by Joshua Wiegert

It has happened to virtually every aquarist at one point or another.  We come across a group of fish in the local store labeled with a hitherto unheard of name, or, more typically, labeled with something wildly incorrect.  Sometimes, we’re lucky and we can identify these fish – eventually.  Other times, we just contentedly keep our unknowns.

There is a certain danger in purchasing an unknown species of fish in that we may never quite figure out how to keep it alive.  Certainly, many unknown fishes have perished due to improper care.  This point has been discussed in many other articles, and it is one I won’t discuss in any real depth.  Many advanced aquarists are able to purchase an unknown fish and, after making certain assumptions about it based on experiences with similar fishes, succeed in keeping it alive.  For instance, one may find an unknown Loricaridae, and with a little knowledge about the various “plecos,” succeed in keeping it alive.  The inherent danger here is that this pleco, like a handful of others, could be an exception – perhaps overly territorial, or perhaps a carnivorous species, like the Zebra Pleco.

However, no matter how lucky an aquarist is, eventually our rare and cherished fish will die, if only of old age.  Thus, the ultimate challenge for an unknown species is not just to keep it alive, but to succeed in breeding it and rearing the offspring.

Fishes can pose an interesting set of challenges in that.  Let’s imagine that we’ve found a tank of “Unknowns,” Ichthyus ignotus, and we’ve purchased some.  We’ve managed to keep them alive.  Let’s look at some of the hurdles we might face in successfully breeding and rearing these fishes.  To illustrate points, I’ll use some common fishes.  Imagine that you lived in an alternate universe where Spock has a beard and these fishes had never been collected before – until now.

One of the most obvious hurdles we might encounter is that we won’t obtain males and females.  This can be because there were not males and females present: for instance, if our unknown is a “contaminant” in a shipment of common fishes, there may only be a few there, or worse, one! (See the online sidebar for some information on calculating the odds of pairs).  Of course, even in a very large shipment of an unknown species, it is possible that only one sex will be obtained.  The sex of Apistogramma dwarf cichlids is often determined by pH.  As a result, an entire pool may be mostly male or female.  Of course, captive bred fish are particularly prone to this; additionally, some breeders will treat a spawn with hormones to produce only males or females.  The genetically engineered danios available are selectively engineered to be all males to prevent “patent infringement,” although enough have slipped through that some people are (illegally) breeding them.  pH is not the only factor to determine sex.  In many species of animals (including but not just fish), sex can be determined by temperature, or even genetics, with some pairs producing only males or females.

The lack of males or females may be the fault of the net jockey, as well – or yours!  Take a good look at the Cherry Barb.  Conditioned males of this species are a bright, vibrant red, while females and unconditioned males are kind of a plain reddish brown.  Many novice aquarists assume that the brighter ones are simply healthier and request only these.  The same hold true of countless cyprinid species, many cichlids, etc.  As such, we should select our fishes randomly (or buy them all!).  Note that selecting them randomly is not the same thing as netting them randomly.  If we were to simply swoop a net through a school of guppies, for instance, we would catch a sample that’s mostly females.  They’re fat and can’t get away as well.  Even in a less extreme case, we may wind up with one sex or another because they appear “healthier.”

Additionally, we may not be able to recognize males and females as being of the same species.  Imagine spotting a few swordtails (the unknown) in with common platies.  I don’t know about you, but I’d be hard pressed to find the female swordtails, especially if I’d never seen a swordtail before.  They look a lot like platies.  Besides, who would assume the swordtail was a sexual feature: I’d probably never look beyond picking the sword-bearers out.

Many species of Peacock cichlid have females that take an expert eye to tell them apart.  The males are bright, colourful, and each with a unique patern.  The females are kind of silvery grey, with the same body form.  All of them.  Many dealers sell Peacocks as “Assorted Peacock Cichilds.”  Try picking out a pair sometime – of the same species.  At the other end of the spectrum, there are fishes like the Chipokae cichlid (Melanochromis chipokae).  Males and females don’t even look like the same species.  Females are yellow; males are blue.  You try explaining this to a customer sometime.

