Independent Lab Project:


Foraging Behavior of the Poecilia reticula In Groups of Different Sizes





Michelle Schmidt


April 30, 2002






            I tested the foraging behavior of the Poecilia reticula to compare the difference between the time it took for groups of varying size to locate food.  On average, the large group of fish (n=20) located food the fastest.  The results supported my hypothesis that a guppy will locate food significantly faster when around more guppies (p< 0.001).  The results were consistent with normal guppy foraging behavior. 


Keywords:  Poecilia retucula, foraging, behavior, guppies, groups.






            This experiment is similar to and originated from the Day et. al (2001) experiment that tested the efficiency of guppies when foraging in small and large groups.  They tested the efficiency of guppies that foraged alone and in groups of three, seven, or fifteen.  The experiment included two foraging tests, one conducted in open water and one conducted with a blockade.  The blockade had a hole on the bottom for the fish to swim through to the other side of the aquarium to locate the food. 

The expected results were that the guppies would find food more efficiently in larger groups than in smaller groups or when alone and that both open and blockade foraging areas would yield similar results (Day et al. 2001).  However, the two foraging setups did not yield the same results.  The experimental results for open foraging indicated larger groups located food faster than small groups or single fish, and blockade foraging indicated smaller groups or lone fish located the food faster (Day et al. 2001).  These results puzzled me so I decided to conduct an experiment with a similar blockade.  My hypothesis was that a guppy will locate food faster when around more guppies.
































20 cm



Fig.1 Experimental Equipment





I measured out and cut a white foam blockade to measure 20x27X3.5 cm and cut a 3cm hole in its center (refer to Figure 1).  This served as the blockade the fish would have to swim through to locate the food.  I then began the experiment by removing a plastic plant from the test aquarium and transferred all of the test fish (n=20), by net, into the 4 liter holding aquarium with water from the test aquarium.  The fish were previously living in the test aquarium where the experiment would take place. 

I placed the foam blockade into the center of the aquarium and let the water settle.  I added food to the middle of one side of the test aquarium and then the fish to the other.  I began timing as the fish exited the fishnet into the water.  For each trial, the fish was released from the net in the direct center of the side that had no food.  The first trial completed was with one fish.  The fish used in the group of one fish trial was then used as the focal fish for the next group trials of five, ten, and fifteen fishes.  Specifically, after the group of one fish trial was completed more fish were added to total the amount of fish needed for the trial.  To illustrate, for the group of five fish trial, the “focal fish” from the group of one fish trial was used and four new fish from the holding aquarium were added to the test aquarium.  After the group of five fish trial was completed, all test fish were returned to the correct starting side and five new fish were added from the holding aquarium.  This pattern was the same for the group of fifteen fish trial.  These trials were repeated five times in total.  If fish did not locate food within five minutes the timing was stopped.  Locating food was noted by having gone through the hole in the blockade and consumed food or made contact. 





The experiment yielded significant findings to support my hypothesis.  The data were evaluated by a chi square test.  The p value was 1.753x10-10. The data show that the time guppies take to locate food decreases as the size of the group of fish increases.  This opposite directionality indicates a negative correlation between the two variables, group size and time to locate food. 


# Fish in Trial

Time in Seconds to Locate Food


Trial 1

Trial 2

Trial 3

Trial 4

Trial 5
























 Fig.2   Actual raw data from trials and average computed on Microsoft Excel 2000.



Group of 5 Fish

Group of 10 Fish

Group of 15 Fish









P value = 1.753x10-10





Fig.3    Chi square test value table. 

Fig. 4. Average time guppies take to locate food categorized by actual experimental group. Group of one fish not included because it did not locate the food within the 5-minute limit


            The results of my experiment differ from that of the research I based mine upon.  The results are exactly opposite.  Day et al. (2001) found that smaller groups of fish or lone fish located the food faster than large groups.  I found that large groups found food faster than small groups and small groups found food faster than fish alone.  Perhaps the fact that I used the same fish for more than one trial and left the focal fish in the water after adding more could have led to my results.  However, the tests I conducted were significant (p=1.753X10-10).  If I were to repeat this experiment I would place the hole on the bottom because the guppies were more likely to swim on the bottom of the tank during the trials.  I would also change the focal fish for each experiment by removing it after each trial.  To better understand the foraging behavior of Poecilia reticula I have analyzed two recent studies relating foraging behavior and shoaling.    

              A recent study by Laland and Williams (1997) explains behaviors of guppy shoaling as a basis for social learning of foraging information.  In this experiment a demonstrator fish was trained to swim one out of the two routes each time it located food.  Subject fish swam with the demonstrator fish for a 5 days period of learning.  The subject fish were then tested alone to determine their preference of route to the food.  The results showed that subject fish were more likely to choose the route of their demonstrator when foraging for food. 

            In a study conducted by Lachlan et al. (1998) they asked the question of “who follows whom” in social learning of guppy foraging.  They tested adult guppies for preferences of different types of shoals of fish and foraging behavior.  The different groups varied by shoal size, size of fish in shoaling group, foraging experience, and familiarity of fish in a shoal.  Their findings yielded results of foraging success of subjects as well as behavior adopted from their shoal preferences.  Guppies were more frequently found to replicate foraging behavior shown by the majority of a shoal rather than a single demonstrator fish.  Subjects also adopted a chosen route to food after having swam with a shoal for three trials (Lachlan et al. 1998).



Day, R.L., MacDonald, T., Brown, C., Laland, K.N., Reader, S.M.  2001.  Interactions between shoal size and conformity in guppy social foraging.  Animal Behaviour.  V62:5  p.917-925.


Laland, K., Williams, K.  1997.  Shoaling generates social learning of foraging information in guppies.  Animal Behaviour.  V53:5 p.1161-1169.


Lachlan, R.F., Crooks, L., Laland, K.N.  1998.  Who follows whom? Shoaling preferences and social learning of foraging information in guppies.  Animal Behaviour.  V56:1 p.181-190.