Modified scototaxis protocol (Adult zebrafish)

This modification refers to the protocol used at LaNeC, and involves tank modifications as well as addition of behavioral endpoints. These additions make the test more sensitive and refine the different variables controlling behavior in the light/dark preference test, justifying the decreased throughput.

Experimental setup

" An acrylic tank (15 cm × 10 cm × 45 cm height × width × length) is used that is divided equally into one-half black and one-half white. Walls and bottom are either black or white, so as to warrant uniform substrata for each compartment. The water column is kept at 10 cm, yielding a final volume of 4.5 liters. Water should be de-chlorinated. The colored material chosen should not be reflective, to avoid the tendency of those animals that present shoaling tendencies to behave in relation to their own reflection. The tank contains central sliding doors, colored with the same color of the aquarium side, thereby defining an uncolored central compartment measuring 15 cm × 10 cm × 10 cm." (Maximino et al., 2010)

Experimental procedures

1. Room illumination is a critical variable, as it can alter fish behavior and the aversiveness of the white compartment. Before each trial, light levels should be measured; variations above or below 2 SDs from the average should be considered as too discrepant for an experiment. Ideally, lighting above the tank should be on the range of 500-600 lux.
2. Use Gaussian white noise throughout the experiment to cover unwarranted noise in the experimental room.
3. Bring the animal in a temporary transport recipient into the behavioral test room.
4. Transfer the animal to the central compartment of the tank with a net. Allow the animal to acclimate to the tank for 3 min
5. Remove the sliding doors, allowing the fish to swim freely in the apparatus for 15 min. Video recording is recommended.
6. Transfer the animal to a discard tank with a net.
7. Videos should be analyzed blindly (i.e., the experimenter should not know the treatment/genotype of the animal) by two experienced researchers. Variables to be recorded (and ZBC references) are:
   1. Time spent in the white compartment (ZBC 1.137)
   2. Latency to enter the white compartment
   3. Number of entries in the white compartment
   4. Duration of entries in the white compartment
   5. "Risk assessment" events (a fast (<1 s) entry in the white compartment followed by re-entry in the black compartment, or a partial entry in the white compartment (i.e., the pectoral fin does not cross the midline))
   6. Duration and number of erratic swimming (ZBC 1.51): a zig-zag, fast, unpredictable course of swimming of short duration.
   7. Duration and number of freezing events (ZBC 1.68): complete cessation of movements except eye and opercular movements.
   8. Time on thigmotaxis (ZBC 1.173): swimming in a distance of 2 cm or less from the nearest wall.

References

Kalueff et al., 2013 (ZBC; doi: 10.1089/zeb.2012.0861); Maximino et al., 2010 (doi: 10.1038/nprot.2009.225); Maximino et al., 2014 (doi: 10.1371/journal.pone.0103943)