Backyard Aquaponics
A place to discuss aquaponics

I'm reworking my aquaponics system soon and want to know what methods everyone uses to do full fish harvests of large tanks. The new tank I'm looking at using is a 9000 l fibreglass tank but I can't see an easy way of doing a complete harvest of fish without too much work or draining the tank. Thanks for your input in advance

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I would suggest you provide a photo, to best advise HOW to do it...

I would do it by using two pipe lengths and some bird netting, the width of the tank plus a bit...

Attach the ends to the pipes and roll it up and using two people, start at a point and follow the walls Slowely, in opposite directions, and concentrate the fish so they can be scouped out..
You will need to adjust to suit plumbing obstacles like SLO's, unlessyou planned ahead and made them removable..

Another idea... a much larger bird netting piecewirh weights on the front edge and using a number of people, feed it over one edge and drag across the bottom and up the other side and just lift it all out.
Again... success will be reliant on the fittings..

You may find it easier with different fish.. eg. PERCH..
drape a tarp over one portion of the tank and get ready with the drag net..
Let things settle for a few days so they get used to the cover... then start making noise at the other end and know the perch will hide in the darkest area..
Lower the drag net in and now the fish are in a narrower area to be more easily caught..

Another thought... big net... bigger than tank.. fix securely to one side and carefully spread into the tank to half way..( weights on submerged end...
Cover the netted end... leave for a few hours... scare fish to the dark end and quickly lift the other end..

And finally... Oil of Cloves.... could be added to calm the fish, if not knock them out but I have NO IDEA if it degrades after a time, to leave the system reuseable....

A few ideas, some based on seeing a commercial farmer harvesting tanks..
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Don't do it....... Use smaller tanks.....

I've tried many methods over the years and they all suck compared with having a smaller easier to harvest tank/tanks. We had 5000L tanks and they were horrible at harvest time, plans were that we'd scrap the 5000L tank and replace it with 4 x 1000L tanks but we decommissioned the systems.

For my Rainbow Trout harvest in 2013, in a 4500l tank, I sewed some tubes into the ends of a length of 1.2m wide shade cloth to hold poles, and a tube along one edge, which I filled with small river gravel, as used in the GB, for a weight. I removed the SLO and we herded them around to a smaller area then netted them out, only a few at a time, to reduce chances of injury. It was pretty easy to do.
Another option is to net them out at night when they cant see the net coming at them.

I made a large circle from two lengths of 20mm conduit which is pretty flexible. Covered it with some insect netting and pushed it down one end, across the bottom and up the other side of a 2.5k litre tank which worked pretty well. Its helpfull if you can pump or syphon at least some of the water out. Always use the finest mesh you can get as the bigger the mesh the more the fins,gills heads whatever get stuck and even if its "the final netting" its damaging and stressful to the fish (and you) trying to get them untangled.

Thanks for all of your inputs, I have a few ideas now running around my little brain. Now to find time to make this thing happen!