Snorkeling with mudskippers?
I have been visiting family in the United States for the past week and although I am very happy to be doing so, I can relate to the title of this blog! The Oxford Dictionary describes a fish as “a limbless, cold-blooded vertebrate animal with gills and living wholly in water”. While there are exceptions to parts of this definition (for example, tunas are warm-blooded fish), it is the last part of the definition that seems incontrovertible. If a fish does not live in water, is it a fish? The answer turns out to be yes.
Mudskippers belong to a unique subfamily of blennies called Oxudercinae (tribe Periophthalmini). Their distinctiveness comes from their ability to breath air through their skin and the lining of their mouth. This method of breathing is called cutaneous air breathing and is common among amphibians like frogs and salamanders. Mudskippers do possess gills, though they do not extract oxygen directly from water the way other fish do; rather they retain a bubble of air within the over-sized gill chamber that they can access when they are submerged. Living on land required more than modifying their approach to breathing; they needed an adjustment to their locomotion as well. Their large pectoral fins are capable of supporting the full body weight of the fish and enable them to walk, crawl, and even climb on rocks and tree roots.
They are commonly found associating with mangroves where they spend most of their active period on exposed mud flats along the shoreline or clinging to exposed branches of mangrove trees. If disturbed, they can make short hops or skips into the water. As an extreme measure of defense, they are capable of twitching their muscles and catapulting – sometimes nearly a meter – away from danger.
Though they spend nearly all of their time on land, mudskippers have not abandoned the sea entirely. They dig underwater burrows along the intertidal mud flats where they lay their eggs. The chambers, however, are immersed in air, and the guarding male fills the chamber with fresh air during each low tide. A fish out of water they may be, but their intertidal burrows and absolute requirement of moist skin keep mudskippers’ close ties to the sea firmly knotted.