The fish of the Audomarois marsh
Le Saint-Omer and Clairmarais marshes includes a rich aquatic fauna gathering more than 25 species of fish! Carnivorous fish, digger fish, forage fish, white fish, molluscs… Here is a short list of the fish species that are most often encountered in the Audomarois marsh, their way of life, their habitat, their mode of reproduction, their diet… We We have of course added the freshwater mussel and the famous American crayfish which also prevails in our region.
The carnivorous fish of the Audomarois marshes
They hunt like no other, are tough predators... Pike, zander, perch... Here are the teeth of the Audomarois marsh!
The pike
Here comes the most serious predator for marsh fish: the pike. Very recognizable by its elongated body and pointed snout, the pike takes its name precisely from this peculiarity of its anatomy, reminiscent of a spit.
The pike or rather the northern pike is an imposing fish adapting as much to brackish water as to fresh water. It is mainly found in dead water, rich in vegetation (lentic environments). He indeed likes the rivers offering caches in order to be able to hunt in ambush. It breeds especially in floodplains.
Rather solitary (it often moves alone or in groups of 2 or 3), the pike can measure between 30cm and 1,10m, for a weight that can rise beyond 10kg. It has a life expectancy of over 20 years.
The pike is partially protected, due to the decrease in the population. It suffers from several ills, such as pollution, human activity, drainage techniques, excessive fishing and poaching, the artificialization of the banks, the disappearance of nurseries, the eutrophication of water and turbidity. too important of it. We should also note the gradual disappearance of floodplains, conducive to its reproduction.
The spawning period occurs from February to April in water whose temperature is between 5 and 12°C.
Why
Common perch is a species of freshwater fish belonging to the family Percidae. Much smaller than the pike, the perch can measure up to 55 cm and moves in groups to hunt and live (gregarious fish). At an advanced age, the perch asserts a more solitary character. It particularly hunts molluscs, small fish, insects and small aquatic animals. In case of scarcity, it can fall back on plants or consider cannibalism.
Present in many rivers in Europe, the perch was once widely introduced here and there for sport fishing.
This fish likes soft, calm waters and appreciates places where it can hide. To hunt, he is equipped with a real vibration detector, good eyes and an ultra-efficient taste organ.
In terms of reproduction, the perch lays eggs at the end of winter near the bottom or the banks, on aquatic plants or submerged branches serving as spawning grounds.
Zander
Zander is a species of freshwater carnivorous fish that can nevertheless adapt to brackish water. The name Sander comes from the German Zahn meaning "tooth". Its size can vary between 30 cm and 90 cm on average, although some specimens caught have already reached 1,25 m!
If the pike swims and hunts between two waters, the zander prefers deeper waters.
Note that this fish hunts much smaller fish than pike. Indeed, although the pike-perch's mouth is wide, its throat is much narrower. They thus eat a lot of crayfish and forage fish.
Its reproduction takes place in a nest located about 1,5 m deep, from April to June, when the water temperature is around 12 to 14°C.
The zander likes large, slow-moving rivers with sand or gravel bottoms, as well as the calm waters of lakes, ponds and reservoirs — provided the bottom is not muddy and they are of a sufficient depth. The Audomarois marsh is thus an ideal place to live for this carnivorous fish.
Note that although it is rather diurnal, the zander has excellent night vision.
eel
The European eel or common eel is a species of snake-like fish, belonging to the Anguillidae family. The eel can weigh up to 4 kg and measures on average between 40 cm and 1 m (some specimens can be 1,5 m).
It is a migratory fish that will, during its life, pass through environments with different salinity levels. The eel thus migrates towards the sea, in particular to reproduce.
An extremely resistant and hardy fish, the eel is able to breathe the air and accept pollution. However, his body accumulates it and fixes heavy metals and other polluting agents, thus making his consumption highly regulated.
Unfortunately, the eel is now a highly endangered species. In question: pollution, pumping or drainage installations, parasitism, but also and above all overfishing and poaching of eels at the elver stage, in estuaries. It takes nearly 3000 elvers for one kilogram and this dish sells for exorbitant prices in some markets, looking like caviar...
There was a time when eel fishing in the Audomarois marsh was free. A good number of market gardeners have memories of “tufted” fishing trips during stormy summer evenings. Now it's just an old memory...
“White” fish: forage fish, burrowing fish and benthic fish
Here are some species of small common fish as well as the so-called "white" fish. This name has nothing to do with their apparent color, but with their pale flesh. In the kitchen, we generally oppose carnivores to whites whose taste has less character.
Bottom and deep water fish, digger fish
In the bottom of the rivers of the marsh flourish many digging fish, such as carp, tench, bream...
bream
The common bream is characterized by its flat body, small head and protractile (folding forward) mouth. It differs from the border bream thanks to this particularity, but also thanks to its bronze color on the flanks and its gray-green back, while the border bream is rather silvery.
This common fish in the Audomarois marsh measures 30 to 50 cm and has an average lifespan of 20 to 25 years. It lives in groups in calm waters and muddy and loamy bottoms. In this sense, our marsh is perfect for her!
Like carp, this digging fish is benthivorous and filters the sediments it suspends. In this sense, it participates in the turbidity of the water and plays a role in the mixing of the layers of water. The bream also feeds on plants, zooplankton, small molluscs and larvae. In the mud, common bream often rub shoulders with black bream and roach, to the point that it is not uncommon for these fish to mate.
