Archives for April 2013

Fry Update – April 2013

As of this morning, all of our chum fry have been ponded – around 60,000 of them in total!

Ponding is a process of introducing swim-up fry to food once their yolk sacs have been absorbed. At this stage, their swim bladders should be developed so they can move up and down in the water column easily. Before ponding all of the fish, we test to see if a sample will rise to the surface when placed in a bucket. We then feed them a little bit of size zero feed, which is so small that it floats until they peck at it. Floating food elicits their inquisitiveness, and when they find out it’s edible they eat it all up! If it’s not to their liking though, they will spit it back out.

After determining that a particular batch of fish is ready by the above-outlined method of “pre-ponding”, we transfer trays of fish to a larger container. Our trays, troughs, and tubs all have flowing creek water to ensure the fish get enough oxygen and waste gets transported out of their living space. It also gives them a scent to hone in on for when they’re adults.

Salmon are special because they start off in streams, head to the ocean, and return to the same stream when they’re ready to breed. This makes them anadromous, like the three-spined stickleback that can also be found locally. Most aquatic animals live in either fresh water or salt water their entire lives because the two environments require vastly different mechanisms of managing internal salt concentrations. Switching between the two is quite taxing, and is one reason why returning adults can look tired and battered around spawning time.

When collecting eggs from female adults, we cannot force synchronous release. This is why our coho fry have varying age groups and different sizes. While most of the coho have also been ponded, today a single tray remains. These fish are nearly fry, but still barely alevins. That is to say, most of their yolk sacs have been absorbed. Temperature influences the speed of metabolism, so warmer water encourages them to “stitch up” faster. We call it this because yolk sacs shrink until they disappear into their belly. The resulting red line on their ventral side looks like a stitched gash becoming smaller and smaller.