My biggest blogging regret last year was not writing more about fish. Ferrebeekeeper has traditionally addressed fish more-or-less exclusively by describing catfish (the order Siluriformes). Only occasionally have I mentioned other sorts of fish–like the bizarre oarfish or the gigantic extinct Leedsichthys, but all of that is about to change! In order to enliven 2015 (and celebrate the extraordinary beauty, diversity, and complexity of the natural world), we are going to write about all sorts of fish from now on! Ichthyophiles rejoice! And, if, for some perverse reason, you do not love fishes—ancient, ancestral, beautiful, and sacred—then Ferrebeekeeper is out to convert you!
To start out on this enormous topic we are starting with an enormous fish—Mola mola, the common ocean sunfish. Some of my American readers may know sunfish as the endearing little freshwater fish which live in ponds and small rivers everywhere. However the ocean sunfish is nothing like bluegills, bass, and crappies (er, except for the fact that it is indeed also a fish). The Mola mola is the largest bony fish in the world in terms of mass. It lives in tropical and temperate waters around the planet ranging from Norway in the north to Patagonia in the south (and continuously east and west). The first time I saw a mola fish I had an unreasoning moment of horror that a huge shark had bitten the poor fish in half! The molidae lack caudal fins—which gives them the appearance of giant truncated heads. To swim, the fish relies on large powerful dorsal and anal fins (although the clavus of the sunfish is a sort of pseudofin). Because of this unique anatomy, the great fish is as taller than it is long. And it can be quite tall indeed: the largest specimens measure 4.2 m (14 feet) from fin tip to fin tip, although they are a more modest 3.3 m (11 feet) in length. The sunfish is very heavily built and weighs up to 2,300 kg (5,100 lb) in mass. Among fish, only the largest cartilaginous fish are bigger.
To reach this prodigious weight, the sunfish is an omnivore. It eats ocean grass, small fish, crustaceans, and mollusks, however, most of all, the great fish feeds on jellyfish and salps (free-swimming tunicates). Adults lose the ability to open and close their mouth–which forms into a beak-like structure (with four teeth fusing into a sort of funnel). Sunfish do not have swim bladders. Additionally, they have only 16 vertebrae, the smallest number among all fish (though not among vertebrates: some amphibians have only a single vertebra).
Adult sunfish are too large for most animals to prey on, however they are sometimes eaten by sharks and killer whales. Sea lions will occasionally tear off sunfish fins for fun and then leave the poor finless fish to die! Sunfish fry are smaller and thus vulnerable to a much greater number of predators. To protect themselves, Mola mola fry take the shape of stars covered with spikes! Just try swallowing a dodecahedron, and you will learn how these creatures survive long enough to become the largest teleosts!
Naturally, the practice of swallowing sunfish has been readily adopted by our own voracious species. Sunfish are eaten by humans in East Asia (although there is an unresolved debate about whether they contain toxins like their close relatives the pufferfish). Additionally they are also threatened by plastic bags, which they eat in the mistaken belief that they are jellyfish, and by fishers who catch them accidentally and then throw them away dead as by-catch. Because they are primarily pelagic (living in the deep ocean) their numbers have never been accurately calculated, so we don’t know if they are endangered (!) but there are certainly far fewer these days than there used to be.