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Fishery

Classification and Types of Fish

Fishes vary not only in their habitat characteristics such as water source and type but also in body skeleton. Thus, fish can be either temperate or tropical types, freshwater or saltwater types, or bony and cartilaginous types. Each sub-group consists of a large and variable number of fish types and distinguishing characteristics.

Fish are classified using various schemes. These bases of classification include;

 Classification and Types of Fish
Bluefin Tuna in a netted ranch

1. Water Source

Fish are classified through their water source as;

1a. Tropical fish

These are the fish that live in either salt or freshwater but which need a warm (tropical) medium or temperature to live. The types can be Tropical Freshwater species or Tropical Marine species.

1b. Cold water fish

These fish can be salt or freshwater fish that need colder water temperatures. Like tropical fish, coldwater fish can also be Coldwater Fresh water species or Coldwater Marine species.

2. Type of Water Body

Fishes are classified based on their body water type as;

2a. Fresh water Fish

These are the fish that live in freshwater, usually found in inland rivers and streams of most continents.

They can be as colorful as marine fish and yet need less care. Most freshwater fish in the ornamental hobby are tropical fish, which require a heater. Freshwater fish can be further grouped based on temperament, lighting needs, habitat needs, and swimming level, as shown below:

Fish type TemperamentLighting needsHabitatSwimming levelSize (cm)


Shovelnose (catfish) peaceful


reduced


plants/rocks


bottom


2.8’’
Bristlenose(algal eater) peacefulreducedplants/rocksbottom2”
Giant (crab) peacefulbrightplants/rocksall4.75”
Butterfish peacefulreducedplants/rockstop4.75”
Pacu peacefulbrightplants/rocksmiddle20”
Spotted Puffer aggressivebrightplants/rocksall6”

Freshwater fish can also be classified based on shared characteristics of categories as;

1. Killifishers and livebearers- livebearers, killi fishes, mosquito fishes, gambusies, pup fishes;

2. Darters and sculpins- darters, sculpins, longperches;

3. Flatfishes, sunfishes, and perchlike fishes- flounders, sunfish, perches, basses, crappies;

4. Elongate fishes with long snouts- paddlefish, sturgeons, pikes, pickerels, gars;

5. Eel-like fishes and catfishes- lampreys, eels, bowfins, catfish, bullheads;

6. Minnows and shiners- daces, shiners, long minnows, shads;

7. Trouts and salmons- whitefishes, trouts, salmons, graylings;

2b. Marine Fish

These are the fish that live in salty seawater. Most commonly, marine fishes need a tropical climate.

Saltwater types of fish are also categorized as above into;

1. Sharklike fishes- sharks, dogfishes, ratfishes;

2. Skates and raylike fishes- rays, mantas, string rays, skates

3. Eellike fishes and long dorsal-finned fishes- hagfishes, morays, wolffishes, eelpouts, midshipmen;

4. Drumlike fishes, cods, trouts and catfishes- trouts, drums, sea catfishes, clds, cobias;

5. Sticklebacks- sticklebacks;

6. Long, slender fishes- cutlass fishes, flying fishes, needlefishes, pipefishes, trumpetfishes;

7. Seahorses- seahorses;

Read Also: Guide to Fisheries and Fish Production

8. Fishes with spiny rays or tapering bodies- rockfishes, scorpion fishes, lizard fishes, sculpins;

9. Basslike fishes, grunts and snappers- temperate basses, seaperches, grunts, snappers;

10. Angelfishes and disc-like fishes- angelfishes, opaleyes, spadefishes, surgeonfishes, butterflyfishes;

11. Parrotfishes and wrasses- parrotfishes, wrasses;

12. Spindle-shaped fishes and large, robust fishes- jacks, whitefishes, tunas, bonefish, bonitos;

13. Flatfishes- sanddabs, halibuts, flounders, soles; and

14. Puffers, box fishes, and fishes with lures- goosefishes, boxfishes, filefishes, puffers, lumpfish.

3. Basis of Body Skeleton

Fish can be divided into three groups.

3a. Jawless Fish

These include the lampreys (Class Cephalaspidomorphi) and hagfish (Class Myxini/Hyperotreti).

3b. Lampreys

A lamprey (lamprey eel; Family Petromyzontidae) is a jawless fish with a toothed, funnel-like sucking mouth. They are known for boring into the flesh of other fish to suck their blood; they constitute a minority and have vastly different morphology and physiology. They have no scales but measure up to 13-100 cm.

Also, they have no paired fins but have large eyes, one nostril on the top of the head, and seven gills on each side. They have a cartilaginous skeleton and are regarded as the sister taxon of jawed vertebrates (gnathostomes) hence, not classified within the Vertebrata itself.

