Shipping frozen fish successfully comes down to three things: proper insulation, the right refrigerant, and fast transit. Get all three right and your fish arrives rock-solid. Miss one and you risk a thawed, spoiled package. Here’s how to do it step by step.
Choose the Right Insulated Container
Expanded polystyrene (EPS) foam coolers are the standard for shipping frozen fish. They’re lightweight, which keeps shipping costs down, and they insulate well enough to maintain freezing temperatures during transit. Wall thickness is the key variable. Coolers with 3/4-inch to 1 1/4-inch walls hold temperature for one to two days of shipping. If your package needs more time in transit, look for coolers with 1 1/2-inch walls, which can maintain temperature for up to five days.
For most shipments, a 1 1/2-inch wall cooler is the safer choice. Even overnight packages sometimes get delayed, and the extra insulation gives you a buffer. The foam cooler should fit snugly inside a corrugated cardboard outer box, which protects the foam from punctures and gives the carrier a surface to attach labels.
Use Dry Ice, Not Gel Packs
Dry ice is the only practical refrigerant for shipping frozen fish. It sublimates (turns from solid to gas) at minus 109°F, keeping the interior of your package well below freezing for the entire trip. Gel packs, by contrast, are designed for chilled products like live shellfish or fresh fillets. They won’t keep fish frozen.
Plan on 5 to 10 pounds of dry ice for a 15-quart container over 24 hours. If your container is larger or transit might stretch beyond a day, scale up accordingly. A few practical tips for working with dry ice:
- Never handle it bare-handed. Dry ice causes frostbite on contact. Use insulated gloves.
- Don’t seal the container airtight. As dry ice sublimates, it releases carbon dioxide gas. A completely sealed container can build pressure and burst. Leave a small vent or use a cooler lid that isn’t taped shut on every seam.
- Place dry ice on top of the fish. Cold air sinks, so positioning the dry ice above your product keeps the entire package cold more evenly.
- Buy dry ice as close to ship day as possible. It sublimates at a rate of 5 to 10 pounds per day even in a cooler, so purchasing it days in advance means you’ll have less than you planned on.
Prepare and Pack the Fish
Start with fish that is already frozen solid. Packing fish that’s only partially frozen or freshly caught gives you a much shorter window before it thaws. If you’re freezing it yourself, get it to 0°F or below at least 24 hours before packing.
Wrap each piece or fillet in plastic wrap or vacuum-seal it. Vacuum sealing is ideal because it removes air, which slows freezer burn and prevents any leaking if the fish begins to thaw. Place the wrapped fish in a leak-proof plastic bag as a secondary barrier. Even with dry ice, you want protection against any moisture reaching the cardboard outer box.
Layer your cooler with the fish on the bottom, then place dry ice slabs or chunks on top. Fill any empty space with crumpled newspaper or additional foam inserts. Air gaps inside the cooler act as warm pockets that accelerate thawing, so you want the interior packed as tightly as possible. Close the cooler lid, place it in the outer cardboard box, and tape the box securely on all seams.
Ship Early in the Week, Overnight if Possible
Timing matters more than almost anything else. The USDA recommends shipping perishable food at the beginning of the week so packages don’t sit in a warehouse or sorting facility over the weekend. Monday through Wednesday are your best ship days. A package sent on Thursday or Friday risks spending Saturday and Sunday without refrigeration in a facility that may not be climate-controlled.
Overnight shipping is the gold standard. The shorter the transit time, the less dry ice you need and the lower the chance of something going wrong. Two-day shipping can work if you use a thick-walled cooler and extra dry ice, but every additional hour in transit is another hour your dry ice is sublimating. Ground shipping is not a viable option for frozen fish.
Schedule your shipment for the earliest pickup or drop-off time available. The sooner your package enters the carrier’s system, the more likely it arrives the next morning rather than the next evening.
Label the Package Correctly
Carriers require specific labeling for packages containing dry ice. Mark the outer box with “Dry Ice” or “Carbon Dioxide Solid, UN 1845” and include the net weight of the dry ice in the package. Most major carriers provide pre-printed dry ice labels or allow you to generate them online when you create your shipping label. Failing to label a dry ice shipment can result in your package being refused or delayed.
Also mark the box as “Perishable” and add an arrow indicating which side is up. If you’re shipping to someone who might not be home, include a note asking them to refrigerate or freeze the contents immediately upon delivery. Some shippers add “Keep Frozen” stickers for extra clarity.
Carrier Rules and Restrictions
Each major carrier has its own limits on dry ice quantity per package, typically in the range of 5 to 10 pounds for ground and air shipments. Check your carrier’s specific dry ice policy before packing, because exceeding the limit can get your shipment rejected at the counter. Dry ice is also prohibited on some aircraft routes, so confirm that air shipping is available for your origin and destination.
UPS, FedEx, and USPS all accept dry ice shipments with proper labeling, but their rules differ on maximum weight, packaging requirements, and surcharges. Budget an extra few dollars for hazardous materials or dry ice handling fees that some carriers add on top of the base shipping rate.
What the Recipient Should Do
Let the person receiving the fish know when to expect the package and what to do when it arrives. They should open it promptly, check that the fish is still frozen solid or at least still has ice crystals throughout, and move it to a freezer immediately. If the fish has fully thawed and feels warm to the touch, it should be discarded.
Any remaining dry ice in the box should be left in a well-ventilated area to sublimate on its own. It should never be placed in a sink, toilet, or sealed trash container, as the expanding gas can cause plumbing issues or pressure buildup.