Effects of species composition on schooling preferences in glowlight tetras

By Avery Nagy-MacArthur, Cybele Sabitry & Samantha Shaw

Introduction

• Schooling is an important form of social organization among fish– Predator avoidance

• “dilution effect” increases as school size increases• Confusion effect

– Increase feeding success • Improves detection of food resources• Increases competition between individuals within school• Overcome interspecific competition by schooling to access

resources defended by competitor

Introduction

• Schools may be composed of a single species or variety of species– Conspecific fish school only with their own species– Heterospecific fish school with other species

• Heterospecific schooling may be advantageous for duller fish if they can associate with brighter fish

• Advantage depends on relative composition of school

dull fish < bright fish

Are schooling preferences dependent on relative school composition?

Test subjectsGlowlight tetra

(Hemigrammus erythrozonus)

• Heterospecific schooler

Neon tetra(Cheirodon innesi)

• Conspecific schooler

Hypothesis

• Schooling preference will change based on species composition of available schools– As the proportion of conspecifics in an available

school increases, glowlight tetras will increase their preference for the school composed completely of neon tetras

Procedure

• Offered test fish two different schools• Acclimated test fish for 3-5 minutes• Every 30 s recorded position of fish, for 15 min• Reversed jars and switched test subject• 4 trials for each of three treatments

= 12 tests total (24 test fish)

Split treatment4 glowlight tetras4 neon tetras

8 neon tetras

Conspecific-weighted treatment6 glowlight tetras2 neon tetras 8 neon tetras

Heterospecific-weighted treatment2 glowlight tetras6 neon tetras

8 neon tetras

Results

2 glowlights & 6 neons

No fish 8 neons 0

5

10

15

20

25

30

35

40

45

.

perc

ent ti

me

Heterospecific-weighted treatment

4glowlights & 4neons No fish 8neons0

10

20

30

40

50

60

perc

ent ti

me

Split treatment

6glowlights & 2neons No fish 8 neon0

10

20

30

40

50

60

perc

ent ti

me

Conspecific-weighted treatment

Discussion

• High variation in data• Possible trend for??– More time spent with heterospecifics when the

proportion of conspecifics is low– Increasing proportion of conspecifics may

increase time spent with mixed school

BUT…

– Our sample size was small (24 test fish used)– We couldn’t control for sex or age of test fish– May have repeatedly sampled some test fish due to small

source population– External environmental influences (shadows, reflections,

etc)

Other influences on schooling:

– Fish may prefer familiar heterospecifics over foreign conspecifics

– Variation in size may have influenced schooling preference

– Social hierarchies developed while kept as a group could have caused test fish to avoid certain individuals regardless of species

Suggestions for further research

• Taking into account importance of chemical cues • Controlling for size differences• Larger sample size• Better control over environmental conditions of fish

both during and outside of experiment

QUESTIONS ?