Strange fish symptoms… rainbow fish

[Magnum Man]

These have been in my tank for over 6 months
These are supposed to be juvenile yellow axlerodi… everything has been the same for the last 6 months… water is what it is ( whole house softener… I know… I know…. ) Anyway all look normal, but just the last couple days, one has gotten thin along it’s spine, about a 1/3 of the way back, and starting to look a little more humpback… pictures are challenging, as it’s swimming around like normal … in the1st picture the one, of the bottom 2 in that picture, above one of the other " that looks normal, is the effected fish ( there is a red male at the top left of that picture, that is just starting to "hump up a bit" so I'm aware they do that, but this yellow looks thinner along the spine ( maybe that's how it starts, but I didn't notice that on the 2 red males that are "humping up" right now )… the 2nd picture is of the effected fish

 

[Colin_T]

The extra body height is possibly due to the fish maturing. Adult male rainbows of many species (including Melanotaenia herbertaxelrodi) develop quite high bodies. This starts when they are about 6-12 months old and they are usually full size by 2 years.

The skinny sunken in back could be a microsporidian infection, a muscle wasting disease or intestinal worms. However, worms don't normally cause fish to lose weight along the dorsal side of the body, they normally lose weight around the belly first. Salt would be my first choice and I know there is sodium in the water but add some sodium chloride and see if it helps. If there's no improvement after 2 weeks of salt, stop using it and post more pictures and maybe a video of the fish. You can upload videos to YouTube, then copy & paste the link here. Then maybe deworm the fish.

Section 3 of the following link has info on deworming fish.

What to do if your fish has Stringy White Poop.

Fish do a stringy white poop for several reasons. 1) Internal Bacterial Infections causes the fish to stop eating, swell up like a balloon, breath heavily at the surface or near a filter outlet, do stringy white poop, and die within 24-48 hours of showing these symptoms. This cannot normally be...

www.fishforums.net

Make sure the fish get plenty of plant matter in their diet. At least half the food they get should be plant based.

----------------------

SALT
You can add rock salt (often sold as aquarium salt), swimming pool salt, or any non iodised salt (sodium chloride) to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres (5 gallons) of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

The salt will not affect the beneficial filter bacteria, fish, plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

When you first add salt, add the salt to a small bucket of tank water and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.