The problem may be timing.  Especially when dealing with marine fishes, we encounter fishes that are synchronous hermaphrodites.  Synchronous hermaphrodites differ from simultaneous hermaphrodites in that they start off life as one sex and then become another.  The best-known examples of these are clownfishes, which begin life as male and then become female.  In most species, this is a one-way change.  So, we can buy jumbo clownfish until we’re orange in the face: they ain’t breeding.  And if we buy just small ones, we might have a wait until they do breed.

Numerous fishes require more than just a male and a female to spawn.  Many cyprinids, tetras and even catfishes spawn en masse.  While a male and female may spawn, the best results are obtained in groups.  There are also those species that spawn best in a harem, with one male to several females.  If kept as a single pair, the male may become a bit too amorous and do harm to the female – even in relatively peaceful species, such as dwarf cichlids.

Worse, there a handful of species that spawn with something else entirely – they require the spawning activities of another species to serve as a trigger and may act as parasites upon it.  The best known example of this is the cuckoo catfish (Synodontis multipunctatus), which lays its eggs on the spawn of mouthbrooding cichlids.  The cichlids take up the catfish and rear them – in gratitude, the baby catfish eat the cichlid’s brood.  There are dozens of Cyprinid species that similarly spawn over the nests of other fishes.

Even in pair spawners, there is always the issue of compatibility.  Many cichlids will form a monogamous pair, and some species are particularly choosy.  Simply plunking a male and female together is not sufficient – they have to be a compatible male and female.  Interestingly, in the absence of a compatible member of the opposite sex, some cichlids will “spawn” with a member of the same sex.  I had a pair of angels that would regularly lay very large, infertile spawns.  I couldn’t figure out why they wouldn’t hatch, until a fellow angelfish breeder took a look at some pictures and pointed out that both had ovipositors.  These two females “paired up” from a group of 25 or so juveniles, a group which surely must have included a male.  They just preferred each other.

So, let’s assume we’ve got our males and females and whatever else might be needed to breed.  Our next problem is going to arise from fertility.  It’s fully possible that our fishes are not being kept in adequate conditions to spawn, even if they’re otherwise perfectly happy and healthy.  I’ve successfully kept Apistogramma, discus or cardinal tetras in the liquid rock that flows from my tap.  In some cases, they’ve even laid eggs.  Unfortunately, these are species that require soft water to rear their offspring.

There are many species of temperate fishes that will not spawn without a “cool down” period.  In order to produce gametes (eggs or sperm), they must be maintained at a cool temperature for a few weeks or months.  Notable among these is the weather loach, a very common aquarium fish.  Many species of darters also require a cool period to become fertile.  These will spawn if kept in a cool garage during winter, but if kept inside, not a chance.

Fishes may also require a particular trigger to spawn.  There’s an anectode that perpetually floats around about an aquarist who had a pair of somethingerather that wouldn’t spawn.  Late one night, he accidentally spilled a cup of coffee in the tank.  The next morning, they’d spawned.  Guess they couldn’t sleep and had to do something.  For other species, it might be a little wine, fresh oysters and Barry White.

The number of interesting triggers could take up an entire feature.  Corydoras and related catfishes spawn after heavy rainstorms, and this is simulated in the aquarium by doing a large water change with slightly cooler (2-3°) water just before (or during) a heavy storm.  Many marine species spawn based upon phases of the moon, with some species using the moon’s phase as a preparatory signal and the intensity of sunlight the next day as a precise signal, allowing them to time spawning down to the minute.  (These are sessile invertebrates.  They simply release all gametes into the water column, and missing everyone else by even a few minutes could result in no offspring).  For some species, the amount of daylight must be lengthened or shortened, simulating the change in seasons.  I admit, I find thunderstorms, moonlight and spring to be romantic, too.

You never know just what change might be required.  In many snowy regions, the pH of the water can drop dramatically in spring – snow is slightly acidic naturally, and the meltwater rushes into bodies of water, reducing their pH.  pH can also change based upon rainfall – even without acid rain — meaning the pH of a pool may change with the dry and wet seasons.  While I’m not aware of any species that uses a pH change as a trigger, it is not far fetched.  Who knows what it might take?  A sudden decrease in salinity, a change in temperature or pressure, and only when Venus is in perihelion during a solar eclipse?

