Some will argue that there is no humane way to kill and in a way I agree. Killing should never really be easy anyway, this gives us the moment and incentive to have a thought for nature and how the circle of life works, take that moment to give thanks and commune with whatever spiritual element you believe in.
So on to the more graphic, or actually not so graphic in this situation, part of this post.
CO2 can be used to anesthetize fish for handling or harvest. This can be done using special equipment and compressed CO2 gas, however most small operations or backyard Aquaponic Gardeners are not going to have that equipment. (Keep in mind some pH buffering may be needed if only anesthetizing for handling and not killing.) I am not going into details on how to do this with compressed CO2 gas because I don’t have the equipment for that nor the experience.
For the Average person without special equipment, it is still possible to anesthetize fish for harvest, by stopping by the grocery store and getting some dry ice right before you plan to harvest some fish. Remember to take a cooler with you to the store since dry ice evaporates quickly so you want to keep it insulated until you are ready to use it. Also remember safety when handling dry ice (insulated gloves/oven mitts for handling and goggles if breaking it into smaller pieces.) Never keep large quantities of CO2 or dry ice in a small enclosed room with anything you want to stay alive, like pets or people and don’t stick your head into a large cooler with dry ice. Keep dry ice away from children. DON’T make dry ice bombs with drink bottles, it is actually very dangerous (think of it like shooting a gun in which you have no way of knowing which direction the bullet will go) and I know of instances where the cops showed up and wrote tickets.
The procedure is actually quite simple. Prep a bin 1/2-3/4 full with some water next to your fish tank, Drop in a pound or so of busted up dry ice and let it bubble out some of the oxygen and elevate the CO2 content of the water for a bit. Then net out the fish for harvest and drop into the bin with the CO2 water. Leave it there for a few minutes or until it stops moving. It will then be far easier to handle for cleaning.
We did this the other day when harvesting 30 large channel catfish. It was far easier/safer than trying to conk them on the head. We probably used less than 5 lb of dry ice.
As of the time of this posting, April 24, 2015
We have over 70 large (between 2-5 lb mostly) channel catfish available for sale. Whole On ice. (You bring the cooler and the ice as well as a couple pounds of dry ice) We can’t clean or fillet them for you as there is no commercial kitchen at the farm.
These are aquaponicly grown clean tasting channel catfish.
If you are interested in getting them, contact me for pricing and to make arrangements.