The Fish and Fish Diversity

The Fish and Fish Diversity

  • THE ‘FISH’ [ = ‘Piscesin Latin;Poissonin French;Piscadoin Spanish;Piscein Italian;Fisch in German;Machliin Hindi;Matsya in Sanskrit etc.]:

Fishes are a quite diverse heterogeneous assemblage and exhibit a phylogenetic continuity. To most biologists, the term ‘fish’ is not so much a taxonomic ranking as a convenient description for aquatic organisms as diverse as hagfishes, lampreys, sharks, rays, lungfishes, sturgeons, gars and advanced ray-finned fishes. Recognizing this diversity, fish has been defined as:

“a poikilothermic, aquatic chordate with appendages (when present) developed as fins, whose chief respiratory organs are gills and whose body is usually covered with scales”.[ TM Berra, 2001, Freshwater fish distribution.].

Some workers restrict the term ‘fish’ to only jawed bony fishes viz., Actinopterygii, Latimeriidae and Dipnoi. Some also prefer to include sharks, rays and their relatives (because some sharks have the term ‘fish’ in their common name e.g., ‘dogfish’). Similar is the case with jawless Hagfishes and Lampreys. Nelson (2006) used this term as a matter of convenience, essentially to describe those vertebrates studied by Ichthyologists.

Despite their diversity, ‘fishes’ have been defined (artificially) as:

aquatic vertebrates that have gills throughout life and limbs if any in the shape of fins’.

  • ‘FISHES’ vs. ‘FISH’:
    The term ‘fishes’ is used when referring to individuals of more than one species e.g., 100 individuals including those of Labeo rohita, Catla catla and Cirrhinus mrigala will be correctly called as ‘fishes’.

The term ‘fish’ is appropriately used when one is referring to one or more individuals of one species e.g., 100 individuals of Labeo rohita as ‘fish’.

    Fisheries is a collective term where the cultivation and capture of fish(es), Molluscans, Crustaceans, any other aquatic animal and even sea weeds is included.

According to the Food and Agriculture Organisation (FAO), US, a ‘Fishery’ is defined in terms of the ‘people involved, species or type of fish, area of water or seabed, method of fishing, class of boats, purpose of the activities or a combination of the foregoing features’. This definition also includes a combination of fish and fishermen of a region, the fishermen fishing for similar species with similar gear types. A fishery may involve the capture of wild fish or raising fish through fish farming or aquaculture.

As per the Dictionary, Fishery (Sing.) / Fisheries (Plu.) include(s) the following:

The occupation, industry or season of taking fish or other sea animals (as sponges, shrimp or seals).

  • ICHTHYOLOGY [Gk. Ichthys, a fish; logos or logy, a discourse):
    A discipline of animal sciences involving all pure and applied aspects of fish(es).
    Basically, he/she is a student/professional of fish systematics, skilled in constructing phylogenies and classifications. In addition he/she also determines evolutionary trends based on comparative information from morphological and other studies. On the whole, the scope of Ichthyology is enormous and like any other allied disciplines, an Ichthyologist, too, is concerned with exploring taxonomical, morphological, anatomical, histological, physiological, embryological, ecological, genetical, biotechnological, pathological, immunological, economical and other applied aspects of fishes.
    • NUMBER OF FISH: Out of approximately 54,711 recognized living vertebrate species, fishes constitute slightly more than one half of it. As will be evident from the distributional diversity, the greatest number of fish species in the world inhabits the Southeastern Asian region. It is worth mentioning here that in contrast to Amphibians, Mammals and Reptiles, the known diversity of living fishes exceeds that of known fossil taxa. Nelson (2006), based on revisions, reports on new species, corrections and Web-based sources (like FishBase) etc., reported an estimated 27, 977 valid species of fishes, belonging to 515 families. Out of 27,977, 108 are jawless fishes (70 Hagfishes and 38 Lampreys); 970 are cartilaginous Sharks (403), Skates and Rays (534) and Chimaeras (33); and the remaining 26,000+ are bony fishes.
  • As per Fish Base (a global information system about Fishes) November 2019 data there are about 35315 species.

