Puzzle feeder as a cognitive enrichment strategy determines long-term welfare improvements in a teleost fish

Providing access to cognitive tasks, such as puzzle feeders, holds promise as enrichment strategy to enhance the welfare of captive animals. Despite the substantial number of teleost fish in captivity, the effects of cognitive enrichments in this group remain relatively unexplored. To address this gap in knowledge, we investigated the response of zebrafish to a puzzle feeder. In the first experiment of this study, zebrafish were presented with the option of a puzzle feeder or freely available food. While the subjects exhibited a preference for the latter option, they demonstrated some interest in the puzzle feeder, continuing to use it even though there was easily accessible food nearby. In a subsequent experiment, zebrafish groups were maintained in either a cognitive enrichment condition, where food was consistently provided through puzzle feeders, or a control condition with no cognitive enrichments. Welfare effects of the treatments were then assessed using standard behavioural indicators in the open-field test (i.e., time spent in the centre of the apparatus; number of entrances in the central sector; swim velocity; erratic swimming). Results unveiled an improvement in three welfare indicators due to cognitive enrichment, becoming apparent approximately 20 days after the treatment. Our study underscores the significance of puzzle feeders as cognitive enrichments in captive fish welfare, although consideration of other welfare indicators and different types of puzzles that elicit a more pronounced attraction is required.