Freshwater Aquarium
Most fish selected by importers and dealers for the home aquarium is highly adaptable to various conditions, and they need to be. In nature, freshwater environments are subject to sudden violent fluctuations in temperature and water conditions due to rain and seasonal changes, and the fish are adapted to cope. Thus it is relatively easy to keep freshwater fish from various contrasting habitats together in the aquarium, under ‘average’ conditions, although, for perfect health or for breeding, more insight into their real requirements may be necessary.
The most difficult habitat to recreate is the fast-flowing stream where the water has high oxygen content. Fish from this habitat usually prefer lower temperatures. They either are powerful swimmers, enabling them to keep position against the current, or perhaps have sucker mouths to cling to stones. In contrast, fish from deeper, slower-moving rivers are very easy to keep, as their natural habitat, like that of lake-dwelling fish, is not too different from that in the aquarium. In all cases, the water may be hard or soft, acid or alkaline, depending on the rock and soil over which the water flows. But generally the stream-dwelling fish will be intolerant of the dirty-water conditions which are part of the natural habitat of river dwellers. Many of the hardiest and most successful aquarium fish live in drainage ditches and swamps in Southeast Asia or South America: they are naturally tolerant of filthy water with low oxygen levels, and consequently can easily survive a certain amount of aquarium mismanagement.
The nearer fish live to the sea, the more tolerant they become to salt water. Some, like the Archerfish, live entirely in brackish water. This is a difficult environment to reproduce. The normal aquarium plants do not live in brackish water, which quickly becomes turbid.
Probably the most extreme habitat of all is that occupied by seasonal’ fish, represented in the aquarium by some of the Egg-laying tooth carp family. They live in puddles and pools in very dry territory. Their pools fill with rain only during the wet season, and then rapidly dry up, going through various stages of foul water and mud.
In order to reproduce in the aquarium the wide range of habit-tats experienced in the wild it would be necessary to keep most species separately. We set up a ‘natural-looking’ aquarium, but this bears little real resemblance to the conditions under which the fish would naturally live. In the wild, clear water and bright light are the exceptions, not the rule. Aesthetic designs and plants are for our benefit - the fish would be just as happy swimming among flowerpots as among expensive and carefully arranged rock terraces in the aquarium. The breeding tanks of the expert aquarist are normally plain water-filled boxes, with no attempt to recreate a natural’ appearance. Fish spawn happily on pieces of slate, nylon wool, flowerpots or beds of marbles.