      • HABITAT DIVERSITY: Fishes live in almost every type of aquatic habitat viz., fresh, brackish or marine, from the tropics to the Polar Regions. Many freshwater and marine species are also common in brackish water estuaries. About one-third of families have at least one species with individuals that spend at least part of their life in freshwater. About 12,000 species (43%) of all species, live exclusively in freshwater lakes and rivers that cover only 1 % of the earth’s surface and account for a little less than 0.01 % of its water (the mean depth of lakes is only a few meters). About 15,800 species live in oceans, which cover 70% of the earth’s surface and account for 97% of its water with a mean depth of about 3,700 m.

    Fishes are found to live up to an elevation of 5,200 m in Tibet, where some Nemacheilines (Cobitidae) live in hot springs. In the world’s highest (3,812 m) Lake Titicaca (South America), a group of Cyprinodontids has undergone much radiation. Fishes also live in the world’s deepest Baikal Lake (at least 1,000 m) and up to 7,000 m below the surface of the ocean. A few species make short excursions onto land. Subterranean or hypogean fishes are found confined to total darkness of caves or other underground areas or in the fast torrential streams (= Hill Stream Fishes) of Tibet, China and India.

    Oreochromis alcalicus or Alcolapia alcalica (the soda Tilapia; Order Perciformes or Cichliformes, Family Cichlidae) is endemic to hot soda Lake (hypersaline lake), Magadi (Kenya) at temperatures as high as 42.5°C. At the other extreme, Cod ice fishes, Trematomus (Order Perciformes, Fam. Nototheniidae) live at about -1°- 4°C under the Antarctic ice sheet, on account of producing antifreeze glycoproteins, preventing formation of ice crystals in blood (hence often called cryopelagic). Many species have acquired air-breathing organs, being essentially independent of water for respiration and live in stagnant, tropical swamps (especially Lungfishes).

    Lake-dwelling species may show a preference for deep, cold, oligotrophic lakes or for shallower, warmer and more productive mesotrophic and eutrophic lakes. In lake waters they may show a preference for the open-water limnetic zone, the benthic zone or shallow littoral zones. Stream fishes may prefer riffle or quieter zones and a zonation of species is found from the headwaters to the mouth of a river.

    Some fishes also inhabit deep-sea thermal vents in the eastern Pacific Ocean. In oceans, majority of fishes are coastal or littoral. The animals living in the deep sea live under extreme conditions of darkness, high pressure and temperature changes. The fish life of the deep-sea habitat is among the most specialized of any habitats in the world. The continental shelf at about 200 m depth has been considered as a boundary between ‘shallow’ and ‘deep sea’. Most diverse deep-sea assemblages occur between 40°N and 40°S latitudes. In general, any species that is found at extreme ocean depths, more than 500 m and even beyond 8,000 m, is defined as a ‘deep-sea fish’, characterized by elongated to dorso-ventrally flattened or eel-like body, large mouth, pointed fang-like teeth, enlarged or minute eyes, bioluminescence etc. The fish in the deep tend to be much smaller than on the surface, with minimal bone structure and more jelly-like flesh. They are, therefore, slower and less agile than fish living near the surface. They also tend to grow more slowly than surface fish. Some take many years to reach sexual maturity. These adaptive features are, obviously, the outcome of evolutionary adaptations to extreme pressure, cold and darkness and such similarities among unrelated fishes are due to convergent adaptations.

    The upper 200 m of the open sea is known as Epipelagic or Euphotic zone. There are three major regions of ‘open waterviz., Mesopelagic (200 – 1,000 m), Bathypelagic (1,000 – 4,000 m) and Benthopelagic or Abyssopelagic (4,000 – 6,000 m). The deep sea regions below 6,000 m are often referred as hadal depths. The bottom-associated or benthic species swim just above the bottom (= Benthopelagic) or live in contact with the bottom (= Benthic). More than 1,000 species inhabit open waters of the deep-sea and another 1,000 species are benthic, with fairly good representation of Cartilaginous and bony fishes.

