You can find out more about the fish of Lake Geneva in the following issues 20, 92 and 112 of our quarterly magazine Lake Geneva region as well as in our News in 60 seconds. You can find all these fish at home thanks to our poster The native fish of Lake Geneva.
Everyone has seen fish, but very few people are familiar with the fish of Lake Geneva. Except perhaps those that we find on our plates, such as perch, trout, pike or whitefish (Féra). However, there is a wide variety of species in the lake.
Fish don't have it easy. The shores of Lake Geneva are highly urbanised, with many towns on its banks, and the development of the lake's banks has led to the disappearance of valuable habitats. The quality of the water, polluted in particular by microplastics and micropollutants (pesticides and other chemical products) can also affect it. The lack of trees surrounding the banks of lakes and rivers increases the water temperature and limits the number of hiding places for fish. As a result, fish are more exposed to predation by birds. Fishing also takes its toll on fish for human consumption. Climate change could also have an impact on water temperature. Many species cannot tolerate water that is too warm and less oxygenated. The rise in temperature also encourages the proliferation of disease. Winters that are too mild mean that the lake water is no longer able to circulate during the winter, which prevents oxygen from circulating in the deeper strata. All these factors, and there are many more, are making life difficult for fish, and some populations are declining at an alarming rate.
Fortunately, there are many projects to improve the quality of life for fish, such as the redevelopment of natural riverbanks. Improvements to sewage treatment plants and bans on certain toxic products are also helping to improve water quality and allow plants to grow again, providing breeding grounds, hiding places and food for fish.
Fish are adapted to life in water: among other things, they have fins to... swim and navigate in the water, mucus-covered scales to glide through the water, gills to breathe by capturing the tiny air bubbles around them and a swim bladder that allows them to float in the water without having to swim actively.
Fish reproduce externally, i.e. the female lays her eggs, which are then covered with the male's semen. The eggs may be laid in gravel (trout) or under stones (sculpin), stuck in aquatic vegetation (perch) or released into the water to settle on the bottom (whitefish).
The eggs hatch according to the water temperature. During the early stages of their lives, fish larvae, known as fry, have a yolk sac, a pocket of food that they gradually consume. Once the sac has been consumed, they will have reached a size that allows them to feed in the environment.
The location of the mouth tells us where the fish feeds. The presence or absence of teeth provides information about their diet. A forward-facing mouth will be used to catch other prey, such as smaller fish, or to feed on aquatic plants. An upward-facing mouth is used to capture insects on the surface of the water. A mouth pointing downwards will be used to rummage through sediments and stones to catch small animals or plants living there.
Each fin plays a very specific role for fish. The dorsal fin helps to keep the fish stable vertically and prevent it from rolling. It helps it to turn and stop suddenly. A fish can have several of these, up to two for the fish of Lake Geneva! The tail fin is located at the end of the fish's tail. This powerful fin enables it to displace a large volume of water and thus propel itself forward. The anal fin is located under the fish after the anus and completes the stabilising effect of the dorsal fin. The pectoral fins correspond to our arms! Always in pairs, they act as swimming stabilisers for vertical movements. Depending on the species, their shape can vary greatly. They enable some fish to walk (anglerfish, sea fish). The ventral/pelvic fins correspond to our legs. Also in pairs, they work in tandem with the pectoral fins in vertical movements and stabilise rapid changes of direction. They also enable the fish to slow down or brake. Finally, the adipose fin is absent in many species, but is mainly found in Salmonidae such as Trout and Arctic Char.
♣ Species present in our book of determination sheets (sold in our shop)
Carp can be recognised by their long dorsal fin, well-defined scales and two pairs of barbels (small whiskers that allow them to touch the environment around them).
It is the oldest fish species domesticated by humans: traces of breeding dating back to the Neolithic period (14,000 years ago) are known. ♣
Tench have a humped back, a trapezoid tail and a pair of barbels (a kind of small whiskers that allow them to touch the environment around them).
Elle vit en solitaire et peut s’adapter facilement à son environnement. Elle hiberne en hiver en s’enfonçant dans la vase. C’est un poisson qui supporte mieux que la plupart des autres poissons de faibles quantités d’oxygène. ♣
The Chevaine has a slender, elongated body and large scales embroidered with a dark border. The young live in shoals, but the adults are solitary. A 35 cm female can lay around 40,000 eggs, with record clutches of up to 100,000 eggs. ♣
Le Gardon possède des nageoires orangées, la nageoire dorsale étant alignée sur les nageoires pelviennes. Il se reconnait également à son œil rougeâtre. Il montre un curieux phénomène d’inversion sexuelle ; en vieillissant, les mâles se transforment en femelles. ♣
The perch is easily recognised by its seven vertical stripes and its highly developed, spiny first dorsal fin, which it erects in the face of danger to dissuade its predator from attacking it.
Les jeunes vivent en bancs, les adultes sont solitaires. ♣
The Pike's body and head are elongated and its dorsal fin is small and set far back, giving it great power in the water to catch its prey.
Il guette ses proies, caché dans la végétation, sa mâchoire peut contenir jusqu’à 700 dents acérées, une fois une proie capturée, elle n’a aucune chance de s’échapper. Le Brochet peut vivre plus de 30 ans ! ♣
Le Silure possède un corps cylindrique et allongé avec une longue nageoire anale qui s’étend sur plus de la moitié de son corps. Sa tête est large et aplatie avec un large bouche entourée d’une paire de longs barbillons (sorte de petites moustaches qui lui permettent de toucher l’environnement qui l’entoure) sur la lèvre supérieure et de deux paires de barbillons plus courts sur le menton. Le Silure ne possède pas d’écailles. La femelle dépose ses œufs dans des cuvettes creusées dans le sol ou des nids dans la végétation et c’est le mâle qui garde la ponte.
