Guppies in the puzzle box: innovative problem-solving by a teleost fish

Behavioural innovations allow an individual to solve new problems or find new solutions to an existing problem. Despite being considered an important source of phenotypic plasticity and evolutionary changes, innovative problem-solving remains poorly understood, except in a few species of mammals and birds. We investigated innovative problem-solving performance and its underlying psychological mechanisms in a teleost fish, the guppy Poecilia reticulata. We assayed guppies in Thorndike's puzzle-box problem: we placed them in a small chamber, where they had to learn to dislodge an object to access a tunnel leading to their home tank. Guppies showed heightened performance with most individuals (23 out of 24) solving the problem, within, on average, three trials. After a fish solved the task for the first time, improvement was still visible in the form of an increased likelihood to solve the problem over trials. An individual's sex and willingness to solve the task were unimportant, but behavioural traits related to neophilia significantly predicted problem-solving performance. High exploration in a new environment and high attraction towards novel objects favoured the guppies in learning the task solution. Our finding suggested that this fish species shows remarkable performance and individuality in innovative problem-solving. As observed in warm-blooded vertebrates, these cognitive features may have important consequences for individual fitness and the species' invasiveness in nature.Significance statementBehavioural innovation is an important mechanism that allows animals to adapt to their environment. Among the others, it permits solving new problems and obtaining new resources. However, innovative problem-solving remains poorly understood except for a few species of mammals and birds. Our study suggests that fish can learn a novel problem-solving task and improve over time to find the solution. Fish learned to dislodge an object to access a tunnel leading to their home tank. Problem-solving performance was linked to the propensity to explore novel objects and novel environments. Individuals with greater neophilia may have higher propensities for innovative problem-solving.