Garden Ponds

Andrew Cooper's observations on the crucians in his garden pond, extracted from correspondence with Pete.

The Pond:

A couple of years ago I created a pond in my garden and, in March last year (2019), I stocked with ten 5-inch crucians, five golden tench and a small shoal of golden rudd and roach. All but the roach (which suffered from white spot) have thrived in their new home and, amazingly, both the crucians and tench spawned successfully in the first year (2019). I didn't witness the crucians spawn, and so didn't believe my daughters when they claimed to have seen 'baby fish' in the pond at the beginning of June, but they grew quickly and numbers of tiny fish could soon be seen feeding on the algae growing on the pond liner. These were easily identifiable as crucians due to the shape of the dorsal fin. The black spot on the caudal peduncle was also clearly visible, but this is a feature shared with juvenile tench, so was not diagnostic. I do wonder what the purpose of this feature is, as it seems unlikely to help with camouflage.

The tench spawned later and were far more obvious with their activity, but they seem to have been far-less prolific. This is probably not surprising; I only saw one tiny tench, but this fish was very obvious from its bright orange colouring. It looked like an animated pomegranate seed and any siblings it may have had would have been an obvious target for predation. I hadn't realised that golden tench are coloured from birth and never go through a change like goldfish do, but apparently this is due to a recessive condition which restricts the production of melanin and guanine, this phenotype is homozygous, so it would be expected that all progeny in my pond (with no green tench present) will be golden. Amazingly, despite a kingfisher regularly visiting the pond during the winter floods, this fish has survived and is growing well, it is currently around 3” long.

The adult crucians have probably quadrupled in size since last year, so will have carried a far greater quantity of spawn this season. I am starting to see just how quickly a crucian pool can fill up with fish! If they hadn't grown so well, they would now be difficult to distinguish from their progeny. The largest youngsters have grown even more rapidly than the tench and there are now two or three amongst them that are close to 4”. The smaller fish, around 1½ - 2”, must have come from a later spawning. (I've attached a couple of photos of these fish taken in November 2019, the larger of the two fish was 1½”)

Andrew Cooper Crucians Andrew Cooper Crucians

I must admit that I haven't followed through with my suggestion of stocking ruffe alongside the crucians, partly due to their scarcity, but mostly because I'm not sure I want to watch any of my baby crucians being consumed! You questioned (I'm tempted to say 'pondered'!) whether ruffe would do well in a pond. It must be about twenty years since I last caught one, but all of the ruffe I have caught came from either ponds or, more often, canals, so I had always thought of them as a still-water fish. Apparently the current record is also a stillwater specimen of 5oz 4dr, caught from West View Lake, Cumbria in August 1980. I don't imagine it is a record we will see broken again any time soon, a shame as I have a soft spot for the species, it being the first fish I ever caught.

Having seen the rate at which my pond is filling with fry, I am seriously considering the idea of transferring some of the youngsters to another water. I don't think any more of my garden can be given over to aquaculture, so my family have found themselves taken on more than one detour, investigating blue dots on the local O/S map to assess their suitability. Obviously this could only be carried out with permission from the landowner and the environment agency, but sadly, the quality of field ponds locally seems to be in decline, so the search must continue. If not, I may have excess fish available to a good home in future years.

A Note on Spawning:

This year I have been lucky enough to witness the spawning activity of each species in the pond. The rudd, together with the solitary roach, attempted to spawn at the beginning of April but the activity didn't last long and I doubted they were successful. The crucians were next to spawn, with the males beginning to show an interest in nudging and chasing the females during a cooler spell after a few very hot days in May. The actual spawning took place in the morning on an overcast day with two or three males chasing each female through a thick clump of hornwort in an effort to get alongside. The hornwort seemed to be the preferred spawning medium, but a couple of fish were also pushed onto the top of a basket of flag iris as they attempted to deposit eggs in the roots. All activity had ended by midday and the pond had lost its usual clarity due to silt and decayed algae being suspended in the water. From what I could see of them, the females had deposited the majority of their roe as their girth appeared considerably reduced.

