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Using video stimuli to study the schooling behavior of Tiger barbs
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One fish was caught from the holding tank and was transferred to the test tank in a cylindrical tube. A plastic square was placed over the opened end to hold the fish in while placing the tube upside down in the tank. The fish was held in the center of the tank for 2 minutes. This was to allow the fish to acclimate to the test tank. The fish was released and the side that the fish swam to was recorded at time 0. Each test lasted 5 minutes and times were recorded for when the fish switched sides of the tank.
Three test groups were studied; Large vs. Same, Same vs. Small, Large vs. Small. Fourteen fish were used for each test group. Seven were used for the experiment and a different set of seven fish were used for the control. In the control the screens were moved to the opposite side to ensure that the fish did not prefer one side over another. Each test group was replicated three times.
Why Fish School
There are benefits for a fish to school with others. One benefit is protection from predators. When fish school together they create the “confusion effect”, which makes it hard for the predator to target on one fish (Theodorakis, 1988, 1). Another benefit of schooling is that it allows a higher success rate of foraging since they are spending less time keeping an eye out for predators (Peurkuri, 1997, 271).
How Fish School
There are different factors a fish will choose to group with in a school. One factor is familiarity. In a study by Magurran et al., they found that female guppies tend to school with the familiar ones over the unfamiliar ones (1994, 404). When swimming with familiar neighbors a fish has the benefit of knowing the other fish’s swimming behavior in predator avoidance and how well that fish forages (Magurran et al., 1994, 404). Another factor that fish sort by is parasite load. This is due to the parasites leaving black spots on the skin of the fish (Hoare et al., 2000, 552). When the fish have too many parasites on them they become phenotypically different and end up standing out from the rest of the school (Hoare et al., 2000, 552). One of the major assortments found in a school of fish is by size. Because of the “confusion effect”, they tend to swim with similar size fish (Theodorakis, 1988, 11). Hemelrijk and Kunz found that large fish tend to swim along the outside edges of the school but moved to the center when a predator was near by (2004, 183). With small fish the opposite was true. They tended to stay near the center and then forced to the outside when a predator was near by (Hemelrijk and Kunz, 2004, 183). If a fish is dissimilar in size from the rest of the group they tend to forage less when they are the large-odd fish (Peuhkuri, 1997, 274).
The mean of time, in seconds, spent on each side was calculated and a t-test was done.
A 10 gallon tank was used for the test tank and the video stimuli were played at each end of the tank. A large screen and a smaller screen were used to play the video stimuli during the experimentation. This was to make the largest and smallest stimuli distinctive from each other to the fish. To reduce the reflection in the tank, blue poster board was posted around the tank and around the viewing area of the video when it was not played at full screen.
A school of 17 Tiger barb fish was recorded for 15min and edited down to 9min using Windows Movie Maker. The video was then played back using Windows Media Player.
Use of Video Stimuli in Previous Studies
Large vs. Same
Large vs. Small
Same vs. Small
There are some benefits and problems when using video stimuli in research with animal behavior. One of the benefits is that it allows one to look at just one variable at a time (Gonçalves et al., 2000, 351). It also allows for a variety of different manipulations that could not be easily done with a model or with a live stimulus (Gonçalves et al., 2000, 351). One problem with using video stimuli is that the animals may have problems perceiving the video image (Clark and Stephenson, 1999, 322).
In a study by Gonçalves et al., video stimuli were used to see if Salaria pavo would respond (2000, 352). The test fish was presented with a live fish on one end of the tank and a video recording of that exact fish on the opposite end of the tank (Gonçalves et al., 2000, 353). They concluded that Salaria pavo did not respond to the video stimulus (Gonçalves et al., 2000, 355).
Clark and Stephenson, studied the response to video stimulus using Tiger barb fish (1999, 318). They compared the response to the live stimulus with the response to the computer stimulus and the computer animated stimulus (Clark and Stephenson, 1999, 318). Since there was no significant difference among the results, they concluded that the Tiger barbs did respond to the video stimulus (Clark and Stephenson, 1999, 321).
There was no significant difference between the stimuli with the test groups Large vs. Same and Large vs. Small. There was a large significant difference in the test group Same vs. Small. The fish used for the test group Large vs. Small spent most of their time swimming back and forth instead of schooling with the stimulus on either end. This may have reduced the significance between the stimuli in that test group. Although there was no significant difference, there was still a slight preference for the larger stimulus in each test group. A study done by Peuhkuri found that foraging of the odd-sized fish was only suppressed when they were larger than the fish in the shoal (1997, 274). All the other fish within that school was the same size and so the test fish was the only one a different size (Peuhkuri, 1997, 274). This may be due to the fact that when they are smaller than their shoal mates they “feel” that they don’t stick out as much (Peuhkuri, 1997, 276). Since they “feel” less at risk when they are the smaller odd-sized fish, they would then prefer to stick with the larger fish over the smaller fish.
Manipulations of the video stimulus were made so that the fish in the recorded school was larger than the test fish, the same size as the test fish, and smaller than the test fish. This was done by playing the video at full screen or 200%. The large stimulus was played on the large screen at full screen. The small was played on the small screen at 200%. The same stimulus was played either on the large screen at 200% or on the small screen at full screen. When the same stimulus was compared to the large stimulus it was played at full screen and when it was compared to the small stimulus it was played at 200% during experimentation.
Clark, D.L. and Stephenson, K.R. 1999. Response to video and computer-animated images by the tiger barb, Puntius tetrazona. Environmental Biology of Fishes. 56: 317-324.
Gonçalves, D.M., Oliveira, R.F., Körner, K., Poschadel, J.R., and Schlupp, I. 2000. Using video playbacks to study visual communication in a marine fish, Salaria pavo. Animal Behaviour. 60: 351-357.
Hemelrijk, C.K. and Kunz, Hanspeter. 2004. Density distribution and size sorting in fish schools: an individual-based model. Behavioral Ecology. 16 (1): 178- 187.
Hoare, D.J., Ruxton, G.D., Godin, J.J., and Krause, J. 2000. The social organization of free-ranging fish shoals. OIKOS. 89: 546-554.
Magurran, A.E., Seghers, B.H., Shaw, P.W., and Carvalho, G.R. 1994. Schooling preferences for familiar fish in the guppy, Poecilia reticulata. Journal of Fish Biology. 45: 401-406.
Peuhkuri. N. 1997. Size-assortative shoaling in fish: the effect of oddity on foraging behaviour. Animal Behaviour. 45: 271-278.
Theodorakis, C.W. 1988. Size segregation in minnow schools. A Thesis. Ohio State University..
Ward, A.J.W., Hoare, D.J., Couzin, I.D., Broom, M. and Krause, J. 2002. The effects of parasitism and body length on positioning within wild fish shoals. Journal of Animal Ecology. 71: 10-14.
*Same is the actual size of the test fish.
An individual fish will choose to swim with a school composed of larger fish over a school composed of smaller fish.
Acknowledgements: Dr. Hogan, Dr. McShaffrey, Brittany, Emily, Valerie, Katherine, Belpre Aquarium and Pet shop, and Fish-n-Stuff