Here are some facts and some suggestions about how to preserve crucians and crucian fishing
Nineteenth century books describe the crucian as a rare fish. I think that this has been partly because of the difficulties of identification - confusion between low-backed and high-backed forms, brown goldfish and hybrids. The smaller, less obvious crucians, together with the lookalikes were often called "Prussian carp" and people weren't quite sure whether this was a separate species or not. The high-backed form would always have been scarcer before the days of managed fisheries because that shape was a characteristic of crucians in a mixed species water. In such a lake or pond, crucian numbers would have been low - hence "a rare fish".
Today, although it is not, as far as I know, on an official list of endangered species in this country, anecdotally the crucian is under considerable pressure. For example, I have seen it stated that it is "extinct" in Norfolk. Now, that may be an over-statement but it is an indication that we ought to be worried. There is at least one conservation project aimed at restoring crucian habitat and numbers in that county, the Norfolk Biodiversity Action Plan, a six year plan running from February 2010 to January 2016. The plan is the work of G.H.Copp and C.D.Sayer.
The reasons for the comparative scarcity of good crucian fishing today are straightforward enough. First, many of the small waters where they once thrived have either disappeared through neglect, been built over or been stocked with common carp. Secondly, hybridisation with carp and goldfish has become more of a threat as fish are moved around from water to water, especially since the advent of commercial waters and the resulting bag-up mentality that demands more and more heavily stocked club waters. Thirdly, predation by cormorants has increased considerably - and the crucian is an ideal sized prey for such birds. Fourthly, clubs and individuals stocking with crucian carp have often done so without understanding the very special requirements of the fish.
A Way Forward
The crucian is a prolific breeder in the right circumstances and there would be no difficulty maintaining its numbers were it not for the ways in which it is managed in modern fisheries. I go into detail about this below in the crucian fishery stocking and management section.
One solution to the problem of declining numbers is to imitate the Scandinavian situation, where big populations of small crucians survive in mono-culture conditions - i.e. where they are the only species, except perhaps for tench. This was the situation here as recently as 50 years ago, though our crucian nurseries were small by Scandinavian standards - i.e. the tiny field ponds, pits, moats and small estate lakes that were once so common. It is too much to expect that we can ever return to that situation but those of us who value the sport and atmosphere of crucian fishing can do our bit to improve matters in our own local areas. So, dig or take over a small pond and manage it as I suggest in the next section.
Though the crucian reproduces prolifically in that sort of situation, it does not compete well in a mixed species water. To look at the Scandinavian situation again, the giant crucians are found in lakes (and even the Baltic Sea) where predators and other less obviously detrimental species abound. Our equivalents here would be pits, reservoirs and big estate lakes. In waters such as these, the numbers of crucians will be small unless artificially boosted by a regular stocking policy. I go into detail about methods in the next section.
Thirdly, it is essential to avoid goldfish and crucian-and-goldfish hybrids. This can only be done if we recognize these problem lookalikes and I hope that the identification section will help all of us to do just that.
A remarkable fish
The crucian can survive extreme conditions such as intense cold and heat; it tolerates acidification and de-oxygenation, conditions that kill almost all other fish. It is a fish that perhaps one day may help scientists to understand the process of brain survival without oxygen, with all the potential benefits to human health.
Nevertheless the crucian's famous powers of survival will not protect it against the mistaken fishery policies of 21st century UK. It really is time we anglers did something about it. Official conservation projects are of course important but they do depend upon public funding and that will probably be in short supply over the next decade. In the meantime, enthusiastic individuals can do quite a lot to improve the situation - I've done it here and so can YOU!