Additionally, we may have to provide our fishes with a proper place to spawn, some of which can seem as unusual to us as the backseat of a 1957 Chevy must seem to them.  Hoplo cat’s, for instance, are bubblenesters who will construct their nests under a surface.  In the aquarium, they spawn best under a plastic lid – and yellow lids seem to be their version of a mirrored ceiling.  Tanganyika dwarf cichlids spawn in large snail shells (which goes against the classic advice of no shells in the aquarium).  Angelfish will spawn on flat, smooth surfaces.  Some types of neotropical cichlids spawn on mobile platforms – large leaves and the like.  Some sunfish build large nests – and without a proper substrate to build their nests in, spawning might be impossible.  Then, there are the sticklebacks which weave intricate nests out of plants.   Or, the bitterling that spawns in the mantle of a clam.  Splash tetras spawn on overhanging leaves – actually leaping from the water to deposit their eggs on these leaves.  Without just the right spot, these fishes may not spawn.

Ok, so we’ve got the trigger and the place right, and they’ve laid eggs or given live birth or split in two or spontaneously generated somehow.  Now, we come to a major hurtle – raising the spawn.  Fry and eggs may have weird requirements of their own.  Many tetra eggs and fry – neons infamously – are photosensitive.  Just remember, bright light hurt Mogwai.  Some annual killifish eggs require a dry period.  The eggs have to be stored in a container, moist – but not wet – for several weeks before they’ll hatch (although, truth be told, the dry period isn’t a strict requirement).

It may also turn out that, while your adult fish are able to handle your water conditions and even spawn in it, their offspring are not.  As stated before, I’ve had softwater fishes spawn in hardwater – and their eggs simply won’t hatch.  You may have a temperature too low, a pH too high, or a trace too much nitrate.  Any number of environmental factors could kill eggs, fry or juvenile fish.

Many species of marine fish spawn constantly, but are impossible to rear for the average aquarist because they require such small food.  Even the traditional “greenwater” is too big for many marine fry.  This isn’t limited to marine fish, either.  I once saw a baby brine shrimp eat a Celestial Pearl Danio fry – honest, I swear.  Discus and Uaru feed primarily on skin secretions from their parents, and the hormones contained in this secretion greatly benefit the fry (this appears to be a lot more common among cichlids than we thought, too).  This is a first food we really can’t simulate.

There are many species of fish in which the fry experience die offs quite frequently for unknown reasons that may be environmental, or nutritional.  When the T-bar convict (Archocentrus sajica) first began to appear back in the early 90s, I was fortunate enough to obtain a dozen juveniles.  They spawned for me easily.  The fry grew for a few days, and all vanished.  Repeatedly.  Nothing I tried could fix it, and this was reportedly a common problem with this species.

Problems may arise as the fry mature.  Many males will attempt to drive a spawn away in order to spawn again.  In the confines of an aquarium, this can result in the loss of the entire spawn!  As they mature, the spawn may turn upon each other.  In some cases, this simply means cannibalism: those individuals that are a little bit bigger than everyone else, well, they eat everyone else.  Strict aggression can be a problem.  Try spawning bettas sometime: once the males reach a certain size, they thrash each other.

Successfully spawning an unknown aquatic organism can offer the aquarist quite a few challenges, and it’s important to understand just what stumbling blocks may exist.  However, it’s also important to note that, fortunately enough, most of our aquatic organisms can be quite plastic and are willing to spawn under less than ideal circumstances, and often raise fry under them.  So while the stumbling blocks mentioned here are very possible and real, they should be seen as challenges, not as absolute blockades.

It’s also important to note that it is not only fishes and aquatic organisms that have bizarre requirements for successful breeding.  There is a terrestrial organism that takes the cake for bizarre mating rituals – males of the species are known to actually tear the reproductive structures of various angiosperms and present them to prospective mates in an attempt to demonstrate prowess and gain acceptance, most frequently in the dead of winter (mid-February).