A Fish Known for Its Voice

What fish sings and grunts, is nocturnal, and has the face of a frog?

It is the plainfin midshipman. They are a kind of toadfish. Sometimes called the ‘roaring bullhead’ for their loud vocalizations. They are usually the size of your hand, but grow up to 50 cm or 20 inches.

Recently, at the boat launch construction site, the machines were moving rocks at the waters edge to build the ramp.  The environmental monitor was moving sea stars, and crabs out of the way. Their job is to protect sensitive animals and their homes from the construction work. Under one of the rocks was, a male plainfin midshipman guarding his eggs. The bubbly orange eggs were stuck to the rocky den. Plainfin midshipman lay their eggs in late spring and summer. Not a surprising thing to find, but still exciting!

The Boat Launch Construction site. Plainfin Midshipman eggs were found under rocks on the end of the ramp (left hand side of the image).

Plainfin midshipman live in the pacific from Baja Mexico to central British Columbia. In the southern part of their range they have bioluminescence. That’s right! They glow fluorescent green. The fish use light to attract mates. Light can also help avoid predators. But, in the northern part of their range the glowing effect is not observed. The light organs dotting their body resemble the buttons on a navy officer’s uniform. That is where the midshipman name comes from.

Plainfin Midshipman (photo source: wikimedia commons)

Plainfin midshipman are very noisy fish. People living on the water report the vocalizations of many plainfin midshipman keeping them awake at night. Males make a long humming sound (100hz) to attract females to their den. Females and males will also grunt when fighting or otherwise disturbed.

The females will lay eggs in the male’s den under rocks, in shallow water. The male will stay close to guard the eggs. Laying eggs in the intertidal zone does not seem to be very smart for a fish. During the last few weeks we have had some of our highest temperatures and lowest tides. But the fish and their eggs adapt to the dry conditions. The fish are able to extract oxygen from the air. The males will take care to hydrate the eggs during prolonged time out of water. The eggs take 20-40 days to hatch. Once hatched the larvae remain stuck to the rock where they rest and build up strength. Once mature enough they swim off as juveniles.

On Vancouver Island, bald eagles will feed plainfin midshipman to their eaglets. Many other gulls and herons will also prey on these fish, as do seals and sea lions.

The boat ramp construction at the waters edge has paused. The construction will resume once the eggs are all hatched and the fish finish spawning. The Malahat Environment Department is checking under rocks to see the spawning progress. We have seen many eggs go from orange sacs to empty casings as the fish hatch. It looks like popped bubble wrap on the underside of rocks when they have hatched. Still, there are more males with fresh eggs. By checking on the eggs every few days, we are getting familiar with the many other species that live in the rocks. Sea stars, kelp crabs, red rock crabs, oysters and burrowing cucumbers are a few of the species we have seen. We are learning more and more about the animals that live on the shore in Malahat territory. The more we know the better we can protect them.

Savannah points at Plainfin Midshipman eggs at the boat launch construction site.

If you are at the beach, find a rock, no bigger than your head. Turn it over and see what is underneath. You might find a bunch of crabs but sometimes you will find a fish den and eggs. Have a look and remember to carefully return the rock!

Posted in Environment