      • DISTRIBUTIONAL DIVERSITY: In both fresh and marine waters, the largest number of species occurs in the tropics. The number is reduced towards Polar Regions. For the tropics on one hand, a large number of freshwater fishes are found in tropical Africa, southeastern Asia and the Amazon River, but on the other hand, because of the characteristic physiographic and geological history, relatively few freshwater species are found in Central America. Africa exhibits the greatest diversity of non-ostariophysan (i.e., lacking Weberian Ossicles) freshwater fishes but South America is poor on this basis. Contrary to it, in temperate regions, Eastern North America shows the greatest diversity of non-ostariophysan fishes. Most oceanic islands and continental areas recently exposed from the last ice age (e.g., northern regions of North America, Western Europe and Asia), lack indigenous fishes confined to freshwater.

    As far as the marine environment is concerned, representatives of many marine genera and of some species occur in the temperate and polar fauna of both hemispheres. The vast majority of species, however, are tropical, most of the rest occurring only in the Northern or only in the Southern Hemisphere.

    About 130 marine species are known to extend around the world in tropical or subtropical waters. The Indo-West Pacific (Red Sea and Indian Ocean to Northern Australia and Polynesia) is the richest, with most species occurring in New Guinea to Queensland. In terms of diversity, Southeastern Africa and Queensland have the largest number of marine shore fish. The West Indian or Caribbean fauna (southern Florida to northern Brazil) is also appreciably rich. The West African marine fauna, however, is relatively poor. Arctic and Antarctic faunas are depauperate i.e., lacking in numbers. In all, the greatest number of fish in the world inhabits the southeastern Asian region.

      • BIOGEOGRAPHICAL DIVERSITY: Biogeography is a new discipline that attempts to document and understand spatial patterns of biodiversity. It is actually a branch of ‘Physical Geography’, concerned with the present and past distribution of animals and plants along with the examination of physical environment affecting the distribution of a particular species across the world. In other words, the science of biogeography attempts to document the geographic distribution of taxa (i.e., descriptive biogeography) and to explain their distributional patterns (i.e., interpretive biogeography). It is an active field of study in Ichthyology, finding solutions to various problems related with the distribution of fishes.

    There are two approaches to interpretive biogeography i.e., the ecological biogeography which involves various environmental factors (viz., temperature, pH, dissolved gases, turbidity, salinity, currents, competition etc.), limiting the distribution of a species within a water body; and historical biogeography which focuses on the origin of distributional patterns (i.e., paleontological studies or the study of fossils). Paleoclimatic changes are often invoked in historical biogeography, especially when postulating that discontinuous distributions result from dispersal events.

    Dispersal and vicariant events are two methods of distribution of fishes. Dispersal, active or passive, is a movement to areas new to the existing population. Barriers of varying effectiveness may be involved. It is of greatest biogeographic significance if the breeding range of the species is increased. Vicariance, on the other hand, is a process by which the geographical range of an individual taxon or a whole biota is split into discontinuous parts by the formation of a physical or biotic barrier to gene flow or dispersal e.g., through tectonic plates. Both dispersal and vicariant approaches are used to explain disjunct or discontinuous distributions i.e., the occurrence of a taxon in different areas with a marked geographical gap between them e.g., Prosopium coulteri (Fam. Salmonidae) in western North America and in lake Superior; Geotria australis (Fam. Petromyzontidae) in Australia, New Zealand and South America etc. Further, Lungfishes found distantly in Africa, South America and Australia are potential examples of vicariance, suggesting that this group represents an ancient distribution limited to the Mesozoic supercontinent Gondwana and the fossil record suggesting that advanced lungfish had a widespread freshwater distribution and the current distribution of modern lungfish species reflects extinction of many lineages.



