Step 6: Add two more triangle-like shapes as guides for the dorsal and anal fins. Draw a big angled line at the top of the body to the left of the main circle and another at the body to the left of the pelvic guide.
That's it for the initial sketch! From this point on, press harder with your pencil to get a more defined sketch.
Step 7: Draw the eye as a circle inside the arc near the top, close to the tip. Add a smaller circle inside for the pupil and shade it in. Add a few lines around the pupil for extra detail.
Step 8: Draw the neon tetra's mouth at the tip of the arc. Draw a line with a diagonal orientation for the actual mouth. Then follow the path of the arc to draw the top and bottom lips.
Step 9: Draw the rest of the head using the initial arc as a guide. Follow the path of the arc as you darken the lines to draw the top and bottom of the neon tetra's head.