>>> I did read that some minnows for example have not air bladder at all<<<
Moose, the darters and daces generally lack air bladders. When we do the electro-shock fish sampling with the MetroParks biologist in the local streams, one of our biggest jobs is scooping up these fish before they sink into the rocks. Chubs and "minnows" will float to the top, but the rainbow darters, black-nosed daces and related will sink like a rock. They normally use their pectoral fins to walk on the bottom in search of food. They are also good indicators of stream health.
BTW, Roland Martin killed the fish, whether he wants to admit it or not. - Roberta
"Anglers are born honest,
but they get over it." - Ed Zern