Learning by Doing: The Use of Distance, Corners and Length in Rewarded Geometric Tasks by Zebrafish (Danio rerio)

Abstract

Zebrafish spontaneously use distance and directional relationships among three-dimensional extended surfaces to reorient within a rectangular arena. However, they fail to take advantage of either an array of freestanding corners or an array of unequal-length surfaces to search for a no-longer-present goal under a spontaneous cued memory procedure, being unable to use the information supplied by corners and length without some kind of rewarded training. The present study aimed to tease apart the geometric components characterizing a rectangular enclosure under a procedure recruiting the reference memory, thus training zebrafish in fragmented layouts that provided differences in surface distance, corners, and length. Results showed that fish, besides the distance, easily learned to use both corners and length if subjected to a rewarded exit task over time, suggesting that they can represent all the geometrically informative parts of a rectangular arena when consistently exposed to them. Altogether, these findings highlight crucially important issues apropos the employment of different behavioral protocols (spontaneous choice versus training over time) to assess spatial abilities of zebrafish, further paving the way to deepen the role of visual and nonvisual encodings of isolated geometric components in relation to macrostructural boundaries.

Visual discrimination and amodal completion in zebrafish

“…A choice was scored whenever the animal entered one of the two tunnels (to score the choice the whole body had to be inside the tunnel). In similar exit learning tasks, zebrafish spontaneously tend to enter the tunnels, possibly reflecting a preference for small enclosed spaces over the open space of the test tank [ 40 , 41 , 58 , 59 ] (see also [ 61 ], which exploits zebrafish tendency to spontaneously pass through small holes). Once inside the tunnels, they could see the external environment through the lower part of the door (made of transparent plastic), which motivated them to press it with their snouts and open it.…”

“…Our research group has perfected a visual discrimination task, based on multiple forms of reward, that is quite effective in other fish species (e.g., [ 19 , 52 – 56 ]). This behavioral task is based on an exit learning procedure, initially developed to test spatial orientation in gold fish [ 57 ], and later adopted to test spatial and numerical abilities of zebrafish [ 40 , 41 , 58 , 59 ]. In this visual discrimination task, male fish are confined in a central tank with two potential exits leading to a rewarded external environment, where food, shelter and female conspecifics can be found.…”

Learning and memory formation in zebrafish: Protein dynamics and molecular tools

“…They can discriminate between visual stimuli such as shapes and colors ( Colwill et al, 2005 ; Risner et al, 2005 ; Gatto et al, 2020 ; Santacà et al, 2021 ; Santaca et al, 2022 ), different odors ( Braubach et al, 2008 ; Namekawa et al, 2018 ), and individual fish ( Madeira and Oliveira, 2017 ). These cues have been used to train fish during complex spatial learning tasks ( Williams et al, 2002 ; Levin et al, 2003 ; Xu et al, 2006 ; Baratti et al, 2019 ; Baratti et al, 2021 ). For example, fish can use the geometry of an arena to orient themselves in order to find the exit and gain a reward ( Baratti et al, 2021 ).…”

“…These cues have been used to train fish during complex spatial learning tasks ( Williams et al, 2002 ; Levin et al, 2003 ; Xu et al, 2006 ; Baratti et al, 2019 ; Baratti et al, 2021 ). For example, fish can use the geometry of an arena to orient themselves in order to find the exit and gain a reward ( Baratti et al, 2021 ).…”

The Geometric World of Fishes: A Synthesis on Spatial Reorientation in Teleosts

“…Similar results were previously found in 2-year-old children in reorientation tasks within segmented rhombic and rectangular arrays [ 90 ]. Baratti and colleagues [ 91 ] recently trained zebrafish under the experimental conditions defined by Lee and colleagues [ 89 ]. Different groups of fish underwent the rewarded exit task, and each of them was presented with one of the three boundary-related arrays as described above.…”