All attempts to introduce the fish were successful, except the Dodge and Big Bear Reservoir introductions,[5] the latter of which may have been partially attributable to chemical treatments meant to eradicate stunted crappie and goldfish.

[5] In 1994 they were detected at the State Water Project pumping plant for the first time, and by 1998 the fish could be found throughout the estuary including the Suisun and San Pablo Bays.

[5][7][9] Because the two species are very similar in morphology and life history, the wakasagi presents several potential threats to the endangered delta smelt.

Besides direct competition for nutritional resources and the possibility that wakasagi may prey on the eggs and larvae of delta smelt,[5] hybridization could either dilute the species or cause population decline due to sterilizing effects.

Misidentification of the species is an additional concern, which could lead to inaccurate assessments critical to making policy decisions; however this problem may be mitigated if genetic markers are used for identification.