Le Silure a été introduit dans le Rhône, vraisemblablement pour la pêche sportive, avant de colonisé le Léman. Il s’agit donc d’une exotic species. Its large size makes it a difficult animal to extract from the water. Its flesh can be eaten, but it is mainly its performance that interests the fishermen who catch it. Little by little, it colonised the whole of Lake Geneva, eating large quantities of other lake animals. ♣
Le Corégone présente un corps fuselé terminé par une petite tête et de petites écailles argentées. Le Corégone est un salmonidé, il possède donc une nageoire adipeuse. La Féra ayant disparu du Léman, notamment à cause de la surpêche, une « nouvelle » Féra, un Corégone provenant essentiellement du lac de Neuchâtel, a été réintroduit par l’humain. ♣
Trout are born in rivers, some staying there for the rest of their lives, while others go down to the lake to live and only come back up in winter to reproduce in the same waterway where they were born.
River trout (fario) and lake trout (lacustrine) adapt to their environment. Lake trout have room to grow and an abundance of food, and can become very large (50 to 70cm). Their colour is silvery with lots of black spots. A member of the Salmonidae family, it has an adipose fin. ♣
L’Omble est un poisson sombre avec des points plus clairs. Son ventre est blanc à rougeâtre et devient orange vif chez les mâles lors de la reproduction. Le bord antérieur de ses nageoires pectorales, ventrales et anale est généralement blanc brillant.
Comme les autres Salmonidés, il possède une nageoire adipeuse. L’Omble apprécie les eaux bien oxygénées et transparentes, il n’aime pas l’envasement. L’Omble se reproduit dans les profondeurs du Léman, entre 50 à 120m de profondeur. ♣
The barbel has a streamlined, almost cylindrical body and a flattened belly. It has a long snout, a mouth that opens downwards and is bordered by two pairs of barbels (a kind of small moustache that allows it to touch the environment around it). It feeds on small animals living in the sediments and bottoms of lakes and rivers, on the eggs of other fish or on organic waste.
Barbets spend the winter in a form of hibernation, in small groups. They are great travellers, and distances of over 300km have been recorded.
Grayling are easily recognised by their very large dorsal fin. Like other Salmonidae, it has an adipose fin and is silvery-grey with small black spots. This fish is very sensitive to pollution and high water temperatures. Grayling like the mouths of streams, where they alternate between rivers and lakes.
The body of the Bremen is tall, humped and very compressed laterally. Its anal fin is long and its tail is indented. It is a gregarious fish, meaning it likes to live in groups. Breams breed in large groups in dense vegetation.
The eel is a serpentine fish whose dorsal, caudal and anal fins form a continuous band. Eels hatch in the western Atlantic and migrate for 3 years as larvae towards the coasts of Europe. They then transform into glass eels (juvenile stage) and migrate upstream. They live for 5 to 12 years in lakes and rivers with slow currents.
After this stage, they transform into silver eels, stop feeding and return to the Sargasso Sea to reproduce. Eels have not been seen in Lake Geneva for a long time, but perhaps they are still hiding in our waters...
The monkfish is an elongated fish with a broad, flattened head with a long chin barbel and two very short nostril barbels (a kind of small whiskers that allow it to touch the environment around it). Its dorsal and anal fins are very long.
It likes cool, clear, oxygen-rich water. It can be seen under shipwrecks where it likes to hide.
The Rotengle is a rather tall, laterally compressed fish. Its pelvic fin is further forward than its dorsal fin. The outside of the ventral, anal and caudal fins are bright red. It lives in small schools and likes vegetation. In winter, it overwinters in deep water. Adults die after breeding.
The Vandoise is a small fish with a slender, almost cylindrical body. Its anal fin is concave. It lives in schools and swims very quickly. It needs clear, pure water.
The Ablette is a small fish with a laterally flattened body, an upward-pointing mouth and a long anal fin. They live in large shoals close to the surface. They are not very sensitive to lack of oxygen or pollution. Its scales, silvery and shiny but also easily deciduous, were used to make pearls.
The Spirlin is a small fish with a laterally compressed body, a long anal fin and a forward-pointing mouth. It likes very clean, oxygen-rich water and lives in small groups.
The Gudgeon has a cylindrical body and a long snout surrounded by a pair of short barbels (a kind of small whiskers that allow it to touch the environment around it). It can adapt its colour to the environment! It lives in small shoals on the bottom and eats small organisms in the sediment and organic waste. In winter, they migrate to deeper areas.
The minnow is a small fish with a cylindrical body and large eyes. Its scales are very small. 
It lives in clear, oxygen-rich waters, in shoals and close to the surface.
Small fish with a frog-like head and large fan-shaped pectoral fins. A bottom-dwelling fish. The female sticks her eggs under stones and the male guards them until they hatch. The sculpin has no swim bladder enabling it to float, which is why it lives at the bottom of the water.
The Red Loche has a cylindrical, elongated body and three pairs of barbels (a kind of small whiskers that allow it to touch the environment around it). It is covered in dark mottling. The Common Loche is active mainly at night. The male guards the eggs until the fry are free-swimming.
We look forward to seeing you in January to continue our work, share useful knowledge and work together to protect Lake Geneva. Your loyalty and commitment give our mission its full meaning, and we'd like to offer you our sincerest thanks.
