I have seen articles with boats using keep nets
Fine for small fish in calm water and small tides, not sure about the congers though and hard when it comes to a move
I have kept congers alive for hours in the bilge locker on GW, by adding buckets of sea water occasionaly, with the lid down they just go quiet in the dark.
They soon liven up when its time to get them back out
Flounders are OK in a few inches of water in a fish box
Wrasse and even bass have been ok in the bait tank
Charlie
I think its better to try and keep them alive and fail than to just knock them on the head straight away. But I do not let them suffer if I think its not going to work they get released or knocked
Charlie