Rainbow Trout Egg and Fry Production

It has been a good month for the development and hatching of rainbow trout ova, which were collected from Great Lake spawners in October. A total of 360,000 eggs were collected in early to mid October for diploid fish production and 250,000 were collected at the end of October for the triploiding process.

The diploid ova hatched in early-mid November and after a period of two weeks living on their egg sacs (alevin stage), the hatchlings became ‘swim up fry’ and were ready for their first feed. The first feed is critical for survival of the young fish, so they were watched closely during this phase. When the fry were observed feeding well in the incubator troughs, they were transferred to the tanks.

The triploid rainbow ova meanwhile have just commenced hatching. It’s hoped that the mortality rate for these triploids can be reduced this year to achieve a survival rate of between 40-50% of the total number of eggs. This is achievable given the benefit of using the new triploiding vessel (imported from France in August) on the rainbow trout eggs and with careful husbandry during incubation.

This is comparative to the rates achieved by some commercial hatcheries for triploid salmon and trout of around 50% or less. These commercially-reared brood fish are intensely bred and selected for better conditioned ova that can withstand the intense pressure of the triploiding process. Wild fish stock are believed to be slightly harder to triploid because of the greater variability in ova size and membrane strength.