Mermaid scales and tails not showing up while swimming!!

this is my first post, sorry if i did it wrong!

I don't do C.C & I'm having this issue as well. This is really ruining my mood in playing completely. 

Okay, I had a similar problem.

SHORT VERSION:  Go to a mirror.  Choose your Sim's Mermaid form.  Click your Sim.  Click on Tail.  Choose a tail.  VOILA!!  Your Sim now as a tail! ... hopefully.

LONG VERSION:  So, my Sim turned into a mermaid by eating Mermaid Kelp (I had no idea that would happen, I thought it would allows him to use the stupid shell) but his tail never rendered when he swam.  I tried repairing the game but that only fixed an issue with my rose bush not producing roses (on a side note, I now have a ton of daisies).  So, I went to google and found what I THOUGHT was a post about this issue.  It suggested I have my Sim go to a mirror and "change" his tail, which would force the game to either (A) generate his original tail or (b) give him a tail.  I did and it worked.  It was only later, when I went back to the post to say it worked, that I realized the post was for SIMS 3 and not Sims 4.

Still, it worked for me and it might work for you, so give it a try.  On a side note, it kinda makes you wonder how much of this "new" game is actually just re-purposed code from previous games.  If that's the case, WHY CAN'T WE HAVE APARTMENTS, HOBBIES AND BUSINESSES RUN OUT OF RESIDENTIAL LOTS!!!????

.... sorry.

I can't report a bug (not sure if this is to do with the member system or not) but i'm experiencing a bug that does not match all of the posts i've seen entirely.

When my sim is a mermaid (female, young adult, ate sea kelp) in the ocean (100% of the time), she swims as expected but her tail is missing. and i don't mean she has human legs, the entire lower body disappears! on top of that the top half is changed into some sort of business jacket. the bottom half is missing also in the bath, but the top is nude. I have never once installed any mods. 

I know this will probably be dismissed because it's not in the correct format etc. but it is made incredibly difficult for anyone normal to report an issue!! I know it must be annoying to have the same one pop up over and over but I can't find this exact glitch anywhere! Just ones saying the scales don't show up, or a jacket but only in the tub, or only children!  

Hello, @pennyjarkins  You are describing what happened to my Sim, so you are not in the wrong place.  When my Sims jumped into the ocean to swim in his mermaid form, his entire lower half disappeared and his face changed.

The way I fixed it is the way I described above.  Basically, I had him go to a mirror and I chose "Change Sim"  Once there, I clicked on his Mermaid form and it forced the game to generate a tail for him.  I was then able to change the tail to one of my liking and fix his face (he is clean shaven with dreadlocks in human form but for some reason the game gave him a full beard and bald head when in mermaid form).  Give that a try and see if it helps.

I have the same problem, and can verify that the solution given by @Valnatron works. The problem indeed occurs when a normal sim eats a mermaid kelp. I hope when they fix this bug, they can have the default tail design and colour scheme matching the design and colour scheme of the swimsuit top that is being worn. And if there is no swimsuit top, then use a random tail. 

I have the same issue so I tried your solution but I can even edit the mermaid form. It is as if it wasn't existing at all. Do you have any ideas about how I could solve this problem?