# A Comparison of Detour Behaviors in Some Marine and Freshwater Fish Species

## TL;DR

This study shows that both marine and freshwater fish can navigate around obstacles to reach a goal, suggesting similar environmental pressures across different aquatic habitats.

## Contribution

The first evidence of detour behavior in marine fish using the four-compartment box task, alongside comparative insights with freshwater species.

## Key findings

- Marine fish demonstrated detour behavior in the four-compartment box task, a first for this group.
- Freshwater fish confirmed prior detour behavior findings and showed distinct exploratory patterns.
- Danio rerio exhibited differential spatial exploration, suggesting possible mental representation of the goal.

## Abstract

Detour behavior refers to the ability to reach a goal object that is not directly accessible due to an obstacle (opaque or transparent) by circumventing it. It varies among species, suggesting that environmental adaptation may drive insight behavior. Some species of marine and freshwater fish were placed in a corridor with social stimuli at the end, not directly accessible due to an opaque barrier. Two symmetrical apertures positioned midline in the corridor allowed the fish to temporarily abandon the view of the goal and attempt to circumvent the barrier. All fish showed the ability to move around an interposed obstacle. This is the first evidence of detour behavior in marine fishes within the “four-compartment box task”, while results in freshwater fishes confirmed previous evidence. The comparable performance of marine and freshwater fishes suggests similar selective ecological pressure even in different aquatic habitats (e.g., sea and freshwater basins). Moreover, different exploratory behaviors emerged between correct and incorrect compartments (particularly in Danio rerio), providing evidence for a possible mental representation or “permanence in existence” of the goal while performing the obstacle circumvention, as opposed to a more parsimonious idea suggesting that the detour ability emerges only from primitive forms of exploratory behavior such as taxis.

Evidence of detour ability to reach a salient goal in marine fishes (Chromis viridis, Chrysiptera parasema, Dascyllus aruanus) and freshwater fishes (Xenotoca eiseni, Danio rerio) has been observed using a “four-compartment box task” with an opaque barrier. The first experiment investigated this ability in marine fishes (Chromis viridis, Chrysiptera parasema, Dascyllus aruanus). Fish were placed in a four-compartment box, with social stimuli not accessible due to an opaque barrier. Two symmetrical apertures midline in the corridor allowed the fish to temporarily abandon the goal’s view and attempt to circumvent the barrier. Marine fish showed searching behavior in the two compartments near the social stimuli. In the second experiment, the detour abilities of a marine fish (Dascyllus aruanus) and two freshwater fishes (Xenotoca eiseni, Danio rerio) were compared using a modified version of the apparatus, with elongated compartments continuing further from the obstacle barrier and social stimuli. This enabled the evaluation of the dependence on effective distance to achieve the social goal. Both marine and freshwater fish exhibited detour skills. Additionally, Danio rerio’s differential spatial explorations inside compartments supported an active interest in searching for conspecifics, suggesting possible social object permanence retention. Overall, these results highlight the ecological salience of detour skills in fishes, irrespective of species-specific adaptations.