Wels catfish
Silurus glanis
The Wels catfish is a large predatory fish with an elongated, scaleless body and a broad, flat head. It is characterized by two very long barbels on the upper jaw and four shorter ones on the lower jaw, which serve as sensory organs. Its coloration varies from dark gray to olive green, often with lighter, mottled flanks and a whitish belly.
Details
Identification
Scaleless body, very long anal fin, two long barbels on the upper jaw, four short ones on the lower jaw, small eye diameter.
Social behavior
Predominantly solitary and territorial, but sometimes forms groups in deep pools during the cold season.
Diet
Opportunistic carnivore; feeds on fish, crustaceans, amphibians, waterfowl, and small mammals.
Hunting strategy
Ambush and active nocturnal predator that sucks in prey by suddenly opening its mouth (suction-feeding mechanism).
Spawning substrate
Plant roots (especially willow roots), aquatic vegetation, or shallow pits prepared by the male.
Overwintering
Winter dormancy in deep, low-current water sections with a significantly reduced metabolism.
Ecology
Ecological role
Apex predator in the aquatic ecosystem; regulates populations of cyprinids and removes sick animals.
Natural predators
Juveniles are preyed upon by pike, zander, or otters; adult Wels catfish have almost no natural predators.
Competitor species
Northern pike and zander (especially during juvenile stages regarding food and habitat).
Ecosystem service
Biological control of invasive fish species and contribution to the nutrient cycle.
Threats
River regulation, loss of floodplains as spawning habitats, and chemical water pollution.
Scientific profile
Morphology & ID
Coloration
Dark upper side (olive green to blackish blue), marbled flanks, whitish-yellow belly.
Distinguishing features
Six barbels (2 long on the upper jaw, 4 short on the lower jaw); very small dorsal fin; extremely long anal fin.
Confusion species
Black Bullhead (Ameiurus melas) and Brown Bullhead (Ameiurus nebulosus) – these possess 8 barbels and an adipose fin.
Sexual dimorphism
Males often smaller and mature earlier; genital papilla narrower in males.
Habitat
Fish region
Bream zone (metapotamal) as well as lakes and lagoons.
Preferred zone
Benthic (bottom-dwelling).
Flow preference
Limnophilous to weakly rheophilous.
Substrate preference
Mud, sand, submerged wood, dense vegetation.
Oxygen requirement
Low; tolerant of low oxygen levels (3.0-3.5 mg/L).
Migration
Migration behaviour
Short migrations to spawning grounds in shallow, vegetated littoral zones.
Reproduction
Spawning substrate
Plant nests (phytophilous); root systems of willows or reeds.