amur population spawn
intervals between spawnings may increase to six to at the same spawning grounds and at the same time
eight years. as individuals from the estuary population. These
Fecundity in 411 females ranging from 16 to 30 fish migrate from the lower Amur to the spawning
years from the estuary population ranged from grounds from May to the first half of June. The pro-
186 000 to 4 225 000 eggs (mean = 977 465 ± cess of maturation and intervals between successive
23 692). Relative fecundity was 3300 to 15 100 eggs spawnings appear to be similar in both populations.
kg–1of body weight. In some females, the coelenter- Individuals from the lower Amur population grow
ate parasitePoIypodium hydriformecaused a de- more slowly and are probably adapted to the higher
crease in individual fecundity by 19% (Svirskii water temperature of the lower Amur.
1984).Gonads of most of the future spawners were The middle Amur River population of kaluga ex-
at stage IV of maturation (according to the stages of tends approximately 900 km from the river mouth
Nedoshivin 1928). In autumn and early winter, most and includes the upper part of the lower reach of the
of these future spawning fish migrate from the estu- Amur River and lower part of the middle reach of
ary into the Amur River, where they spend the win- the Amur River. Many individuals of the middle
ter in preparation for spawning during the next Amur population reach sexual maturity much earli-
spring (Krykhtin 1986). A smaller group (about er than do those of the estuary population. From
5%) of all of the spring spawners migrates into the 1988 to 1992, 11–16 year old females constituted up
Amur River during the spring, spawning soon after to 25% of the females migrating to spawning
migration. Thus, there are two seasonal forms of ka- grounds from the lower region of the middle reach
luga in the estuary, which we call winter and spring. of the Amur. Such early maturation was never ob-
The winter form predominates. served in the estuary population. Individual fecun-
Most of the mature fishes from the estuary pop- dity varied from 238 000 to 4 868 000 eggs in 126
ulation spawn 50–150 km upstream from the town females studied at 11–16 years of age. Their relative
of Nikolayevsk-na-Amure, while a small portion fecundity varied from 5000 to 11 000 eggs kg–1body
spawns on sites located less than 500 km upstream weight.
from the mouth of the river. Some individuals mi- Major spawning grounds of the middle Amur
grate as far as Khabarovsk, nearly 1000 km from the River population of kaluga are located in the lower
mouth, and spawn in the middle Amur. region of the middle reach of the Amur. Smaller
Spawning takes place during a small increase in spawning grounds are located in the Sungari and
the water level, from the end of May until the begin- Ussuri rivers. The spawning migration of the mid-
ning of July, when the water temperature ranges dle Amur population takes place from May to the
from 12 to 21°C. The peak of spawning usually oc- first half of June. Their free embryos drift down-
curs in the middle of June.Pebble deposits in the stream from the spawning grounds to the regions
main river bed and some large side channels serve with well-developed flood plains.
as spawning grounds (Svirskii 1976a). After spawn- The Zeya and Bureya populations are nowrepre-
ing, the fish return to the estuary to feed. sented by rare individuals in the upper region of the
Embryonic development until hatching lasts 82– middle reach of the Amur, in the upper reach of the
I12 h, and development of free embryos until the Amur, and in the lower regions of the Zeya, Shilka,
transition to active feeding takes 7.5–14 days at 14– and Argun rivers. They migrate to spawning
martin jones
(Martin Jones)
#1