I read of someone that had great success with a few Oscars in his troughs.It also took care of the Tilapia fry that escaped into the grow-beds. I imagine a catfish or 2 would do the same trick.
Of course this only makes sense if you have deep-flow troughs, not media-filled beds.
The problem with snails(Especially Malaysian trumpet snail (Melanoides tuberculatus)) is ,when they are in your growth beds you will never get rid of them. These guys love digging into substrate and only come out at night to feed. Oscar's/Malawi's/Some catfishes will assist in your ponds but that is how far it will go. A way that i have dealt with them, is by physically trapping them and removing them at night and reducing the PH and calcium levels in my aquaria's. In this way you gradually weaker there shell's until they brake and cannot recover thus killing the reproductive cycle. No big snails, no eggs.
The best way to get rid of them, is to never have them in your system at all though.
At times I have had snail problems... my grow beds were filled with media.
When I had a problem with snails in the grow beds I use to flood my grow bed to the brim and leave the water at this level for a few minutes.
The snails in my system use to come up or drown..I found the snails to live just below the stones
And I use to pick them up flouting dead or just about and fed them to my fish.
By flooding my grow beds on a regular basis I overcame the problem.
Interesting problem. I have not read on this topic before and to be sure, I grabbed the only book on aquaponics that I own and there is nothing in there either. If you are referring to grow beds I presume you are referring to media beds, and that the snails are not aquatic. I will try to do a search for this one and see what I can find. Do you have any pictures of the culprit?
Are you sure the snails are eating the plant roots? The snails in my aquarium eat algae from the glass and clean up the dead leaves (detrivore). A search for copper sulphate found: Copper sulfate is very toxic to fish. Its toxicity to fish varies with the species and the physical and chemical characteristics of the water (12). Even at recommended rates of application, this material may be poisonous to trout and other fish, especially in soft or acid waters. Its toxicity to fish generally decreases as water hardness increases. Fish eggs are more resistant than young fish fry to the toxic effects of copper sulfate (3). Very small amounts of this material can have damaging effects on fish.
I came across this intresting articale on a fish keeping magazine website about snails. Some good info on the little critters.
I have found that the 'best' natural enemy to a snail, even the slug type, is the parktown prawn. This hideous looking cricket devours snails at a fast rate. http://www.insecta.co.za/index.php?option=com_content&view=arti...
When your snail problem is taken care of, you can place baiting trays with little bit of moist sluggem out to then get rid of the crickets.
Personally I hate them, they look like something from a horror movie. But they work.
Hope this helps.