Fish learn more in a changing environment

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A diet that fluctuates in quality produces smarter cichlids, according to research published in a recent issue of the journal PLoS Biology.

Alexander Kotrschal and Barbara Taborsky carried out a series of experiments on the cichlid Simochromis pleurospilus to investigate how performance in a learning task would be influenced by different juvenile feeding regimes.

The authors subjected groups of juvenile fish to four different feeding regimes:

1. a high food ration both in early and late life;
2. a low food ration both in early and late life;
3. a high food ration in early life, switched to a low food ration in late life;
4. a low food ration in early life, switched to a high food ration in late life. 

The diet switches were carried out when the fish were either 77 days or 133 days old (although the authors found no significant differences in the cognitive abilities of the fishes between those whose diets switched at 77 days and those switched at 133 days and subsequently pooled the results for analysis). 

The fishes were then trained to associate a visual cue with food and tested for how often they selected the positive stimulus, with their cognitive performance being tested twice (at the end of the juvenile period and a year later as adults).

The authors found that fish that experienced a change in food ration early in life outperformed those kept on constant rations in the cognitive test, irrespective of the direction of the implemented change and the mean rations received.

According to the authors, the results of the experiment support the hypothesis that changing environments improve learning abilities. They also suggest that the improvement of cognitive abilities in response to environmental change is adaptive for S. pleurospilus.

The cichlids, being algae grazers, spend most of their time as juveniles in shallower waters where food is more abundant. While some fishes spend their whole lives in shallow waters, some move out to deeper areas, where food is less plentiful.

Improved cognition may help them to find and remember patches of high-quality turf algae, while fish that remain in the natal habitat do not necessarily require a better cognitive performance.

For more information, see the paper: Kotrschal, A and B Taborsky (2010) Environmental change enhances cognitive abilities in fish. PLoS Biology 8, e1000351. doi:10.1371/journal.pbio.1000351