Introduction to Fisheries / Classes of Fish

Warmer waters

Fish farming or Fisheries involves all the activities and processes of training and raising fish / fishes both for consumption and sales. It involves the rearing, management and selling of fish and other aquatic organisms.

Classes of Fish / Fisheries

There are different classes of fish / fisheries. Fishes are classified according to their habitat (where they live), and their morphology. Now let use discuss the different classes of fish below.

1 Classification of Fish / Fisheries Based On Habitat

According to habitat, there are three classes of fish:

  1. Freshwater Fish
  2. Marine Fish
  3. Migrating Fish

A few examples of each of these classes are given below:

1.1  Freshwater Fishes

Freshwater fishes or Fisheries like the name implies are those kinds of fishes that live and survive on fresh waters without or little salt taste, fishes in the ponds, springs, lakes, streams etc. can survive in very low levels of salinity (salt). Examples include: Puffer Fish,  Piranha, Cat Fish, Swordtail Fish, Archer Fish, Cichlid, Butterfly Fish, Discus Fish.

1.2 Salt water/Marine Fishes

Saltwater fishes or fisheries also known as marine fishes are those fishes that spend some or all of their lives in salt water such as oceans or salt lakes. Marine fish are classified into three types, based on their feeding habits which are:

  1. Herbivorous: these are those types of fishes that can feed on plant materials.
  2. Carnivorous: these are those types of fishes that can feed on other fishes or other animals.
  3. Omnivorous: these are those fishes that can feed on different varieties of food sources ranging from plants, animals, fungi, algae and bacteria. They are popularly known as general feeders because they can generally feed on any food source in order to survive.

Examples are:  Cardinal Fish, Surgeon Fish, Tang Fish,  Damsel Fish, Hawk Fish, Grouper, Squirrel Fish, Nurse Shark

1.3   Migrating Fishes

Fishes migrate for reproduction and diet. Migrating fishes can be divided into 2 types according to their movement:

  1. Catadromous fishes:

These are the fishes which are born in marine/saline water, but migrate to freshwater sources to spend the major part of their lives. They migrate back into the saline water when they want to reproduce.

2. Anadromous fishes:

They are those fishes that are born in freshwater, but migrate to salt water bodies to spend most part of their adult lives. They return to freshwater bodies when they want to reproduce.

Examples: Tuna, Salmon, Dolphin,  Sail Fish,  Char, Trout, Capelin Fish,  Bullshark

  1. Amphidromous fishes:

These are fishes which are born in freshwater / estuaries but migrate to the saline water to spend most part of their young lives. They return back to the freshwater to grow up into adults and then reproduce there.

  1. Potamodromous fishes:

These are those fishes or fisheries that are born in upstream freshwater but migrate downstream inside the fresh water to spend most of their adult lives. They return back to the upstream when they want to reproduce.

  1. Oceanodromous fishes:

These are those fishes that are born near the spawning ground but migrate to the ocean currents to spend most of their adult lives. They return back to the spawning grounds when they want to reproduce.

Read Also: 8 Uses of Fish and Fish Products

Fisheries

Classification of Fish / Fisheries Based On Morphology

According to their morphology, There are 3 major classes of fish / fisheries:

Bony fishes (Chondrichthyes): This class of fish has jaws, and is characterized by their bony skeletons, but they lack of bones in their body. This class is divided into three types: sharks, skates, and rays.

Cartilaginous fishes (Osteichthyes): These are also jawed fishes which have cartilaginous skeletons and no cartilage. This class is of fishes is subdivided into two:
1. Sarcopterygii: these are fishes which are the lobe-finned, and
2. Actinopterygii : these are fishes which are the ray-finned.

3. Jawless fishes (Agnatha): These are those fishes that have no jaws, and undeveloped backbones. For example: hagfish and lampreys.

1. Bony fishes (Chondrichthyes): These are those fishes that have bony skeletons, gills and an operculum which they use to breathe when resting. Bony fishes are classified into the following 4 groups based on their feeding patterns:

  1. Herbivorous: these are those types of fishes that can feed on plant materials.
  2. Carnivorous: these are those types of fishes that can feed on other fishes or other animals.
  3. Omnivorous: these are those fishes that can feed on different varieties of food sources ranging from plants, animals, fungi, algae and bacteria. They are popularly known as general feeders because they can generally feed on any food source in order to survive.
  4. Detritivores: these are those types of fishes that feed on different sorts of organic matter and this helps in their habitat as the process help to keep their clean.

2  Cartilaginous Fish (Chondrichthyes)

These are those classes of fish that has a cartilaginous skeleton. The young ones have a notochord when being given birth to which later turns into a cartilage. They also have scales, gills, and paired fins.

3 Jawless Fish (Agnatha)

These are those classes of fishes that have no jaws and they don’t have a defined stomach, fins, or the ability to regulate their own body temperature. For example: hagfish and lampreys.

Classification of Fish / Fisheries Based on other Types of Aquatic Organisms

1 Shell Fishes

Shell fishes also called crustaceans are mainly harvested during fishing in rivers, lakes, seas and oceans. They are not fishes but they can be eaten by human beings. Examples of shell fishes include: crabs, prawns, crayfish, oysters etc.

2 Reptiles

Reptiles are cold-blooded vertebrate animals of a class that includes: snakes, lizards, crocodiles, turtles and tortoises. They are characterized by having a dry skin and typically laying soft-shelled eggs on land.

3 Mammals

Mammals are warm-blooded vertebrate animals of a class that is distinguished by the possession of hair or fur, their females secrete milk for the nourishment of the young and they typically give birth to their young ones. Examples of the mammals that live in the water include: hippopotamus, whale etc.

Related: Anatomy of Fishes: Female Fish and their Reproductive Strategies

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