1. Introduction  The purpose of this experiment was to test if Betta splendens can successfully cohabitate in captivity when a large enough space is provided.  Male Betta splendens cohabitate in their natural habitat of rice paddies, but they are known to exhibit aggressive behavior in captivity.  The aggressive behaviors counted were gill flares, body curls, and nips.  The predicted outcome was that if space was increased then aggressive behavior would decrease (Figure 1). Acknowledgments We thank Chantel Begin for her introduction to the concepts involved with creating this lab experiment and then executing it successfully. Materials & methods  This experiment was done while eliminating any possible biases: learned behavior, pairings, feeding schedule and water parameters. 10 Bettas were paired randomly using www.random.org Fed 1.5 hrs prior to each replicate day Oxygen levels maintained by aeration system Water test kit used to measure chemical composition as well as water changes when necessary (Figure 3).  The pairs of Betta splendens were respectively combined into five tank sizes for a cycle of five days.  The specified tank sizes, in gallons, were: 6.875, 13.75, 27.5, 41.25, and 5 (Figure 2).  Each day, all of the randomly paired fish were combined in a controlled setting via ten minute intervals.  The time choices were made to control biases and maintain the overall health and integrity of the Betta splendens.  Three distinct types of aggressive behaviors were measured: gill flares, body curls, and nips.  The frequency of aggressive behaviors during the appropriately specified time, in the varying tank sizes. Conclusion  If the experiment had been replicated 50+ times, instead of only 5 times, there may have been a significant trend in concordance with the predicted outcome.  Future experiments might include investigating behavioral effects over time to better understand intimidation-retreat versus intimidation-attack behavior and the effect of tank size below the range used here.  If this experiment were to be conducted in the future it would be beneficial to include other factors such as plant coverage, increased tank sizes, and of course an increased number of replications. Spatial effects on the aggressive behavior of Betta splendens Candace Calvert, Melody Harrell, and Kimberly Tarre Department of Biology, USFSP Figure 3. Water tested each replication day to eliminate biases. Figure 3. Graphs A, B, and C A.Mean # of Nips vs. Tank Sizes, Error Bars show the inclusion of Standard Deviations B.Mean # of Gill Flares vs. Tanks Sizes, Error Bars show the inclusion of Standard Deviations C.Mean # of Body Curls vs. Tank Sizes, Error Bars show the inclusion of Standard Deviations For further information Please contact cmcalvert@mail.usf.edu, melody8@mail.usf.edu, and ktarre@mail.usf.edu. Results  In this particular setting, we found no significant difference in the aggressive behavior among the varying tank sizes.  The amount of space was not a determining factor in Betta aggression.  This outcome led to the rejection of the alternative hypothesis and the accepting the null hypothesis.  The alternative hypothesis was experimentally and statistically shown disproven. Literature cited Braddock, J. C. and Z. I. Braddock. 1955. Aggressive Behavior Among Females of the Siamese Fighting Fish, Betta Splendens. Physiological Zoology 28 (2): 152-172. Print. Goldstein, Stephen. 1975. Observations on the Establishment of a Stable Community of Adult Male and Female Siamese Fighting Fish (Betta Splendens). Animal Behaviour 23 (1): 179-85. Print. Itzkowitz, Murray. 1971. Preliminary Study of the Social Behavior of Male Bambusia Affinis (Baird and Birard) (Pisces: Poeciliidae) in Aquaria. Chesapeake Science 12 (4): 219-24. Print. Figure 2. 55 gallon tank with 5 sizes labeled and divider. Tank size (gal) 27.5 13.75 41.25 6.875 Total # of aggressive behaviors displayed 55 Figure 1. Predicted outcome graph showing a linear relationship between aggressive behaviors per tank size. Figure 4. Mean number of aggressive behaviors (A. Nips, B. Gill Flares and C. Body Curls) of Betta splendens per 10-minute encounter with a conspecific, for various tank sizes. Error bars represent standard deviation bars. Figure 5. Numbered containers in which the fish were kept between replications. Figure 6. Betta splenden displaying an aggressive behavior - gill flare. Jaroensutasinee, M. and K. Jaroensutasinee. 2001. Sexual Size Dimorphism and Male Contest in Wild Siamese Fighting Fish. Journal of Fish Biology 59 (6): 1614-21. Print. Matos, R. J. and P. K. McGregor. 2002. The Effect of the Sex of an Audience on Male-Male Displays of Siamese Fighting Fish (Betta Splendens). Behaviour 139 (9): 1211-21. Print. Skomal, Gregory. 2005. Freshwater Aquarium. Hoboken, New Jersey: Wiley Publishing, Inc.