These lesions probably caused the onset of debilitating gout, said Paolo Martelli, one of four veterinarians with the World Conservation Union sent in to examine the dead reptiles.
Gout is painful inflammation caused by a buildup of microscopic crystals of uric acid in the joints. Kidneys normally remove most uric acid from the blood.
The doctors also found surprising amounts of fat in the animals' tissues, Martelli added, which could be explained by the growing abundance of a cichlid fish from Africa known as tilapia in Indian rivers.
The species was introduced in the region a few years ago to boost Indian aquaculture. It has since grown so plentiful that gharials now feed on it almost exclusively.
As tilapia move from polluted rivers into the Chambal, they ingest and store chemicals in their tissues. Gharials eating the abundant fish therefore accumulate even larger amounts of potentially harmful substances in their body fat.
"When cold temperatures came, the uric acid precipitated [separated into a fine suspension of solid particles] and began causing problems," said Martelli, who is based in Hong Kong.
"So winter coupled with excess food could have made the gharials more susceptible to the toxin," he said.
"As the temperatures warm up, the animals will improve. But next winter may again be a delicate time for the gharials."
Two Indian laboratories are still trying to determine exactly what kind of chemical is to blame.
Experts think that the agent is either an industrial chemical being released into the Yamuna by a new facility or one that was used by an older plant that shut down and illegally dumped all its waste in the river.
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