Crucian Identification


Perhaps the best way to confirm that your stock of crucians is true is either to have a fin clip or scale DNA tested or to dissect a casualty and examine the key internal features, which I'll explain later. Most of us, though, want to identify the fish in the landing net and it is likely to be a true crucian if the following apply:
  • there is no trace of barbules around the small mouth, which slopes up slightly to the front when shut. The crucian has the typical bottom feeding cyprinid protrusile mouth, which can be extended to sieve through detritus
  • there are between 32 and 34 scales along the lateral line. This scale count has been confusing people for a long time. In the early twentieth century a count of 28-35, possibly first stated by Tate Regan, was commonly used by popular writers including, later, Bernard Venables. That was because not many people in those days seem to have known about brown goldfish or hybrids. If you examine closely any good photograph of a true crucian carp the lateral line scale count will almost always be 32, 33 or 34, with, more often than not, the slots missing on some of the scales. Ignore any half-scale that you may find just before the tail fin begins.

    That doesn't rule out 31 or 35/36 as belonging to a true crucian but at those extremes I begin to suspect crucian x goldfish and crucian x common carp respectively. Incidentally, the slots run out usually towards the tail of the fish but there can be gaps anywhere along the lateral line; typical of the inconsistent crucian, you'll sometimes find crucians where the slots are complete from head to tail. And I have seen goldfish and goldfish hybrids with slots missing, though this is not usual. You can see the problems of relying totally on the lateral line scale count.

    So a count of 32-34 suggests strongly that your fish is a true crucian, but we have to remember that it needs to be taken in combination with the other characteristics. For example, a goldfish x crucian hybrid can have 32 lateral line scales and a goldfish x common carp hybrid (F1) can have a scale count of, say, 34, approximately mid-way between a carp's 35 - 39 and a goldfish's 28 - 30. So a lateral line count on its own is not enough to identify a crucian correctly, though it is a good place to start.
  • often, though not always, the lateral line slotting is interrupted and/or incomplete, disappearing towards the tail end of the fish
  • there are 7 (occasionally 8) scales on the diagonal between the front of the dorsal and the slotted scale on the lateral line and 6 or 7 between that scale and the front of the ventral fin. Don't count the slotted scale
  • the lower fins are brown or reddish, sometimes orange, sometimes darker, particularly towards the tip
  • the caudal (tail) fin is almost straight or only slightly forked when extended vertically
  • the dorsal fin is large and convex; sometimes split, perhaps as a result of trauma such as spawning
  • the back just in front of the dorsal fin is ridged rather than rounded ("carinated", as scientists say)
  • there are tiny, hardly noticeable serrations on the main hard ray on the dorsal and the anal fins. Serrations on the back of the spine-like dorsal ray are smaller and more numerous in crucian carp (28-29) than in goldfish (10-11)
  • the anal fin consists of 6 or 7 soft rays above the hard, spiny ray. Note that the last one is split at the base and is easy to miscount as two.
  • the fish is soft to the touch (a goldfish usually feels harder, perhaps because of the spinier fin rays). Young crucians lose scales much more readily than goldfish so the latter's scales may be tougher.
  • the body is deep and flattish rather than torpedo-shaped, more like a bream than a chub.
Crucians vary in shape. Some are very flat and have very high backs, like the well-known Yateley fish. Others are slightly rounder and are lower-backed, like the Marsh Farm fish. There seem to be "strains" of crucian in the same way as there are well-marked "strains" of common carp and, of course, goldfish.
Crucians also differ in colour. Young fish are sometimes more silvery than older ones. Fish in small ponds over-shadowed by trees are often darker than those in more open waters. In peaty waters, crucians can be almost black.
Usually, though, the backs of crucians are olive-green or browny; the flanks are brassy, with the yellowness intensifying towards the belly and onto the gill covers and head. Quite often the lower fins are orange, sometimes darkening towards the tip, sometimes they are browner. The graduations of colour are much more subtle than those of the ornamental goldfish. Confusingly, the crucian is much more golden than a "brown goldfish", which is an ornamental goldfish that has not "turned" gold.
If you can't check on all these details by the waterside, then take a good photograph so that you can do so later. Usually a "trophy shot" is not much good for checking all the features of the fish - thumbs and flash flare mask scale details, dorsal fins are flat, tails are not extended, etc.

Info supplied courtesy of Peter Rolfe @