Fish – Evolution and Ecology Study Guide

Fish Evolution and Ecology

  • Fishes are cold-blooded creatures that breathe through gills, live in water, and move with fins.
  • They have a streamlined body that helps them swim without much resistance in the water.
  • They also have fins to assist them in swimming.
  • They are bilaterally symmetrical, triploblastic organisms.
  • They have a segmented body, and internal segmentation is present.
  • The majority of the fish are spindle-shaped.

Evolution of Fish

evolution of fish

Evolution of Fishes

The first vertebrates were fish. Understanding fish evolution is crucial for what it teaches us about fish groups and what it tells us about vertebrate evolution and, ultimately, our species.

Dermal and endochondral bone and their descendants (vertebral centra, bony endoskeletons, braincases, teeth), jaws, brains, appendages, and the internal organ systems define all vertebrate groups today were all developed throughout fish evolution and passed on to higher vertebrates.

Fishes invaded and ruled the oceans and fresh waterways during 500 million years of evolution, finally emerging onto land, albeit briefly. Major clades thrived and then died out or were supplanted by other groupings with supposedly greater advances.

The transition from hagfish to finned fish is a lengthy and complicated process.

  • The development of gill function is one phase in this process.
  • The gills of invertebrate chordates are used to filter food from water, not to absorb oxygen.
  • Fish evolved to use their gills to absorb oxygen rather than filter food early on in their existence.
  • Gills are made up of many thin, folded tissues with a lot of surface area for oxygen absorption.
  • Fish might become considerably larger and more active if their gills absorb more oxygen.


The earliest vertebrates are assumed to be the ancestors of hagfish! Their skeletons date from around 550 million years ago.

Around 450 million years ago, the first fossils of cartilaginous fish with jaws resembling current sharks appeared in the fossil record.

They were followed by the bony fish around 50 million years later.

fish fossil

  • Invertebrates, maybe cephalochordata, have evolved the earliest fishlike vertebrates.

  • The early “fishes,” on the other hand, have no fossil record, and their shape and connections are unknown.

  • Complex tissue types had developed by the time fishlike fossils occurred in Early Cambrian strata, around 530 million years ago, including filamentous gills, V-shaped myomeres, and a unique dorsal fin.

  • The lobe-finned bony fish were far more abundant in the beginning than the ray-finned bony fish that now dominate.

  • Amphibians are descended from lobe-finned fish, and Amphibian legs and lungs developed from their stump-like appendages and lung-like organs.

  • Bony fish with ray-finned fins may have been the first to develop in freshwater, and they eventually evolved into the most varied and prominent fish group.

Fish Ecology

fish ecology

  • Fish have a wide range of habitats and diets. They may be found in saltwater and freshwater lakes, ponds, rivers, and streams.

  • The majority of fish are predators, although the type of their prey and how they devour it varies greatly between classes and even within classes.

  • Hagfish live in the ocean’s deepest depths. They eat other fish, both alive and dead. They go into their prey’s body through the mouth or anus, and then they practically devour the insides out of their victim.

  • Lampreys like to dwell in freshwater or shallow ocean water. With their sucker mouth, they either eat tiny invertebrates or suck blood from bigger fish.

  • Sharks and other cartilaginous fish may live at the ocean’s bottom. The majority, however, reside in the water column, and they eat plankton or hunt other fish and aquatic animals.

  • Bony fish may be found in both salt and fresh water, and they eat a broad variety of meals. Depending on the fish species, they may consume algae, smaller fish, debris, or dead creatures.

  • Because fish retain a high amount of ecosystem nutrients in their tissues, transport nutrients farther than other aquatic animals, and excrete nutrients in dissolved forms that are easily accessible to primary producers, fishes play an important part in nutrient recycling.


  • Fish evolved from using their gills to filter food to absorb oxygen from the surrounding water.
  • About 550 million years ago, the first fish, which resembled living hagfish, developed.
  • A full vertebral column, jaws, and an endoskeleton formed of bones rather than cartilage were among the adaptations that fish finally acquired.
  • Fish may be found in both saltwater and freshwater lakes and streams.
  • Most fish are predators, but the kind of food they eat and how they eat it differ.
  • Human activities such as water pollution and overfishing have jeopardized many fish species.


1. What is the evolution of fish?

Fish began to evolve during the Cambrian explosion approximately 530 million years ago. The early chordates formed the skull and spinal column at this epoch, giving rise to the earliest craniates and vertebrates. The Agnatha, or jawless fish, are the earliest fish lineages. During the Late Ordovician epoch, the first jawed vertebrates most likely evolved.

2. Why are fish important to evolution?

Fish were the planet’s earliest vertebrates, and their basic form and body laid the foundation for millions of species and millions of years of evolution. They have evolved several times throughout the years, surviving huge extinctions and significant changes in the temperature and structure of the globe.

3. What is the ecology of fish?

Because fish retain a high amount of ecosystem nutrients in their tissues, transport nutrients farther than other aquatic animals, and excrete nutrients in dissolved forms that are easily accessible to primary producers, fishes play an important part in nutrient recycling.

4. How did fish evolve lungs?

Although Darwin believed that lungs evolved from gas bladders, the fact that fish with lungs are the earliest bony fish and molecular and developmental data suggests that lungs originated before swim bladders. Swim bladders are assumed to have originated from lung tissue, and they appeared shortly after the lungs.

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