Category: Cyprinids

All about Cyprinids.

What’s New In Cyprinid Studies: Part 3


Cyprinids are great ones for schooling; a survival mechanism that evolved as an anti-predator measure (many eyes watching are better than just two), and as a food-finding mechanism (better a small share in the crowd frequently than the occasional big bite by yourself). It is known that cyprinids can recognize each other as individuals, and prefer to school with familiar friends rather than strangers, just as humans prefer to hang out with the old gang. The bigger a school is, the better it is for predator defense and food hunting. A recent study on the minnow Phoxinus phoxinus showed that given a choice between a shoal of friends or a bigger one of strangers, they prefer their friends [3]. However, this preference decreases as the relative size of the school of strangers increases. When the strangers are about twice the size of the friends group, an individual minnow presented with a choice between the two will go with the strangers.

So from a practical point of view for the aquarist, what does all this business about schooling mean? Basically, it suggests that cyprinids are happier in groups rather than solitary fish in a tank. The bigger the group, the better, and probably the more successful you would be at spawning them. This is not to say that you would not be able to spawn a solitary pair, but if you are having problems, it is wise to consider how the fish behave in natural conditions.


Cyprinids are understandably timid fish, as in habitat they are usually more eaten than eater. The schooling mechanism of social behaviour is a common defensive mechanism against predators, since more fish mean more eyes watching more angles of attack.

A group of chemicals known as alarm pheromones are used to alert nearby fish about risks. There is a problem of false alarms, since there are numerous possible stimuli in habitat which might provoke false alarms. Cyprinids therefore not only have to keep an eye out for predators but to decide if an object is worth getting excited about. There are two types of chemicals needed to react to predators. Firstly, the predator leaves an odour in the water, and secondly some experienced fish has to secrete alarm pheromone when it detects the odour. Cyprinids can quickly learn to associate the two chemicals, such that when they smell the predator in the water they will automatically go on full alert [6].

There is also visual detection of predators. A recent study on this aspect used the fathead minnow Pimephales promelas as a test indicator [1]. The experiment showed that motion was used as a more reliable alarm rather than shape. Lots of fish are fish-shaped, but one moving in a purposeful manner with gaping mouth directly to another fish can only spell trouble. Random motion, with fin-flicking, will not likely trigger alarms.

Historically, most aquarists forget or don’t know about pheromones in the water. Humans are visually oriented, and we have one of the poorest abilities to detect scents in the animal kingdom. What may seem to be clear water in a peaceful aquarium could be a stress-inducing soup of pheromones to the cyprinids in a community tank with potential predators. To take a commonly seen example, consider a community tank with angelfish and danios. The angelfish are predators, poor ones perhaps, but predators nonetheless. Small cyprinids can out-swim their attackers, but are unable to get away from them. They thus live in a soup of alarm pheromones and predator odours that stresses them.

It is known that minnows prefer to forage at night to escape attention of predators, but as hunger increases, they are more active during the day [4]. This suggests that if an aquarist is having trouble finding the cyprinids in the tank, skimping on the food will make them more conspicuous. There is a common practice among many aquarists based on this idea. Fish intended for showing at a club exhibition should be starved for a couple of days prior to the show. Hunger increases activity and foraging behaviour, and will also increase the likelihood of impressing the judges. A well-fed fish entered in a show is more likely to laze about with droopy fins not doing much of anything, leaving the judges to pass it over in favour of its neighbour right up front at the glass wagging its body in the hope of food.


Cyprinid courtship usually involves the male displaying bright colours and/or unusual body characteristics such as over-developed finnage. Colours depend on diet, and females proceed on the assumption that a male with bright colours has a better diet and is healthier than a drabber male. However, there is a limit to extravagant ornamentation for sexual selection. If too extreme, it will affect adjacent body tissues or organs [2]. In the aquarium this may not matter so much, but in habitat, a long-finned goldfish would not be able to out-swim a predator. The egg-shaped breeds of goldfish with cramped guts and a waddling gait would quickly be picked off by predators in habitat. What does matter for aquarists is that extreme ornamentation might affect the fish’s physiology, such as bizarre body shapes that produce distorted internal organs with concomitant internal troubles. Among the domesticated cyprinids, the only such suspect fish are goldfish breeds. This is when you see reference to some breeds as being delicate and difficult to keep. The real point is that they manage to stay alive, not that they are difficult to keep.

