Build a narrow tail base first
The body should taper into a narrow connector before the tail spreads outward. This connector makes the tail feel flexible. If the tail begins at the full height of the body, the fish can look like one solid sign instead of an animal that bends.
Draw the upper and lower body contours moving toward each other, then let them turn outward into the tail. Keep the transition smooth. A sharp notch on both sides makes the join look cut out.
Choose a tail for the motion
A forked tail uses two pointed lobes and suggests sustained speed. A rounded tail suggests slower, controlled movement. A broad fan tail creates display and personality, while a narrow tapered tail feels agile. Select the shape that supports the story of the drawing.
Use one center line from the tail base outward before drawing the edges. Tilting that line slightly up or down gives the whole fish a swimming gesture. The two lobes can differ a little, but they should share the same direction.
Attach fins with short roots
A fin begins along a section of the body, not at a single point. Mark a short root, extend the leading edge, then return with a softer trailing edge. This construction makes the fin feel supported rather than pinned on.
Place the dorsal fin on the upper body and the anal fin below, often farther back. The side fin begins behind the gill plate. You do not need every fin in a small drawing; choose the ones that clarify balance and depth.
Use angles consistently
For a fish moving right, angle the fin tips and tail rays slightly backward. Repeating this direction suggests water flowing past the body. One fin pointing forward can indicate braking or turning, but it should look intentional.
Avoid making every fin perpendicular to the body. That creates a static symbol. Change the angles by small amounts while keeping a shared flow from head to tail.
Create depth with near and far fins
The near side fin can overlap the body with a clear edge. A far-side fin may peek below the belly and should be smaller, lighter, or partly hidden. This difference establishes which side faces the viewer.
Keep busy pattern marks away from the fin roots so overlaps remain readable. A small quiet area often describes the connection better than a dark outline around every part.