The tench spawned during bright sunshine later in the month, causing a huge commotion with all five fish involved in sinuous cavorting through and on top of the hornwort, the irises and, unlike the crucians, around the stems of the dwarf pond lilies. I had thought that this was the end of the activity, but within a couple of weeks the female fish of both species had clearly swollen and were preparing to spawn again. The crucians spawned for the second time on the morning of 14th June, once again the weather was overcast and warm after an electrical storm had passed over (without cloud-fall) during the night. The routine was the same, with a couple of males chasing a single female through the hornwort and iris root (but not the lilies), and once again, all activity was confined to the morning.

The tench spawned for their second time on the following day. The sun came out mid-morning and this seemed to stir them into action. Four fish were involved, (two males and two females) and, for around two hours, the females were repeatedly pushed into the thickest part of the weed until they were immobilised. They freed themselves through vigorous splashing, at which time the males moved into the space they had vacated. After this activity ceased, the tench moved to cavort around the lily baskets for the next couple of hours, although I cannot be certain whether this was spawning behaviour or the fish cleaning themselves on the mesh and gravel. They stopped immediately as soon as I threw food into the pond and they began feeding.

A third spawning took place on 24th June, a very hot day with bright sunshine. The fish were far more aggressive in their chasing, performing high-speed circuits of the pond. Once again, one female was pursued by two males who repeatedly butted and crashed into her. Strangely, all activity stopped a few minutes before midday and the fish retired to sulk on the bottom. Again the tench spawned on the following day; I haven't yet seen both species active at the same time.

The progeny from the earlier spawnings are now free swimming. Most are identifiable as crucians (due to the black spot) but a few amongst them look decidedly different, perhaps the rudd were successful after all?

Crucian Feeding Habits:

When digging my pond, I deliberately created a wide marginal shelf, approximately 18” deep and with a steep drop-off into the deeper water (3-4'). My intention here was to provide a platform onto which I could introduce foodstuffs, whilst having a clear view of the fishes' reaction and feeding behaviour. As already mentioned, I have baskets of dwarf pond lilies on this shelf, providing cover and allowing the fish to feed in confidence. I can now lie on my lawn and while away the hours watching their behaviour; this has proven most interesting and has suggested answers to a few questions I've had.

Usually, the tench (despite their gaudy colouring) are more confident and will spend more time higher in the water or in the shallows browsing amongst the lily stems or nudging though the accumulated detritus. The crucians almost always feed in short bursts throughout the day, but they spend surprisingly little time in the margins outside of this. When not feeding, most of the fish hang in midwater, level with the depth of the marginal shelf.

I generally feed the fish using 2mm and 3mm sinking pellets and bloodworm pellets, but this diet is often supplemented with the remnants from my bait box. When food is introduced, the crucians move in more quickly than the tench, but do not initially feed with much confidence. They appear to sample the food, rapidly sucking and blowing until they find a morsel they are happy with. Frequently the tench will move in alongside and confidently consume the food immediately the crucians eject it. The old adage that tench like a moving bait certainly appears to be true. The bloodworm pellets break-down more quickly and these appear to be eaten in preference if both types are introduced simultaneously.

Relating this to my fishing, I have frequently caught tench when, from the bite, I have expected a crucian. I wonder how often this is because a tench has taken a bait that a crucian has just rejected? Would a self-hooking rig catch a greater percentage of crucians vs. tench in any given session, assuming the crucians would be unable to eject the bait? The crucians' sucking and blowing behaviour usually lessens as the pellets absorb water, swell and soften, possibly suggesting that the crucians prefer softer food. I have always been most successful using large (¾” diameter) discs of punched bread, very similar to that described by Jeff Hatt in his marvellous Idler's Quest blog. Fish seem to take these confidently and produce clear lift-bites, although there are still (too many) days where I am too slow and miss five good bites in a row!

