How do you weigh a Japanese giant salamander?
We have a little tub that we put them in, and that goes on a scale. It’s a really quick process. We use a net to get them out of the water and into the tub, weigh them and then gently ease them back into the water. They do have sharp teeth and can bite really hard, so we are very careful to stay away from the head. We also work quickly so they don’t get too agitated.
Has the Zoo had success breeding Japanese giant salamanders?
Not yet, but we are always trying new things and think we are getting closer every year. Honolulu Zoo was the first to get eggs in a North American zoo. That was last year, but the eggs didn’t develop. Male Japanese giant salamanders grow faster than females, so our males are already sexually mature. Females reach sexual maturity when they are about 23.5 inches long. Our females are 18.8-20.5 inches now and still growing.
What are some of the challenges?
Honestly, it’s replicating the water that is found in their wild streams. Asa Zoo in Japan, where they have the most success breeding, has something called an “open system.” It uses water from the streams where the animals are naturally found. We use a temperature cycling system and play with different water levels. In seasons when there would be heavier rains in Japan, we raise the water level. When it’s warmer and drier, we lower the water level. We are trying to trigger them with the same cues that they would have in the wild, without any interference from keepers.
Trying to do that artificially is very challenging, but hopefully we will find the right recipe. We also try to replicate their underwater den sites where breeding takes place and the eggs are laid and fertilized. In the wild, den sites would be rocks and caves. Our artificial dens are basically hollow PVC tubes that lead to upside-down flowerpots. They are based off what our colleagues at Asa Zoo use. Our salamanders will also shack up in the dens and use them as a lounge spot. Japanese giant salamanders are nocturnal, so they pretty much sleep all day.
What does their typical breeding season look like in the wild?
The breeding season starts in July and has been recorded going as late as November. Each den site has one big, dominant male who is considered the den master, but multiple females will come in and out to lay eggs. They each lay about 400 to 600 eggs, and the male fertilizes the eggs. Different males will also sneak in to participate in that process, but the den master is ultimately the top dog of that space.