Put the summary of the bug you're having here
What I expected to happen was...:
Feeding tropical fish to axolotl would breed them
What actually happened was...:
Nothing happened
Steps to Reproduce:
1. Get tropical fish
2. Go to Axolotl
3. Right click them
Environment
Put your operating system (Windows 7, Windows XP, OSX) and Java version if you know it here
WAI. Tropical fish items no longer work after 21w20a. Use a bucket of tropical fish instead.