The effects of a female audience on the aggression of male Siamese fighting fish, Betta
splendens, based upon size of male.
Bayan Yazdi and Farhad Esmaeilzadeh
Department of Biological Sciences,
Saddleback College, Mission Viejo, CA 92692
Betta splendens (Siamese fighting fish) are a naturally aggressive species that have been
bred for larger body sizes and hyper-aggressive temperament for commercial use. It was
hypothesized that male Betta splendens are more aggressive when a female is visibly
present, and that larger males are more aggressive than smaller males. Nine males and one
female B. splendens were used in this study. Randomly determined pairs of males were
allowed to view each other through a clear divider for five minutes per trial. Based upon
this data, size of male is not correlated to aggression levels (p= 0.902), however males are
significantly more aggressive when a female is present (p= 0.001).
INTRODUCTION:
Male Betta splendens typically have
a high propensity towards aggression, which
has arisen from male competition and
mating rituals (King, 1973), and has been
made more prominent by selective breeding
for larger body sizes and hyper-aggressive
temperaments (Monvises et al., 2009). Upon
visual contact, male B. splendens display
specific aggression reactions such as
approaching, tail beating, biting attempts,
and extending gill covers (Verbeek et al.,
2005; Braud and Weibel, 1969). By utilizing
these aggressive displays, each male B.
splendens attempts to create the illusion that
it is larger than its opponent. The gill cover
display involves the attacking fish facing its
opponent head-on and flaring its opercular
gill covers, increasing its size relative to its
opponent. Each aggressive display typically
lasts for a few seconds, and each “fight”
usually ends in the retreat or death of one
fish (Bronstein, 1983).
Scale coloration has been shown to
have no significant impact on male Betta
splendens aggression (Bucknam et al.,
2013). It was hypothesized that a larger male
B. splendens would have a more aggressive
nature, and males regardless of size would
be more aggressive when in the presence of
a female.
MATERIALS AND METHODS:
Nine male and one female Betta splendens
were purchased from PetSmart (San Juan
Capistrano, CA, and Aliso Viejo, CA).
Subjects were measured from the base of
their tail to their mouth and were placed on a
size spectrum to determine if they fit into the
large or small size category. The subjects
were held in PetSmart standard Betta
holding containers (Petsmart, Phoenix, AZ)
approximately 20 cm apart and were kept
isolated in this way for at least three days to
acclimate to laboratory conditions. Subjects
were fed twice daily at 8:00 am and 5:00 pm
with Top Fin Betta Bits (Petsmart, Phoenix,
AZ). All testing took place between 8:00am
and 11:30am under controlled and
standardized lighting, temperature (25°C),
and pH. For the experiment, all pairings for
the trials were randomized by Random.org:
True
Random
Number
Service
(Random.org, Dublin, Ireland). For each
trial, two male fish were held in an Aqueon
Betta Bowl (Aqueon Aquarium Products,
Franklin, WI) on separate sides of the
divider. The testing tank was equipped with
a clear and darkened divider. Subjects were
acclimated to the test tank for five minutes
prior to each trial, with the darkened divider
in place. After five minutes, the darkened
divider was removed and subjects were
allowed to view one another for five
minutes. During trials that involved the
female, a separate Aqueon Betta Bowl
(Aqueon Aquarium Products, Franklin, WI)
containing the female was attached to the
first bowl, so that the males would be able to
view the female for the entire ten minutes of
the experiment. During the trial time, the
number of gill cover flares, tail beats,
approaches, and biting attempts of the male
were counted and documented.
Figure 1. Diagram depicting tank trials were
conducted in. Both transparent and darkened dividers
in place between the two male fish during first five
minutes. Only transparent dividers in place during the
following five experimental minutes. Transparent
divider in place between female and males for entire
duration of experiment.
RESULTS:
Figure 2. Comparison of aggressive behavior in male
Betta splendens with and without female Betta
splendens. Chi-square =58.9. Probability = 0.001.
Male fish are significantly more aggressive when
female is present as opposed to when female is
absent.
Figure 3. Comparison of aggressive behavior in male
Betta splendens based upon size. Chi-square= 2.19.
Probability = 0.902. There is no correlation between
size and aggression levels in male Betta splendens.
Without
Female
Audience
With
Female
Audience
Gill
flare
371
Approach
244
Tail
beat
51
Bite
attempt
68
479
304
106
250
Table 1: Total aggressive displays of all male Betta
splendens tested with and without female audience.
Small/large
Small/small
Large/large
Gill
flare
28
37
23
Approach
16
25
16
Tail
beat
5
5
5
Bite
attempt
9
19
8
Table 2: Mean aggressive displays of all male Betta
splendens tested, categorized by size.
Figure 4. Profile of subject C displaying gill flare.
Figure one reflects the tank all
subjects were tested in. Size and color
pairing categories were compared using a
chi-squared test. Figure two depicts bar
graph of total number of gill flares,
approaches, tail beats, and biting attempts
displayed by male Betta splendens, based
upon whether or not female was present.
Fish with a female audience were
significantly more aggressive than fish
without a female audience (p=0.001, chisquared test). Table two is the mean
aggressive displays of all male Betta
splendens tested, categorized by size. Figure
three reflects table two as a bar graph; mean
aggressive displays based upon size of male
subjects. There was no correlation between
size and aggression in male Betta splendens
(p= 0.902 chi-squared test). Figure four is a
picture of subject C displaying a gill flare,
an example of an aggressive display.
DISCUSSION:
There is no correlation between size and
male B. splendens aggression levels. Male
B. splendens are more aggressive when a
female is visibly present. Further research
may be done on the effects of the size of the
female on male B. splendens aggression.
More research could also take into account
the effect of the coloration of the male on its
aggression. Bucknam, Esmaeilzadeh, Yazdi,
and Yuen found that color and size do not
affect male B. splendens aggression when
there is no female audience. Our results
indicated that size is not a factor in
aggressive behavior even if a female is
visibly present. Therefore, another study
could be conducted to evaluate if color plays
a role in aggressive behavior when a female
is visibly present.
LITERATURE CITED:
Braud, W. G. & Weibel, J. E. (1969).
Acquired Stimulus Control of Drug-Induced
Changes in Aggressive Display in Betta
Splendens. Journal of the Experimental
Analysis of Behavior. 12 (5): 773-777.
Bucknam, K., Esmaeilzadeh, F., Yazdi, B.,
Yuen, N. (2013). The Effects of Body Size
and Coloration on Aggression in Male
Siamese Fighting Fish (Betta splendens).
Saddleback Journal of Biology.
King, J. A. (1973). The ecology of
aggressive behavior. Annual Review of
Ecology and Systematics, 4: 117-138.
Monvises, A., Nuangsaeng, B.,
Sriwattanarothai, N., Panijpan, B. (2009).
The Siamese fighting fish: well-known
generally but little-known scientifically.
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