I was off for a while and tried to catch up with the changes by reading the recent news but couldn't find anything about those two items that I've seen recently:

Fish eggs? they seem to come in at least 2 colors. What are they and where do they come from?

And what's a transmitter? What is it good for and where to get it?

The fish eggs and the transmitter are from a previous event (Salamander Hunt)

Yellow eggs:

Feed this to your pet to increase its breeding limit by 5 for females and 25 for males.

Pink eggs:

Feed this to a pregnant female to make her give birth to twins.

I think the Transmitter was for lvl up a pet, but I am not sure I did not get any of these.

All of the items are not available anymore exept in trading with other users

so, from a previous event, I see...

thanks a lot for your answer -