koi fish, animals, fish

Page Purpose

You have chosen a career to follow and prepare for, now it’s time to learn more about the species (and breeds) you will work with. 

Read about the basic facts and join one of the Fish Groups to learn even more about them, as well as how to work with them, and how to gain experience if you want to work with them. If you are not a member, join us in the OZT Community!

Definition of a Fish

A fish is a cold-blooded vertebrate animal with gills used for breathing in water and lacks limbs with digits.

Although fish have been primarily used as food, certain species have gradually been adopted by families as pets. Fishkeepers use aquariums to keep fish, invertebrates, amphibians, aquatic reptiles such as turtles, and aquatic plants.

Basic Facts

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Average Length

8 mm to 36 m (0,3 in 110 feet)

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Average Weight

1 g to 21 tonnes (0.03 oz and 21 tonnes)


Average Lifespan

8 weeks to 175 years


Average Offspring

up to 300,000 eggs


Swimming Speed

112 km/h (70 mph)

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Active Time

Mostly diurnal

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Main Diet

Carnivorous, herbivorous, omnivorous - depends on species

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Distribution & Habitat

Fresh and saltwater - oceans, rivers, lakes, dams

Global Population

Estimated Global Population

3.5 trillion +

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Conservation Status

Least Concerned to Near Extinction

OZT Community Logo

Join one of the 3 Groups

Status: Active

Learn even more about Fish by joining one of the three GROUPS, depending on the kind of fish you want to work with.

  • ^ Freshwater Group (All species)
  • ^ Saltwater Group (Excluding sharks, rays)
  • ^ Shark & Ray Group

Members of the Groups can access all the different Short Courses, win awards and meet other fish lovers from around the world. Gain experience points with each short course and compete for the top spot on the leader board!

Topics covered in the FISH GROUPS:

  • ^ General fish knowledge (Anatomy, Habitat, Behaviour, Diet, Ecological Benefits & Conservation)
  • ^ Fish Care & Health
  • ​^ Fish Creative (Including education, art, design, publishing, media, news and photography)
  • ^ Species (courses on over 100 different species)


This is also the place where you will find links to all of the Animal Organizations that work with fish. Join their special Groups and learn how you can gain valuable experience by volunteering or interning with them.

Career profiles and resources

Contributions by expert members are always appreciated to allow the students to make informed decisions. Please add your contribution through the attached form:

Contribution Form

List of Species Mentors/Educators who have contributed to the info:

One Zoo Tree

A few excellent pictures on the species: