Mother in law has got a big plec of circa 20 years old.

Unfortunately some what look like bloody ulcers on his stomach.

Any ideas, particularly how to treat.

Cannot really get him to a vet…..

Call the vet, take photos, and/or talk to your local aquatics place, they've probably seen most problems.

Ulcers could be caused by bacteria or fungi getting into wounds from other fish (is the plec being bullied?) or by dodgy water parameters causing stress to the fish and reducing its slime coat (and hence natural resistance to nasty stuff in the water.

First thing I'd do is check for Ammonia/Nitrite/Nitrate, and doing appropriate water changes to reduce any harmful parameters.

I've had a lot of luck using Melafix and Primafix on smaller fish (upto about 10cm) but I've never had a plec with problems.

Hope this helps

Plecs tend to be lazy especially when they're old. Out of interest does he sit on the bottom and not move alot? If so it'll be an anaerobic bacterial infection; best thing to do is clean the gravel with a gravel cleaner. If you haven't got one Blue Peter one with syphon tube and a plastic bottle.The ulcers will need treating depending on how bad they are so it's probably best to look for an antibiotic but do bear in mind that it'll probably kill the filter as well so you'll need a back up/ quarantine tank.
I should qualify that I'm not a vet but know a bit about fish.
Good luck hope it gets better.
Matt

Ditch going to a vet for this.
Most decent aquatic/fish shops have a good range of fish drugs & meds. The The "Interpet" brand's range has a little booklet in the boxes that tells you what to use & when. Plus the guides on the boxes themselves will give you clear advice.

First thing to do is to check the water parameters. Use a liquid test kit for that or take a sample to your LFS.
Melafix is good but so is aquarium salt. The salt will coat the skin with a protective film. I used to use it all the time when I had a piranha shoal as they were always nipping each other! Now just keep solo piranha.

You shouldn't use aquarium salt with plecs. If you do (and I'd strongly advise against using it in a tank with scaleless fish like plecs), it's best to build up to required concentration over a matter of days.

Most plec species aren't biologically equipped to handle a change in the salt content of water.

Salt acts as an irritant, so encourages fish to produce more slime which has a protective, and possibly anti-bacterial effect. It doesn't actually coat them.