When feeding my fish, I usually allow some food to fall across the edge of the marginal shelf to encourage them to venture into the shallow water to look for more. The top of the slope at this point is the fishes' favourite feeding position and seems to be the only place where they will take food really confidently and without initially sucking and blowing. The deeper water is bordered by a dense clump of hornwort that reaches to the surface, with shorter strands of this and filamentous algae often lining the bottom. When food is introduced into this deeper water, the crucians will often take 'on the drop', but will usually eject the food and allow it to fall into the weed where it will sometimes be eaten overnight, but in cooler weather it will frequently remain there for days until I remove it.

I've noticed that the shelf-type feature is often the 'hotspot' in the lakes I fish. I usually fish the lift method with a short reversed quill, slightly (2-3”) over-depth for the marginal shelf and with very marginally too much weight on the line, so that the float will just submerge in the deeper water. I overcast and allow the float to cock before submerging the line, by slowly retrieving the tackle the shot comes to rest on the edge of the shelf. The bait should therefore be resting in direct eye-line of any fish patrolling the shelf, or more likely, 'hanging around' as my fish seem to do. The line being taught between the rod and the float allows the float-tip to be adjusted, helpful if a ripple is on the water. Bites are usually dramatic lifts, but the float will sometimes slowly submerge if a cautious fish backs away with the bait into the deeper water. Bites must be struck during the lift; else they are invariably missed.

Since the warmer weather, and the corresponding increase in water temperature, the crucians in my pond have started to feed on the bottom in the deeper water. When doing so, they produce the huge clouds of fine bubbles we are so familiar with. I've never seen this from any other pond fish, despite having kept goldfish, tench and carp in the past. I've watched this happen a few times when the light has been at the necessary angle to see the bottom of the pond. What has intrigued me most is how these bubbles appear to be produced: The fish have not had their heads in the silt as I had always imagined would be the case, nor has it appeared that the bubbles were emitted from the gills as I had always assumed. It looks as though the fish are taking gas into their mouths when browsing on the algae, this is then blown out through the mouth and rises to the surface before separating into many smaller bubbles. Watching them puts me in mind of an experiment we used to do in school; observing (and counting) the oxygen bubbles given off by a strand of Elodea under varying conditions. I had always assumed that the bubbles produced by feeding fish were primarily methane, now I'm not so certain.

I noticed one more thing of interest this week. Three of the larger fish had been feeding on pellets that had been in the water for an hour or more. After a couple of minutes, the fish started to regurgitate small clouds of pellet. Were they rejecting the food, or had they gorged themselves and could no longer contain it?

My fish appear to have developed some interesting feeding habits. When feeding upon 3mm ‘coarse pellets’, they will consume large quantities of softened pellets and then return to hang in midwater under the hornwort. A few minutes later, the fish begin regurgitating the pellets, forming clouds of the stuff, which settles on the bed of the pond. This doesn’t happen with other foodstuffs, so I have decided to remove ‘coarse pellets’ from their diet. Is this behaviour vomiting, or am I anthropomorphising? Are they just gorging themselves and rejecting the excess, or are these pellets actually bad for them?

Since the heron attacks, the fish no longer feed confidently, but rush out from cover to take a few mouthfuls before dashing back. They are no longer so selective in their choice of food, taking the closest mouthful and rarely ejecting it - it is possible to watch as the food is cleared in an arc emanating away from the nearest cover. With this change of behaviour in mind, I have tried them with sweetcorn again… They ate it all! It appears that they have a preference for softer foods under normal conditions, but this is less important when there is a choice between food or safety. Another consequence of the heron attacks is that the amount of bubbling has been considerably reduced, perhaps because the fish are less active when sheltering.