Just as with other types of aquarium fish such as cichlids, the cyprinids have dominance hierarchies. It has been previously shown that dominant males should be removed from a tank after they’ve spawned a few times in order to allow other males to contribute something to the gene pool. It does matter, however, what condition the smaller, sub-dominant males are in. In Pimephales promelas, small males will advance their spawning when the dominant males are removed, and will produce as many offspring. Such offspring are smaller though, which in habitat is because the small males didn’t have time to get their young plumped up before end of season [5]. In the aquarium, where seasons don’t exist, this effect means that the young will have to be fed heavier and longer to get them up to par. Normally this would not be an important effect in the fish room, but for those aquarists who raise fish in outdoor ponds it might mean smaller juveniles. To summarize from a practical point of view, if you want to get a fresh burst of spawning from your fish, remove the dominant male and be prepared to feed heavily the next batch of fry.


You do weekly partial water changes on your aquariums, right? The filter is also rinsed out in the change bucket at the same time, right? It is not enough to say the aquarium is in good condition because the water is clear. Many problems are invisible, as not all toxins are pigmented or otherwise indicate themselves. Cyprinids tend to be messy fish, and even minnows will raise water turbidity and turn the tank into a phosphate soup if regular water changes are not done [7].


1] Wisenden, B.D., and K.R. Harter (2001) Motion, not shape, facilitates association of predation risk with novel objects by fathead minnows (Pimephales promelas). ETHOLOGY 107:357-364

2] Emlen, D.J. (2001) Costs and the diversification of exaggerated animal structures. SCIENCE 291:1534-1536

3] Barber, I., and H.A. Wright (2001) How strong are familiarity preferences in shoaling fish? ANIMAL BEHAVIOUR 61:975-979

4] Metcalfe, N.B., and G.I. Steele (2001) Changing nutritional status causes a shift in the balance of nocturnal to diurnal activity in European minnows. FUNCTIONAL ECOLOGY 15:304-309

5] Danylchuk, A.J., and W.M. Tonn (2001) Effects of social structure on reproductive activity in male fathead minnows (Pimephales promelas). BEHAVIORAL ECOLOGY 12:482-489

6] Korpi, N.L., and B.D. Wisenden (2001) Learned recognition of novel predator odour by zebra danio, Danio rerio, following time-shifted presentation of alarm cue and predator odours. ENVIRONMENTAL BIOLOGY OF FISHES 61:205-211

7] Zimmer, K.D., M.A. Hanson, and M.G. Butler (2001) Effects of fathead minnow colonization and removal on a prairie wetland ecosystem. ECOSYSTEMS 4:346-357 ?

What’s New in Cyprinid Studies: Part1

Aquarists spend a lot of time trying to get their pet fish to spawn. When frustration sets in, reference is often made to accounts of how the species spawns in habitat. This is certainly useful information, but as many an aquarist knows, fish do not read the books about how they are supposed to do it and will often do it another way. Aquarists need to understand that most species are not as rigid in their spawning requirements as often thought. In habitat the fish may spawn according to such-and-such circumstances, but nature is often capricious and a spawning pair may suddenly have to alter their behaviour to accommodate drought, predators, or other unexpected factors.

For cyprinids, spawning is usually seasonal. Like many freshwater fish, cyprinids want to get their fry hatched at the peak season for food and living space. This peak season is normally tied to rains or food availability, generally associated with high water levels from seasonal floods. Humans, however, do not appreciate floods, and everywhere in the world are building dams that reduce variation in river and lake levels. Fish species adapted to spawning in seasonal floods must therefore adapt themselves to a lack of seasonality if they are to survive. One recent study [1] on the tinfoil barb (Puntius schwanenfeldii) shows this is exactly the case, as the barbs have had no choice in their native Malaysia but to switch to aseasonal reproduction. Their native rivers are dammed and floods are no longer a trigger for spawning.

This is not such a bad thing; it allows them to spawn at any time rather than once a year during the flood season. It is of practical importance to aquarists because the aquarium is not a flood-prone environment (we hope). Aquaria usually maintain the same water conditions continually, removing any cues for its inhabitants to spawn. For some species, this does matter. But others are not able to adapt to an unvarying environment because they are hardwired for specific cues to trigger spawning. The aquarist must therefore fiddle about with the tank to induce those cues if spawning is wanted. But for many fish, such as tinfoil barbs, spawning can be released from such compulsory observation of cues, and it becomes much easier for the aquarist to get fry.


