Many publications and grey literature revealed the European catfish diet is very plastic, depending on available resource opportunities.
Feeding on terrestrial prey
Cucherousset j, Boulêtreau S, Azémar F, Compin A, Guillaume M, Santoul F (2018) ‘‘Freshwater Killer Whales’’: Beaching Behavior of an Alien Fish to Hunt Land Birds. PLoS ONE 7(12):e05840. doi:10.1371/journal.pone.0050840
Catfish individuals were observed to intentionally crossing the water-land interface to capture pigeons on land in the Tarn River, within the historical city center of Albi in France. Among a total of 45 beaching behaviours observed and filmed from June 30th to October 19th 2011, 28% were successful in bird capture. Stable isotope analyses of catfish individuals and their putative preys collected in the observation site in September-October 2011 revealed a highly variable diet between catfish, and a highly variable dietary contribution of pigeons among catfish individuals, suggesting distinct trophic specialization. Body size comparisons suggest a potential effect of individual body size on the display of this beaching behaviour, catfish observed hunting for pigeons (900 to 1500 mm) tending to be somewhat smaller than the estimated body size range of the individuals sampled in the study area (900 to 2000 mm). Two explanations were that smaller catfish individuals are probably less competitive than larger ones to prey upon fish prey and that the risk of being stranded on the riverbank and the energy cost of attacking pigeons might be lower for smaller catfish than for larger-bodied specimen (>1500 mm).
With its large gap size, the European catfish is a potential predator to many if not all fish species. Owing to their large body size, anadromous adults were historically invulnerable to fish predation during their spawning period migration. This invulnerability has disappeared in Western Europe since the European catfish was established.
Feeding on anadromous fish
Syväranta J Cucherousset J, Kopp D, Martino A, Céréghino R, Santoul F (2009) Naturwissenschaften (2009) 96:631–635. DOI 10.1007/s00114-009-0511-3
Guillerault N, Boulêtreau S, Santoul F. 2018. Predation of European catfish on anadromous fish species in an anthropized area. Marine and Freshwater Research 70(5): 682-686.
We assessed the contribution of anadromous fish to the catfish diet using stable isotope analysis during summer 2007 by comparing diet in the River Garonne and in the River Tarn, a tributary of the Garonne. Due to the presence of dams, anadromous fish cannot enter the Tarn. European catfish individuals caught in the Garonne had considerably more enriched mean δ13C values than those caught from the Tarn. The δ13C values of the catfish from the Garonne varied considerably, some individuals were clearly specializing on freshwater prey, whereas others specialized on anadromous fish. The mean contribution of anadromous fish to the entire European catfish population was estimated to be between 53% and 65%, depending on the fractionation factor used for δ13C. Such substantial contribution of marine-derived carbon in the diet of catfish was confirmed on 64 other catfish individuals we sampled in March-August 2013 in two other stretches of the Garonne
An additional threat for declining migratory species
Boulêtreau S, Gaillagot A, Carry L, Tetard S, De Oliveira E, Santoul F. 2018. Adult Atlantic salmon have a new freshwater predator. PLoS ONE 13(4): e0196046.
In the Garonne, we showed the European catfish interrupts the freshwater migration or reproduction of the most migratory fish of South-West France: Atlantic salmon, sea lamprey and allis shad. The Atlantic salmon has benefited from a reintroduction plan and restoration program in the Garonne basin from the 1980s. Big challenge persist for salmon migration with many impassable barriers on the Garonne. Dams are also suspected to reduce the survival of migrating organisms by increasing predator encounter rate or decreasing prey ability to escape predators. We assessed the risk for the Atlantic salmon to be predated by catfish inside the fishway of the Golfech power plant, the most-lower dam of the Garonne. Our observations made with acoustic camera and RFID telemetry demonstrated that 14/39 (35%) salmon have been predated from the 4th of April to the 26th of May 2016 spawning period. Such predation was attributed to a few specialized catfish individuals that adapted their hunting behaviour to salmon prey by shifting their daily activity rhythm with that of salmon (more occurrences by the end of the day).
Boulêtreau S, Carry L, Meyer E, Filloux D, Menchi O, Mataix V, Santoul F. 2020. High predation of native sea lamprey during spawning migration. Scientific Reports 10:6122.
We demonstrated the European catfish is a substantial factor of sea lamprey reproductive adult mortality in the Garonne-Dordogne system, and has to be added to the long list of factors that seriously threaten the declined native populations: dams, overfishing, pollution, spawning ground deterioration, ans climate change. We found that 39 among 49 (80%) of sea lampreys tagged with predation tag coupled to RFID telemetry were preyed upon within one month after their release in both Garonne and Dordogne rivers.
Boulêtreau S, Fauvel T, Laventure M, Delacour R, Bouyssonnie W, Azémar F, Santoul F. 2021. “The giants’ feast”: predation of the large introduced European catfish on spawning migrating allis shads. Aquatic Ecology 55: 75-83.
We also reported the endangered allis shad is threaten by catfish attacks during spawning act in the river Garonne. Shad spawning act occurs at night and consists of at least one male and one female swimming side by side, trashing the water surface with their tail and therefore producing a splashing noise. The splashing noise (35 dB) can be heard from the river bank. We observed spawning acts above a spawning ground in the for 34 nights from May 2 to June 28, 2019 and recorded the numbers of total and disturbed acts for 60 h of auditory survey. Catfish attacked 12% of the 1024 spawning acts. At the same period, we also analyse stomach contents of 329 catfish individuals from the same river stretch. Shad represented 82% of identified prey items of sampled stomach contents, confirming allis shad was the preferential prey of catfish in the stretch during shad spawning period in 2019.
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