Concerned over the deaths, the wild life department has sent the blood samples of some sick gharials for test to forensic laboratories, sources in the department said.
The sanctuary, stretching from Madhya Pradesh to Pinahat town in Agra, was in the news in 2008 when around 100 gharials died after eating toxic fish.
However, this time, reason of the deaths was not clear after the post mortem, the sources said.
Meanwhile, a team of experts from the Madras Crocodile Bank Trust and Madhav National Park has reached the sanctuary to find out the reasons for the deaths, source said.
According to the conservationists and wild life officials, blood samples of ill crocodiles in Gyanpur have been sent to the Bhopal Research Institute and the Indian Research Institute at Bareilly.
While, the blood samples of ill crocodiles in Kachhuee village have been sent to the Centre for Wild Life Forensic Laboratory in Jabalpur.