Effects of species composition on schooling preferences in glowlight tetras

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

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

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

4. 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

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

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

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)

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. Results Heterospecific-weighted treatment

12. Split treatment

13. Conspecific-weighted treatment

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

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)

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

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

18. QUESTIONS ?