On the hunt for a real oddball? Look no further than the quirky freshwater flatfish, writes Chris Sergeant.
FROM A MORPHOLOGICAL standpoint, some of the most unusual fish have to be the flat ones. This can occur from both directions, with individuals compressed dorso-ventrally (from top to bottom), or laterally (from side to side), and there are benefits to each. Dorso-ventrally compressed fish (or depressiforms), are typically benthic-dwellers, and have utilised their shape to keep a low profile. Many often deploy a coat of camouflage, adapting their colouration to match the substrate around them, or failing that, a flick of their flattened form and they can disappear beneath a shower of sand or mud. The ocean supports more than its share of depressiform fish, with elasmobranchs in the form of angel sharks, wobbegongs and a host of rays and skates being the most obvious, but crocodile fish and monkfish also sport such flattened contours.
Then there are Pleuronectiformes, or flatfish to you and me. Appearing flattened from top to bottom, this group of plaice, soles, flounders, dabs, halibuts, and turbots, are laterally compressed, meaning that they lie and swim on their sides. Characterised by their bizarre, oval-shaped bodies, Pleuronectiformes are asymmetrical oddities, with the clue being in their name: ‘pleura’ meaning ‘side’ and ‘necto’ meaning ‘swim’ in Greek. In contrast to the depressiforms, fish that are flattened from left to right are known as compressiforms, with this body design more typically associated with reef-dwellers like angelfish, whose deeper body shape enables them to manoeuvre through complex reef structures at speed. In the case of flatfish, they have opted for a more sedentary lifestyle in the demersal zone, reclining on their side.
Now, as a nation of prolific fish consumers, you might typically associate flatfish more with the dinner plate rather than undulating across the substrate at your local aquarium stockist. Not only that, but seeing as those edible species of flatfish found in your local chippie will have been harvested from the sea, it’s easy to assume that they are marine only too, but rest assured for those that lack a full reef set-up, there are some alternatives.
Freshening up
It is important to note that the term ‘freshwater flatfish’ can be misleading. As with numerous other ‘freshwater’ fish traditionally associated with marine environments, some of them come with the caveat that they do need a little (and somet
