the left fin or also known as the dorsal fin
my dicktionary
Dolphins move up and down. Fish move mostly in a straight line.
Up and down. I've also noticed that mammals, such as whales and dolphins, beat their tail up and down, while fish, like sharks, beat their tail side to side. Hope this helps!
Whales are not fish. Fish move their bodies sideways when they swim; whales move their bodies up and down.
swim bladder
They assist in stabilizing the fish so that it doesn't roll side to side. It also helps it change its depth in the water working like a wing so it can move up and down.
to move up and down in water
to move up and down in water
With their tails; although the subs is mechanical.
Fish can control their buoyancy using an organ called a swim bladder, which helps them move up or down in the water. If a fish has too much gas in its swim bladder, it may float to the surface; if it has too little, it may sink. Factors like water temperature, food consumption, and depth can also impact a fish's buoyancy.
The paired fins, pectoral and pelvic, act as hydroplanes and control the pitch of the fish, causing it to swim downwards or upwards according to the angle to the water at which they are held by their musclesalso the swim bladder - Novanet
Gravity helps you move down the slope but works against you on the way up.