Is a fish amphibian

info fauna
Coordination office for amphibian and reptile protection in Switzerland (karch)

The topic of fish and amphibians is always a topic of discussion. Amphibians are on the menu of many fish species. Literature research shows that the following fish species have been shown to have a predation against amphibian larvae, eggs or adults: Predatory fish such as perch, trout, arctic char, brook trout, pikeperch, sunfish, pike, dwarf catfish, but also species such as sticklebacks, minnows, tench, rudd, roach , Alet, eel, carp and goldfish.

In principle, amphibians are an important link in the food chain not only for fish but also for birds and mammals. Naturally, this does not endanger their populations. Amphibians have developed strategies against excessive negative effects such as large numbers of spawning, hiding eggs, swarming of larvae, morphological adaptations, etc. The predation pressure is not the same for all amphibian species.

The common toad is least affected. Eggs, larvae and adults do not seem to be popular with the fish for reasons of taste. Effects on common toad populations have only been demonstrated when there is a shortage of food and a lack of structure. Common frog larvae and eggs, on the other hand, are frequently and gladly eaten by most of the fish species examined. The same applies to the mountain newt. Free-swimming larvae such as natterjack toad, yellow-bellied toad, tree frog and newt (adults and larvae) are strongly affected by predation. In the crested newt and tree frog, fish stocks are listed as one of the main causes of the sharp decline in species in parts of Europe. An assessment of the magnitude of the negative effects must always be made taking into account the local conditions.

The introduction of non-native species into a naturally fish-free body of water poses a threat to local amphibian populations.

Under certain conditions, fish and amphibians can coexist
The common habitat must consist of a larger body of water (small lake) with well-developed siltation zones, rich vegetation, good food sources and a natural density of fish. If the structures are sufficient, stocking with game fish can also be coped with, as shown, for example, by most of the Mittelland lakes.

But there are situations in which the predation pressure is too high - the reproductive success can no longer compensate for the losses. The greatest conflicts between amphibians and fish arise in waters that used to be naturally fish-free.
A distinction can be made between two cases: The first case, the introduction (intentional or unintentional) of fish in naturally fish-free small and micro-waters with an abundance of amphibians. Since this type of water is neither intended to be used for fishing nor to protect rare small fish, the fish should be completely eliminated as quickly as possible. The only suitable means is to pump out or drain the water, if possible for several weeks in winter. Other measures such as electric fishing and releasing pike are not recommended. The former only causes a short-term decimation despite a great deal of effort. The second measure also only leads to a reduction in fish stocks. In addition, the amphibians also suffer from this predatory pressure. In addition, more targeted education of the population is needed so that in the future no more fish are used in the mentioned water types.

The second case, the introduction of fish in naturally fish-free, larger bodies of water for the purpose of exploitation for the fishing industry, gives more cause for discussion. Take mountain lakes, for example: in many cases, mountain lakes are or were naturally free of fish. Such bodies of water have been stocked for a long time, but have increased in recent years. Species of fish that are particularly interesting for anglers, such as char and trout, are used, i.e. species that exert great pressure on amphibians. In addition, the population density is kept relatively high so that the anglers have a chance of success. The waters are often poor in structure with little hiding place for amphibians. Due to the low water temperature, they are not very productive and there is a shortage of food. The effects on the amphibian populations must therefore be classified as very large. Concrete studies from the USA and Italy confirm this statement. The damage is usually not only shown by the extinction of certain amphibian species in a region: In the mountain lakes there are also other fauna and flora elements that have been specially adapted to the alpine conditions and that can suffer from the fish.

A second example is the use of small rivers as trout rearing waters. Fire salamander or midwife toad larvae usually disappear after a short time in such cases. The habitat available, which has already been massively reduced by the drifting in of many rivers, is being further restricted for these amphibian species.

What can now be done to avoid negative effects on amphibian populations?
According to the ordinance to the Federal Law on Fisheries, the stocking of rainbow trout in hydrologically closed waters, in mountain lakes and alpine reservoirs without free fish migration is permitted; a permit is not required. The first step is to inform the groups of people affected about the problem so that exposures are voluntarily refrained from in the future. In the case of stocking plans, it is advisable to contact the karch. Using the distribution database or targeted inspection, it is easy to clarify in many cases whether and which amphibians are present.

The effects on amphibians can be estimated on the basis of the existing range of species in the affected and closest waters. Based on this, it can be decided whether a stocking is responsible and whether compensatory measures such as alternative spawning options are necessary and possible. Any measures must be taken before a local population, possibly an ecotype, has disappeared. Depending on the spawning water density, repopulation of a region is difficult. Even if no amphibians are affected, one must be aware that indigenous, possibly protected or protected species can still be affected.

The common toad seems to be the only species that can handle fish in the water

Project study on the occurrence of fish in small bodies of water
Under certain conditions, fish and amphibians can coexist. But when fish appear in small bodies of water that were originally fish-free, amphibian populations can be decimated or even made to disappear. How fish can get into water is currently a controversial issue. One theory is that fish eggs are carried away by ducks. It can also happen that the fish migrate through streams and canals.

We tried to find out with a small survey how often fish appear spontaneously in small bodies of water. A summary of the results of a survey can be found in the download area on the right. We would like to thank everyone who filled out the questionnaire!