The side that gives them less adhesion/less traction to the side of the bucket.
I'm guessing the hook side works better than the fuzzy side.
Or you could eat the purslane yourself.
FYI suddenly trying to change the fish's diet just a few weeks before harvest, is probably more likely to have the fish refusing the new feed and possibly even losing weight rather than changing the omega balance in the meat.
I don't even know if there is much actual scientific evidence that feeding chickens flax actually makes their eggs omega 3 eggs but apparently they are allowed to market them as omega 3 eggs simply by offering flax seed to the birds.