The key to a realistic fluid effect is a smooth, curved line. Hand-drawing with a mouse rarely works; the is your best friend here.
A subtle sperm effect (abstracted) is popular in "swim schools," fertility clinics, and marine biology startups because it conveys forward momentum and life. sperm effect photoshop
Studios like Nucleus Medical Media use a refined version of this technique to illustrate fertilization. The sperm effect Photoshop technique is used for storyboarding before 3D rendering. The key to a realistic fluid effect is a smooth, curved line