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October 25, 2001

Strange Tails

Greenhouse effects might be to blaim for the rising number of birth defects in aquatic animals.

Q: One of the captains in my Agana, Guam, charter-boat fleet caught a triple-tailed mahimahi during a charter in April 1998. I've never seen anything like it in my fishing life. How often would a mahimahi like this occur? And why does it happen? - Masao Tembata, Agana, Guam

A: I've never seen this exact variation in an offshore fish, either, although I've seen many other multiple fin and bill styles. It may be caused by a genetic defect, or it may be due to an injury very early in the fish's larval development.
Birth defects in offshore fish and other aquatic organisms seem to be growing more common, like the famous three-legged frogs being discovered in estuaries around the country. At first, scientists thought such defects might be due to pollution, and pollution certainly can cause many illnesses. But it appears that exposure to ultraviolet (UV) radiation from the sun - which many people believe is rising due to the increase in greenhouse gases in the atmosphere and the subsequent breakdown in the ozone layer which protects us from the sun - has the most direct effect on the fragile DNA of creatures whose eggs are exposed to light. Dolphin (mahimahi) eggs float on the surface, so I assume their genes are susceptible to UV rays.
The ocean is a harsh, predatory environment, and most mutated creatures are not well-adapted to survival. In this case, the fish's triple tail seems to be no detriment. Who knows? It may even have been to the fish's advantage.