i have 4 tiger barbs and 1 rainbow shark in a 20 gal and i do water changes once a week, today i did a very big water change in preparation to go to go to my local fish store and get more barbs, i noticed my red neon tiger barb was in oddly shaped. When i bought this tiger barb he was already naturally in a more long shape rather than a triangle like the rest of my tiger barbs, he seemed healthy aswell. today he seems to be even more slender and looks to have an indent making him look like he has a neck. it doesn’t look like anything that is affecting the fish at the moment as he/she is swimming and eating normally. Does anyone have any idea what could be going on? the other fish are all acting perfectly normal, the red neon tiger barb also has a split on his fin on his back(i’m not sure the scientific name). i just really hope everything is okay and thank you for taking the time to reply