Delta smelt (Hypomesus transpacificus) is an endangered small fish species inhabits the upper San Francisco Estuary, California. The UC Davis Fish Conservation and Culture Laboratory (FCCL) has been culturing a refuge population of Delta Smelt to prevent them from extinction. Currently, FCCL produces more than 600,000 eggs annually to achieve the goal and to propagate fish for wild fish supplementation. To obtain an optimal hatching rate, FCCL has been implementing a standard operation procedure that requires staff to manually take out dead eggs during the incubation processes to prevent fungal infection. The procedure is particularly labor- and time-consuming. Therefore, alternative methods are highly demanded.
In this study, two alternative methods were tested, including separating eggs by the specific gravity (SG) difference between live and dead eggs and by introducing ramshorn snails (Helisoma anceps) to identify and consume dead eggs. By far, separating eggs by the difference of SG shows promising outcome. The time needed to separate eggs at different SG is shown in Fig.1. A follow-up study for the effect of solution used on the hatching will be conducted. Also, a device for the separation will be designed accordingly. For the method of using snails to remove the dead eggs, preliminary results have shown that snails preferred to consume dead eggs rather than live ones (Fig.2). Putting together, either method shows the potential to be an alternative method to improve the current operation.