I bought 7 yoyo loaches for my 75 gallon aquarium today. They're the only fish in the tank. I noticed that they seem to be taking turns......a few of them rummage throught he gravel looking for food while the others swim up and down the back/sides of the tank (the highest the go is midway up). Then they switch, the loaches that were rummaging start to swim up and down while the ones that were swimming start to rummage. Is this normal behavior?