The Effect of Environment on Learning in Carassius auratus
There are many studies which have shown that the existence of social interaction as well as enriched non-social stimuli influences the memory and learning ability. Especially, rodents in the enriched environment displayed the improvement in the learning and memory tasks, regardless of the existence of social interaction (Lambert et al., 2005). I formed a hypothesis that the goldfish living in an enriched environment would learn faster and better than the goldfish living in a simple environment. I tested two groups of the goldfish, Carassius auratus, in a net-escaping task over ten trials, two trials a day. However, the result showed no significant difference between two groups.
Key words: spatial memory, a net-escaping task
Spatial memories are crucial for survival in animals; remembering the location of the food, dangerous areas where predators live and the way to go to roost. Chimpanzees, Pan troglodytes, especially, show their ability to memorize where the food is and find it without difficulty (Menzel, 1973). Although fish are notorious for their poor memory, so that there is a notion that fish have three-second memory, many researchers have demonstrated that fish also have spatial memory.
In the experiments with guppies, Poecilia reticulata, about the spatial memory, the subject guppy was supposed to go and find the reward chamber, in which a female guppy existed (Burns and Rodd, 2008). As the number of trials increased, the performance of guppies improved. On the other hand, there was research that indicates the effect of social interactions on problem-solving performance in rainbowfish, Melanotaenia dubiously (Brown and Warburton, 1999).
In addition, rodents in the enriched environment displayed improvement in learning and memory tasks, regardless of the existence of social interaction (Lambert et al., 2005). The enriched environment induces morphological change in synapses in the parts of the brain involved in memory and learning and the growth of dendritic branching. Leggio and her colleagues (2005) observed the morphological change in the parietal lobe, and the enriched environment produced more dendrites.
On the basis of all this information, I designed an experiment with the hypothesis that the goldfish, Carassius auratus, living in an enriched environment would learn faster and better than one living in a simple environment.
I bought eight goldfish at the Petco pet store and divided them into two groups. There were two circular water tanks (a radius of 10.5 cm, a height of 21 cm). In one water tank, there were one real and two artificial water plants and one temple-shaped decoration. In the other tank, there was nothing, and every wall of the water tank was covered with white sheets. One day after I bought the fish, one of them died, so I proceeded with the experiment with seven fish. After three days, the seven fish performed a net-escaping task in a bathtub (105 cm ´ 38 cm ´ 34 cm). The subject fish was supposed to escape from the net through a hole in that net. To escape from the net sooner, fish should remember the location of a hole in the net and get out through that hole. The size of the net was 17 cm ´ 12.2 cm ´ 13.2 cm, and the hole was located on the left side of the net, a radius of 1.6 cm.
Before the task, I gave a fish one minute for habituation after I released a fish into the bathtub. Before and during the task, there were two other fish in the bathtub, outside the net which could motivate the captive subject fish to escape out of the net. In order to let the fish know about the existence of the net, I pretended to catch the subject fish with the net before the task was started. Once the task started, the time it took to escape was recorded. The task was performed over ten trials, two trials a day. I tested one fish at a time and the fish in the simple environment performed first.
To analyze the results, I averaged the time to escape of all ten trials. I used the T-test to judge whether the difference between the two groups was statistically significant or not (tail 1, type 3). In this experiment, the different effect between two environments on the performance in a net-escaping task of goldfish was not statistically shown (P=0.07). Also, contrary to expectation that performance of each group in the second trial was better than that in the first trial, this difference was not statistically significant (P=0.11) (Fig. 1).
Figure 1. The time it took for fish from an enriched environment and a simple environment to escape from the net
Many studies in humans and nonhumans have shown the crucial role of the environment in learning and memory (Burns and Rodd, 2008; Lambert et al., 2005; Leggio et al., 2005). It is known that the enriched environment can induce improvement in learning and memory by changing the synapses and neurons morphologically in the parts of brain, which are involved in learning and memory.
Although this experiment was carried by on the assumption that the goldfish living in an enriched environment would learn faster and better than that of the goldfish living in a simple environment, the result did not statistically support the hypothesis. The number of the subjects, which participated in the experiment, might be too small (n=7). During the experiment, there was an interestingly different behavioral pattern between the two groups which was observed soon after being releasing into the bathtub, which was a new environment. The fish from the simple environment moved more vigorously than ones from the enriched environment. It seems that the short-timed deprivation of environmental stimuli made the fish in the simple environment respond actively to a new stimulus. In turn, this more active behavioral pattern might produce the likelihood to escape from the net. Also, the age of fish was not completely controlled. If the same net-escaping task is performed with fish which are raised in the assigned group after the birth until they become adults, the result may be different from the result obtained in the present experiment.
Brown, C. and Warburton, K. (1999). Social mechanisms enhance escape responses in shoals of rainbowfish, Melanotaenia duboulayi. [Electronic version] Environmental Biology of Fishes, 56 (4), 455-459.
Burns, J. G and Rodd, F. H. (2008). Hastiness, brain size and predation regime affect the performance of wild guppies in a spatial memory task. [Electronic version] Animal Behaviour, 76 (3), 911-922.
Lambert, T. J., Fernandez, S. M., and Frick, K. M. (2005). Different types of environmental enrichment have discrepant effects on spatial memory and synaptophysin levels in female mice. [Electronic version] Neurobiology of Learning and Memory, 83, 206-216.
Leggio, M. G., Mandolesi, L., Federico, F., Spirito, F., Ricci, B., Gelfo, F., and Petrosini, L. (2005). Environmental enrichment promotes improved spatial abilities and enhanced dendritic growth in the rat. [Electronic version] Behavioural Brain Research, 163, 78-90.
Menzel, E. W. (1973). Chimpanzee spatial memory organization. [Electronic version] Science, 182 (4115), 943-945.