Elephant fish: It is the largest fish of Iran's internal waters, which has been ranked first in terms of quality of caviar, and samples of it have been caught with a weight of about 1400 kg and an age of more than 100 years. It spawns once every 2 or 3 years and matures between 14 and 17 years old. Due to the best caviar, it ranks as the most expensive fish and caviar in the world. It has a height equivalent to one and a half meters to more than four meters, its catch record in Iran was 980 kilograms along with 120 kilograms of caviar.​​​​​​