Tiger Barb

Probably either something it ate or a prolapse. Can you get a picture? Is it in any distress?

If it’s a prolapse I don’t think there’s anything you can do.

When did you notice this lump?
Is the fish having any other problems? Is it still eating, swimming, and behaving normally?

I've not seen anything like this previously.
Good to hear that the fish is swimming & eating normally though.
Having had a rummage around to find out more about @Hampalong suggestion of a prolapse, that fits with your information. A few sources note that a prolapse would be white, which is what is showing in the picture. If it has been caused by straining the suggestion seems to be to change the food to more vegetable based food. Chopped pea is popular, and most of my gang will eat that. When I kept tiger barbs they had chopped/crushed pea (without the skin) on a fairly regular basis, perhaps once every other week.
Some sources also suggest leaving the fish without food for a few days.
Perhaps don't feed for a couple of days, then provide vegetable based food (pea, blanched carrot) for a few days. Monitor the situation. Also worth increasing cleaning and water changes to be on the safe side.
Is this a single species tank? How are the rest of the fish?

Any update on your tiger barb @Colin1056 ?

Thanks for the update.
Glad to hear that your tiger is swimming and feeding well. 

Have you guys heard of AI chatbots?


I decided to use your question as a test case. Here is its answer.


“ It sounds like your Tiger Barb may have a case of constipation. Constipation in fish can be caused by a variety of things, including a poor diet, stress, or a blockage in the digestive tract. In order to help your fish, you should first try to identify and address the underlying cause of the constipation. This may involve making changes to your fish's diet, providing a more stress-free environment, or removing any potential blockages in the tank.”

Too generic?

https://chat.openai.com/chat

If only we could suggest places to visit for a better answer. 

Not too generic, just incorrect. A protruding whitish lump doesn’t sound at all like constipation.