Replacing Tilapia with koi mesh

The fact that you've replaced the mesh in some circumstances but not all strongly suggests that either a) there are different meshes for those circumstances where the mesh has not been replaced, and you need to find them and replace them, or b) there are different references to which mesh to use in different places in the game for those circumstances where the mesh has not been replaced, and you need to find them and change them.

It'll have to be someone else who offers the hints, I do not actually have modding skillz. I just figured there was a logical conclusion to be drawn from the partial success. You've turned on show debug in S4S and keyword searched?

Found out that what controls the swimming fish id is under Object Definition. The box called "Tuning ID"
Change the number to 76082 and yoru fish will automatically look like a koi while it swims. The problem is, it will only referance the base koi texture, so whatever texture the base koi has, the tilapia koi will wear as well.
I have to find out where 76084 (tilapia) tuning ids are stored.

The following screenshots have another mod running at the same time! This is an override object that changes the normal koi into white koi. The only reason I have this mod running at the same time is to prove that the tuning id always references the skin imported into the koi model, rather than finding the koi skin somewhere else.


Ok so the tilapia, when swimming, automatically referenced the TuningID 76084.
So I extracted the Object Tuning file from the koi (76082) created an empty package, and added the koi tuning file to it. Then I changed the tuningID in the empty package using the data tab to 76084 (tilapia) and ran the game.



Swimming tilapia in the game turned into koi.

Then I went back in to the edited koi tuningID that I used before, and changed SOME of the instances of koi to tilapia (yellow highlights). I left the fishbowl as koi to see what would happen.(red arrow)

and this is what happened

The circled yellow one is what happens when I have
<E n="inventory_type">AQUARIUM_STANDARD</E>
<U n="base vfx name">
<T n="vfx_name">tilapia</T>

the circled red one
is what happens when I have
<T n="fishbowl_vfx">s40_fishbowl_koi</T>

If I were to change these out for tilapia, koi, trout, or anything else, the swimming mesh AND skin would be referenced back to the whatever fish I put in.
I could easily make all fish in the fishing spot koi, but they would all have the same skin, and i want a bunch of different skins.

To find the mesh you will need to use the VFX tool, you want to copy the IID, open up the "game file cruiser" in sims 4 studio "tools", and paste it into the instance, and click on "all", to find the texture you want to select the "model" entry, go to "edit items"
















copy the instance, and paste it again in the "game file cruiser" and click on "all" and you will find the texture

Changing the instance won't work, you'll need to import the koi meshes to replace it. Try following this tutorial.
sims4studio.com/post/148488/thread
And then once the mesh has been replaced, you can give it the original instance again and delete everything else that the package had that you didn't need. Hopefully that works.

Your other alternative is to clone the VFX to create custom koi instead of overriding the tilapia.

Exciting news! I made a package using the VFX editor!
I changed the ColorCurve to the values that I thought would give me purple, based on the tutorial on the VFX editor's thread.
The tilapia did not turn purple.
But he did start twitching while swimming so even though I haven't figured out how to change his mesh yet, I know I am editing the correct effect.