Size, fecundity and condition factor changes in endangered delta smelt Hypomesus transpacificus over 10 generations in captivity

The once abundant delta smelt Hypomesus transpacificus is now on the verge of extinction. At the UC Davis Fish Conservation and Culture Laboratory, a refuge population has been maintained since 2008 as a safeguard against extinction and to breed and provide fish for research. Due to artificial aquaculture operations, it is assumed that the fish are impacted by life in captivity leading to questions about differences between cultured and captive wild fish. This study looked at the differences in fork length (FL), body weight (BW), fecundity (F) and condition factor (K) of cultured and wild (captive) delta smelt over the last 10 generations (2009–2018) to determine if there were any changes of life-history traits between the two, which may indicate domestication. Results revealed that the cultured population had significantly higher FL, BW, F and K than the wild population. The correlation tests found significant positive relationships between all measured traits except FL and K of wild fish. Significant changes in the measured traits of the cultured population over time were found, whereas none was observed in most wild fish year-classes. This study demonstrated changes of life-history traits in a well-managed fish population over 10 generations in captivity and provides critical information to the coming supplementation plan for the species.