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The Scent of an Enemy

By Chitra Padmanabhan

It seems the fish were always a smart lot. Only, humans took some time to realise the fact. Some years ago, scientists had discovered that they identify family members with their smell. Now, scientists in Glasgow University, have discovered something new, according to a report in the journal 'New Scientist'. They have discovered that the salmon fish go a step further. They actually keep a nose out for fish that smell like outsiders and not like family. Then they get tough with them.

The reason may be that they use smell to mark out their territory, the scientists feel. And so, when they get a very strong smell of outsiders, they feel threatened.

How did the scientists discover this? They brought up 44 salmon from two different families and kept them in several water tanks. All the water tanks had members of both families. In some tanks, water was let in and let out. In other tanks they kept circulating the same water. When that happened the fish scents also got stronger. For water gathers more and more of the scent with time.

The results were very interesting. In the tanks where water was let in and let out, the fish did not get very strong smells of family or outsiders. But in the tanks where the same water was circulated again and again, the fish scents were much stronger. The salmon in these tanks could easily distinguish the smell of family from outsiders. They got nasty, their fins became erect, they attacked and bit the latter.

Scientists feel this discovery will help people who raise wild fisheries. For, now they know that if they put salmon belonging to the same family in a fast flowing stream, they will not develop very strong bonds. But if they put them in pools they will grow together and multiply.