UC Davis

At the UC Davis Fish Conservation and Culture Laboratory (FCCL), Delta Smelt (Hypomesus transpacificus) and Longfin Smelt (Spirinchus thaleichthys) are being cultured for conservation. While the aquaculture processes for these species were established, they are not perfect and demand extensive labor and time, particularly for fish egg treatments. This study explored alternative egg separation and adhesiveness removal methods. In the first part of the study, Epsom salt solutions with varying specific gravity (SG) were utilized to separate live and dead eggs. The results showed promising effectiveness for specific gravity value of 1.08, 1.10, and 1.12, which effectively separated dead eggs for both species with minimal impacts on hatching rates. In the second part of the study, Ramshorn Snails (Helisoma anceps) were utilized as natural egg separators. The result showed these snails preferred dead Delta Smelt eggs compared to live eggs. This behavior was first discovered and opened a potential route for future fish egg separation methods. In the last part of the study, alternative fish egg adhesiveness removal methods were compared to the traditional bentonite clay method. The results showed excellent egg adhesiveness removal capability for sodium hypochlorite and tannic acid, while the effectiveness of Alcalase enzyme increased with concentration and achieve the same effectiveness at the higher concentration of 5% (v/v). However, the results also showed the negative impacts of sodium hypochlorite to the hatching rate of Delta Smelt eggs, which no eggs hatched after being treated. Tannic acid and Alcalase, on the other hand, showed no significant impact to the hatching rate. From the findings of this study, the Epsom salt solution method for fish egg separation has been successfully integrated to the hatchery-scale fish production at the FCCL, yielding notable time and labor savings for egg treatments. However, the approaches using Ramshorn Snails and alternative adhesiveness removal techniques require further study and optimization.