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So now you're a foster parent
Nature being what it is, it isn't really the task of the fish keeper to persuade fish to spawn - they are quite keen on the idea all on their own. Provided you are giving them the environment they need, with lots of the right food, suitable water, and a suitable place - and of course a suitable partner! - most fish will oblige with verve and enthusiasm. Indeed, many aquarists must have started their interest in breeding fish in the same way I did - coming home to find a new batch of eggs had suddenly appeared with no particular effort on my part and no particular warning on the part of the fish.
However, this is where your effort is just beginning. There are many pitfalls between first spotting the translucent eggs and some reasonably sized fish that can be returned to the main tank, given to friends, or sold to the fish shop.
Caring for the eggs themselves can be problematic. Some fish, like goldfish, produce eggs of a similar delicacy to old boots. Goldfish eggs appear to be practically indestructible, and will succeed in hatching in just about any conditions. Other fish, however, produce eggs of a much more delicate disposition. My first, surprise, batch of eggs belonged to golden minnows. Since these were in the community tank I was convinced they were going to be eaten any minute, and quickly removed them to a rearing tank. Here I had the dubious pleasure of watching the little black eye dots quickly obscured by furry fungus, which grew at a pace that was almost visible. Fortunately the golden minnows weren't giving up, and there was another batch for me to try my parenting skills on a few weeks later. This time I added an antifungal agent to the water, and an airline to make oxygenated water flow over the eggs. This held back the furry plague for all of several hours. The poor little minnows kept trying, and eventually I gave up my efforts and just left them where they were. The male golden minnow was overjoyed to be left with his family, and cared for them diligently. Within a few days the panic was to remove the tiny little slivers of baby minnows that were rapidly being picked off by the other fish.
Since then I have come to the conclusion that parentally inclined fish will look after their eggs far better than I can. Although these days I can hatch such batches of eggs if absolutely necessary (with batteries of anti-this, anti-that, and airlines like a drunken spider's web), a more successful hatch is practically guaranteed if the parent is allowed to look after his own eggs until a few hours before hatching. The care that such fish put in, fanning their eggs and picking out any trace of decay for twenty-four hours a day cannot be duplicated by any normal fishkeeper. If you can persuade your fish to spawn in a spawning tank that makes life a lot easier, but mine are always rather bloody-minded about this, swimming vaguely about for months until I put them back in the main tank where they promptly spawn. However, after a few efforts you will learn the time it takes for the eggs to hatch (there's no hard and fast guide - I can't tell you, for example, that it always takes 76 hours for golden minnows, because it depends on the temperature and conditions in your tank and varies widely) and be prepared to rehome the spawn just before the little fish wiggle their way out.
Fish that do not practice parental care seem to have tougher eggs, which are far easier to hatch. As they are left to get on with it in nature, the same plan is likely to be successful in the aquarium, like the afore-mentioned goldfish. Your chances of success are likely to be greater if you ensure clean, oxygenated water that has been properly dechlorinated. Eggs are just as sensitive to pH and hardness as the fish, although keeping to the same parameters as the place they spawned will usually work. Unfortunately, having actually hatched the eggs doesn't mean all your troubles are over. Having had a pair of goldfish oblige with what appeared to be thousands of eggs one New Year's Eve, I gave up on the intended traditional evening's entertainment and spent the night painstakingly moving all the eggs to their own tank. I put a lot of effort into that tank. It had lots of fine plants for the little fish to nibble at, water carefully dechlorinated and adjusted to precisely the same temperature as the main tank, and an undergravel filter rather than an internal one so that the little fish wouldn't get sucked in. The goldfish duly hatched after a few days, and spent their first twenty-four hours clinging to the sides like tiny little slivers of glass before becoming free-swimming. The next day there was a cloud of goldfish fry exploring the centre of the tank. Within a few hours the first of them had discovered the gravel, and over the course of the next week all except one burrowed down into it, only to become trapped and die. There was a happy ending for the one survivor - with no competition he thrived and grew rapidly, and is currently resident in my mother's pond. Still, one fish out of a thousand is not a great success rate. Since then, the order of the day has been sponge air powered filters (the sponge-on-a-stick sort) which don't suck in the little fry and they can't get lost in. They also have the added advantage of growing tiny jungles of thriving micro organisms on the surface, that the fry will enjoy picking at. As soon as they are too big to get lost you can move to an undergravel system.
Once you are able to keep all the fry alive, there is a deep subconscious urge to do so. Every little fish lost feels like a failure. It is only when you have a three foot tank with four hundred little goldfish in it that you suddenly realise that it will be 'standing room only' before they are ready to move on to new homes. It is better to take ten or twenty eggs for hatching, as you have a much better chance of actually ending up with fish at the end of it. If the fry are overstocked, the first problem to appear is keeping the water clean - in order to grow they need copious amounts of fine powder or liquid food, which can turn the water rank very quickly. Since a major-league filter will also eat the fish, it is necessary to go with smaller sponge filters and a lot of elbow-grease on water changes - and water changes can be quite interesting in a tank full of fish a couple of millimetres long! By keeping the stocking at a reasonable level (which means the tank looks practically empty at first - remember that if all goes well the fish are going to grow a lot) then the filters will be able to cope and a lot of angst saved. Water pollution does not have to be at a level to kill the fish to do harm. Take a look in any fish shop that takes fry from aquarists, and sooner or later you'll see batch where several of the fish have kinks in the spine or strange malformations. This is the effect of mild pollution at the crucial stage when the bones and bodies are forming.
Of course, in order to form good bones and bodies they don't just need clean water. Food and lots of it will be required. There are now excellent proprietary fry foods on the market, both as a liquid and a powder. I have found that feeding by the normal 'sprinkling on the surface' method is a good way to end up with a filthy tank and a lot of hungry fish. More food actually reaches the waiting mouths if you mix it with a bit of tank water then use a turkey baster to squirt the mixture straight into the middle of the group of fry. The more food your fish eat, the less waste is just overloading the filter. Live food is always appreciated, but most of it is too big for tiny fish. Brine shrimp nauplii are easy to hatch, and they have the great advantage that you can see if the fish are eating them. After you've fed some brine shrimp nauplii take a look at your fry. If they all have round pink bellies, then they are eating them. If they don't, then stop feeding the brine shrimp until they've grown a bit more, as they are just dying uneaten in the tank and making a mess. Really tiny fish can sometimes be got through the first few days with green water. If you know a happy event is looming, keep a container of clean water in bright sunshine for a few days. Pond water has lots of tasty things in too, but does carry the risk of introducing parasites or disease.
Once you have avoided all the pitfalls, rearing little fish is one of the best aspects of the hobby. Watching your resident fish court, waking up to find the new eggs, seeing the tiny little dots appear of the little fish looking out through the egg membranes, all the way through to a tank of new fish, all fit and healthy... This is an experience that never palls, and all fishkeepers should try it at least once! Hopefully by the sad tales of some of my early mistakes you will be able to achieve it with a minimum of heartache.
This article has been kindly provided by Kathy Jinkings and cannot be reproduced without her permission
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