Climate change leaves fish friendless

Elevated carbon dioxide levels expected next century cause fish to struggle to find their friends, new research has shown...

Researcher Lauren Nadler, from James Cook University in Australia, made the discovery by exposing tankfuls of reef-dwelling tropical damselfish to levels of CO2 that - present trends predict - will be seen in the atmosphere by the turn of the century.

After three weeks the fish were given a choice test in which they select between joining a school of fish with which they were already familiar, or joining a school of foreign fish they've never encountered before. Compared with control fish kept in water with normal CO2 levels and which showed a strong preference for joining the fish they already knew, the fish exposed to the elevated carbon dioxide conditions lost their bias and more frequently joined the unfamiliar fish group.

"Over half of all fish species 'school' at some point in their lives, including a number of economically important groups," says Nadler, pointing out that more research will be needed to discover how this might impact on these species in future.

Importantly, she also highlights that studies have shown that smaller species appear to be more vulnerable to the effects than larger ones, favouring predators and threatening some populations.

However, Nadler acknowledges that her experiment is artificial since it does not take into account the potential for fish to adapt over long periods of time. In the present study the fish were literally dropped in at the deep end, experiencing immediately a sudden increase in CO2, which she speculates, causes biochemical disturbance within the fish nervous system, hampering the function of smell, vision and other senses. "More research is needed," she points out, "to see to what extent these animals can acclimatise to a steadily rising CO2 level."