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In response to Federal listing of the Delta Smelt Hypomesus transpacificus as a threatened species in 1993, intensive fish culture techniques were developed to provide a supply of fish for research activities. The Delta Smelt was listed as endangered by the state of California in 2009, and several agencies worked quickly to develop a captive refuge population under genetic management. Captive 2-year-old wild-origin Delta Smelt served as the founding population in 2008. Each year, 250 genetically selected, single pair crosses are made in vitro, and the resultant full-sibling families are combined to rear in multifamily groups. Typically, eight families are reared together from egg to adult stage, with 80% or more of the initial families represented at the adult stage. Multifamily rearing provides an efficient way of achieving a breeding population of 500 in a smaller facility. Juvenile survival increased from 18% in 2009 to …