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Freshwater Tropical Fish

Blue Gourami

One of life’s more rewarding hobbies is keeping freshwater tropical fish.

Can anyone keep freshwater tropical fish? With simple equipment and a little attention to detail keeping tropical fish is a fulfilling and rewarding hobby, whether you are eight or eighty years of age.


Keeping tropical fish in their native climate has long been a hobby in tropical areas, where the fish could live happily in an environment similar in nature to their natural environment.

It may surprise you to learn that the ancient Sumerians were, as long as 4,500 years ago, keeping fishes in manmade ponds and Encyclopedia Britannica suggests that it was the Sumerians who were the first true aquarists.

Fishes were kept in ancient Egypt and by the Assyrians but it is generally acknowledged that it was the Chinese who were the first actively to breed fish, specifically carp, which they bred for food as long ago as 1,000BCE.

Japan is generally acknowledged to be where the selective breeding of ornamental carp was introduced and perfected.

The Roman Empire bred fish both for food and for entertainment and are generally acknowledged to be the people who introduced the first marine aquarium by constructing ponds that were filled with seawater.

In England during the 18th century, goldfish were successfully kept in glass aquariums but it took a further century or so before the relationships between the fish, the plants and oxygen in the water became better understood.

Until the 19th century, an aquarium, as we understand it today, was a glass case in which aquatic plants were kept. In the mid-19th century, Philip Henry Gosse, an English naturalist, built the first “modern” aquarium in the county of Devon, England. As a naturalist, Gosse found the artificial world of an aquarium an ideal environment in which to study all forms of marine life.

Glass aquaria

It was only during the mid-19th century that glass aquaria became a realistic proposition. From then until the mid 20th century, glass aquaria were constructed using iron or steel frames into which sheets of glass were fixed using waterproof glazing putty. The bottom of the tank was often comprised of slate.

With the introduction of silicone sealants, it became possible to construct an aquarium using only glass and the adhesive sealant and gradually the iron or steel frame was rendered obsolete.

More recently, modern materials have enabled hugely sophisticated aquaria to be built, particularly in respect of marine aquaria where people can observe marine life through huge viewing panels and even walk through long tunnels surrounded by the transparent, curved walls of public aquaria.

Heating an aquarium

The ancients are not known to have maintained aquaria that maintained the water at other than the surrounding temperature although it is known that the Romans did invent under-floor central heating systems.

What is known is that during the 19th century, glass aquaria had slate or stone bottoms and could and were heated from underneath.

With the introduction of mains electricity and the development of electrical heaters and thermostats, it became possible accurately to regulate the temperature of an aquarium, as we understand it today.

My introduction to keeping tropical fish dates back to 1972 when I found the book “Exotic Aquarium Fishes” by William T. Innes which was first published in 1938. The hobby, as we understand it today, is now more than one-hundred years old.

Life in the Aquarium

Within your aquarium, you are creating a world in which your fishes will live. That said, it is not merely your fishes that will live in your aquarium but all of the plants together with the multitude of micro-organisms and chemicals that will interact to make sustained, aquatic life possible.

Your plants are living just as much as your fishes are living and the two enjoy a symbiosis in which both can thrive.

The micro-organisms and chemicals in your aquarium help to nourish both the plants and the fishes and having an imbalance can cause real problems to the health of fishes, plants or both.

Your filter system is designed to remove any excess of particulates or chemicals in your aquarium but any filter system can only do so much if the aquarist doesn’t have the skills or knowledge properly to maintain a healthy aquarium.

The four main families of freshwater tropical fish

Whilst there are many hundreds of different species of freshwater tropical fish, tropical fish tend to fall into one of four main families:

  1. Livebearers
  2. Egg-layers and egg-scatterers
  3. Bubble-nesters
  4. Catfish

Each of these four main groups has many species of different fishes included within them but each group is distinctive in particular aspects and the purpose of the remainder of this article is to highlight the main characteristics of the individual groups.

1. Livebearers

There has long been a general consensus that all fish lay eggs but in the world of freshwater tropical fishes, this is certainly not the case.

