There is a LOT of Arduino activity in Aquaponics.
See: 1-wire | Aquaponic DIY Automation Blog for some temperature measurement stuff I worked on with them.
Temperature measurement on the ArduinoInfo.Info WIKI HERE:
Rik Kretzinger's blog: indoor aquaponics | Aquaponic DIY Automation Blog
Also see:
http://community.theaquaponicsource.com/
Let us know how it goes...