Artificial spawning and larval rearing of klamath River green sturgeon

Two female and five male prespawning green sturgeon Acipenser medirostris t hat were caught and held in cages in the Klamath River, California, were in duced to spawn by injections of gonadotropin releasing hormone analog (GnRH a) and domperidone. All broodfish produced mature gametes for artificial fe rtilization and were sampled for age, body size, sperm motility, hatchery f ecundity, and oocyte diameter. The females were estimated to be 25 and 32 y ears old, respectively: they weighed 38 and 48 kg and produced 52,000 and 8 2,000 ova. The mean diameters of fully grown oocytes in the two females wer e 4.52 and 4.24 mm. The males ranged from 18 to 30 years in age and from 23 to 55 kg in weight. Their sperm exhibited 100% motility in river water For up to 5 min. Ovulated eggs were fertilized with milt pooled from all five males, and the eggs were transported to university facilities in oxygenated bags and incubated in MacDonald jars. Fertilization rates were 26% and 41% for the two females' eggs. In all, 23,000 (28%) normal embryos hatched fro m the female with the higher fertilization rate; the eggs from the other fe male were discarded at 4 d owing to the low number of viable embryos (<5%). Five-d post hatch larvae were reared in circular flow-through tanks and fe d a commercial semimoist diet, either alone or in combination with live Tub ifex worms. The survival to metamorphosis (age 35 d, length 66.4 mm, and we ight 1.78 g) was significantly higher fur fish in the treatment with the co mbined commercial and live diet (74.2% versus 85.5%, P < 0.05), but there w as no difference in the length and weight of juveniles.