Đi sâu xác vấn đề cá chết hàng loạt ở Nam California. (có script)

Im Alex Villarreal with the VOA Special English Agriculture Report, from http://voaspecialenglish.com | http://facebook.com/voalearningenglish People in a c...

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People in a community on the Pacific coast in Southern California awoke in March to a sea of dead fish. About eight hundred fifty sailboats and powerboats come and go from the marina at King Harbor in the city of Redondo Beach. But the sardines that swam into the marina never swam out. Estimates put the number of dead fish in the millions. Reporter Pete Demetriou from KNX Newsradio in Los Angeles spoke to a man who has lived in the area for twenty-six years. The man said the die-off was as bad as he'd ever seen. But it was cleaned up pretty quickly, so there was not too much smell. He remembered that about five years ago there was another serious kill-off of fish in King Harbor. It was caused by a harmful algae bloom, a so-called red tide of microscopic organisms that spread from time to time. But this time scientists found no toxic algae in King Harbor, so it was a mystery. A scientist at the University of Southern California released findings of continuing research in his laboratory. Professor David Caron said fish collected on March eighth, the day of the kill, tested "strongly positive" for domoic acid in their stomach contents. Domoic acid is a powerful neurotoxin produced by one kind of microalgae. Fish such as sardines and anchovy can get poisoned when they eat plankton that have eaten the algae. Researchers from USC confirmed that plankton collected about twenty kilometers southwest of Redondo Beach the next day had very high levels of domoic acid. This would support a theory that the fish became poisoned in coastal waters before entering the harbor. High levels of domoic acid in the sardines may have worsened the effects of oxygen loss in the water as the fish crowded into a limited space. Or the domoic acid may help explain why they entered the marina. Professor Caron said research shows that domoic acid poisoning can cause abnormal swimming in some kinds of fish.Harmful algae blooms are a common cause of fish kills. Domoic acid can also cause neurological disorders and death in animals that eat fish poisoned with the neurotoxin.

For VOA Special English, I'm Alex Villarreal. If you ever miss one of our programs,go to voaspecialenglish.com to find transcripts and MP3s of all of our reports.

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