I've had a similar experience with ricefish fry. I had 10 shipped from Hawaii to Ohio and once they reached a sexable size, all are male. Disappointed with the ratio, I looked into it a bit. Turns out that starvation during the larval stage can cause genetically female fry to change to male. A period of 5 days is enough to cause the change, so shipping young fry can lead to a male-heavy ratio. Here's a post with more information : Medaka Sex Change.
Quote
Scientists had already discovered that environmental factors, such as temperature changes in the brackish andfresh waterswhere medaka fish live, are likely involved in their sex reversal. Tanaka and his team wanted to know if nutrition also played a role.
They starved medaka larvae for five days. This was enough time to affect their metabolism without killing them. Three to four months later, the team examined the fish and found that 20% of the genetically female medaka had developed testes and characteristically male fins. The same did not occur in larvae that were not starved.
Sourcing Fish
in General Discussion
Posted
Hi NordernAquariums -
I've had a similar experience with ricefish fry. I had 10 shipped from Hawaii to Ohio and once they reached a sexable size, all are male. Disappointed with the ratio, I looked into it a bit. Turns out that starvation during the larval stage can cause genetically female fry to change to male. A period of 5 days is enough to cause the change, so shipping young fry can lead to a male-heavy ratio. Here's a post with more information : Medaka Sex Change.