The experiments aimed at prey selectivity in two Siluriformes predators. African catfish, Clarias gariepinus, and wels, Silurus glanis, were performed under laboratory conditions. Prey fish (12-22% TL of predator) were submitted to one.year.old African catfish (~220 g) and wels (~150 g) originating from intensive culture, ie with no previous experience with live fish food. In African catfish, negative selectivity (avoidance) was shown for Nile tilapia (Oreochromis niloticus) and topmouth gudgeon (Pseudorasbora parva) whilst rudd(Scardinius erythrophthalmus) and sunbleak (Leucaspius delineatus) were preferred (positive selectivity). The intensity and efficiency of African catfish predation were quite low because its feeding strategy is based rather on prey searching than hunting. Prey fish, wounded and/or dead from its clumsy attacks, were sonsumed preferably overnight. Not one successful attack of African catfish on healthy prey fish was registered. The SGR and FCR of clarias fed live fish were 0.39%. day-1 and 4.73 respectively. In wels, strong negative selectivity (avoidance) was proved for roach (Rutilus rutilus) and topmouth gungeon, and lower avoidance for Prussian carp (Carassius auratus gibelio) and chub (Leuciscus cephalus). Asp (Aspius aspius) were found to be low preferred but high preference was shown for sunbleak, rudd and bitterling (Rhodeus sericeus). Both catfishes preferred smaller prey fish during the 10.day experimental period whilst those which remained non-consumed belonged to the mean or above-mean size categories.Istraživanja su bila usmjerena na selektivnost plijena u dvije vrste grabežljivaca siluriformes - afričkog soma (Clarius gariepinus) i soma (Silurus glanis). Istraživanja su provedena u laboratorijskim uvjetima. Riba plijen (12-22% TL grabežljivaca) poslužila je jednogodišnjem afričkom somu (~220 g) i somu (~150 g) porijeklom iz intenzivnog uzgoja bez prethodnog iskustva u prehrani živim ribama. Afrički je som pokazao negativnu seletivnost (izbjegavanje) prema nilskoj tilapiji (Oreochromis niloticus) i amurskom čebačoku (Pseudorasbora parva), a crvenperka (Scardinius erythrophthalmus) i bjelica (Leucaspius delineatus) bile su preferirane (pozitivna selektivnost). Intenzitet i efikasnost proždrljivosti afričkog soma bila je posve niska, jer je njegova hranidbena strategija u osnovi zapravo na selektivnosti traženja, a ne lova.
Plijen, ozlijeđen ili mrtav u tijeku neefikasnog lova, bio je bolje konzumiran za vrijeme noći. Ni jedan uspješan napad afričkog soma na zdravi plijen nije registriran. U soma je bila dokazana jaka negativna selektivnost (uklanjanje) za bodorku (Rutilus rutilus) i amurski čebačok (Pseudorasbora parva), a slabije izbjegavanje za babušku (Carassius auratus gibelio) i klena (Leuciscus cephalus). Bolen (Aspius aspius) nisko je preferiran, dok je visoka preferiranost pokazana za bjelicu (Leucaspius delineatus), crvenperku (Scardinius erythrophthalmus) i gavčicu (Rhodeus sericeus). Obje vrste soma preferirale su manji plijen za vrijeme desetodnevnog eksperimentalnog razdoblja, dok su oni koji su ostali nekonzumirani pripadali kategoriji srednjih ili većih riba
