Why hasn't this Clown loach grown?

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Bob Mehen offers advice for a reader with a group of Clown loaches that are growing well - with the exception of one, which hasn't grown at all...

Q. About 12-18 months ago, I bought five very small (2.5cm/1") Clown loaches.

Four of them are now 7-8cm/2.75-3.25" — but the other one hasn’t grown!

All five are very healthy and look immaculate. There’s no sign of bullying, in fact the tiny one seems extra-happy — he’s out most of the time and schools with my five Chain loaches.

The other Clown loaches do school together but spend time hiding away, which I know is normal.

I’ve almost 50 years' experience of fishkeeping and have never come across this before in a fish that would normally reach such large proportions, meaning the relatively small size is so obvious.

If all five Clowns were tiny, I’d presume there was something wrong. But this doesn’t make sense.

Other stock includes eight Red-line torpedo barbs (around 10cm/4" long) four Marbled hatchets, a Snowball plec (I've had this for about five years) two 10cm/4" Pearl gouramis, a 15cm/6" Bristlenose (also about five years old) and the usual selection of Neons, Rummy noses, Corydoras and so on.

The tank is 260 l/57 gal and has been running about five years. It’s well-planted and I’ve had no deaths in the last year. The fish are fed a wide range of dried foods. I change about 80 l/18 gal of water every 2-3 weeks.

Any ideas?

Sharon, email

A. There are a number of reasons that could explain why one of your Clown loaches is remaining small, while its companions grow.

These are social fish and soon establish a rigid pecking order usually with a large, dominant female at the top, and the smallest male at the bottom.

It is possible that in your small group this smallest fish is unable to get the food it requires and its growth is suffering as a result.

Clown loaches are largely nocturnal so you may not be witnessing this behaviour as it is occurring after the lights are out. This could also explain this small loach's active daytime behaviour as it searches for food away from the larger sleeping fish.

Larger groups usually help spread out any bullying and allow all the fish to get their share, but this isn’t possible in your tank. These fish can easily top 12"/30cm and at that size need a tank considerably larger than your current one – 1.8m x 60 x 60cm/6'x2'x2' or larger is usually recommended for a group long term.

While your other Clowns have certainly grown since introduction I would expect them to be bigger than 7cm/2.75" by now. While they take many years to reach their full adult size, early growth should be rapid and I’d expect them to be nearer 10-15cm/4-6" each if conditions were ideal. Your stock levels do appear high for the tank's volume and stunting and its associated health problems could already be an issue for these fish.

It’s also possible this small fish is simply a 'runt' and despite your best efforts will never match the growth rates of the others or perhaps is suffering from a gut parasite infestation, but your reports of its general good health and vigour make this seem less likely.

Diet could also be a contributory factor – adding a selection of fresh and frozen foods such as bloodworm, brine shrimp, cucumber and blanched peas to supplement your current choices will be beneficial.

However, in the long term these fish simply need a bigger tank and if this isn’t feasible they’re probably best re-homed.

Bob Mehen

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