Early Life History of Fishes in the San Francisco Estuary and Watershed

Early Life Stages of Delta Smelt

Randall C. Mager, Serge I. Doroshov, Joel P. Van Eenennaam, and Randall L. Brown

doi: https://doi.org/10.47886/9781888569599.ch11

Abstract.—Delta smelt Hypomesus transpacificus juveniles caught in the Sacramento–San Joaquin Delta were reared in the laboratory to full sexual maturity, and embryos were obtained by in vitro fertilization and natural spawning in tanks. Duration of embryo development to hatching was 11–13 d at 14.8–16.0°C, with a development rate similar to other Hypomesus. Newly hatched larvae were 5.1–5.7 mm total length and resorbed the yolk sac within 6 d and lipid globule within 10 d. Exogenous feeding on rotifers started 5–6 d posthatch. Delta smelt have indirect development with a prolonged larval phase prior to juvenile metamorphosis. Fin differentiation began at 10–12 mm, 20–30 d posthatch, and was completed at 19–20 mm and 50–60 d, concomitant with swim bladder inflation. Metamorphosis was completed in 120 d when juveniles were about 35 mm total length. The prolonged larva fin fold stage lacking a functional swim bladder may be an adaptation to passively use water currents in estuarine nursery areas.