Practical Fishkeeping Diploma - Week 1, Day 4

Here's the fourth of a five-part series of lessons to guide new aquarists through the basics of fishkeeping.

Week 1, Day 4: Temperature

Fish have evolved to live within a range of temperatures. In species like Goldfish, this range can be wide, allowing them to survive in water from just 4°C to high tropical temperatures.

When we define a tropical fish, we typically mean any fish that has a natural range within the two tropics: The Tropic of Capricorn and the Tropic of Cancer. Fish found within the tropics usually have a stable, relatively high temperature requirement of somewhere around 25°C.

On the fringes and outside of the tropics, live temperate and subtropical fish. Some of these, such as the Zebra danio, Danio rerio, thrive in temperatures lower than those usually offered to most tropical fish.

Temperature has a huge effect on a fish’s metabolic rate. At higher temperatures, a fish requires increased food, and subsequently creates more waste. Some fish have their breeding cycles regulated by temperatures.

As well as affecting fish directly, temperature has an effect on water quality and dissolved gases. At high temperatures, oxygen level is reduced. Another problem of high temperatures is that they lead to the release of free ammonia.

Finding the correct temperature for the fish you keep is essential. Remember that while fish from the wild may be recorded as being found at extremes of temperature, they will usually not live at these extremes for long periods. For most species, a temperature somewhere in the middle of their tolerances is about the right temperature for long term care.

Be careful when stocking an aquarium not to overlap fish at the extremes of their temperature tolerances. If one fish likes water of 18°C, but has an extreme tolerance of 25°C, while another fish likes water of 30°C and has an extreme tolerance of 25°C, they will not both be happy being kept ongoing at 25°C.

Aquariums are usually heated in one of two ways. For a domestic, standalone aquarium, tropical temperatures are maintained with the addition of a thermostatically controlled aquarium heater – often called a heaterstat.

Alternatively, some aquarists will opt for a controlled temperature room. This will be a well-insulated room or fish house, in which the air temperature is regulated using a large room heater. A fish house heated this way may contain dozens of aquaria, but because of the way that air confirms to a temperature gradient – hot air rises, while cold air sinks – those tanks higher up will be warmer than those at the bottom of the house.

Click here for next lesson: Gas and movement

How to gain your diploma: Once all the course modules and revision pages have all been posted online, we will open a link to a website that allows you to take your free online exam. If you pass the exam, you will digitally receive your very own Fishkeeping Diploma, to show that you have successfully completed the course, and which is yours to display on the wall near your aquarium, hang in your fish house — or keep somewhere safe where you can take it out and just look at it from time to time.

Note: The Fishkeeping Diploma is not a formal or accredited qualification and should not be confused with the type of diploma presented by colleges, universities and other educational establishments.

Further reading from our sponsors

Treating common aquarium problems 

Routine aquarium care

Troubleshooting for green cloudy water