Goldfish Care Tips

A Free Monthly Resource For Goldfish Enthusiasts
June 2026
Issue #150

In This Issue
Juvenile Selection (for breeders)

At the end of the breeding cycle, the successful Goldfish breeder will be faced with the dilemma of having to choose which juvenile fish s/he wants to keep from a spawn, and which fish to move on.

Juvenile Selection (For Breeding)

This Season's Black Moor Juveniles

I use the word dilemma because if your spawning has gone to plan, you are left with the best 2-5% of the spawn, and, unless you have unlimited space, you have to make the final decision on the few you are going to keep, and the ones that will be on-sold.

In my case, I had 50 Moors from this season’s small spawn of around 800 fry. I had sold off the rest to growers who grow them to retail size.

I planned to keep 10, and grow them up to 70-80mm (2.75-3.00”) body length before making my final selection of 5 or 6, once I know what sex they are next breeding season.

In the past, I have made my final selection quite early and often regretted my choices a few months later.

This year, I grew the top fish up to a good size, some over 40mm (1.50”) body length, before making my final selection. The larger you can grow fish before making the final selection, the better, as minor faults can become much more obvious as the fish get larger.

Selection Process

This is the process I use to select juvenile fish, ranked by importance.

Size: I lean towards choosing the larger fish first, but there are dangers with this, particularly when selecting telescopic-eyed fish.

What happens is that some fish develop their telescopic eyes later than others, so they can see food better than those that develop their eyes early; hence, they grow bigger faster. You want fish that have early eye development, so don’t focus on just the biggest fish.

The mistake I was making with my Moors was selecting early and focusing on the larger individuals, which meant I was ending up with Moors with small eyes.

Body shape: This is very important for deep bodied varieties. Again, it is often the mid-sized or smaller fish that have the best body shapes.

Fin Development: A mistake often made by inexperienced breeders is choosing small fish with excellent fin development. It is a mistake because the fish has good fin development, but it has stopped growing. Experienced breeders look for average-to-small fins that are well-formed, with no kinks, bends, or folds, as these are often a sign of stunting. Look particularly at pectoral fins, as folded pectorals seem to be becoming more common.

Color: Color intensity, or evidence of a color change taking place, is next. You should select early-coloring, metallic-scaled individuals and those showing the most color in nacreous (calico) varieties. The Moors were all black, though some leaned towards brown.

Attributes: Here I’m talking about telescopic eye development, and Water Bubble Eye fluid sacs. Wen (hood) development may be advanced enough on Oranda, Ranchu, or Lionhead juveniles to enable selection, but they would need to be at least 4 months old.

The same rule for well-developed fins applies to small fish with well-developed attributes at an early age. The dilemma is, have the attributes contributed to its small size, or is it something else? If the fish is particularly good but small, you can always isolate it and see if it grows.

Deportment: Once you have isolated your selected few, spend some time observing how each fish moves through the water and how it carries its fins.

You are looking for head-down behavior when it stops swimming, and fins that remain close to the body when moving, not bending out at strange angles.

This selection process is also applicable when you are purchasing fish from a tank full of juveniles at a pet shop.

Comments? Ideas? Feedback? I'd love to hear from you. Just reply to this e-zine and tell me what you think, or what topics you want to be covered.

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