We investigated whether the piscivorous wolf-fish, Hoplias malabaricus (Bloch, 1794), showed preferences for attacking a ‘straggler’ or a shoal using guppies, Poecilia reticulata (Peters, 1860), as prey. Predators should show a preference to attack single prey items rather than grouped prey to overcome the confusion effect, which has been shown to negatively affect their capture success. However, they may attack groups more frequently because they are more likely to detect them because of their greater conspicuousness. In our study we looked at predator choice for grouped or single prey and whether this was affected by larger shoals being more conspicuous. We offered Hoplias binary choices of a single guppy (straggler) and shoals of 2, 6 and 10 fish. Hoplias preferred to attack the shoal over the straggler with regards to both frequency of attacks (initial and subsequent) and attack duration. The implications for predator–prey interactions of such a preference are discussed.