Ask anyone for a list of five fish species and there’s likely to be a tuna among them. This fame is of course not entirely unrelated to the fact that we consume it in rather large quantities, which has led to a serious decline in tuna stocks around the world (making the old nickname “common tunnyfish” somewhat less fitting nowadays). What few people realise, however, is that the tuna is one of the top predators of the oceans, right up there with the big sharks and toothed whales. Continue reading “Weekly Water Critter – The Tunnyfish”
After some soul searching I have recently decided to expand my territory from weekly fishes to weekly water critters in general, for the seas, lakes and rivers of the world are filled with too many amazing animals to just limit myself to the scaly ones. And what better way to start than by presenting one of my favourite animals of all time, the little marine sea slug Glaucus atlanticus. Known by various wonderful names including sea swallow and blue dragon, this stunningly beautiful creature employs one of the most nifty acts of thievery in the animal kingdom. Continue reading “Weekly Water Critter – The Blue Dragon”
Fishes can be quite slippery. Slimy even. Grabbing hold of one can be rather challenging. There are exceptions of course, sharks for instance are famously unslippery (though one might be wary of grabbing a shark for reasons of personal safety). At any rate, fish-eating fishes have had to deal with the problem of slippery prey for ages, and have come up with two main solutions. The first is suction-feeding, where the predator creates negative pressure in its oral cavity to suck in and swallow its prey, thus avoiding the need to grab onto the slippery victim. The other is to use teeth. Lots and lots of teeth. Continue reading “Weekly Fish – Choking Fish Syndrome (Fish Maws Part III)”
Fishes are a bit unsubtle when it comes to teeth. In their various grabbing, biting, crushing and grinding exercises, many fishes employ teeth not just in their jaws, but also elsewhere, such as on the palate or their gill arches. Indeed, the gills can play an important role in moving food from the mouth down into the stomach. Many fishes have these so-called “pharyngeal jaws”, but it is only in the moray eels that they are truly worthy of the name.
Continue reading “Weekly Fish – The Four-Jawed Moray Eel (Fish Maws Part 2)”
Most mammals and birds have fairly straightforward mouths; two jaws with single rows of teeth (or none in most birds) and a single joint that lowers or raises the lower jaw, thus opening and closing the mouth. Fishes, however, show a truly staggering diversity in the way they use their mouths, so the coming few weekly fishes will concern fishes with distinctive ones. First up, the most gaping maw of them all. Continue reading “Weekly Fish – The Gulper Eel (Fish Maws Part 1)”
It is hard to think of a fish that is more mundanely everyday than the goldfish, but this was not always so. When the little golden carp was introduced in Europe in the 18th century, it enjoyed several decades of exalted status among the well-to-do. Known initially as the “kin-yu”, it was imported from China by the British and slowly but steadily made its way through Europe. Early reports from colonists had described it as a very fragile fish (shaking a bowl of goldfish would kill half of them, they said) that was extremely hard to breed. Once introduced to Europe, it was soon found that the goldfish wasn’t all that fragile, and actually really easy to breed, so it soon took over the continent and lost most of its exotic allure. Continue reading “Weekly Fish – An Ode to the Goldfish”
Fins can be modified in striking ways, as illustrated by the (rather cute) Remora, or suckerfish. Its modified, flattened dorsal fin functions as a sucking disc, creating a vacuum that allows the fish to attach itself to its host, usually on the belly or under the gill covering. Remoras are often specialized in particular host types. Thus, whale suckers cling to whales, marlin suckers have a strong preference for marlins, and shark suckers (you guessed it) are usually found on sharks. Often multiple Remoras attach to the same host animal, who can even be a meeting place for mates. Indeed, hosts have been found with a male Remora under one gill covering, a female under the other. Continue reading “Weekly Fish – Why Remoras Suck”