Is re-frozen food safe to feed?

I have been unable to buy frozen black mosquito larvae in local aquatic shops, but I managed to find an online supplier, so I ordered some. However, when the food arrived via a 48-hour delivery service, it was all thawed out and felt like jelly.

I contacted the supplier who insisted that the food could be re-frozen. I argued that bacteria and pathogens could have manifested in the food, but the seller said that as the food is gamma irradiated it is still safe to feed. Please could you advise on whether I could feed the re-frozen food to my fish?

MAJID ALI

NEALE REPLIES:

The short answer is that your supplier is probably right, but it’s hard to be 100% sure. A lot of food we buy from supermarkets has been frozen before being sold defrosted (fish, for example, from the fish counter) and the label or packaging will often say ‘freeze on day of purchase.’ That’s perfectly safe, so long as the fish was cold, clean, and refrozen quickly.

Likewise, so long as the frozen mosquito larvae were cold when they arrived, and the packaging unopened, you can refreeze them without any major issues. Gamma irradiation should kill all the microbes in the fish food, and again, so long as the packaging was still tightly sealed, there’s no way bacteria can get in. So, again, this is reassuring, and personally, I’d have no issues refreezing a thawed package of bloodworms or whatever provided the package arrived cold and unopened — but these two factors are key.

The food must still be cold because, even in the absence of bacteria, simple chemical reactions such as oxidation can cause nutrients to change or break down when food warms up. There are also enzymes that will quickly break down nutrients once food becomes thawed.

The other caveat is that the packaging is securely sealed. A pinprick-sized hole is all that’s needed for bacterial contamination, and once that happens, food can spoil very quickly at room temperatures. If the food arrived within 24 hours of being dispatched, the risk of spoilage is very low, even if the packaging was damaged. But it wouldn’t be zero, and I’d discard any obviously opened or unsealed portions before freezing the rest.

Some retailers do guarantee their frozen food will arrive frozen, but you may well pay a more for that. After all, insulation, ice packs, and 24-hour delivery all cost money, but you’ll have the peace of mind that comes with seeing the food still frozen.

For what it’s worth, if frozen foods aren’t easily obtained where you live, they’re not something I’d worry about too much. For freshwater fishkeeping they’re a nice addition to a balanced diet but not essential. The flake and pellet foods from the established manufacturers are excellent: nutritionally balanced, inexpensive, and easy to store. Most community fish will take them readily.