1. Predators and the Strength of Preferences for Familiar Schools in the Fathead Minnow, Pimphales promelas Jessica A. Jadlocki York College of Pennsylvania INTRODUCTION: Schooling is an adaptation by many different fish, which has numerous associated benefits. One of the most significant benefits is to reduce capture by predators. Recent studies have found that preferences for familiar schools benefit schooling fish. Schooling fish prefer to join schools of familiar conspecifics as opposed to schools they have never before encountered (Magurran et al. 1994). These familiarization preferences have shown to maximize certain antipredator behaviors such as school cohesiveness (Chivers et al. 1995). One of the most recent studies examined the strength of these familiarization preferences (Barber et al. 2000). Benefits of familiarity were found to be equivalent to the benefits received from schooling with a non- familiar school which was twice as large. Although one of the main adaptive reasons for schooling is to reduce predator risk, the strength of preferring familiar schools has not been examined while in the presence of a predator. QUESTIONS: 1. Will the presence of a predator increase or decrease the strength of familiarity preferences and/or will the size of the school become more important? 2. While in the presence of a predator, at what school size will a small familiar school become less attractive than a large non- familiar school? HYPOTHESES: 1.The results of the first three trials will agree with those of Barber et al. (2000). As the familiar school becomes smaller in number and the non-familiar school becomes larger, the preference for the familiar school will become less. 2. Preferences for schooling with familiar fish will become stronger with the presence of a predator. Experiment 1: Familiarity preferences were tested by giving the test fish a choice between two schools of even size. One school was composed of 10 familiar fish and the other school was composed of 10 non-familiar fish. Experiment 2: School size preference was determined by presenting the test fish with two schools composed of non-familiar fish in different size combinations: 10 vs. 10, 9 vs. 11, 7 vs. 13, and 4 vs. 16. A titration scheme was chosen so that the number of test fish in the experimental tank remained constant at 20 fish. Experiment 3: In order to determine the strength of familiarity preferences the titration technique was also utilized, however the smaller school was always composed of familiar fish. Experiment 4: This test examined the strength of familiarity while in the presence of a predator. A sunshine bass, Morone chrysops / Morone saxatilis, was placed behind the settling chamber in a clear perforated aquarium. All other methods proceeded the same as in experiment 3. Table 1. Number of recordings, all test fish combined, spent within each 15 cm section near the familiar or the non-familiar school. Table 2. Mean number of observations test fish spent within 45 cm of the familiar or non-familiar school during each trial. An unpaired t test determined the significance level between the mean number of observations recorded for familiar and non- familiar schools. CONCLUSIONS: 1.Contrary to the expected results only the 10-10 familiarity trial duplicated the findings of Barber et al. (2000), and showed preference for the familiar school. Barber et al. found that the 7-13 trial resulted in little to no preference for the familiar school or non-familiar school and the 4:16 trial produced a much greater preference for the larger, non-familiar school. 2.As predicted, the preference of schooling with familiar conspecifics became stronger while in the presence of a predator. However, as the familiar school became smaller and the non-familiar school became larger the presence of a predator increased the preference for the larger school. Thus, fathead minnows prefer schooling with familiar conspecifics and these familiarity preferences increase while in the presence of a predator. However, the preference for familiar schools is dependent on the size of the familiar and non-familiar schools. FUTURE RESEARCH: How do predators affect the strength of preferences for familiar schools in the wild? Do schools of fathead minnows living in a predator free environment have less preference for familiar schools than those living under heavy predation? Could preferences for familiar conspecifics regulate school size and prevent departure to larger non-familiar schools? METHODS: Experimental Set-up: The experimental tank was approximately 120 cm long and about 52 cm high. A piece of poster board was divided into eight; 15 cm sections and was placed on the back of the aquarium. There were 4 sections on the familiar side and non-familiar side of the aquarium, with section 4 being the closest to the familiar or non- familiar school and 1 being the furthest away. A recording RESULTS: 1.In all the trials the test fish were most often observed within 15 cm or the fourth quadrant of one of the schools (Table 1). 2.In the 10:10 familiarity trial the familiar school was preferred over the non-familiar school. Excluding the 4:16 trial, in which very little preference was shown, the rest of the trials indicated a preference for the larger non-familiar school (Figure 1). 3. In the 7:13 bass trial the familiar group was preferred more often than in the 7-13 trial, while the preferences for the non-familiar school remained the same. 4.In the 4-16 trial the familiar school was preferred more than in the 4-16 bass trial where as the non-familiar school was preferred more in the 4-16 bass trial than in the 4-16 trial. 5.An unpaired t-test, comparing differences between familiar and non-familiar schools, was performed for all the trials and the resulting P-values were not significant (Table 2). Trials 10-10 7-13 7-13bass 4-16 4-16bass Familiar 17.7 11.0 13.4 16.4 12.5 Non-familiar 14.0 18.3 18.4 15.6 20.4 P-value 1 0.5614 0.1745 0.4346 0.8988 0.2624 1 unpaired t test Familiar Non-familiar 0 2 3 4 0 2 3 4 10-10 1 11 48 90 7 10 26 97 7-13 - 19 15 75 11 28 36 108 7-13bass - 49 29 55 9 22 34 117 4-16 6 21 30 105 13 24 52 68 4-16bass 1 14 20 90 14 25 51 110 Mean 1.6 22.8 28.4 83 10.8 21.8 39.8 100 of 0 indicated that the test fish was making contact with the fish in one of the schools. At both ends of the tank there were clear, perforated cylinders, which were the height of the tank. Another perforated, clear, plastic cylinder functioned as a settling chamber. The test fish was placed in the settling chamber for 10min to assess both schools before being released. The position of the test fish in the aquarium was recorded every 10s for 6min, and the proportion of observations the fish spent within each section was calculated (Barber et al. 2000) ABSTRACT: This study examined predator effects on preferences for familiar schools in the fathead minnow, Pimephales promelas. A test tank contained two schools at opposite ends of the tank and test fish position was recorded. Interactions between preferences for familiar schools and for larger schools were examined. Lastly, predator effects of a bass on test fish preferences were determined. In the familiarity test, the familiar group was preferred, while in the rest of the trials the larger non-familiar group was preferred. The preference of schooling with familiar conspecifics became stronger when in the presence of a predator. However, as the size difference between schools became larger the preference for the larger school increased. Due to a small sample size, an unpaired t test considered all results not significant. In conclusion, the strength of familiarity preferences increases when in the presence of a predator, but is dependent on the size difference between familiar and non-familiar schools. LITERATURE CITED Magurran, A. E., Seghers, B. H., Shaw, P. W. and Carvalho, G. R. 1994. Schooling preferences for familiar fish in the guppy, Poecilla reticulata Journal of Fish Biology 45: 401-406. Chivers, D. P., Brown, G. E. and Smith, R. J. F. 1995. Familiarity and shoal composition in fathead minnows (Pimephales promelas): implications for antipredator behavior. Canadian Journal of Zoology 73: 955-960. Barber, I. and Hazel A. W. 2000. How strong are familiarity preferences in shoaling fish? Animal Behaviour 61: 975-979. ACKNOWLEDGEMENTS Thanks to Dr. Rehnberg for his guidance and support and thanks to the library staff for helping with my literature search.