"The trickiest situation is where some of the fish in a water are hybrids. This is where a lake has big roach, big rudd, and also big roach/rudd hybrids. Just because some of the fish are hybrids doesn?t mean all of them are hybrids."
Totally true.... but with Roach, Rudd and Crucians the presence of hybrids means the biggest fish are more likely to be hybrids.
"It does mean that you?ve got to check any big ones you catch very carefully."
Yopu can look but you may spot obvious hybrids but you will not spot them all. The latest research from Hull showed not only f2 hybrids but also found many fish were reclassified after dna testing because they had been incorrectly idetified on the basis of how they looked.
If you want to catch true Roach or Rudd look for a water that contains only one of the species and if you want a true cruican look for a water that hasn't had goldfish or crucian hybrids introduced.
i fished a lake in the south of France earlier in this year and had loads of Roach, Rudd and Roach Rudd hybrids. the biggest went 2 lb 6 oz and the locals were convinced it was a monster Rudd (the french record is apparently 3 lb 8 oz) but I wouldn't have counted it as a true Rudd. There were loads of hybrids and they covered the whole range from Roach to Rudd. Mine was the biggest that had ever come from the lake to my mind that made it almost a cert to be a hybrid.