probably the ones I catch??

no I think it maybe the small perch, everyschool boy probably caught one of these first and in many cases without even realising it until he pulled his rod in, mind you they soon learn, the larger perch are a different ballgame

Dumbist? New word on me.....

I go with Cakey. Went fishing one day on upper Medway for barbel. Fed an area for about 2 hours until I introduced a hook bait.

Trouble is I only had lobs and maggots (it was a de-tour on the way from work so only had some very basic stuff as the wife couldn't know).

After 2 hours of feeding maggots I chucked in a lob on a paternoster. 2 mins. Bang! Then nothing, no hook left. Hacked off.

15 mins of feedeing mags and then chucked in a big bunch of mags on a paternoster. Bang! 10 seconds cracked off.

Now I only had two hook links left, which were home tied braid length. Put on a lob, chucked out, two minutes and then bang! And again, within a couple of mins cracked off.

Now this strecth was well known for big barbel, so I was steaming! Final hooklink left, tried again with a bunch of maggots. Bang!

This time I managed to keep the fish going and after a while realised I may land it! I didn't see it until I got it to the surface right under my rod tip, and slipped the net under a.................

.........12lb pike. With every damn one of my hooks in its mouth.

Still a cracking looking fish though.

EITHER....

Pike: As a kid, I used to fish a pool in the town I live in which is in front of a hotel.  I'm not proud of this (and frankly at 11 years old we knew no better) but 2 mates of mine and me all caught the same pike in the same afternoon.  Each time it went back in, it sulked off to the same shallows in full view, and each time one of us would throw a spinner or deadbait at it.  As memory serves, I caught it second and it still had a little bit of go.  Third time it came in like a bream (unsurprisingly).

OR

I've seen this species get certain members on this site unecessarily excited, but what about the ruffe (slapper)?  They don't seem to inhabit the waters I fish now, but it seemed in the 80's when I was a kid, you could stare at a float/ quiver for a good long while without so much as a twitch - then you retrieve only to find a three inch ruffie attached!

dumbist

This is a very difficult one. From my own experience I would say the Tigerfish.

Amongst British species, the barbel do seem a bit thick, as do small pike at times. Certainly medium sized bream in large shoals can prove very easy to catch, not so big ones however.

I think that all immature fish are a little behind in the intelligence stakes. It is when they get bigger that they can prove difficult to catch , remember the laws of survival. A big fish has not go there through being stupid. They have learned a few lessons along the way.

The two most inquisitive British fish in my opinion are the tench and the perch. 

Peter Stone wrote in his book (Bream and Barbel 1963)  about the Barbel in the Royalty not fighting as hard as on the Stour, Kennet etc. and he described a 9 pound barbel which just went round in circles as an example of them not putting up much of a fight (which is definately not normal for Barbel who size for size normally fight much harder than most other fish) ; and he wrote that Richard Walker had a theory that because they had been caught so many times on the Royalty that they had learnt to just give up; knowing that very soon they would be free again. (NB. This was in 1963 when the Royalty was a mecca for Barbel enthusasts and the best swims were permanently booked by anglers).

Im not sure that mug fish are always quite the mugs that we seem to think; Im not suggesting that they are intelligent but maybe just not quite as stupid as we think. (unless they always fight as hard each time they are caught of course).

The fact that Royalty barbel did not fight in those times is quite true.

Yorkshire barbel used to fight like demons. Peter Wheat made a trip up to Yorkshire at that time and could hardly believe the diffence beween them and the Avon fish.