16. May 202216. May 2022

Species of the week #101 – Mud loach

“Stormfarter” is a somewhat disrespectful nickname for the Mud loach, which is also called weatherfish. These names refer to a very special characteristic – accessory intestinal respiration. The mud loach stretches its mouth above the water surface and swallows air. It can absorb oxygen through its intestinal mucosa, which has a strong blood supply. The used air is released through the anus and produces a squeaking sound. Since it can sense the slightest fluctuations in air pressure, it becomes restless when a thunderstorm is approaching and appears whistling and bubbling on the surface of the water. The accessory intestinal respiration enables the mud loachs whiptail to survive prolonged periods of heat or drought unscathed. It buries itself in the mud and stops gill breathing. Thus, this unusual ability is a real survival advantage.

Distribution status in Rhineland-Palatinate	Threatened with etxtinction
Remaining occurance	Poland, Hungary, Estonia, Latvia
Last sighting in Rhineland-Palatinate	2020 near Heßheim
Habitat	warm, shallow waters with dense vegetation
Threat	Bare banks and ditches, drying out of floodplains, pesticides,

The mud loach is largely insensitive to water pollution and can sometimes be found in heavily polluted waters. Its snake-like body, flattened laterally in the tail region, reaches a length of 15 to 30 centimetres. The caudal fin is rounded. The brownish-orange body is decorated with dark and light longitudinal bands. The skin is slimy with very small round scales. The underside of the mouth has 10 barbels.

Mud loaches are very nocturnal. They feed on a variety of invertebrates such as worms, insect larvae, small crustaceans, mussels and snails. The barbels make it easier to find food on the ground. During the day, the fish usually bury themselves in the mud, up to 70 centimetres deep as the water depth decreases and in winter.

Despite many survival advantages, the species’ population is now in sharp decline. Drainage and “optimisation measures” have converted many suitable small water bodies into intensively used agricultural areas. The draining and silting up of marshes, Rhine oxbows and floodplains means habitat loss. Drainage ditches are potential replacement habitats, but they are subject to considerable development and maintenance measures. Due to the hidden habitat of the mud loach, damage is often caused by clearing and weeding with mechanical trenchers, which also remove the fish buried in the mud. It can survive where ditches are less “properly” maintained or are still weeded by hand in the traditional way. Rock fills on the banks, which later cover the entire river bed, also affect the old fish population. Pesticides and heavy metals can additionally damage the species despite its high resistance to chemical stress.

Annual stocking measures are carried out to restore the species to a good conservation status. For this purpose, mud loach larvae are reared in spring in the Ecosystem Research Branch of the University of Landau, the Eußerthal facility, and released into suitable regional waters after a few weeks.

In order to conserve the mud loach, its habitats and remaining occurrences in protected areas must be safeguarded as a matter of priority. Occurrences or plant-rich ditches should be protected against drift and input of agrochemicals by wide unused riparian strips.

Political necessity:

– Conservation and targeted management of habitats

– Conservation and rewetting of floodplains

– Wide riparian strips

Photo: Eußerthal Ecosystem Research Facility, University of Landau

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