        • SMALLEST FISHES: They all include Fishes from 4 Orders of Bony Fishes:

    Order- Cypriniformes

          • Paedocypris progenetica [Images] (Fam. Cyprinidae, Subfamily – Rasborinae): This translucent fish from Indonesia has been claimed not only the world’s smallest fish (7.9 mm) but also the smallest vertebrate, particularly before the description of the smallest (7.7 mm) frog (Paedophryne amanuensis) in 2012 from Papua New Guinea.

    The Ichthyologists, Maurice Kottelat from Switzerland and Tan Heok Hui from the Raffles Museum of Biodiversity Research and National University of Singapore discovered it in 1996 and described in 2006.  The recorded maximum size of 1.03 cm is in females whereas 0.98 cm in males. The smallest known mature specimen was a female (0.79 mm), smaller than the female of any other vertebrate species.

          • Danionella [Images] (Fam. Cyprinidae, Subfamily – Danioninae): 4 species of Danionella, lacking scales, barbels and lateral line, are among other smallest cyprinids. The females of Danionella translucida from lower Myanmar, ripe at 1.0 – 1.1 cm (longest about 1.2 cm).

    Danionella mirifica from upper Myanmar is slightly larger (1.4 cm). Danionella dracula (1.0 – 1.2 cm; max. 1.7 cm), another species from Myanmar, is unusual in having teeth made of bone, rather than the true teeth of other fishes but the males have a pair of bony fangs, used for sparring (fighting) with their mates.  Danionella priapus (max. 1.6 cm) is endemic to India (West Bengal).

          • Sundadanio [Images] (Fam. Cyprinidae, Subfamily – Danioninae): Still larger (about 2.3 cm in standard length), 8 sp. of Blue Neon Danio (Sundadanio) are from freshwaters, peat swamps and blackwater streams of Indonesia – Sumatra, Bangka and around the Anjungan and Kapuas drainage in Borneo.

    Order- Perciformes:

          • Schindleria brevipinguis [Images] (Stout Infantfish, Fam. Schindleriidae): Native to Australia’s Great Barrier Reef and Osprey Reef in the Coral Sea, this species grows to a maximum total length of 8.4 mm, with males maturing at about 7.0 mm.
          • Trimmaton nanus [Images] (Midget dwarfgoby, Fam. – Gobiidae): Distributed in the Indian and the western Pacific Ocean, occasionally found in outer reef areas and lagoons, up to a depth of 5.0 to 30 m, it was the shortest known fish and vertebrate ( until 2004.


          • Mistichthys luzonensis [Images] (Sinarapan, Fam. – Gobiidae): Commonly named after a fishing gear, called ‘sarap’, having tiny holes in the net, it was considered to be the world’s smallest commercially harvested fish, found in the Lakes Bato and Buhi in Camarines Sur, Bicol Region of the Philippines. It has been listed in the Guinness Book of Records as the ‘smallest food fish’. The average length is about 1.25 cm, the males being smaller than females. Males (max. 1.35 cm) mature at about 1.0 cm while females (max. 1.4 cm) at about 1.1 cm.


          • Pandaka pygmaea [Images] (Dwarf pygmy goby, Fam. – Gobiidae): Found along the shady river banks in Rizal Province of Luzan (Philippines), it was endemic to the rivers of Malabon (Metro Manila) but has also been collected from the sea at Culion Island (Philippines). Besides, it is also found thriving well in the brackish waters and mangrove of Indonesia and Singapore. It is regarded as one of the smallest fish in the world by mass (av. weight 4.0 to 5.0 mg) and one of the shortest freshwater fish (mature males up to 1.0 cm and females up to 1.5 cm in standard length).


          • Eviota zonura [Images] (Naked-headed Goby, Fam. – Gobiidae): Widely distributed in the western Pacific, Ashmore Reef (Timor Sea) and Waigeo (Indonesia) to Samoa, Fiji and throughout Micronesia. Male’s maxmimum length is 1.7 cm and often adjudged to the ‘smallest marine fish’.

    Order- Lophiformes


          • Photocorynus spiniceps [Images] (Anglerfish, Fam. – Linophrynidae): Widely distributed in the Atlantic and Pacific Oceans. Curiously enough, the mature males are quite small (6.2–7.3 mm), smaller than any other mature fish or any vertebrate and remain parasitic on significantly larger females (up to 5.0 cm).