Livebearers, as the name suggests, is a subsection of the freshwater tropical fish world where the mother does not lay eggs, rather she gives birth to live fishes known as “fry”. The fry are immediately able to swim and, from birth must look after themselves. As an aquarist, you will quickly learn that the favourite food of fishes is fish. Given the chance, the mother will devour her own young, as will other fishes in the aquarium – unless you can separate the fry from the fishes.

The traditional understanding from fish such as trout or salmon is that the female fish lays her eggs, for example, in a trench of a riverbed and the male then fertilises her eggs by ejecting sperm (usually known as “milt”) upstream of the eggs such that the milt passes over the eggs and the eggs become fertilised.

With livebearers, the female produces eggs but never lays them. Instead, the eggs remain within her body and are fertilised by the male through a form of sexual contact.

The anal fin of the male livebearer has modified into a tube known as a “gonopodium”. The gonopodium is inserted into the egg cavity of the female and the milt is secreted directly into that cavity thus fertilising the eggs with a significantly higher chance of success.

A female livebearer carrying eggs is said to be “gravid” and this term covers any fish carrying eggs and livebearing fish carrying as yet unborn young.

An aquarium is an ideal place for young children to understand the process of life and reproduction, especially if that aquarium contains livebearing fishes because they will see for themselves the attention that the male fish gives to a gravid female in order to fertilise her eggs.

In addition, because the female gives birth to live young (fry) a child will gain an understanding of the full process of reproduction.

2. Egg-laying and egg-scattering fishes

One of the best known freshwater tropical fish is the Angelfish.

Angelfish form long-term bonds and, in the wild, take great care of their young. Most Angelfish are bred in captivity so have somewhat lost their good parenting skills.

Typically, when ready to spawn the Angelfish will choose a suitable place to spawn such as a leaf, a flat rock or even the glass of the aquarium. After meticulously cleaning the chosen surface the female will lay her eggs upon it in a line and the male will then pass over that line of eggs and fertilise them. This process will be repeated until the female has laid up to 1,200 eggs. The parents take turns to look after the fertilised eggs, keeping the water moving over the eggs.

Once the fry hatch they feed off their yolk sac for around one week after which time the aquarist should feed them small, live food.

Egg-scattering fish, such as the Fiveband Barb will merely scatter the eggs on the aquarium substrate and will proceed (along with the other fishes in the aquarium) to devour the eggs so your task, as the aquarist, is to spot this and rescue the eggs if you want them to have any chance of hatching.

3. Bubble-nesters

Bubble-nesters come from Asia and the far east and are more properly named Gouramis. They lay their eggs in a nest made from bubbles which they build on the surface of the water.

This family of fishes includes the so-called Siamese Fighting Fish, the male of which should never be placed in an aquarium containing another male.

In general, Gouramis are very peaceable fishes, extremely beautiful to observe and, in the Malay archipelago, giant gouramis, are big enough to eat.

4. Catfish

The best-known sub-species of catfish is a family group named Corydoras (but there are other sub-species) and there are over 160 distinct breeds within this group.

Typically, catfish live at the bottom of the tank and feed off vegetation, and other organisms found there. It is not untypical to observe catfish dart up to the surface periodically to take a gulp of air, as the bottom of the aquarium has the lowest concentration of oxygen and the highest concentration of carbon dioxide. Keep an eye on this characteristic because if there is a problem with the water in your tank then your catfish will alert you to it first.

It is preferable to include sinking pellets of food if you plan to keep catfish to ensure that there is available food at the bottom of the tank. Catfish cannot compete with other fish if all the food is floating on the surface.

Catfish are very peaceful fish in general and get along with the rest of the fish in your aquarium.

Catfish are egg-layers. and tend to lay their eggs in a nest of bubbles on a firm surface (such as a slate) at the bottom of the tank.

It’s worth noting that catfish prefer the substrate of the tank to be sandy rather than pebbles, as they use the barbels around their mouths to feel for food so pebbles or sharp stones or glass can damage their barbels.

Tropical fish – Video

Mike Wheeler

I started keeping freshwater tropical fish in 1972 and it has been something of a passion ever since. In this website, my aim is to build up an everyman's guide to help the everyday aquarist get the best from this inspiring and entertaining hobby.

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