Completed & Tutorial: Fish Costume

I’ve been secretly stitching on my son’s Halloween costume all week in preparation for my first guest post on The Train to Crazy’s Handmade Dress Up Series. Grab your favorite beverage and a comfy seat for this post. It’s a doozy.

Last year when my son asked to be a zebra for Halloween, I took on the challenge and came up with the world’s cutest costume. It’s furry, too!

zebra 1 zebra 2 zebra 3

This year when I asked him in August what he wanted to be, he said a ghost. I was disappointed. Anyone can cut some holes in a sheet. I wanted to do some real sewing. Two weeks later, he had changed his mind. He wanted to be a green fish. After asking him several more times, his mind was set. A green fish it is.

I brainstormed for weeks and Googled fish costume images for hours. I settled on using his TNT hoodie pattern vintage McCall’s 5709 paired with a TNT pants pattern New Look 6880 as the base – the same combo I used for the zebra.

IMG_0029 IMG_0031

And here’s how they look as a fish:


The fashion fabric is a knit tricot base foil printed with green scales. It was labeled as “mermaid foil” on the bolt end. That solved my issue of making scales, but this stuff is a nightmare to work with. It’s knit so it stretches, but the foil is simply adhered to the surface and doesn’t stretch – it cracks. That means that any time the base knit stretches, the foil gets cracked and distorted. Ugh!

I decided to minimize the stretch by underlining the whole thing. I chose a green flannel for the underlining because Halloween is often quite chilly around here and a decently warm costume is usually a good thing. Now watch the weather turn to 75 degrees on October 31. LOL!

The fins are a contrast green lame fabric which is fairly sheer. I was trying to mimic the sheer nature of natural fish fins here. As you’ll see later, the dorsal fin isn’t sheer anymore because I had to interface it. Oh well.

Want your own little fishy? Here’s a tutorial.

Materials Needed:

fashion fabric – preferably with scales, yardage based on hoodie and pants pattern envelope

1-5/8 yards contrast sheer fin fabric (this is for 3T, adjust for larger/smaller child)

1-1/4 yard very stiff double sided fusible interfacing (if you can’t find double sided, get some spray adhesive and stiff sew-in interfacing)

white felt remnants

black felt remnants

green, white, black thread

very heavy green thread

1-1/2 yards boning

1 yard fishing line or heavy duty monofilament thread

drawstring for hoodie

French curve, design ruler, or a good eye for drawing a tail-shaped curve

strong safety pin

Let’s begin!

Cut your main fabric using the hoodie and pants pattern as instructed.

Lay the hoodie front (or back, doesn’t matter) piece (#4) perpendicular to the sleeve piece (#8), matching at the armpit. Measure the distance from the armpit to the cuff hemline of the sleeve. This is the width of the side fin. Gauge how far down the side of the child you would like the fin to extend and make that the length of the side fin. Using pattern tissue, sketch out a pleasing fin shape. Once you’re happy with it, cut it out and cut the contrasting fin fabric. Make sure that the fin doesn’t extend into the portion of the sleeve which is intended to be the hem.


Construct the hoodie according to directions, leaving the side underarm seam open. Once the shoulder seams are stitched, set the sleeve cap into place from armpit to armpit while the sleeve underarm seam is still open.

Finish the raw edges of the fins. My narrow hem foot and I weren’t getting along well on this project so I settled for serging the edges.


Now pin the fin to the underarm seam with the fin rolled up inside of the sleeve:


Double check at this point that the fin isn’t extending into the hem portion of the sleeve. It should look like this at the sleeve end before you close it up.


Pin all the way down the side seam. Stitch, being careful you’re not catching part of the rolled up fin by accident.


Once the hood is constructed, cut large circles from white felt and smaller circles from black felt for the eyes. Stitch black pupils to whites of eyes. Try it on your child to determine placement of eyes. Stitch eyes to hood through all layers. Ignore the fact that there is already a dorsal fin in this picture. I made the poor decision to sew the fin before the eyes, making it much more difficult to stitch the eyes on. Do as I say, not as I did.


For my size 3T child, I cut two dorsal fin pieces 39″x7″ from the contrast fin fabric. Adjust as needed for a larger or smaller costume. I allowed a half inch seam on these so they finish 38″x6″.


Leaving one long edge open, stitch the dorsal fin pieces, right sides together, along three sides. Turn. Press. Cut the stiff, double sided fusible interfacing to your finished measurement of 38″x6″. Slide it into the pocket you created by stitching the three sides. Here it’s partially inserted to show you.


Press to fuse the interfacing. Finish raw edge. I serged it.

Mark lines across the fin every 1.5″ with the first and last sections two being a little more than 2″ wide. (Excuse my poor math. I didn’t divide before I cut. You can make them all even if you want!) Top stitch through all layers along these lines. Sorry it’s so hard to see here. This fabric is terrible to photograph.


