Wing-like fins generate lift when the fish is propelled forward. Since the density difference between fish body and medium is not great, the fin area and associated drag does not have to be great.
Fish can move freely up and down in the water column.
Suitable only for cruising specialists or bottom predators. It is a high speed option. Buoyancy Lipid inclusion. Fine tuning is not available to adjust for a heavy meal, etc. Only a very small buoyancy margin is available, so other tissues must be lightened.