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Take one look at the classic children’s book The Rainbow Fish, and it’s clear: Fish are the perfect subject for a watercolor painting. With bold, vibrant colors, textured scales, and delicate fins, these creatures of the sea are fun and interesting to illustrate with watercolor paints. 

Whether you’re new to watercolors or an experienced painter, try taking on the fun challenge of painting watercolor fish. Below, we share a step-by-step guide. 

How to Paint Watercolor Fish 

watercolor fish
Delicate, beautiful watercolor fish

To begin painting fish in watercolor, you will need a few basic supplies: watercolor paper, a pencil, an eraser, a few colors of watercolor paint (this tutorial uses blue, pink, and orange, but feel free to use any color combination you prefer), watercolor paintbrushes, and drawing gum or masking fluid. 

If you’re not familiar with drawing gum or masking fluid, they are solutions used to keep certain areas of your painting color-free. In this tutorial, you’ll see how masking fluid can help you create unique and easy watercolor fish

New to Watercolors? 

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Step 1: Sketch Your Fish 

fish sketch
Sketch the fish, focusing on the outline and main features, like the eyes and fins. 

Sketching is an essential step before painting any animal in watercolor. Creating a sketch will allow you to get the proportions of the fish correct, as well as map out the entire composition—in other words, whether the fish are centered, how far the fish are from each other, and how far the fish are from the edge of the paper. 

If you aren’t familiar with the shape of the fish you want to paint, don’t hesitate to use a reference picture that you take yourself or find online. 

Make sure to keep your lines light enough that they don’t show through the paint. At this point, you also don’t need to include small details, like the texture of the individual scales. Focus on the outline of the fish and the placement of any main features, like eyes and fins. 

Step 2: Apply Masking Fluid 

masking fluid paint
Use masking fluid to create a pattern on the fish’s body. 

Before you add any paint, use drawing gum or masking fluid to create a pattern within the body of the fish. Because masking fluid is essentially a glue, make sure you don’t use a favorite or high-quality brush to apply it—the masking fluid will dry on the brush, which can ruin it. If you don’t have a spare brush, try using a toothpick. 

You can make these details as simple or elaborate as you’d like. You might, for example, aim to create a more realistic watercolor fish by applying the masking fluid in a scale pattern, or you could go in a more decorative direction, making a leaf or floral pattern. Whatever pattern you choose, make sure it doesn’t take too much time, because masking fluid dries very quickly. 

Step 3: Paint the Tail and Fins 

watercolor fish
Use a wet-on-wet technique to paint the tail and fins. 

To add the first wash of paint, use a wet-on-wet technique. Use a clean, damp brush to wet the fish’s tail. Then, apply your first color—blue, in this example—around the edges of the fin. While the paint is still wet, add a few brush strokes of your second color (pink). Let that layer dry completely. 

Then, repeat the process to add a second layer. This time, use a damp brush to add just a few brush strokes of water to the base of the tail. Then, add in a more pigmented and vibrant wash of your pink paint, letting it blend along the damp area. 

Use the same general process to paint the fish’s other fins. Using a wet-on-wet technique, add in a foundational wash of blue paint, focusing on the outer edges of the fin. Then, closer to the body of the fish, add in strokes of vibrant pink paint. Ultimately, the areas close to the fish’s body will be pink, while the areas furthest away—the tips of the tails and fins—will be blue. 

Step 4: Add in Details

watercolor fish
Use a thin brush and pigmented paint to add fine lines and other small details.

Now that you have a base layer of paint, use a thin brush and highly pigmented paint—in other words, paint mixed with just a little bit of water—to add in smaller details. For example, you could add fine lines that run along the fish’s tail, or create a more defined outline along the outer edges of the fins. Pay attention to where the fish might need more dark tones or highlights, and make those adjustments now. 

Step 5: Color the Body of the Fish 

watercolor fish
Use a contrasting third color—like orange in this example—to add visual interest to the body of the fish.

Using some pink paint mixed with a good bit of water, paint the body of the fish. As you paint, you’ll see that the areas covered with the masking fluid essentially repel the paint—that’s by design, so don’t be alarmed! Before that layer dries, use your third color—orange, in this example—to add some contrast and visual interest to the body. If you’re not using this exact color palette, make sure to choose a color that will stand out from the two other main hues of your painting. 

When painting the fish’s face, make the top portion of the head darker and the bottom half lighter. Keep the main portion of the eye white, and then add a smaller black circle in the center. 

Step 6: Remove the Masking Fluid

watercolor fish
Remove the masking fluid to reveal the beautiful pattern underneath. 

Once the painting has dried completely, remove the masking fluid. In a pinch, you can do this with your finger, but it’s easiest to use an eraser, being careful not to press too hard. As you erase, you will reveal the beautiful white pattern underneath the paint. 

Dive Into Watercolor Painting

The addition of masking fluid makes these easy watercolor fish unique and eye-catching. Have fun adding different markings and details—and then be prepared for a breathtaking reveal when you remove the masking fluid to unveil your pattern. It’s an enjoyable and easy way to make painting fish in watercolor feel fresh and new! 

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