This year’s fry have now attained a size where identification is becoming easier. There is a small shoal of eight golden tench (though they might, possibly be golden rudd) and a much larger shoal of crucians. The crucians are far more active and are noticeably larger (both longer and deeper in the body) despite having been spawned at much the same time. This is reflected in the yearlings, where the solitary golden tench is perhaps only half the size of the largest crucian. I’ve seen both species described as slow growing, but it appears that it is not until at least the second or third year, that the growth of tench begins to outstrip that of the crucians. Is that also your experience with raising these species?

Crucian Feeding Habits:

I’m always surprised by how crucians feed in very, very shallow water, sometimes not much deeper than they are! The sucking and blowing account for the infuriatingly difficult bites!

Interesting theory that they prefer soft baits. Would you rate sweetcorn as soft or hard, I wonder. Bread seems to be an excellent bait.

Bubbling – your observations are very interesting. I’ve seen it suggested that gasses come from the vent, but I’m yet to be convinced of that. When a small tench is hooked at The Wetland ponds there is often a mass of bubbling in the swim at the same time and apparently caused by the disturbance. Movement of fish in the silt? – yet the bubbles are not like methane, ammonia bubbles, but masses of little ones - PJR

Activity in Winter:

The crucians in my pond were not active on very many days during the winter. Like the tench, they remained buried in the remnants of the hornwort in the deepest part of the pond. I didn't introduce any food between late November and around the last week in February when they began to appear more regularly. My pond is just less than 4' deep, so may become cold throughout. It may be that in deeper water, crucians will remain active for longer and could be encouraged to feed throughout the year.

Sexing Outside of Breeding Condition:

You mention in Always Summer, that you are interested in whether it is possible to sex crucians outside of the breeding season. I assume that your primary method during the season is to look for tubercles in males and the swollen abdomen, indicating the presence of roe, in females? If so, I believe I may have spotted an additional method. My fish were very easy to sex during most of April and the early part of May, mainly due to the impressive width of the females. I didn't take the opportunity to weigh any of my fish, but I would be surprised if the largest was carrying anything less than 20% of her normal weight in spawn, she was very rotund! Observing the fish closely, I noticed a secondary difference. Most anglers and fish-keepers will be aware that tench can be sexed by the appearance of their pelvic fins, the size, shape, and position in relation to the vent is starkly different between the sexes. From my observations, I am now convinced a similar, but more subtle, difference exists in Crucians.

Viewing the fish from above, and only when at rest, the lower fins, and in particular the pelvic fins, of each of my obviously-male crucians are clearly visible: These fins are held out from the body and are a quite vivid red-orange which stands out from the background. By contrast, the pelvic fins of the obviously-female fish are a more muted-shade and they darken more obviously towards the outer edge. In the females only the very tips of the fins could be seen from above, due to their being held more in line with the abdomen and closer to the vent. I had questioned whether this difference was due to the abdomen being swollen and pushing the fins into a lower position, obscuring the view of them from above. Following the spawning in May this differentiating characteristic persisted even though the females had lost most, if not all, of their girth. It may be that, even following the second and third spawnings, the fish have remained in breeding condition, and that this difference will subside over time. I'd be interested to know whether anyone else has observed anything similar.

To clarify my descriptions, I have attached some diagrams to show the differences I believe exist. I'm no David Carl Forbes, so I have also attached some photos of my own fish to hopefully illustrate my observations more clearly! (Female above, male underneath.)

Andrew Cooper Crucians
Andrew Cooper Crucians Andrew Cooper Crucians

My crucians are not DNA tested (it seems to be impossible to find such fish in small quantities) but were sold to me as pure-bred crucians. They do look 'right' in all respects that I have examined, apart from a couple of fish that have an interesting patterning in their scales (I've enclosed a couple of photos taken as I released the fish last year). Both fish have very broken and indistinct lateral lines (not particularly unusual) and the scales do not sit in neat rows, in a similar manner to some fully-scaled carp i.e. those I assume may have Ssnn alleles. Are these fish potentially the future parents of a Mirror crucian?

