9 Questions

What is the approximate number of described fish species?

What is the deepest living fish in the ocean and where was it found?

What are the three mechanisms by which fish breathe air?

Which nitrogenous waste do fish release and through which organs?

What are the different types of fish ovaries?

What is the term used to describe fish with fins and gills, excluding aquatic mammals and reptiles?

What is the difference between a shoal and a school of fish?

What is the primary threat to edible fish such as cod and tuna?

What is the term used to describe the process of apoptosis of follicular cells after oocyte release?


Fish: An Overview

  • Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits.

  • The earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period.

  • Fish exhibit greater species diversity than any other group of vertebrates, with 34,300 described species.

  • Fish are an important resource for humans worldwide, especially as food.

  • Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies.

  • Fish are ectothermic ("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change.

  • Fish can acoustically communicate with each other, most often in the context of feeding, aggression or courtship.

  • Fish can be found in nearly all aquatic environments, from high mountain streams to the abyssal and even hadal depths of the deepest oceans.

  • Fish range in size from the huge 16-metre whale shark to the tiny 8-millimetre stout infantfish.

  • Fish species diversity is roughly divided equally between marine (oceanic) and freshwater ecosystems.

  • The deepest living fish in the ocean is the snailfish (Pseudoliparis belyaevi) which was filmed in the Izu-Ogasawara Trench off the coast of Japan at 8,336 meters in August 2022.

  • Fish from multiple groups can live out of the water for extended periods.The Anatomy and Physiology of Fish

  • Fish have a variety of mechanisms for breathing air, including absorbing oxygen through their skin, absorbing air through their digestive tracts, and using paired lungs similar to tetrapods.

  • Fish have a closed-loop circulatory system, with a heart that consists of four parts, including two chambers and an entrance and exit, and a bulbus arteriosus that connects to the aorta for oxygenation in the gills.

  • Fish ingest food through the mouth and break it down in the esophagus and stomach before processing it in finger-shaped pouches called pyloric caeca, with the liver and pancreas adding enzymes and the intestine completing digestion and nutrient absorption.

  • Fish release their nitrogenous wastes as ammonia, with some of the wastes diffusing through the gills and blood wastes filtered by the kidneys.

  • Fish scales originate from the mesoderm and may be similar in structure to teeth.

  • Fish possess highly developed sense organs, including color vision, chemoreceptors for taste and smell, ears for sound, and the lateral line system for touch and hearing.

  • Fish brains are divided into several regions, including the olfactory lobes, telencephalon, diencephalon, optic lobes, cerebellum, and brain stem, with some fish having relatively large brains and others having primitive eyespots.

  • Fish move primarily by alternately contracting paired sets of muscles on either side of the backbone, with fins functioning like an airplane's flaps to increase speed and adjust buoyancy.

  • Endothermy is rare in fish, with only a few bony and cartilaginous species exhibiting the ability to generate heat through swimming muscles to warm their bodies and maintain higher body temperatures.

  • Fish reproductive organs include paired testicles and ovaries, with gonads of similar size that can be partially or totally fused, and secondary organs that increase reproductive fitness.

  • Fish ovaries may be gymnovarian, secondary gymnovarian, or cystovarian, shedding ova directly into the coelomic cavity, oviduct, or ovary lumen with continuity to the oviduct.

  • Fish have been shown to exhibit behaviors linked to self-awareness, contingency testing, spatial memory, visual discrimination, tool use, and responses to pain and fear, raising concerns about animal welfare in fishing practices.Fascinating Facts About Fish

  • Postovulatory follicles are structures formed after oocyte release and are rapidly reabsorbed in a process involving the apoptosis of follicular cells.

  • Over 97% of all known fish are oviparous, that is, the eggs develop outside the mother's body, with fertilisation taking place outside the mother's body in most species.

  • Some fish, like the California sheephead, are hermaphrodites, having both testes and ovaries either at different phases in their life cycle or simultaneously.

  • Newly hatched young of oviparous fish are called larvae, which are usually poorly formed, carry a large yolk sac, and are very different in appearance from juvenile and adult specimens.

  • Ovoviviparous fish are those in which the eggs develop inside the mother's body after internal fertilization but receive little or no nourishment directly from the mother.

  • Some species of fish are viviparous, in which the mother retains the eggs and nourishes the embryos, with examples including the surf-perches, splitfins, and lemon shark.

  • Fish can produce either stridulatory sounds by moving components of the skeletal system, or can produce non-stridulatory sounds by manipulating specialized organs such as the swimbladder.

  • Oyster toadfish produce loud grunting sounds by contracting muscles located along the sides of their swim bladder, known as sonic muscles.

  • Fish suffer from diseases and parasites, but vaccines have become widely used in aquaculture and with ornamental fish.

  • The 2006 IUCN Red List names 1,173 fish species that are threatened with extinction, with freshwater fish particularly threatened.

  • Overfishing is a major threat to edible fish such as cod and tuna, causing population collapse.

  • Habitat degradation including water pollution, the building of dams, removal of water for use by humans, and the introduction of exotic species is a key stress on both freshwater and marine ecosystems.Fish: Importance to Humans, Culture and Terminology

  • Introduction of non-native fish species through ballast water and deliberate introductions have caused ecological problems.

  • Fish are a source of dietary protein for humans, with fish farming becoming increasingly important in many nations.

  • Fisheries provide income for millions of people worldwide. The annual yield from all fisheries is about 154 million tons.

  • Fish have been recognized for their beauty and are often kept as ornamental fish in ponds or displayed in aquariums.

  • Recreational fishing is fishing primarily for pleasure or competition, and is particularly popular in North America and Europe.

  • Fish have symbolic significance in many religions, such as ancient Mesopotamian fish offerings to the gods.

  • The fish theme is prominent in art, literature, and movies, such as Finding Nemo and Jaws.

  • "Fish" is used as a singular noun or plural for a single species, while "fishes" is used to describe different species or species groups.

  • "True fish" or "finfish" are terms used to describe fish with fins and gills, excluding aquatic mammals and reptiles.

  • A "shoal" is a loosely organized group of fish, while a "school" is a tightly organized group with synchronized swimming.

  • Fish are a source of happiness in Buddhism, symbolizing complete freedom of movement in water.

  • Fish are associated with primary industry and associated food, feed, pharmaceutical production, and service industries.


Test your knowledge on fish with this informative quiz! Learn about the anatomy and physiology of fish, their importance to humans and culture, and fascinating facts about their behavior and diversity. From their role in ecosystems to their use in art and religion, this quiz covers it all. Challenge yourself and see how much you know about these aquatic creatures.

Ready to take the quiz?

Play Quiz