A simple semi-automated home-tank method and procedure to explore classical associative learning in adult zebrafish

An appetitive olfactory learning paradigm for zebrafish in their home tanks

Olfaction is a subject of increasing interest in fish biology, but there are few learning paradigms available to investigate olfactory behaviour. In the present study, groups of zebrafish were trained in their home tanks retrofitted for automated conditioning with a microprocessor-controlled syringe pump and feeder to deliver odourant and food, respectively, and responses recorded remotely to minimize researcher interference. Fish were presented with phenylethyl alcohol (PEA), and a food reward was given 15 seconds later for experimental groups or at a variably delayed interval for controls. This schedule continued for 48 trials over four days. Both groups showed initial attraction to PEA, but by the end of Day 2 all fish exhibited reduced interest in the odourant. Further experiments with different fish indicated that this attraction was dependent upon high food motivation, as starved animals reacted more than non-starved animals to the novel stimulus. On Day 3, experimental fish began once again to show attraction associated with the odourant, thus indicating that they formed an association between the PEA and food reward, which increased by the end of Day 4. Conversely, control fish showed little or no response to the odourant on Days 3 and 4. When exposed to a water-only trial, trained fish largely ignored the cue, indicating that odour and not turbulence was the main stimulus for learning. This experiment demonstrated that an appetitive learning paradigm, using olfactory cues presented in home tanks, is both feasible and cost-effective for testing olfactory behaviour in zebrafish.

A framework for a low-cost system of automated gate control in assays of spatial cognition in fishes

Automation of experimental setups is a promising direction in behavioral research because it can facilitate the acquisition of data while increasing its repeatability and reliability. For example, research in spatial cognition can benefit from automated control by systematic manipulation of sensory cues and more efficient execution of training procedures. However, commercial solutions are often costly, restricted to specific platforms, and mainly focused on the automation of data acquisition, stimulus presentation, and reward delivery. Animal welfare considerations as well as experimental demands may require automating the access of an animal or animals to the experimental arena. Here, we provide and test a low-cost, versatile Raspberry Pi-based solution for such use cases. We provide four application scenarios of varying complexities, based on our research of spatial orientation and navigation in weakly electric fish, with step-by-step protocols for the control of gates in the experimental setups. This easy-to-implement, platform-independent approach can be adapted to various experimental needs, including closed-loop as well as field experiments. As such, it can contribute to the optimization and standardization of experiments in a variety of species, thereby enhancing the comparability of data.

Zebrafish models for studying cognitive enhancers

Cognitive decline is commonly seen both in normal aging and in neurodegenerative and neuropsychiatric diseases. Various experimental animal models represent a valuable tool to study brain cognitive processes and their deficits. Equally important is the search for novel drugs to treat cognitive deficits and improve cognitions. Complementing rodent and clinical findings, studies utilizing zebrafish (Danio rerio) are rapidly gaining popularity in translational cognitive research and neuroactive drug screening. Here, we discuss the value of zebrafish models and assays for screening nootropic (cognitive enhancer) drugs and the discovery of novel nootropics. We also discuss the existing challenges, and outline future directions of research in this field.

A search for effective reinforcers in appetitive conditioning for adult zebrafish: Ecologically relevant unconditioned stimuli

Learning and memory related brain disorders represent a large unmet medical need. Laboratory studies with animals may model brain disorders and facilitate uncovering their mechanisms. The zebrafish has been proposed for such studies. However, numerous factors that influence performance in learning tasks have yet to be understood in zebrafish. One such factor is what motivates zebrafish. Here we introduce a novel reinforcer, an ecologically relevant unconditioned stimulus (US). We placed a photograph of gravel underneath quarter of the bottom of an experimental tank on one side and also positioned artificial plants there, the "natural" US. First, we showed that this stimulus was preferred by zebrafish. Next, we investigated whether this stimulus could serve as US for associative learning. We marked the walls of the tank on the side where the US was presented with red paper, the conditioned stimulus (CS+) we found neutral before, and we also marked the walls on the other side of the tank where no US was placed with blue paper (CS-). In addition to fish receiving this "paired" training, we also ran unpaired training with another group of zebrafish, in which the fish saw the US associated with blue and red in a random manner. After having trained the fish in this manner, we tested the performance of the paired and unpaired group of zebrafish in a memory probe trial during which no US was present, and only the CSs (blue and red walls) were shown. We found the paired group of zebrafish to show significant preference for the CS+, as they spent more time and swam closer to the red side compared to the unpaired group and compared to chance. We conclude that ecologically relevant stimuli can serve as efficient US in appetitive conditioning of zebrafish.