Egg Collection:
As rainbow darters lay their eggs in the substrate, finding the location of the eggs for collection can be tricky.
Step 1: A gravel siphon is used to siphon all the substrate in the tank, and a small net at the end of the hose is used to collect anything removed from the rocks.
Step 2: The collection net is removed and sorted through to separate any eggs from the fish waste.
Step 3: Eggs are placed in a petri dish and checked under a microscope for fungus. Fungus can be detected if the egg is white in color rather than clear with a defined yellow yolk spot.
Step 4: Eggs are treated with Maroxy, a fungus treatment, and left to sit for a few minutes.
Step 5: Eggs remain in the petri dish and are placed at the bottom of a basket that hangs on the side of the tank.
Step 6: It takes approximately 10 days for the eggs to develop and hatch (see right).
Raising Fry:
Once the 10 day incubation period is over, eggs will begin to hatch. Hatchlings are approximately 1 cm in length, and are no wider than a needle. They are clear in coloration and practically invisible to the naked eye.
Photo by Kristi Harraman, OSU
They remain in the egg basket to protect the newly hatched fry from the adults in the tank. Initially, they are fed solely Artificial Plankton Rotifer (APR) powder until they are large enough to consume newly hatched brine shrimp, called nauplii. At approximately 3 days of age nauplii are introduced along with the powdered food until the fry are about 3 weeks old, when APR powder is gradually phased out of their diet. Fry will eat nauplii until they are large enough to eat adult brine shrimp at approximately 3 months of age.
Photo by Kristi Harraman, OSU
Fry are kept in a unit called a Benchtop AHAB (see above image) in separate tanks according to age and size. These tanks each have their own water input valve, and water flows through the tanks and out the back of each to a common sump, where the water is filtered and recirculated throughout the system. Because darters are river-dwelling fish, the flow to the tanks is kept fairly high.
Juvenile Rainbow Darter, approx. 23 weeks old, 1 1/2 inches long:
Photo by Kristi Harraman, OSU
When they are a year old, they have reached approximately 1/2 - 3/4 of their adult size. They are now ready to be utilized by the mussel project.