    Order – Siluriformes


          • Scoloplax [Images] (spiny dwarf catfishes, Fam. – Scoloplacidae), represented by as many as 6 species, is the smallest of catfishes (max. 2.0 cm) native to freshwater streams and lakes of South America.
            • LARGEST / LONGEST / HEAVIEST FISHES: These fishes are quite diverse representing various Orders of Cartilaginous to Bony Fishes:

    Order – Orectolobiformes

          • Rhincodon typus [Images] (Whale Shark, Fam. – Rhincodontidae): Found in all tropical and warm-temperate seas of the world, this is the largest (12.0 – 18.0 m;

    20, 000 kg) pelagic fish, living in open sea (up to about 1, 800 m). This largest fish feeds on smallest ones i.e., filter – feeder.

    Order – Lamniformes

          • Cetorhinus maximus [Images] (Basking Shark, Fam. – Cetorhinidae): This is supposed to be the second largest (10.0 – 15.0 m; 5, 000 kg) cosmopolitan migratory species, found in all the world’s temperate oceans, venturing up to the depth of about 900 m. Like whale shark, it is also a filter-feeder.

    Order – Lampriformes

          • Regalecus glesne [Images] (Oarfish or Ribbonfish, Fam. – Regalecidae): It an oceanodromous, world’s longest, ribbon-like, carnivorous bony fish (3.0 – 11.0 m; 270 kg), venturing up to a depth of 1, 000 m.

    Order – Cypriniformes

          • Catlocarpio siamensis [Images] (Giant Barb or Siamese giant carp, Fam. – Cyprinidae): It is the largest (3.0 m; 300 kg) Cyprinid from the freshwaters of Mae Klong, Mekong and Chao Phraya river basins of Indochina. Their large size is supposed to be due to polyploidy (tetraploids). Large-scale cultivation is undertaken in Vietnam.
          • Tor putitora [Images] (Golden Mahseer, Fam. – Cyprinidae): On account of habitat loss, habitat degradation and overfishing, this endangered species has been popular to the fast flowing Himalayan and southern Asian streams. There was a time when they have been claimed to grow up to 2.5 – 3.0 m (about 54 kg) [but now the catch size is tremendously decreased e.g., 13.5 cm (28.0 g) – 52.5 cm (1.65 kg) in the streams of Garhwal region (Central Himalaya).
          • Ptychocheilus luclus [Images] (Colorado pikedminnow, Fam. Cyprinidae): It is the largest (1.8 m; 45.0 kg) predatory Cyprinid from Colorado River basin of North America and one of the largest in the world. Now a days, the specimens longer than 80.0 cm are an unusual sight.

    Order – Acipensariformes

          • Huso huso [Images] (White Sturgeon or Beluga, Fam. – Acipenseridae): This anadromous fish from the Caspian and Black Sea basins up to Amur river in E. Asia, valuable for its ‘roe’ (beluga caviar), is among the largest (7.2 m; 1, 571 kg) freshwater fish in the world. Today, the most common catch size is 1.4 – 3.2 m (19.0 – 264 kg).

    Order – Osteoglossiformes

          • Arapaima gigas [Images] (Pirarucu, Fam. – Osteoglossidae): This air breathing longest fish (2.0 – 4.5 m; 200 kg) is the native of freshwaters of South America (Amazon River).

    Order – Tetraodontiformes

          • Mola mola [Images] (Ocean Sunfish, Fam. – Molidae): Native to tropical and temperate seas of the world, this is supposed to the heaviest and highly fecund (3.0 million eggs) bony fish (247 – 1,000 kg) in world. Its average length is 1.8 m and dorsal to anal fin-to fin length (height) is about 2.5 m (max. 3.3 m; 4.2 m across the fins, weighing up to 2, 300 kg).

