1. By Avery Nagy-MacArthur, Cybele Sabitry & Samantha Shaw
Effects of species composition on schooling preferences in glowlight tetras
By Avery Nagy-MacArthur, Cybele Sabitry & Samantha Shaw
Cybele

2. 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
Straggler fish are predated at a higher rate than schooling fish, so strong selection forces for schooling
Avery

3. 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 species may prefer schooling with other species over schooling with their own
Varies between and within species

4. dull fish < bright fish
Are schooling preferences dependent on relative school composition?
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
Advantage is greatest when there are many more bright fish than dull fish, because the bright fish are more conspicuous to predators
Advantage weakens when number of dull fish in a school decreases

5. (Hemigrammus erythrozonus)
Test subjects
Glowlight tetra
(Hemigrammus erythrozonus)
Heterospecific schooler
Neon tetra
(Cheirodon innesi)
Conspecific schooler
Cybele

6. 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
Avery

7. 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)
Mention fish discarded for lack of activity/movement after six minutes
Carried out experiment in a calmer corner of lab to reduce visual stimulation, kept water temperature the same as the tank which ranged from C
(Sam)

8. Split treatment
4 glowlight tetras
4 neon tetras
8 neon tetras

9. Conspecific-weighted treatment
6 glowlight tetras
2 neon tetras
8 neon tetras

10. Heterospecific-weighted treatment
2 glowlight tetras
6 neon tetras
8 neon tetras

11. Heterospecific-weighted treatment
Results
Heterospecific-weighted treatment
*There was no significance differences among the results for all of three treatments.
In this treatment, statistically it showed no fish preferences
(Cybele)

12. Split treatment
Where as in this treatment, the test fish spend more time with evenly spit treatments rather than the heterospecific but again statistically there was no significant differences among each compartments

13. Conspecific-weighted treatment
Even though there was so significance differences among the results, the test fish spend more time with the conspecific weighted schools.

14. 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
Cybele

15. 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)
Some fish were kept in the same tank as neons during study, eventually all fish were kept in the same tank
(Sam)

16. 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
(Avery)
Test fish may have chosen schools more similar to them in size
If fish were familiar, may have decreased importance of species on schooling preference
But this familiarity effect may diluted in captive-bred fish

17. 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
(Avery)

18. QUESTIONS ?
Sam