What’s wrong with these fry?

I was wondering if you could advise on why my baby guppies have bent backs.

I’m quite new to the hobby of late but used to keep tropical fish about 30 years ago. The guppies are in a planted 85 l tank with some Cherry shrimp. I originally had a male with two females (I’ve since moved the male into the main tank). One of the females only gave birth to one baby and then died, but the other had seven, and while she’s still doing great, I’ve noticed six of the youngsters have bent spines. So, I moved the ‘normal’ fry to the bigger set-up but left the mother in the small tank with the infected babies. I’ve done a lot of research, and I’m wondering whether this is fish TB. If that’s the case, will I need to cull them — and if so, what’s the most humane method of doing so? Would I also have to do same with the mother?

Both my tanks are cleaned and maintained every week. I feed Tetramin food, and the water is spot-on, apart from being a bit hard.

PETER REPLIES: You are correct in that fish TB, caused by

Mycobacterium marinum and other Mycobacterium species, is one cause of spinal deformities, particularly if the fish become infected during early development. This bacterial disease can be passed from an infected female to her young, and some or all the young will be born infected.

Spinal deformities in fish can also be caused by other types of infections, as well as nutritional deficiencies, and by certain chemicals in the water, such as high levels of certain heavy metals.

Other possible causes include genetic disorders and environmental problems during the fish’s development, such as low oxygen levels and high water temperatures, although some of these may be more influential on the egg development of egg-laying fishes, than fry development in livebearers.

My best guess would be either TB or a dietary issue, but I can’t be 100% sure. How are the other young and adult guppies: do they show signs of TB, such as becoming emaciated, or trailing white faeces? I’d also check that your fish food has not gone past its use-by date. If it is TB, then this disease is very difficult to eradicate, as you have probably read.

Assuming the mother looks okay, then I’d leave her by herself (ie. not with the male) and consider culling fry that have the bent spines. I would advocate the use of clove oil (available from a pharmacist) to do this.