Selin

The Selin live in fresh water lakes and rivers through Tjiramor.
They resemble large, thick eels. They can grow to 7 feet in length and up to 30 lbs. in weight. Like eels, selin have a snake-like body, but lack fins. They propel themselves through water by undulating their long bodies.
Selin have grey or brown skin that is often speckled with lighter and darker colors. This coloration provides camouflage against lake and river bottoms. Their undersides are lighter in color to blend in with the lighter water surfaces.
The selin feed on fresh water fish, typically swallowing their prey whole. The food is stored in large pouches along the selin's digestive tract. Toxins in the pouches kill the fish but do not break it down.
Selin will return the collected food to its young. The selin mate and care for their young in mud burrows along the sides of lakes and rivers. Once the selin returns to its burrow, it regurgitates the collected food. A selin can lay up to 100 eggs, of which two or three dozen survive to be hatched. Young selin are hungry and adult selins spend most of their time collecting fish for them.
Early Tjiramor fishermen discovered they could domesticate selin and then gather the fish the selin collect. As long as about a third of the collected fish are left for selin young, the selin don't notice that some of their catch is being removed by fishermen.
This domestication allows Tjiramor fishermen to sustainably fish local rivers and lakes. The selin never deplete the water as nets and rods might. It also allows for fishing in harder-to-reach tributaries and possible dangerous waters.
A market has also developed for taking "full" selin (along with some of their young) to fresh water sources that lack selin.

Fishermen have also developed an antidote of a sort for the selin's toxin. If this is administered to a young selin, that selin's toxin doesn't kill collected fish, but instead paralyzes them. When the young selin becomes an adult and collects fish, fisherman may then take the "full" selin to other fresh water sources to essentially stock them with the new fish.