Now accordion fold along these stitching lines. Using the heaviest thread you have, hand stitch through the accordion folds near the serged edge.


I needed two rounds of stitching to hold the fan shape. Here’s an inside view where you can see my four knots at the ends.


You should end up with something like this that will hold the accordion shape on its own. I wish I had tightened up the stitching to hold more of a semi-circle rather than 3/4 circle.


Carefully wrestle this fin under your presser foot and top stitch it in place using the wider fold on each end flat against the back of the hood and neck. You can see in this photo why I wish it were more semi-circle. Mine pulls a little in the center, trying to fold up more.


Top half done! On to the bottoms.

Construct pants as directed to completion.


For the tail cut one piece of contrast fin fabric 44″(width of fabric)x28″. Fold it on the grain with selvedges together. In this photo the fold is at the top where the waistband is laying. I was ball parking how long I wanted it to be.


Now fold it in half again, cross-grain so it is 22″x14″ as it lays. First fold is at the top, second fold is at the left in the photo below.

Using your French curve or design ruler, mark a curve for the tail fin with the higher end at the second fold, the low end extending toward the bottom corner where you have 4 loose layers. Don’t angle it completely into the corner, though. Leave about an inch from the corner for seam allowance as my design ruler lays in this photo:


Can you see my tailor’s chalk below?


Now trim this curved triangle away.  Open it up and you should have something that looks like this:


If you are serging the edges, go ahead and finish all raw edges now. If you are narrow hemming, finish the curvy edges and one long side. Leave the other long side raw.

Find that first fold you made. See it vertically in the photo above? Run two rows of gathering stitches on either side of the fold line. you’re stitching through a single layer here – not folded.

Cut a strip of boning to the length of your long edge (should be 44″). Position boning so that it is curling upward, away from the fabric. Using a zipper foot, stitch the inside edge of the boning channel to the long edge of the tail fin like so.


Now turn and fold the boning and edge of fabric so the boning is hidden. Stitch in place.


Now that the boning is in place, pull up those gathering threads. If you want to make butterfly or fairy wings. Stop here. If you want a fish tail, read on.


Position tail on back of pants, just below waistband. Boning should be curling down toward the table like this. Top stitch through the center of the gathering threads.


Bring two sides of boning together and stitch through the layers along the inside edge, leaving about 3″ open at the waistband end. I also hand tacked the outside edges in several places, as they wanted to curl away from each other too much. Using that super strong thread, hand tack over the boning in the center just below waistband and about one inch to each side of center. You will have to bend the boning to make it behave like this:


That little open triangle gives the tail some extra stability and keeps it from falling to one side or the other.

Are you still with me? Now let’s give the tail some lift!  Grab the extra piece of boning you cut off the end. Open up the underside of the tail. Hold the boning so the arc of the curve is toward the waistband and the ends point toward the crotch and the tail. Stitch a few inches of the boning in place at the bottom of the crotch curve on the pants. Using that heavy thread, hand stitch the top end of the boning to the tail. This will help support the weight of the tail. It looks like we’re ready to invite the Girl Scouts over to camp in our tent.


One more step. Try the costume on your child. Depending on how strong your boning is, the tail may sag sadly like this:


If this is the case, use that fishing line or monofilament thread to run an invisible support from the tail to the base of the dorsal fin. Cut a long length of line or thread. Thread a needle double and tie the end. Take a few stitches around the boning at a point about half way down the length of the tail. Cut the thread from the needle close to the needle leaving the thread long. Tie a new knot at the end where the needle just was. Hook a safety pin through this loop and pin under the bottom fold of the dorsal fin. Pinning it allows you to safely and easily remove the costume from the child without breaking this support line. Just unpin and remove jacket and pants separately.

Now you have a happy tail and a happy Halloween fish!



This was before the tail was happily suspended but the boy was all smiles!


Swim away little fish! Swim away!

Now go check out the other awesome handmade costumes at The Train to Crazy. Thanks for having me, Andrea!



9 thoughts on “Completed & Tutorial: Fish Costume

  1. Pingback: Tutorial: Fabulous fish Halloween costume for kids · Sewing |

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  3. Pingback: Fish costume tutorial

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  5. Hi! I actually just bought this fabric with the intention of making a Pascal the Chameleon (from Tangled) costume for a one year old. I had planned to line with flannel just as you mention in your post, but as a novice sewer I have a technical question. Did you use any type of interfacing to adhere the scale fabric to the flannel?

    I’m making this for a friend’s child and I’m worried about the scales cracking.

    • I’m sorry it took me so long to reply. Surely you’re finished with your project by now. I didn’t use anything to adhere the two layers. I just treated them as one sandwich, so to speak.

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