Fun fish facts

This fact sheet is designed to answer some of the many questions people ask about fish. It covers a broad range of topics and answers are, of necessity, very general.

For more specific information, please use the recommended reading material suggested at the end of this fact sheet. If you have more questions about fish, please contact one of the institutes listed and their scientists are sure to assist you.


How many fish species are there?

There are over 20 000 fish species worldwide and this makes fish the vertebrate group with the largest number of different species. In South Africa we have over 2 200 marine fish species in our waters.


What is an endemic fish?

A South African endemic fish is only found in South African waters and nowhere else in the world. About 13% of our marine fish species are endemic.


What is the world’s largest fish? smallest fish?

The world’s largest fish is the whale shark, which grows to 13m in length and may weigh several tons. The smallest fish is the tiny dwarf goby, found in the fresh to brackish waters of lakes in the Philippines. It seldom reaches more than 1cm at adulthood. The smallest fish in South Africa is another dwarf goby (Pandaka silvana) that reaches 16mm in length.


How is the age of a fish determined?

Age is worked out by examining the growth zones which are laid down in hard structures such as the bones, spines, scales and otoliths (small bones found in the inner ear) of the fish. These growth rings correspond to seasonal changes in the environment and can be compared to the annual rings found in tree trunks. Each pair of rings usually represents one year and scientists count the rings to determine the age of the fish.


How long do fish live?

Some fish only live for a few years, such as the tiny gobies, while others may live for longer than 50 years such as the coelacanth, found in the warm waters of the Comoros Islands. Some of the fish caught along the South African coast grow very slowly and can reach ages of up to 45 years (e.g. the black musselcracker). Other fish grow very fast and may reach 140 cm in just 5 years (e.g. the yellowfin tuna).


Why is it important for scientists to know the age of fish?

It is important for scientists, who are trying to ensure the wise use of marine fish, to know how fast a fish species grows. Slow growing fish reach sexual maturity very slowly and cannot reproduce as quickly as a faster growing fish. These fish are, therefore, not able to replace the fish that are caught and are very vulnerable to overfishing.


How fast can fish swim?

Although it is difficult to work out the speed of a fish, in some yellowfin tuna bursts of speed of up to 74km/hr have been recorded. In fact, when speeding, the tail of some tuna may beat at an incredible rate of 10 beats per second !! Sailfish can swim at speeds greater than 109km per hour over short distances.


How do fish keep their buoyancy in the water?

Fish are able to maintain neutral buoyancy in the water with the aid of a swimbladder (also known as a gas or air bladder). The swimbladder is found in the abdominal cavity beneath the spine and is an airtight sac lined with a mesh of tiny blood vessels that help to increase or decrease the amount of air in the swimbladder. The amount of gas is precisely regulated to give the fish just the right amount of buoyancy it needs to remain at any required level in the water column.


Which is the most venomous fish in South African waters?

The stonefish is particularly venomous. This solitary fish has poison glands below the dorsal spines, when pressure is placed on these spines they release a poison which is injected into the victim. These wounds are can be fatal and should be medically treated.

The best way to break down the poison it to place an extremely hot compress (bandage) on to the affected area. This helps to break down the powerful protein venom. In addition to their powerful venom, these fish are also very well camouflaged and hardly move. The stonefish, which is often confused with the less venomous scorpionfish, is seldom found as far south as Durban.


Do parrot fish have a beak?

The parrotfish are brightly coloured reef fish which all have a beak-like jaw formed by fused teeth. They use their powerful jaws to scrape algae and bite corals during feeding. The algae living within the corals are then removed in the fish's stomach and the crushed coral is passed out of the fish. Much of the coral sand found around coral reefs has passed through a parrot fish !! 


What is a tuna?

The tunas, mackerel and bonitos are all swift open-ocean predators. They are found worldwide and usually migrate over large areas. They are torpedo shaped and their dorsal and anal fins can usually fold down and fit into grooves along the body. This helps to streamline the body for fast movement through the water. They usually form large schools and prey on plankton, fish, crustaceans and squid. Their flesh is very tasty and they are very popular with fishermen.


How do pufferfish inflate themselves?

They pump water into special sacs to inflate themselves in water. Out of water, the body is inflated with air.


How can I help to conserve our marine fish?

  • Make sure that you and your family understand and obey the regulations concerning the number and size of fish that you can catch.
  • Place your litter (fishing line, bait packets, tin cans etc.) in refuse bins.
  • Recycle as much of your waste as possible.
  • Report dumping of waste and the illegal discharge of effluent into the sea to the relevant authorities.
  • Learn as much as you can about the threats to our marine fish and teach others.
  • Support organisations dedicated to the conservation of our environment.



van der Elst, R.P. 1990. Everyone's guide to sea fishes of Southern Africa. Struik Publishers, Cape Town.

Payne, A.I.L., Crawford, R.J.M. & van Dalsen, A.P. 1992. Secrets of the Sea. Vlaeberg Publishers, Cape Town.

van Der Elst, R.P. 1988. A Guide to the Common Sea Fishes of Southern Africa (2nd ed). Struik Publishers, Cape Town.

Bruton, M. 1995. Questions and Answers. Sea Fishes of Southern Africa. Struik Publishers, Cape Town.

Downloadable fact sheet