The Brown Goldfish
There have been goldfish swimming in our rivers, lakes and ponds since at least 1728, so it's hardly surprising that many of us have caught them and perhaps called them "crucians" because superficially they do look like their very close relative. Goldfish are Carassius auratus; crucians are Carassius carassius - same genus, different species.
If you keep goldfish in your garden pond, you'll be familiar with the dark fish that keep company with your gold, red and white ones. Those are "brown goldfish". These late developers can turn colour at any age or may just remain brown. In the wild, any that "turn" are probably more vulnerable to predators and do not often survive, but they can be found. Look at these two Danish fish, both goldfish (though the brown one is just possibly a hybrid) though you could mistake only one for a crucian! There, they are described as "gold crucians"!
In practice, once you've handled both crucians and goldfish the differences between them quickly become clear: they are really quite dissimilar fish. Until then, though, these guidelines should help you recognize a brown goldfish:
- colouring hovers between brown, olive green and grey on the flanks, darker towards the back. It lacks the brassy/golden overlay of the crucian carp. Unexpectedly, the crucian carp usually looks more golden than the brown goldfish, which has confused the angling press in the past!
- like the crucian, but unlike the carp and carp hybrids, there are no barbules around the mouth
- the feel of the fish in the hand is different: the crucian is soft to the touch; the goldfish is scalier, tougher. Usually, the body is rounder than that of the crucian carp, more carp-like than bream-like, though bigger specimens can be quite deep in the body
- the goldfish's scales are larger than the crucian carp's. The lateral line count will usually be 27-29, most commonly the latter. The slots along the lateral line are usually bold and complete, but not always - so beware
- the oblique scale count from front of dorsal fin to the lateral line, ignoring the slotted scale actually on the lateral line, is usually 6, as opposed to the crucian's 7(or 8)
- the dorsal fin is concave and lower, more carp-like
- the tail fin is noticeable forked, even when extended, and quite often elongated
- the paired fins on the underside of the brown goldfish are sometimes pale and not orange or dark-tipped as in the crucian. They, too, may be longer than looks right
- the main front spine in both dorsal and anal fins is noticeably saw-toothed in the goldfish, hardly detectable in the crucian carp. Goldfish, like common carp, will often hang up in the landing net because of these spiny rays. These little teeth on the posterior margin of the spine-like dorsal ray are smaller and more numerous in crucian carp (28-29) than in goldfish (10-11)
- internally, the peritoneum is darkly pigmented in the goldfish and the gill rakers number 38-43, far more than the crucian's.
Here's an example of an English brown goldfish. Since "gold" goldfish vary in shape, even the common ones, so it would seem logical for "brown" goldfish to do the same. Note the colour, more olive than brown, as is so often the case. Count 29 lateral line scales and 6-ish oblique from dorsal fin to lateral line. Note also the pale lower fins.
This illustration from that famous book, British Fresh-Water Fishes by the Rev. W. Houghton 1879, clearly shows that the Victorians knew what many of us have apparently forgotten, that not all goldfish are gold. Note the dorsal fin shape and the clearly forked tail.