Betta splendens



The Betta splendens are a breed of fish that live in the waters around the Malay Archipelago of Southeast Asia from the family Anabantidae.4 They are commonly referred to as Betta or the Siamese fighting fish. The male Bettas are renown for their long tails and fins that they use to display aggression toward other males. Females, on the other hand, have smaller fins and very rarely attack other Bettas.5 The Betta splendens are a labyrinth fish that gulp air to get oxygen. They have a special auxiliary breathing mechanism called the labyrinth, that has a pair of irregular passages that provide supplemental oxygen to the blood.2 Hence, they can live in low oxygen level waters.1 Their ideal water temperatures are between 70o and 85o F (85o F when breeding).5

They exhibit a behavior of fixed action patterns that are sequences of movements determined genetically.7 Releasers found in the environment of the animal stimulate these patterns.7 In the case of the Betta, the stimulus is another male Betta. The male fighting fish is so aggressive, or agonistic, that in a community tank where other fish are present there can only be one male Betta. When fighting, males will nip at the others fins until one of them is exhausted.4 Bettas will display their fins in all of their color to a mirror since they do not recognize their reflections and think it is another male infringing on their territory. The stretching of the fins and opening of the gills to display the membrane enables the male to look twice his resting size and is called flaring, or displaying.

Males are thought to fight as a means of claiming their territory or as protection of their family. A healthy male will have a territory of his own where he will make a bubble nest in preparation of a female.6 After fertilization, the male places the eggs into the bubble nest. In the world of the Siamese fighting fish, the male looks after the young until they hatch and emerge from the bubble nest.3 At that time, the male pushes the young to the surface to help them breathe.6 All fighting by the Bettas is usually done to ward off other males or defend the fry, or fertilized eggs.

Experiment

The aggressive behavior of male Betta splendens will be assessed using a variety of visual stimuli. A total of six males (3 red and 3 blue) will be kept in separate jars and will be used as the experimental subjects.

Part 1

They will be shown a mirror to determine their response behavior when seeing their own reflections and the sequence of display will be recorded. The mirror will be shown for 1 minute, then removed for one minute to allow the fish to calm down, and then repeated for 1 minute

Results

Table 1: Mirror

Dorsal

Caudal

Ventral

Pelvic

Branchiostegal membrane

Gill operculum

orientation to mirror

Color change?

Red 1

yes

yes

yes

yes

Yes

Yes

head-on

blue streaking

Red 2

yes

yes

yes

yes

Yes

Yes

head-on, sideways, weaving

purple streaking

Red 3

yes

yes

yes

yes

Yes

Yes

head-on, turn around

blue streaking

Blue 1

yes

yes

yes

yes

Yes

Yes

head-on, sideways, weaving

green brightening

Blue 2

yes

yes

yes

yes

Yes

yes

head-on, sideways

blue & red streaking

Blue 3

yes

yes

yes

yes

Yes

yes

head-on, turn around

Blue brightening

Sequence:

Red 1: caudal, ventral, dorsal, gill, membrane, pelvic

Red 2: dorsal-caudal-ventral, pelvic, gill, membrane

Red 3: gill, membrane, ventral, caudal, dorsal, pelvic

Blue 1: pelvic, ventral, caudal, dorsal, gill, membrane

Blue 2: ventral, caudal, dorsal, gill, membrane, pelvic

Blue 3: ventral, caudal, dorsal, pelvic, gill, membrane

Part 2

The Bettas will be shown a variety of colored paper models of males in full display to assess the color that triggers the most response by both red and blue Bettas. A 0 will be given for no response, a 1 if a response is seen but is less intense than a full display, and a 2 for a full display.

For the responses to the colored fish, I hypothesize that the red males will be the most aggressive towards the red male models and that the blue males will be most aggressive towards the blue male models. It is in my opinion that these colors would be viewed as the most threatening for the respective fish in their fight for the right to reproduce as the dominant male.

Results

Table 2: Model Colors

model colors

Red 1

Red 2

Red 3

Blue 1

Blue 2

Blue 3

red

0

0

0

1

0

0

orange

1

1

0

2

0

0

yellow

0

0

1

2

0

1

green

1

1

0

2

2

2

blue

1

2

1

2

0

2

pink

0

2

0

2

0

1

black

0

0

0

2

0

1

white

0

0

1

0

0

1

Part 3

The characteristics of other Bettas that appear intimidating to the six males will then be measured using a variety of paper male cutouts at different levels of display taped to pens. There are a total of eight models (body alone, body with all fins, body with dorsal fin, etc.). First a complete male is presented, then the body alone, and so on until a complete male is again shown allowing the animal 1 minutes rest in-between each presentation. If a response is not seen within 30 seconds then there is a rest and then a repeat and a recording of the second response. A 0 will be given for no response, a 1 if a response is seen but is less intense than a full display, and a 2 for a full display.

My hypothesis is that the males will get progressively more reactive to the model fish as it “displays” more of its fins. The largest reaction will come when shown the fully flared model fish.

Results

Table 3: Fin Display

Red 1

Red 2

Red 3

Blue 1

Blue 2

Blue 3

total response

full fish

1

1

1

2

2

2

6

body

0

0

1

0

1

0

2

Caudal fin

1

1

0

1

2

0

4

Dorsal fin

1

1

1

0

0

0

3

Ventral fin

0

0

1

0

0

0

1

Dorsal/Ventral

1

1

1

0

1

0

4

Dorsal/Caudal

2

1

1

2

1

1

8

Ventral/Caudal

1

1

0

2

0

0

3

full fish

1

2

1

2

1

0

5

Part 4

Finally, a look at who is the most aggressive of the six fish will be determined setting two males in sight of each other for 1 minute and observing their response. This will continue until all males have had a chance to respond to another male and a pecking order has been established.

Conclusions

The most agnostic fish in each color was Red 2 and Blue 1. Both of these displayed their gill operculum and branchiostegal membrane last in the mirror test. This could be a fixed action pattern for highly excitable and protective male Bettas.

In part 2, the most response came from the green and the blue models. The least response or no response was with the white and the red models. This was surprising since I hypothesized the red Bettas would react to red and the blue Bettas would react to blue. However, there are many different colored Bettas and they can interbreed to create hybrid animals. In flaring, the colors of the Betta splendens intensify. From my observations, this often led to a bright blue or bright green coloration, and this flaring technique could explain the degree of display produced by the fish to models of these colors.

In part 3, as expected, the lowest behavioral response was by the “body only” and the “ventral fin” models. The “full fish” did get a large majority of the display behavior, but the top model for aggressive display was the “dorsal/caudal” model. For the single fin models, the “dorsal” and “caudal” fins also showed a significant amount of fixed action pattern. From the sequence in the mirror results, these were the first fins up in aggression for four of the six Bettas. Therefore, I would conclude that these fins together signify an aggressive male Betta prepared to fight.

Finally, the alpha male, or dominant male of the six Bettas I observed was determined to be the Blue1 male. In face-to-face viewing of other males, he was the only one that would continue to display and swim up and down in his jar as intimidation towards the others. When faced with Red 2, there was a standoff of some kind at first as neither intended to give up the fight. Eventually, after several times of this, Red 2 started to move slower in his swimming and eventually turned away, while Blue 1 was consistent in his display pattern.

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