Medaka Rice Fish - possible tumour on stomach

[NewbieJen]

I bought 6 medaka rice fish online about a month ago, 3 were DOA, the other 3 were fine. I think I have two males, one female. They have been breeding for about 1-2 weeks and the female spawning every day.

They are in a 40 gallon with red blue eyed neon rainbow fish, cory cat fish, khuli's shrimp and snails. The tank is heavily planted, with planted and floating plants, lots of caves and hiding places for the bottow dwellers. All very peaceful fish, with the rice fish being the bigger than the red blue eye neons.

40 gallon breeder
PH 7.8
nitrite - 0
Ammonio -0
nitrate - 40
Canister and sponge filter, providing more than is required

I just noticed, what I first thought was the typical clutch of eggs, but upon closer inspection it looks more like a tumour or something on one fish's stomach. It wasn't there yesterday.

any ideas what it is, what could have caused it and more importantly what I need to do.

Thank you so much in advance.

https://youtu.be/05j0xu4DBcI

[Colin_T]

I can't do anything online due to crap internet. can you post a picture of it?

[larochem595]

Took a few screenshots for the posted video to try to help...
Also curious.

[Colin_T]

can't tell, need pictures that are in focus and from both sides of the fish.

as a general rule, there's no cure for tumours and most people euthanise the fish when it has trouble swimming or stops eating.