The most obvious thing about cyprinids is that they swim back and forth in schools. Mostly they swim with members of their own species, although other fish of similar size are known to occasionally join up. One interesting study on tiger barbs (Puntius tetrazona) showed that they will school with images from both analogue video and computer video systems [3]. This sounds like a fun project for the home aquarist, since both types of videos are common enough in the home, although one might have a bit of trouble lugging a tank up to the monitor or vice versa. You might want to try it for fun. Tape your fish, put the tank up against the screen, and see if a single barb will school with the video ones. If you have digitized video via your home computer, you could then fool around with colour and size changes to the video fish. See how far you can modify the video fish and still get a live one to school with it!

Schooling is an anti-predator system, and reduces the chances that a given individual will be successfully attacked by a predator. Firstly, the more fish there are, the more eyes there are to keep watch and sound the alarm, which is why so many animals, not just fish, have developed the herd mentality.

When a predator attacks a school of similar fish, the school explodes outward in a blur of rapidly moving fish that makes it difficult to track one individual. But just as lions usually take out the old gnu or the sick gazelle, so it is that parasitized cyprinids are more likely to be eliminated from the gene pool. A study on the European minnow (Phoxinus phoxinus) showed that minnows infected by larvae of the parasite Ligula intestinalis had trouble maintaining position in a school [2]. The infested fish tended to stray out past the school, where they were easily picked off. Most fish that eat such infested minnows digest the parasitic worms as well, but some don’t, which enables the parasites to use the new host to spread further.


1] McAdam, D.S.O., N.R. Liley, and E.S.P. Tan (1999) Comparison of reproductive indicators and analysis of the reproductive seasonality of the tinfoil barb, Puntius schwanenfeldii, in the Perak River, Malaysia. ENVIRONMENTAL BIOLOGY OF FISHES 55:369-380

2] Barber, I., and F.A. Huntingford (1996) Parasite infection alters schooling behaviour: deviant positioning of helminth-infected minnows in conspecific groups. PROCEEDINGS OF THE ROYAL SOCIETY OF LONDON 263B:1095-1102

3] Clark, D.L., and K.R. Stephenson (1999) Response to video and computer-animated images by the tiger barb, Puntius tetrazona. ENVIRONMENTAL BIOLOGY OF FISHES 56:317-324 ?

The Life and Times Of Fathead Minnows


The fathead minnow, Pimephales promelas, is commonly sold as a baitfish and, in the aquarium trade, as a feeder fish. They are cyprinids that spend their time dashing frantically about along the bottom of the tank or trying to burrow through the glass in a corner of the tank. Typical brainless cyprinid behaviour. However, there is one distinctive difference from the usual cliche of cyprinids that aquarists expect. These minnows are not egg-scatterers as are most cyprinids. They are parental caregivers who guard the nest cichlid-style. I found their spawning behaviour quite fascinating. They are certainly cheap to buy, and easy enough to breed that you can pick up a few BAP points while observing some interesting behaviour.


Pimephales promelas is widely distributed across North America. It is tolerant of a wide variety of conditions in water chemistry. It begins spawning at about 18C water temperature, so it does not need a heated aquarium. Spawning is done frequently in stages, rather than an annual or occasional occurrence. This species is omnivorous, and thus easy to feed. It is short-lived, not usually beyond two years of age [1]. There are two varieties, the normal and the rosy-red (which is more of an orange-yellow). The latter has a lower growth rate than the normal [7].

This species is timid in the aquarium, and prefers to school. The fry that I have raised tend to travel in midwater, while adults stay closer to the bottom. Schooling is an anti-predator tactic used by many fish [6]. A predator attacking a school of fish has a difficult time picking out one individual from all the others and tracking it in the confusion. More fish together also means more eyes to keep watch.


The spawning of Pimephales promelas is fairly complex. The first sign is when the male develops a wen on his forehead. If you don’t know what a wen is, you’ve seen them on fancy goldfish, which are also cyprinids. These are what look like tumorous growths on the head, often with little tufts of white cotton during their development. Hood growths on goldfish such as orandas are merely an artificial selection for increased size of wens. Tubercles or hard white pimples develop on the forehead and gill covers, a sign that the male is ready to breed.

The male fathead minnow stakes out an overhanging ledge or cave and begins defending this territory against all comers. Once a female has been lured in and courted, the eggs are laid on the underside of the ledge in a monolayer. The male guards the eggs until they hatch. He may entice several females into spawning, in which case the final hatch will be a genetic mixture of half-siblings [2]. Fully-conditioned females can lay 200 to 700 eggs. The eggs hatch in 4 to 8 days, depending on water temperature [4].