By feeding in the bottom and the mud, the bream can, like any digging fish, bio-accumulate pollutants as well as heavy metals and become poisoned.
Its breeding season is between May and June.
Carp
Like bream, carp are bottom-dwelling, mud-feeding fish (benthivores). By resuspending the sediments to filter them, it tends, like any benthivore, to make the water cloudy (however, twice less than bream). In addition, the carp is omnivorous and feeds in particular on plant debris, molluscs, larvae, etc.
The common carp has an elongated greenish-brown body, thick, often red-orange fins, a cone-shaped head, and a protractile mouth with thick lips and barbels. It measures on average 60 cm for 7-8 kg, but some specimens can reach several tens of kg!
This animal, which was perhaps the first farmed fish in history, is rather nocturnal. He is photophobic (allergic to light). Carp then prefer bottoms, dark areas and are more active at dusk. In winter, the carp buries itself in the mud and considerably slows down its activity. It reproduces mainly from June to July.
The carp is famous for its longevity, (15 to 20 years of average life expectancy), but certain specimens have reached the centenary!
tench
The tench is a freshwater fish belonging to the Cyprinidae family. We meet it quite regularly in the Audomarois marsh.
The tench has an elongated greenish body and mucus-covered skin. It can reach 70 cm. Its mouth is equipped with barbels, allowing it to search the mud. Rather solitary, it spends the winter in the mud, like carp.
It feeds on small molluscs, larvae, plant debris.
The breeding period of the tench extends from May to July, in still and shallow waters, rich in plants.
Other small fish from the Audomarois marsh
the roach
The Roach is a species of freshwater fish that is found in our marsh and is generally called "rock".
This gregarious fish (living in groups) and rather sedentary, has a small size, an elongated body, red fins. Its dorsal fin and its ventral fins are positioned on the same vertical axis.
This fish likes deep waters, but adapts to all circumstances! It can thus colonize small watergangs 20-30 cm deep, the backwaters of a canal in the middle of the city… However, it appreciates the depth in winter and swims on the surface in summer.
Roach is also hardy and resistant to pollution. It thus tolerates polluted water, but also lukewarm water, water with little sediment, brackish water, etc.
The roach feeds on small molluscs, insect larvae, insects that have fallen into the water or collected from the surface, and plants.
Spawning normally takes place between April and July.
the stud
Le stud is a species of small freshwater fish, about fifteen centimeters maximum. It appreciates calm waters, shallow shores, and sandy or loamy bottoms.
The gudgeon is gregarious: it lives in groups and moves in schools
It is a foraging fish that explores the bottom thanks to two barbels placed on each side of the mouth. It feeds on plant debris, larvae, insects, zooplankton, small molluscs...
The gudgeon spawns from May to June, in strong currents and among stones and vegetation. The gudgeon leaks polluted waters. In this sense, his presence is a good omen. It is considered a good bio-indicator of water quality.
bleak
The bleak is a small freshwater fish with silvery scales measuring between 8 and 18 cm. Its life expectancy is 3 to 6 years.
This schooling, gregarious fish feeds on small molluscs, small insects, insect larvae, small crustaceans and plant debris.
It breeds from May to August near the banks and in shallow areas
Stickleback
The stickleback is a small bony fish presenting a priori between 7 and 16 different species. It takes its name from its backbones. The latter serve as protection against predators, which does not prevent the stickleback from being an excellent meal for pike, heron or egret.
The stickleback is a fish that performs small migrations in marine, brackish or fresh water, but its reproduction always takes place in fresh water, from March to July. On this occasion, the male dons bright colors with his green back and red belly, serving as a sort of courtship display.
stickleback
The stickleback has a more slender body than the stickleback and more dorsal spines. It is also a little smaller (9cm max). Scaleless, it has a light brown back and sides with dark spots.
Stickleback spawning season extends from April to May.
Other types of aquatic animals in the Audomarois marsh
crayfish
The Audomarois marsh once had a few native species of freshwater crayfish. But another species took precedence: the rusty crayfish, which was (by mistake?) introduced in Europe around the 1880s. The first specimens would have been introduced in Germany.
The rusty crayfish adapts to many situations and is very resistant. It feeds on all kinds of organic and plant debris, but also small fish like the stickleback! It can also live by filtering plankton. It is active day and night and supports pollution and temperature differences.
Due to its way of life and its attacks, it contributes to the disappearance of the native species of crayfish. In this sense, it is considered a formidable pest.
The anodont or the freshwater mussel
The freshwater mussel or Anodonta is a bivalve mollusc very present in the marsh of Saint-Omer, as in many rivers in Europe.
The freshwater mussel moves extremely slowly along the bottom of rivers. They play a role of water filter by feeding on impurities. In this sense, it fixes pollutants, toxins, heavy metals which aggregate in its tissues and therefore constitute a toxic mollusk.
If humans cannot eat it, it is the delight of many animals in the Audomarois marshes, such as carp, muskrat in winter, coot and great crested grebe.
With a significant life expectancy (more than 20 years), the freshwater mussel can have a considerable size (sometimes a diameter greater than 20 cm). This mollusc has a habit of using fish to hatch its eggs, hiding larvae in their gills. In return, the bouvière, a small parasitic fish, lays eggs in the shell of the anodont, whose blood serves as a meal for the fry.
sources:
Nature in Caps and Marais d'Opale
