The minnow - friend or foe?
Historically, fishing in mountain lakes (especially in the Pyrenees) was linked to a need for food, with fresh fish present near the valleys in large bodies of water far from the sea. Then the fishing leisure developed, with the desire to discover more and more lakes, and to see if at 2500 m of altitude and after 10 km of hiking, a trout or a brook trout will want to take the bait. This has led the fishing federations to continue or initiate stocking operations in the lakes. Nowadays, with your fishing card, you can freely practice this leisure/sport (in the mountains it is quite sporty) during several summer months, and in sumptuous settings. You just have to be careful to respect the regulations (fishing technique used, period, number of authorized catches and minimum size of fish), but I invite you to get information on the websites of the fishing federations which are very well done.
You have already heard about it if you follow Dirk's work, the fish in the mountains are at the origin of new debates in the scientific world. Indeed, and it is necessary to recognize it even if I am a fisherman myself, they are almost always the result of an introduction by man. With many consequences on mountain lakes: predation of insects and amphibians, increase of organic matter (by their excrements) which increases the possibility of proliferation by algae (heat + nutrients = green water, because filled with phytoplankton and microalgae), stress of young tadpoles, etc. The presence of salmonids (trout and char) in some large high altitude lakes is established, and one could imagine finding a balance with amphibians by leaving free laquettes and caches for amphibians. A lot of work needs to be done in the next few years, and fishermen are obviously to be taken into account for their experience and aspirations.
One fish is less unanimous, even among fishermen: the minnow. Small omnivorous fish, it appreciates fresh and well oxygenated waters. Originally native to trout streams and rivers where it is an indispensable link in the food chain, it has been introduced in many mountain lakes.
Photo 1 and 2: Brown trout (Salmo trutta fario L.). Magnificent fish recognizable by its silvery yellow coat, punctuated with large black or red spots. The small fly imitating an aquatic larva is visible in the mouth. Without barb, it is removed immediately and without injury. @A.Firmin
Photo 3 : minnows caught at the lake of Lhurs (64). The fish are immediately killed to avoid any suffering, and frozen to preserve the integrity of the tissues before analysis in the laboratory. @A.Firmin
Photo 4: Adult minnow. Note the mimetic coat of this fish, and the half-open mouth. Its relatively large size and horizontal orientation allows it to capture many preys, both on the surface and on the bottom. @P.Benzi
Photo 5: Male minnow. This is an adult male with white spots on the tip of his head (a feature present only during the breeding season). @P.Benzi
And this often in an involuntary way: it was mounted in small jugs, and was used as bait to catch trout. Before going back down, it was natural to "release" the remaining fish... in the lakes. With a very good adaptability and a prolific reproduction, minnows have thus formed in some lakes impressive populations. Small in size, but very numerous, they have a strong responsibility on the stress of amphibians, the consumption of eggs or the discharge of organic matter. And yet they are so cute to come and tickle our toes when we dip our feet to relax after a hike... It's all a question of balance and point of view!