As far as the practical details are concerned for the aquarist wanting to set up a tank to breed these fish, an overhanging slab of rock makes the best location for spawning. It is better if it is not more than about one centimetre over the substrate, just a big enough gap for the minnows to squeeze under. This gives room for the fish and allows them to rest on the substrate will standing guard. Since Pimephales promelas is a bottom-dweller, there is no point in making a high stack of caves as you might for cichlids, since the minnows will not venture up into the water column. This species can be spawned in caves made of PVC pipe sections [3], but while practical, is not very aesthetic.


I seldom paid much attention to the fathead minnows I used as feeders for my cichlids. However, one day I noticed a few small fry darting about in the minnow holding tank, so I decided to spawn them in a more formal setup. I set up a 45-litre tank with incandescent lights and an airstone but no heater. The airstone should provide turnover of the water column but at not too high a rate, as turbulence will interfere with feeding by the fry [8]. The tank was on the main floor of my house (in the kitchen, actually, right by the sink) which, like most post-WW2 houses of its age, overheats in the summer and gets chilly in the winter. The water temperature varied with room temperature and ranged from 20oC to about 28oC. The latter temperature was reached after the fry were a couple of months old, by which time the summer heat had begun.

Several rocks were placed in the tank in such a fashion that they created overhanging ledges. The bottom third of the tank was filled with filamentous algae and Java moss. The airstone was set to provide a strong flow of water. There was no filtration but a 25% weekly water change was done using fresh tap water. The female was placed into the aquarium a few days ahead of the male. Because they had previously spawned, I knew they were a pair, but in any event it was easy to separate them. The female was plumper than the male. The male, when added to the tank with the female, developed a clear wen on his head.

The first spawning, as with subsequent spawns, took place on the underside of an overhanging ledge. The female laid the eggs but then immediately turned around and ate them. A week later, another batch of eggs was laid. The male guarded these eggs, swimming in a figure-eight pattern continuously under them. The female showed no interest in the eggs, so I removed her. The day after the eggs were laid, the eyes were visible. On the fourth day the eggs were gone. I was uncertain as to whether the male had eaten them or if the fry were simply well hidden. As it turned out, the fry were seen the next day, having apparently dispersed after hatching into the thick profusion of algae. The male was removed at this time.

The fry were transparent and 5 to 6 mm in length. One fry was a goer and grew quickly to about 1 cm total length, while the rest stayed in the same growth cohort. For most of the first three months the fry were exposed to continuous light, the canopy seldom being turned off. The algae and its associated infusoria provided food for the fry. When they were a little older, crushed and finely-powdered flake food was supplied twice a day. After three months, the orange colour had developed. the fry were slow growing and were averaging about 1 cm in total length at this time. They were somewhat clumsy at catching food, although this could be a matter of taste discrimination. Minnows generally eat food particles about two-thirds of their mouth size and go after moving targets [5]. In still water, they pick out the active food particles, such as live food or sinking flakes.


1] Duffy, W.G. (1998) Population dynamics, production, and prey consumption of fathead minnows (Pimephales promelas) in prairie wetlands: a bioenergetics approach. CANADIAN JOUR. FISHERIES AQUATIC SCIENCES 54:15-27

2] Page, L.M. and P.A. Ceas (1989) Egg attachment in Pimephales (Pisces: Cyprinidae). COPEIA, pages 1074-1077

3] Norman-Boudreau, K., and G.R. Daggett (1989) Improved design for fathead minnow breeding chambers. PROGRESSIVE FISH-CULTURIST 51:111-112

4] Sargent, R.C. (1989) Allopaternal care in the fathead minnow, Pimephales promelas: stepfathers discriminate against their adopted eggs. BEHAV. ECOL. SOCIOBIOL. 25:379-385

5] Scott, A. (1987) Prey selection by juvenile cyprinids from running water. FRESHWATER BIOLOGY 17:129-142

6] Magurran, A.E. and T.J. Pitcher (1987) Provenance, shoal size, and the sociobiology of predator-evasion behaviour in minnow shoals. PROC. ROYAL SOCIETY LONDON 229B:439-465

7] Ludwig, G.M. (1995) Growth and survival of two colour varieties of fathead minnows in deep and shallow ponds. PROGRESSIVE FISH-CULTURIST 57:213-218

8] Landry, F., T.J. Miller, and W.C. Leggett (1995) The effects of small-scale turbulence on the ingestion rate of fathead minnow (Pimephales promelas) larvae. CANADIAN JOUR. FISHERIES AQUATIC SCIENCES 52:1714-1719 ?