The largest group of vertebrates is the fish. The vast majority are symmetrical, the exception being the platterslos galloslos hypoglossallos halibutlos turbotlos soles… A group of fish known as pleuronectiformesfrom the Greek pleura (side) and nektos (to swim), since they are flat fish that characteristically swim sideways.
All of them are fish with delicate and tasty meats, which inhabit the seabed (benthos) under cover of their mimicry, being able to blend in with the environment, they are predators that hunt on the prowl (“sit and wait”).
Pleuronectiformes are a very heterogeneous group of fish. While some rely on mimentism to defend themselves against predators, others have certain aposematic features, that is, anatomical features that are interpreted as warning signs, such as the presence of conspicuous ocelli.
There is a wide range in terms of size and weight, which varies from 4 cm in length and a weight of 2 grams, to a size greater than two meters and more than thirty kilos in weight.
Their diet is also very varied, while flounder and turbot feed on smaller fish and have highly developed teeth, others such as sole feed on invertebrates and may lack teeth on one side of the jaw.
pelagic to benthic
The common sole (Solea solea) is approximately one meter long and weighs around three kilos. It is an insatiable carnivore, it feeds on small fish, crustaceans and invertebrates that inhabit sandy bottoms, showing a special appetite for annelids.
These fish are born in the high seas with an oval and completely symmetrical body that in no way suggests what they will become when they reach adulthood. In spring, coinciding with the rise in seawater temperature, soles lose their swim bladder, the organ that gives them buoyancy, and begin a process of metamorphosis, in which thyroid hormones play a fundamental role.
The fry, disoriented, descend to the bottom, becoming a benthic fish, their morphology becomes flat, but not from bottom to top, as happens with the skate, but from the side.
It is precisely this singularity that has led the Jews to know him as «moses fish», since according to legend these fish split in half when separating the waters of the Dead Sea, or that in ancient Rome they were called the sole of Jupiter.
Added to these morphological changes is another no less important one: one of his eyes –the left one- migrates and is located on the right side, in such a way that it loses the initial bilateral symmetry.
On the seabed they remain lying on the left side -the one without eyes-, which gradually becomes depigmented, so the right side takes on a violet-green or brown color, while the left side is whitish.
Highly profitable breeding
Between three and five years the flounders reach sexual maturity. Their form of reproduction is known as diffusion spawning and basically consists of both males and females releasing their genetic material at the same time into a water column. In this way, the profitability of the eggs being fertilized is greater, reducing the possibility of them being devoured by predators.
It is estimated that the females spawn around three million eggs annually, which will give rise to larvae similar to symmetrical fish, with protective spines on the head, on the gills, and on the pelvic and pectoral fins. Thanks to the swim bladder, they disperse from the ocean floor to more superficial regions, beginning a new cycle.