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  • Source: Copyright Gerald Allen

    Species: Melanotaenia lacustris

  • Source: Copyright

  • Source: Copyright

    Species: Glowlight Tetra

  • Source: Copyright

    Species: Panda Corydoras

Finding The Right Level

Finally all the hard work and hard choices are done, your tank's set up in the corner of your room and all you have to do now (at least until the next tank-cleaning day) is collapse into your armchair and enjoy it. But as you survey your little slice of nature, it might not all be as you expected. Rather than evenly distributing themselves to make a good spectacle, the fish, with a selfish disregard for your viewing pleasure, are all crammed together in one place. Depending on your choices, you may have ended up with a tank where they're all invisible because they're all skimming the surface (just behind that nice plastic bit of the tank frame), or maybe yours are all crammed into a cranny down the bottom. They all get on together, they're all happy and healthy, the tank's fully stocked - but quite often there's nothing to look at.

Fish are single-minded little creatures (well, double minded if you count spawning time) and most of their waking hours are occupied by looking for food. Just because you know they get fed regularly twice a day doesn't mean they know it, and they'll spend all their time hunting for more just in case the next feed never happens. A good guide (although not completely failsafe) to where your fish are most likely to spend their time in this eternal quest is found in the shape of their mouths and bodies. If you look at a guppy, you'll notice that their mouths are slightly tilted upwards, and their backs are relatively flat compared to their stomachs. Guppy life is geared to skimming just under the surface, grabbing bits of food floating (or swimming) there. A suckermouth catfish, on the other hand, has a very flat belly compared to its rounded back, and the mouth is clearly set on the underside. These are never going to be found frolicking at the surface - they simply can't do it. (A noticeable exception is the sturgeon, which although it has its mouth on the underside gives it owners a great deal of pleasure with its acrobatics swimming upside down and nipping food of the surface. However, since it does so very briefly before dying, being a fish that grows up to around a meter long - or more - and requiring cold, clean water, we will bypass it for the sake of this article, and indeed responsible fishkeeping in general).

For an illustration of the different instinctive swimming zones of fish, compare the behaviour of newly born guppies and platies, both of which are just snack-sized and spend the first few weeks of their lives, quite sensibly, in a state of nervous terror. If you watch a female guppy giving birth, you will see that as soon as the babies pop out, they dart straight for the surface. There's no stop to look around - it's out and up. Platies, on the other hand, although related to guppies, are more bottom-oriented. As soon as a baby platy hits the water it's heading downwards. The sense of which way safety and food is most likely to be found is built into them over thousands of generations, and even if the top of the tank is crammed with hungry predators, guppies will still head upwards. This instinctive behaviour continues throughout life.

In between the top-swimmers and the bottom-swimmers there are a whole host of 'fish-shaped fish' (the shape a child draws if asked what a fish looks like). These are neither geared to the surface nor the bottom. You might think that they would stick to the middle - in fact they have the choice, and will usually choose the part of the tank you would rather they hadn't.

Filling your fish tank with fish that will ensure that at least some fish are visible at all times and in most directions is an art form, which needs adjusting periodically owing to the contrariness of the fish. The top swimmers and bottom swimmers, as discussed, are fairly easy to find, and will usually stay in that neighbourhood. Your tank should include at least a few of each, even though they aren't absolutely guaranteed to stay in their 'zones' all the time. (A bunch of active Corydoras catfish are geared up to be bottom dwellers, but sometimes they're just too full of themselves to stay there, especially just after a water change, and then they go zooming around the tank chasing each other. Panda Corydoras are particularly good for this, but make sure they have plenty of swimming space and lots of plants and rocks at the bottom. Sad stressed Pandas don't want to play). In spite of all your efforts the middle of the tank, which you probably envisaged as the main display area, can sometimes look as though the tank is completely empty.

Unless you are keeping fish with a very nervous disposition, a few active swimmers will work wonders. Just as at a dance few people want to be the first on the dance floor, few fish want to be the ones to start swimming in an empty area of open water. After all, there might be some dreadful reason no one else is swimming there. A bunch of little fish who like playing tag are ideal. Not only will they pass regularly through the open centre, as it's next to impossible to chase each other in the plants, but their undamaged presence may reassure more nervy tank members that it's safe to use the open areas. There are several attractive fish which are good for the job. Avoid schools of nippy fish like tiger barbs - there's not much friendly about their chasing. I have a group of three Lake Kutubu rainbowfish (Melanotaenia lacustris) in my four foot tank who keep everything active. In my opinion these are one of the prettiest of the rainbows. Reaching about four inches, they are a dark shiny blue with yellowish tummies. These are quiet, peaceful fish, but in a safe environment they like nothing better than a game of tag up and down the tank. Odessa barbs are another brightly coloured fish of a similar disposition.

Another alternative that has worked well for me is a bunch of non-aggressive tetras. A mix of glowlights, neons, cardinals, platinum, and black neon tetras were the longlived left overs from several small shoals, so they all went to share a tank together in their old age. Being all of a similar size they formed an active little group that is usually found swimming about together in midwater. A retired female guppy, also on her own, even joined the scrum and now swims midwater with the rest of them, albeit lagging behind a bit.

Apart from persuading some fish to swim in the middle to give the others confidence, you can lure them in there by other ways. An open swimming area doesn't have to be completely empty. Try a single tall plant or piece of bogwood that they can chase each other round, or a floating plant anchored in the centre with long pendulous roots.
Water movement also influences your fish a lot. Active fish tend to like moving water. If you position one of your powerheads (or filters) to give a strong current along the length of one side of the tank, that will often encourage the fish to come and swim there. By directing it up one side against the glass you are leaving a quieter area at the back, which means that the more sedate fish who don't like being buffeted can still swim and be seen sometimes. A group of harlequin rasboras are peaceful, pretty and small, and particularly appreciative of a current to play in.

And if everything else fails, just before you settle into your armchair to watch your fish, wash a bag of live daphnia and tip that in. There'll be so many fish out and about you won't know what to look at!

This article has been kindly provided by Kathy Jinkings and cannot be reproduced without her permission.

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