A couple of my danios and a tetra have gill plates that look like they have shrunk . The gills dont look like they join to the body anymore and you can see the red underneath. The tetra only has it on one side so I know its not normal (im very new to tropical fish). Does anyone know why this has happened, any ideas to fix it or stop it happening again?
I have a 250 L tank with community fish mainly tetras, danios, platys and a couple of swordtails. I have about 30 in total. I want to get some more fish of similar size. How many more fish could this tank safely take?