Otters were sacred to the Zoroastrians. The punishment for killing an otter was the loss of all property and land and to have one's daughters given to godly men.
In order to atone for killing an otter one had to fulfill up to 18 possible tasks including kiling 10,000 frogs. 10,000 snakes. 10,000 worms, 10,000 corpse flies, 10,000 tortoises, 10,000 ants, submitting to being whipped 10,000 times and carrying 10,000 loads of wood to a sacred site.
May be verified in the No Such Thing as a Fish Podcast