How Big do Goldfish Fry Have to be in Order to go in to the Tank with the Adults?

by Brooke

I have goldfish fry that are still small but close to a year old and would like to know how big they have to be in order to go back into the tank with the adults.

I just don't want them to get eaten haha

Grant's Reply

Hi Brooke

If your fry are around a year old, their body length should be around 75mm (3 inches). At that size they could be quite safely introduced into the parent tank of even the largest fully grown adults.

I am assuming your fry aren't that size.

Goldfish are non-aggressive, but anything they can get into their mouths is considered food.

Your fry should be much bigger than that, but you may find that initially the fry will get chased by the adults because they are assuming you are putting some tasty morsels into their tank.

Because you haven't given any sizes, I will give a maximum to minimum size difference that I consider would be safe for the smaller fish.

The minimum size I would consider safe for fry would be 1/3rd the body length of the largest adult. In other words, if you have adults with a body length of 75mm, I wouldn't put a fish with a body length of less than 25mm in with them.

The fry wouldn't be eaten if they were smaller than this but Goldfish do become "pushy" at feeding time and the largest fish dominate the food.

Something else to consider is if you are adding more fish to your adults tank, you are increasing the bio-load. Assuming the filter is up to the task, I would gradually add the fry over a number of weeks to allow the filter to adjust to the higher ammonia load.

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Jul 31, 2023
Newborn goldfish what size
by: Grant

Goldfish fry are tiny when they first hatch from their 2mm round egg, around 4.5mm in length.
By the time they become free swimming, which is the earliest Goldfish keepers would notice them, they would be around 5mm in length.
Most pond owners only notice fry in their ponds after some weeks when they are around 15mm in length.

Jul 25, 2023
Newborn, goldfish what size
by: Beth

I have a pond and the babies are still real teeny tiny. I have three that are around maybe 2 inches and you’re right they do chase them but I don’t know exactly what the eggs look like so I am not sure there’s a lot of algae in the pond but I just wish I could send you a picture, thank you for your help

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