Published online 8 November 2007 | Nature | doi:10.1038/news.2007.228

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Antioxidants can change fish behaviour

Sticklebacks on a low-antioxidant diet are poorer parents.

A red belly means lots of antioxidant goodness inside: and energy for the kids.NHPA/LAURIE CAMPBELL

Antioxidants are all the rage, with research suggesting that they may help to prevent cancer, strokes and heart disease. Now a study highlights how these oxygen-mopping compounds affect more than just cellular health: they also seem to effect behaviour.

Male three-spined stickleback fish (Gasterosteus aculeatus) fed on a high-antioxidant diet spend more time and energy fanning oxygen-rich water onto the eggs in their nest, researchers have found.

The results aren’t entirely surprising, as an indirect link between diet, well-being and behaviour makes sense. “I would expect to see some behavioural changes from antioxidants through effects on body condition or immunocompetence,” says Ulrika Candolin, an ecologist at the University of Helsinki in Finland. “But this study suggests a direct pathway, which is interesting.” A lack of antioxidants seems to make the fish’s muscles tire more readily.

Candolin says she thinks it is likely that behavioural changes would be seen in other animals deprived of antioxidants. But whether these changes are the result of fatigue or deteriorating health would require further study.

Red bellies

Stickleback fish feed on fungi and algae that produce organic pigments called carotenoids. These pigments come in reds, oranges and yellows and serve many purposes, but key among them is their importance in sexual display. They give zebra finches their orange beaks, blue tits their yellow feathers and sticklebacks their red bellies. All these characteristics are used to attract mates. Without carotenoids, the animals lose their colour and so will fail to impress potential partners.

When it was discovered that carotenoids also function as antioxidants, Tom Pike at the University of Glasgow, UK, and a team of researchers became interested in how fish would respond to a diet low in the colourful compounds.

Pike and his colleagues placed 40 male sticklebacks in individual aquaria and fed them fish food containing either 10 or 200 micrograms of carotenoids per gram of fish food – within the normal range that they would get in the wild — over six months. The researchers then placed gravid females in with the males, allowed them to spawn, and then removed them again. The males initiated their standard behaviour of fanning their eggs with their pectoral fins, an activity that oxygenates the eggs and improves offspring survival, particularly in hypoxic waters.

The spring in your step

They then watched how fish on different diets responded when oxygen levels in the water were reduced to 30% of normal. They report in Behavioural Ecology1 that sticklebacks on high-antioxidant diets increased their fanning from 49% of the time to 82% of the time, whereas sticklebacks fed low-antioxidant diets did not increase their fanning activities.

“What really surprised us was that there was a behavioural response to a lack of carotenoids,” says Pike. “The fish were otherwise completely healthy, so we think the absence of carotenoid antioxidants caused muscle fatigue in the fish from strenuous exercise.”

As for humans, despite the large volumes of work being done on the effects of antioxidants on our bodies, Pike points out that there has been very little research on antioxidants and behaviour. But he guesses it might have a similar effect: “While I don’t think consuming lots of antioxidants is necessarily going to add a spring to your step, not getting enough could take your spring away,” he says. 

  • References

    1. Pike, T., Blount, J. D., Lindström, J. & Metcalfe, N. B. Behavioral Ecology 18, 1100-1105 (2007). | Article |
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