    Order – Siluriformes


    Some of the world’s largest freshwater fishes are catfishes, including the predatory European wels (Siluris glanis, Siluridae; 5.0 m; 330 kg) from central, southern and eastern Europe; the herbivorous, Critically Endangered, Mekong Giant Catfish (Pangasianodon gigas, Pangasiidae; 3.0 m; 300 kg) from Mekong basin in Southeast Asia (Vietnam) and adjacent China and the long-whiskered Piraiba (Brachyplatystoma filamentosum, Pimelodidae) of South America (3.6 m; 150 kg). The largest catfishes belonging to Family Ictaluridae in North America are the Flathead (Pylodictis olivaris, 1.5 m; 56 kg) and Blue catfihes (Ictalurus furcatus, 1.6 m; 68 kg).


    From typical spindle-shaped to snake-like (Eels), dorso-ventrally flattened, laterally compressed or globular external appearance there is also a great anatomical and physiological diversity. Some species are brilliantly coloured while others are drab. Over 50 Teleosts (mostly Cyprinids, Balitorids, Siluriforms, Amblyopsids, Bythitids and Gobiids) lack eyes and live in caves. When on one hand there is an exoskeleton of scales, with adaptive modifications, some species are smooth-skinned (without scales). A great diversity exists in the locomotory fins, ranging from absence of any of them to modifications as holdfast organs, lures for attracting prey, copulatory structures etc. Respiratory diversity ranges from well-defined typical gills to accessory structures like air bladders or even lungs like structures. Endoskeleton may be cartilaginous or bony.

      As per the instinct, the wide variety of fishes having chosen to live exclusively in water, during the course of evolution, had to acquire various behavioural patterns, obviously, just to minimize the competition of any kind. Therefore, some exhibit schooling, others are highly territorial; some practice parental care, others not; some undertaking long or short range migrations for breeding or feeding purposes (may be anadromous, catadromous or diadromous, oceanodromous, potamodromous); some showing homing tendencies; some highly specialised with stinging apparatus, electric organs, sound production, light producing organs; some indulging in symbiotic (chiefly commensal) relationships and others showing social behaviour etc. A few species have been found to be parasitic on other species or on the female of their own (e.g., Anglerfish, Photocorynus spiniceps ). A wide variety of habitats compelled them to adapt to a wide variety of foods ranging from microscopic phyto-or zooplanktons to macro-animals or plants.

    An individual species may tolerate a wide range of temperatures (eurythermal) or a narrow range (stenothermal). Similarly, they may tolerate a wide range of salinity (euryhaline) or only a narrow range (stenohaline).

    Most fishes are gonochoristic (fixed sexual pattern) but many are hermaphroditic, either protogynous (vs. protandrous) sequential (vs. synchronous) hermaphrodites or where females change to males. Some fishes have a larval stage and undergo metamorphosis. In general, masses exhibit external fertilization but some others have adopted strategy of internal fertilization through characteristic intromittant organs (claspers, gonopodium, priapium, ovipositor etc.)

    Lifespan in fishes may vary from a little over 1 year to about 120 years. Semelparity and iteroparity are the terms associated with span of life. Semelparous are those (less than 1 %) which die soon after a single spawning period e.g., Petromyzontiforms, Anguillids, Pimephale sp. (a cyprinid), some Osmerids, some Galaxioids, five species of Pacific salmon (Oncorhynchus) etc. Contrary to this, majority of species reproduce for more than one spawning season, a phenomenon called as iteroparity.



    • (Slide No. 1- 14) FISH AND FISH DIVERSITY
    • (Slide No. 17) FISH COLLECTIONS
    • (Slide No. 18) FISHERIES
    • (Slide No. 20) AQUACULTURE
    • (Slide No. 21) CULTIVABLE FISH
    • (Slide No. 23 – 24) INDIAN MAJOR CARPS
    • (Slide No. 25 – 28) CHINESE CARPS
    • (Slide No. 29) ORNAMENTAL CARP
    • (Slide No. 30) SUSTAINABLE FISHERIES                                                                                                                  Download [Presentation] Fish and Fish Diversity