It is a delicacy from Bengali ( bangali ) ( বাঙালি ) cuisine.This is an auspicious thing to cook and take a bite of in any Bengali festivals like marriage , onnoprashon ( the first rice eating ceremony of a toddler ) etc. This may look strange and gruesome but given the fact that the Bangalis are from regions that are essentially dependent on fishes, this is a symbol of bounty, prosperity, abundance if not quick protein.