Artificial Spawning and Larval Rearing of Klamath River Green Sturgeon

Abstract

Two female and five male prespawning green sturgeon Acipenser medirostris that were caught and held in cages in the Klamath River, California, were induced to spawn by injections of gonadotropin releasing hormone analog (GnRHa) and domperidone. All broodfish produced mature gametes for artificial fertilization and were sampled for age, body size, sperm motility, hatchery fecundity, and oocyte diameter. The females were estimated to be 25 and 32 years old, respectively; they weighed 38 and 48 kg and produced 52,000 and 82,000 ova. The mean diameters of fully grown oocytes in the two females were 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 from the female with the higher fertilization rate; the eggs from the other female 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 fed a commercial semimoist diet, either alone or in combination with live Tubifex worms. The survival to metamorphosis (age 35 d, length 66.4 mm, and weight 1.78 g) was significantly higher for fish in the treatment with the combined commercial and live diet (74.2% versus 85.5%, P < 0.05), but there was no difference in the length and weight of juveniles.