Lampreys live mostly in coastal and fresh waters and are found in most temperate regions except Africa, because of their low tolerance to high water temperatures.

Lampreys begin life as burrowing freshwater larvae (ammocoetes) but transform in metamorphosis into adults after 5-7 years, which exhibit efficient predatory/parasitic life. The adult attaches its mouth to a fish, secreting an anticoagulant to the host and feeding on the blood and tissues of the host.

This phase lasts about 18 months. There are 40 recorded species in nine genera and three subfamilies, namely Geotriinae, Mordaciinae, and Petromyzontinae.

3c. Hag fish

These are primitive marine vertebrates. They exhibit unusual feeding habits and slime-producing capabilities. They are long (1/2 m in average length), vermiform, and can exude copious quantities of a sticky slime or mucus, which finds use as an escape strategy.

An adult hagfish can secrete enough slime to turn a large bucket into the gel in a matter of minutes. Hagfish have elongated, ‘eel-like’ bodies and paddle-like tails. Their colors depend on the species and range from pink to blue-grey, with or without black or white mottling. Eyes may be vestigial or absent.

They have no true fins or jaws, but there are six barbells around their mouth and a single nostril. Unlike Gnathostomata, they have a pair of horizontally moving structures with tooth-like projections for pulling off food.

The hagfish enter both living and dead fish, feeding on the insides, and polychaete marine worms. They cannot enter through the skin but they often enter through the mouth, gills, or anus. Like leeches, they have a sluggish metabolism and can go months between feedings.

4. Cartilaginous Fish

This consists of fishes that belong to the Class Chondrichthyes. The characteristics are;

The presence of internal jaws (palatoquadrate), paired appendages (pectoral, pelvic fins) supported by an internal skeleton that provides more efficient locomotion, three semi-circular canals;

Teeth-modified dermal scales;

More proficient predators than the jawless fish;

Internal skeleton composed of cartilage, which may be prismatically calcified, placoid scales, second-gill arch (hyoid) involved in jaw suspension, swim bladder or lung absent, have an oil-filled liver to provide natural buoyancy, claspers (modified pelvic fins) present in males (internal fertilization), persistent notochord; ventral mouth; and replacement teeth rows.

There are two subclasses, namely Subclass Elasmobranchii (comprising the rays, skates, and sharks) and Subclass Holocephali (consisting of the Chimaeras/ray fishes). The categories of ray fishes are Subcategories Pristiformes (sawfishes), Rajiformes (common rays and skates), and Torpendiniformes (electric rays).

5. Bony Fish

This consists of fishes found in the Class Osteichthyes. Like all fishes, the fishes are cold-blooded vertebrates that breathe through gills and use fins for swimming. Bony fishes have several distinguishing features, namely a skeleton of bone, scale, paired fins, one pair of gill openings, jaws, and paired nostrils.

The class includes the largest number (23, 500) of living species of all scientific classes of vertebrates.

It consists of 73 fish families ranging from the Sturgeons, Herring, and Tarpon to the Deep Sea Anglers. They account for about 96% of all fish species, except the Chondrichthyes, the Myxini (hagfishes), and the Cephalaspidomorphi (lampreys). The subclasses are;

Subclass Dipnoi (lung fishes), have an upper jaw fused to the braincase, fused teeth, and the presence of an air-breathing organ that opens to the oesophagus. A lungfish’s canal fin is continuous with its dorsal and anal fins. The pelvic and pectoral fins are long and tubular.

Subclass Crossopterygii (coelacanths) have cosmid scales, two dorsal fins, and fleshy paired fins that contain skeletal elements.

Subclass Actinopterygii (all other living bony fishes) is characterized by rayed fins.

Read Also: Aquaculture (Aqua farming) as a Fisheries Technique and Types of Aquaculture

Read Also: What You Should Know Before Venturing Into Fruit Farming

Agric4Profits

Benadine Nonye is an agricultural consultant and a writer with over 12 years of professional experience in the agriculture industry. - National Diploma in Agricultural Technology - Bachelor's Degree in Agricultural Science - Master's Degree in Science Education... Visit My Websites On: 1. Agric4Profits.com - Your Comprehensive Practical Agricultural Knowledge and Farmer’s Guide Website! 2. WealthinWastes.com - For Effective Environmental Management through Proper Waste Management and Recycling Practices! Join Me On: Twitter: @benadinenonye - Instagram: benadinenonye - LinkedIn: benadinenonye - YouTube: Agric4Profits TV and WealthInWastes TV - Pinterest: BenadineNonye4u - Facebook: BenadineNonye

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