The effects of different coloured visual stimuli on Paracheirodon innesi in a fixed

environment

Taylor Brooks, James Holobow & Allyson MacDougall

Paracheirodon innesi

• Fresh water fish

● Native to streams in Colombia, Peru and Brazil

● Iridescent blue with red stripe

● Approximately 3 cm long

P. innesi Eyes ● Rod Pigments absorb λmax of 500-545 nm● Melanosomes: organelles in pigment cells in eyes (melanins)● Light response in the retina activates the migration of

melanosomes and the elongation of cones (colour vision)● Melanosomes and cones meld together to direct incoming light

to the rods● Spectral absorbance of melanosomes is ~ 480 nm

Iridophores

● Scales have alternating layers of guanine and cytosine

● Scatter light to a shine● Minimal light exposure = ultraviolet/blue● Great light exposure = green● Respond to each other best in bright

environments

Purpose

● Examine the response of different coloured stimuli in P. innesi

● P. innesi will stay in close proximity to colours that are within the wavelength range of 500-545 nm

Materials & Methods

• Experimental design was simpleo Limited external variables

• Modelled fish blobs constructed of silicon sealant painted with nail polisho Red, yellow, green, blue, aqua

• Modelled fish were placed inside of a jar paired with an empty control jar at the opposing end of the aquarium

Materials & Methods

• Models were ~3 cm o intended to vaguely

resemble real fish

• The aquarium was split into three sectionso Control o Middleo Coloured Model

Materials & Methods

• 15 minute trialso Position recorded at 30 second

intervalso Trials repeated with

orientation of aquarium reversed

o Repeated test 3 times 6 trials/colour

Results

• P. innesi preferred Green and Aqua systems most

o Time spent next to modelo Green (50.6%, SE ± 0.050)

o Aqua (65.6%, SE ± 0.023)

Results

Discussion● Aqua has a wavelength of ~ 480 nm, the same spectral

absorbance as the melanosomes● Blue and green were the second most popular and are on

either side of the 480 nm on the wavelength spectrum● Green was 2nd most popular and it’s on the higher end of

the spectrum (500-545 nm)

Discussion

Sources of error:● Background stimuli● Fish inconsistency/ Overuse● Issues with our coloured model fish

Why is this Important?

Knowing the most stimulating visual in P. innesi is important because it can give insight towards

● Schooling● Mating● Predator avoidance

Future Studies

• Use iridescent nail polish o Stimulate iridophores

• Compare coloured models against each other

• Use different fish species to compare light absorbances