Andrew Cooper Crucians Andrew Cooper Crucians

July Update; Post-Spawning:

I've also made some further observations that I thought may be of some interest:

Like yours, my fish have suffered from the attention of an avian predator, in my case a heron. Hopefully no fish have been taken, but my largest tench has received a nasty wound just in front of her dorsal. This looks to be healing well, but the habits of all fish in the pond have changed considerably. They now spend most daylight hours hidden deep in the weed, and have become much more sensitive to any shadow cast upon the water, making close observation of them far more difficult.

I'm fairly certain that spawning has finished for this year, so I have tried to establish the veracity of my theory regarding the shape and colouring of the pelvic fins being used to determine the sex of crucians. I'm pleased to report that the differences I had observed appear to have remained consistent. The pelvics of the males are more prominent, being a brighter colour and generally held further out from the body when at rest. There are two males that I can recognise easily (one is a lighter colour, the other has a split dorsal) I have taken photos of these alongside fish I presume to be females to enable comparison. In the first image, the split dorsal fish is in the foreground, the lighter fish is to the LHS, the other crucians are fish I believe to be female.

Andrew Cooper Crucians

In the second image, the split dorsal fish is in the foreground, the lighter fish at the rear and a female between them. The fish were moving forwards slowly in this image, hence the fins being held closer in to the body, but the colour difference is fairly clear.

Andrew Cooper Crucians

A January Update:

I took note of your comments regarding crucians feeding in darkness and have been taking a torch out to the pond these past few months. I hope my observations are of interest:

The hornwort began to die down during October, breaking into shorter strands and gradually thinning (with my help), before (rather suddenly) sinking just before the end of the month. Prior to this, I had seen almost no sign of fish since the summer, save for an occasional glimpse of the rudd from an upstairs window. Food left in the shallows was being consumed overnight, but the fish were spending daylight hours hidden in the weed. Once the weed had died back, I began to see the tench lying up against the lily baskets or alongside the marginal shelf. They seemed unaffected by the torch beam, but a clumsy footfall sent them back into the weed immediately! What I didn't notice for the first couple of nights, were the crucians rapidly disappearing from the shallows, apparently scared by the torch beam. I noticed this on the third night and took to shining the torch into the deeper water on my approach; the crucians were active but were scared by the light.

Subsequent November dusk-visits to the pond were longer; I crouched, with the torch held very still and low to the water, and watched as the crucians slowly drifted out of the weed and came closer to the marginal shelf to inspect the sweetcorn I threw to them, one grain at a time. My movement, being obscured by the beam in front of me, must have been imperceptible to them and within a few minutes I could have six or seven fish feeding happily. I decided to attempt a photograph, but the flash panicked every fish in the pond, and I failed to capture an image of a single one! Rapid movements of the torch later proved to have a similar, if slightly less dramatic, effect. It appears that tench rely more on their lateral line for threat detection, whereas crucians are possibly more visual. This would tie in with previous observations of otherwise healthy blind tench and crucians with disrupted lateral lines that still manage to evade predators.

A similar state of affairs persisted until just before new year, when the pond iced over. The fish may still be feeding when dusk falls - I just can't see them! I haven't taken the water temperature at any point, but I have seen fish feeding when the air temperature has dropped to just below freezing, so hopes of a 'crucian in the snow' picture may not be unreasonable. It won't come from my local water though, as there is no night fishing on that pool!

One more thought about food for crucians: You will have noticed that I fed sweetcorn to my fish, they take this happily now, but they now refuse any kind of pellet. I've had to remove the last few handfuls I've introduced as it was spoiling on the bottom. I wonder if a similar change of taste happens in lakes that are regularly fed with pellets? If so, is it likely that crucians will move away from areas that pellets are introduced?

Pre and Post Spawning Comparisons:

A few images of the crucians in the pond before and after spawning, with male and female fish labelled for reference.

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