mud-scooper

Mudskippers are freshwater fish that belong to the order Cypriniformes and, within that order, to the family Loachidae.

• Length: 15–30 cm, making it the largest native loach species
• Life expectancy: up to 20 years; reaches sexual maturity at 3–4 years

The mud minnow has an elongated, eel-like body that is almost circular at the front and flattened laterally toward the rear. Its body is yellowish-brown in color, with the darker back becoming lighter toward the belly. Its sides feature distinctive brown longitudinal bands with many small dark spots.

The skin is covered by a thick layer of mucus; the tiny scales are barely visible. The caudal fin is rounded. The dorsal, pelvic, and anal fins are set far back.

The small mouth is subterminal and is surrounded by 6 longer barbels on the upper jaw and 4 shorter barbels on the lower jaw.

Mudskippers exhibit very distinct sexual dimorphism. Males are generally smaller, and their pectoral fins are longer and taper to a point. In addition, the second fin ray is thickened. Especially during the spawning season, males can be easily distinguished by the distinct, reddish lateral ridge between the dorsal and anal fins (spawning ridge).

The range of the mud minnow extends across Central and Eastern Europe and Western Asia, roughly from the Loire River in France, along the northern ridge of the Alps, to the Volga River basin. The fish is absent from Scandinavia, the tributaries of the Arctic Ocean, and the Mediterranean region.

In Austria, the species is primarily found in the eastern part of the country, with significant populations in the March and Thaya river basins (March floodplains, Alte Thaya), the Danube floodplains, and the Lake Neusiedl region.

The native habitats of the mud loach are natural, still or slow-flowing bodies of water (e.g., pools, ditches, and cut-off meanders, oxbow lakes, ponds, or bog waters, and floodplains) with soft, muddy bottoms, into which this nocturnal fish burrows during the day.

Mud minnows have a special adaptation for these often oxygen-poor freshwater habitats. With their highly vascularized intestinal mucosa, they can absorb oxygen from the air they swallow. After passing through the intestines, the air escapes through the anus, emitting a whistling sound—which has earned the species the nickname “fart minnow.” Since mud minnows frequently rise to the water’s surface to gulp air—especially when atmospheric pressure changes, such as before a thunderstorm—they are also known in some regions as “weather fish” or “thunderstorm farters.” This special adaptation also enables them to make short land migrations when the threat of drying out looms.

During periods of temporary drought or in winter, mud minnows burrow up to half a meter deep into the mud and reduce their metabolic rate to a minimum. In this state, they can survive adverse conditions for up to a year.

Mudskippers primarily forage for food on the bottom of bodies of water. They eat invertebrates such as snails, insect larvae, crustaceans, and mussels. However, they also eat algae and detritus, and will even eat small fish or their eggs.

Mud minnows reach sexual maturity at the age of 2–3 years. When water temperatures rise above 16°C in April, the spawning season begins. It lasts through July. Optimal water temperatures for the larvae range from 19°C to 23°C. During spawning, the females (spawners) are tightly embraced by the males (sperm producers). In several spawning sessions, the females lay 4,500–13,000 sticky eggs, each about 1.5 mm in size, which are usually attached to aquatic plants or may sometimes lie freely on the bottom of the water body.

Similar to the larvae of caudates (salamanders and newts), these larvae also have external gill filaments, which are covered by a gill cover during metamorphosis. This allows them to make better use of the often low oxygen levels in their preferred habitats.

In the past, the mud loach was found in all federal states except Vorarlberg, Tyrol, and Carinthia. Today, according to the “Red List of Fish in Austria,” it is classified as “critically endangered.” In the 2020 Austrian Report on the Conservation Status of FFH Species (Fauna-Flora-Habitat species) and Habitat Types, the conservation status of the mud minnow is listed as “unfavorable to poor.” The primary causes of this are habitat loss due to river engineering, the separation of floodplains from main watercourses (e.g., through riverbed deepening and climate change), and intensive agriculture.

The protection of floodplains through concrete restoration measures and the reestablishment of dynamic river landscapes, the replenishment of floodplain waters, and the stabilization of the riverbed are necessary to preserve the mudminnow population for the future.