I have made some pictures now about disappearded dolphins. That only happens - sometimes or more often - after feeding fish from Sim-Inventory - equal if it is an aquarius or not or well known with the dolphin or not. The pictures shows "flying" fishes without dolphins or speeking aquarius with invisible dolphin after feeding fish from inventory instead the dolphins are shown in the action loop. The dolphins cackling is still to be heard. Sometimes feeding fish from inventory ends the whole interaction with the dolphin.
I have not seen / read a hint, how big or how many pictures are allowed in this forum. If they are to small - about 800 x 500 - it is not very clear to shown, what I mean.
I have also made pictures of overwriting the feeding option if fish is in the sim inventory. First there is only the option, to feed by sim inventory, just after the dolphin is called. After one or two mouse clicks further on the dolphin, the options for the dolphins are changing. I have never seen this behavior on the dolphins options, if there ist no feedable fish in the sim inventory. Feeding with fish for 2 $ never creates dissappearing dolphins. Since Sims 4 Island Life, there are some issues with Sim Inventory. Maybe it all depends.
Edit to add: Or the dolphins don't like rotten fish, mhhmmm. That could be an, answer which fishes dolphins prefer.
But there are still the other questions of overwriting the feed-Options by first contact when fish is in inventory such as invisible dolphins after feeding fish from sim inventory.
Maybe dolphins became invisible after feeding rotten fish? That could be magic.
(Post edited and merged by CM)