Mud skippers!
Just a word of advice from a previous mudskipper owner...
I had a pair of mudskippers for a few years and they were great. Very interesting creatures.
But I woke up one morning, and they were on the floor and dried.
They had hopped out of the tank, through the lid.
The cheap water heater has stuck ON and the water temp went up very high.
Please keep the lid on, and make sure they can always stay wet, and don't use a cheap water heater. Don't use one at all unless you really need it.
I hope you don't have to have happen to you what happened to me.
Mine like to eat freeze drine brine shrimp.