Sunshine bass are an important food fish raised in US aquaculture. Spawning of these hybrid striped bass is done by manual fertilization of female white bass eggs with male striped bass sperm. The industry grows these fish to ~1.5 to 2 lbs over ~1.5 to 2 years, during whi ch time the females can become fertile and produce eggs. This is a major problem in the industry, as the majority of producers sell these fish whole and there is a considerable loss in weight (i.e., dollars) due to expulsion of eggs caused by handling stress; eggs prematurely released can also lead to considerable water quality issues. Therefore, the industry needs a way to produce sterile fish.
One way to produce sterile fish is through the creation of triploids. Triploidy can be induced through temperature shock applied to the embryo shortly after fertilization ; so far, there has been only limited success. We chose a range of temperatures and times post-fertilization to shock the eggs during initial trials . L arvae produced were then checked for triploidy using a flow cytometer. Based on these data, we chose the highest triploid rates from the cold- and warm-shocks to continue trials. A large-scale trial was performed and l arvae from both treatments and a diploid control were spawned from a single batch of eggs . Fish will be grown for two years to examine growth and gross morphology.
From this large-scale trial, flow-cytometer results on 2 -day old larvae indicated triploid production was 54% in the warm- and 52% in the cold-shock treatment groups. Fish were transferred to a fertilized pond where the larvae ate zooplankton over 28 days and grew to about 2 cm . There were few survivors in the cold-shock pond; none of these were triploid when checked with a Coulter Counter (CC). T here were several thousand fish in the warm-shock pond and a sample of 50 fish indicated 14% triploid (by CC) . Diploid and warm-shock triploid fish were then moved to separate growout ponds and fed commercial hybrid striped bass diets for 5 months; we then determined 7% success rate (by CC) of the triploid survivors . We will grow these until spring spawning 2020 to verify maturation/ gamete production vs diploid fish from the same batch of eggs.