Exercise protects mosquitofish from UV-B rays

From human couch potatoes to captive salmon and even our pets, adopting an active lifestyle can extend life expectancy and improve health. Releasing protective compounds (antioxidants) and enzymes into our bodies that protect against the ill effects of the toxins (reactive oxygen species) that are naturally produced by metabolism, exercise can even reduce the incidence of cancer and the effects of ageing. Knowing this, Frank Seebacher (University of Sydney, Australia) and Craig Franklin (University of Queensland, Australia) wondered whether exercise may also protect animals from the damage caused by a dose of sun. Seebacher explains that exposure to UV-B, one of the wavelengths that causes sunburn, also produces the reactive oxygen by-products that are so damaging to our tissues. So could exercise protect animals from the harmful effects of sun exposure too?

Introduced from the US into Australian river systems with the intention of controlling mosquito populations, the controversial mosquitofish (Gambusia holbrooki) seemed like the ideal species with which to test Seebacher's theory. After collecting the invasive fish from the Manly Dam near Sydney, Seebacher and Ensiyeh Ghanizadeh-Kazerouni kept the fish in tanks of flowing or still water, and exposed some of the fish to several hours of mild UV-B light each day. Having kept up the different treatments for 2 weeks, Ghanizadeh-Kazerouni then checked the fish's fitness by recording the swim speed at which they became exhausted and their oxygen consumption while swimming steadily. Next, Ghanizadeh-Kazerouni measured the fish's antioxidant capacity and the amount of damage to their muscle caused by reactive oxygen species produced by the UV-B exposure.

Needless to say, the fish that had been training in flowing water were better swimmers than the fish that had had an easy time in the still water, although the exercise did not improve their metabolism – their oxygen consumption was essentially the same as that of the untrained fish. However, the exercise did seem to protect the fish from the damaging effects of UV-B exposure. While the muscles of the unexercised fish were clearly suffering the effects of increased exposure to the reactive oxygen species produced by the UV-B exposure, the exercised fish had lower levels of oxidative damage after receiving the same dose of UV-B rays. And when Ghanizadeh-Kazerouni analysed the strength of the fish's protective antioxidant response, the fish that had been swimming against a current were significantly better protected from damage from reactive oxygen species by a protein (catalase) that neutralises the toxins and a scavenger compound (glutathione).

So it seems that in addition to improving physical fitness, exercise can also provide some protection from the damaging effects of UV-B exposure. However, Seebacher and Franklin are concerned that alterations in rainfall patterns and human activity such as dam building could make fish increasingly vulnerable to the harmful effects of the sun's rays as flow in rivers declines and the fish work out less just to stay still.