Abstract :
[nl] The Wels (Catfish) originates from Asia and central European. It was introduced in Europe as early as the Middle Ages and in France the species has released many times since the 19th century. It invaded the Loire river basin at the end of the last century. it is the largest predatory freshwater fish in Europe. Given its geographilcal expansion and recent demographic expansion, there is an urgent need to learn more about the ecology and, above all, the trophic needs. The aim was a diet study based on stomach contents. Professional fishermen participated in the sampling of 104 catfish of all sizes and season in the middle (Gien) and lower (Nantes) sections of the Loire. The prey of the catfish is very varied: fish but also molluscs, crustaceans, insects, birds and mammals: 23 fish and 2 lampreys, 7 invertebrates, 5 birds and mammals.in terms of biomass, however, 70 % are migratory: sea lamprey (23 %), salmon (21 %) thinlip mullet (17 %), allis shad (8 %) and eel (2 %). In terms of biomass downsteam (Saumur), 85 % of catfish prey are migratory : sea lamprey, thinlip mullet and small eel. Upstream, the situation is more diverse, particularly for rheophilic fish, and migratory species are less present (62 %). In spring and summer, catfish consume migratory fish : 80 % in biomass! In winter, more than 50 % are mammals and a few birds and rheophilic fish (35 %). In autumn, the diet is diversified : birds, molluscs, crustaceans, barbel, pikeperch, ruffe, bitterling and mullet. Small carfish (< 40 cm) eat mainly crustaceans, insects and tiny fish (ruffe, gudgeon, bitterling, crucian carp). Catfish between 40 cm and 80 cm eat corbiculas and some fish (mullet, bream, chub, catfish). Above 80 cm, catfish consume 85 % of fish biomass and lamprey. Migratory fish are increasing in biomass: 48 % in the 80 cm-120 cm class, 66 % in the 120 cm - 180 cm class and 82 % beyond. At the very least, a ban on the release of catfish caught by fishing larger than 120 cm. It would be desirable to experiment with the regulation of catfish in certain strategic sectors for the passage of migratory fish and cyclostomes through structures, with associated scientific monitoring.
