Freshwater fish – Fish naturally found in rivers and lakes:
Coldwater: This means fish which can be kept at room temperature without a heater. Coldwater temperatures are between 15-24°C (60- 75°F). Coldwater fish are kept in fresh water, this means tap water which has been dechlorinated. This category includes fish such as common goldfish, fancy goldfish (Such as orandas, black moors and fantails), danios weather loaches and mountain cloud minnows. Please remember that goldfish will grow large and are not suitable for a small aquarium.
Tropical: This means fish kept at tropical temperatures and need a correctly sized heater to keep the water warm. Tropical temperatures are between 24-27°C(75-80°F) but this is species dependant, for example: discus fish prefer higher temperatures around 29°C (84°F). Tropical fish are freshwater fish and are usually kept in dechlorinated tap water. This category includes fish such as guppies, tetras, angelfish, gouramis and fighting fish, to name but a few! Tropical fish are usually perceived to be more difficult to beginners, there are lots of tropical fish species, but some are actually a good choice for a beginner. There are many species each with their own behaviours, adult size, special requirements and diet. It is key to research the species you want to ensure your aquarium is suitable. For example, neon tetras are a small peaceful fish which like to be in groups as they are schooling fish, a group of at least 6-10 in a 60cm aquarium roughly 60 litres is usually a minimum tank size. Whereas angelfish can be aggressive especially when breeding and grow large, a tank size of around 120 litres is a good starting point for angelfish.
Saltwater fish- Fish naturally found in the ocean:
Marine fish: marine fish are generally kept at tropical temperatures using an aquarium heater to keep the water around 24-27°C(75-80°F). Marine fish are kept in saltwater, this can be bought directly from an aquarium shop or can be made up using RODI (Reverse Osmosis De Ionised) water and an aquarium marine fish salt. Salt is mixed until the correct salinity of 1.026ppt is reached. This category includes fish such as Clownfish, Blue tangs and yellow tangs, some of these I am sure you will be familiar with! Marine fish can be kept in fish only systems with live rock or in reef systems with live coral. Keeping live coral is its own challenge, each species requires certain lighting, flow, and parameters. Saltwater aquariums usually work slightly differently to a normal freshwater cold or tropical aquarium, Live rock carries out most of the biological filtration and a protein skimmer is commonly used to remove built up organic waste, marine aquariums usually have a sump system under the aquarium. Be sure to carry out research before purchasing saltwater inhabitants as their aquarium setup is usually more complex than a freshwater system.
Pro Tip: Look up the species of fish you wish to keep before buying your aquarium, this will ensure you are not left disappointed if you are denied a fish at your local fish shop due to your aquarium setup not being correct. Remember each species of fish have their own requirements and behaviour, bear this is mind when choosing fish as some will be more active than others.