It has a glowing tail. It glows. That means it gives you light. Light is good.

1 Glowtail Egg+ 3 Aquatic Mushrooms+1 Cooked Fish+Mejos+Fiber+Water= Glowtail Kibble

They have the best glow then of any of the glow tames. Babies eat meat not berries.

Passive tame, feed 3-4 Ascerbic Mushrooms for easy tame. Encounter in caves usually near water.