Introduction to Fish Biology

What is a Fish?

• A fish is poikilothermic aquatic chordate, typically with appendages developed as fins.
• Their chief respiratory organs are gills.
• A fish's body is usually covered with scales (Berra, 2001).
• A fish is a vertebrate with a backbone.
• They have gills and a body covered with scales, living in the water (Pauly et al., 2014).
• Defining a "fish" may be unrealistic due to the diversity of adaptation among species.
• The term "fish" is a convenient description for diverse aquatic organisms like hagfishes, sharks, lungfishes, and ray-finned fishes.
• Exceptions to the definitions of "fish” give clues to adaptations arising from powerful selection pressures.

The Diversity of Fishes

• Fish occupy a lot of space and have had a lot of time to diversify.
• 70% of the planet is covered in water.
• Fish first evolved over 500 mya.
• Fish occupy an extraordinary array of habitats.
• They thrive in diverse environments like seasonal freshwater ponds, desert springs, oceans, cold mountain streams, and saline coastal embayments.
• Fish can live at temperatures from -1.8°C to nearly 40°C, in water pH values from 4 to 10+.
• They tolerate dissolved oxygen levels from near zero to saturation, in salinities from 0 to 90 ppt, and at depths from 0 to 8,000m.
• Fishes are the most numerous and diverse of the major vertebrate groups.
• They dominate the waters of the world through marvelous morphological, physiological, and behavioral adaptations.
• Estimates for the number of worldwide species of fish range from 25,000 to 37,000.
• Fishes are more numerous than all species of birds, mammals, amphibians, and reptiles combined.
• Jawless Fish (Agnatha): Myxiniformes (hagfishes) and Petromyzontiformes (lampreys).
• Cartilaginous Fish (Chondrichthyes): Holocephali (chimaeras) and Elasmobranchii (sharks, skates & rays).
• Bony Fish (Osteichthyes): Sarcopterygii (lobe-finned fishes) and Actinopterygii (ray-finned fishes).
• There are 108 jawless fishes.
• There are 970 cartilaginous fishes.
• There are 26,000+ bony fishes.
• 41% of fish live in freshwater.
• 1% of fish move between freshwater and seawater.
• 58% of fish live in seawater.
• 13% of fish live in the open ocean.
• 44% of fish live near coasts.

Superlative Fishes

• The world's smallest fishes - and vertebrates, mature at around 7-8 mm, including an Indonesian minnow, Paedocypris progenetica.
• The smallest commercial fish is sinarapan, Mistichthys luzonensis.
• The world's longest cartilaginous fish is the 12 m long (or longer) Whale Shark, Rhincodon typus.
• The longest bony fish is the 8 m long (or longer) Oarfish Regalecus glesne.
• Body masses top out at 34,000 kg for whale sharks and 2300 kg for the Ocean Sunfish, Mola mola.
• Coelacanth gave rise to the amphibians thought to have died out with the dinosaurs, was trawled up in 1938 in South Africa.
• Lungfishes can live in a state of dry "suspended animation" for up to 4 years, becoming dormant when their ponds dry up and reviving quickly when immersed in water.
• Antarctic fishes live in water colder than their blood's freezing point by avoiding free ice.
• Their blood contains antifreeze proteins that depress their blood's freezing point to -2°C.
• Deepsea fishes have forms that can swallow prey larger than themselves.
• Some deepsea anglerfishes have females 10 times larger than males.
• Males become small parasites permanently fused to the female, living off her blood stream.
• Fishes have life spans from 10 weeks (African killifishes and Great Barrier Reef pygmy gobies) to 150 years (sturgeons and scorpaenid rockfishes).
• Some species are annuals, with eggs surviving drought and hatching with rains.
• Some species are simultaneously male and female, while others change from male to female, or from female to male.
• Fishes engage in parenting ranging from simple nest guarding to mouth brooding.
• Some produce external or internal body substances upon which young feed.
• Many sharks have a placental structure as complex as any in mammals.
• Egg-laying fishes can construct nests.
• Some deposit eggs in the siphon of living clams, on terrestrial plant leaves, or in nests of other fishes.
• Fishes are unique among vertebrates because of their ability to produce light.
• This ability evolved independently, achieved autogenically (by the fish) or symbiotically (by bacteria).
• Predatory tactics include attracting prey with modified body parts disguised as lures or feigning death.
• Fish diets include ectoparasites, feces, blood, fins, scales, young, and other fishes' eyes.
• Fishes can change the depth of their bodies by erecting their fins or by filling themselves with water, deterring predators.
• Natural and sexual selection have been experimentally manipulated in guppies, swordtails, and sticklebacks.
• Competition, predation, and mate choice lead to adaptive alterations in body shape and armor, body color and color vision, and feeding habits.
• Fishing has a powerful evolutionary force, affecting population structure and size, reproduction ages and sizes, body shape, and behavior.
• Fishes have become increasingly important as laboratory and assay organisms.

What is Ichthyology?

• Ichthyology studies fish including their classification, structure, physiology, ecology, and evolution.
• Scientists engaged in the scientific studies of fish are ichthyologists.

History of Ichthyology

• Science is a human endeavor, and knowing early ichthyologists gives a sense of the long-established science of ichthyology.
• Ichthyology originates from the writings of Aristotle (384-322 B. C.).
• Aristotle distinguished fish from whales and recognized about 117 species of fish.
• For 2,000 years after Aristotle, few observations about fish were recorded.
• In the 16th century natural historians Pierre Belon (1517-1564), H. Salviani (1514-1572), and G. Rondelet (1507-1566) broke Aristotle’s grip.
• Belon published the first modern systematic treatise on fish.
• Salviani published the first regional faunal work.
• Rondelet published the first ichthyology text.
• Fish knowledge expanded with discoveries by naturalist explorers: Georg Marcgrave of Saxony (1610-1644), John Ray (1627-1705), and Francis Willughby (1635-1672).
• These works provided the foundation for Peter Artedi (1705-1734), known as "Father of Ichthyology," to build a fish classification system.
• Artedi also reviewed previous literature and recommended standard measurements and counts for fish taxonomy.
• Carolus Linnaeus (1707-1778) purchased Artedi's notes after his death and issued them in 1738.
• Linnaeus adopted (and changed) Artedi's classification for his Systema Naturae, the basis for future classification systems.
• Marc Elieser Bloch (1723-1799) first attempted to organize fish knowledge after Artedi.
• J. G. T. Sclmeider (1750-1822) edited Bloch's Systemae Ichthyologiae, with a revised classification system, issued in 1801.
• Georges Cuvier (1769-1832) and his pupil Achille Valenciennes wrote comprehensive volumes between 1828 and 1849.
• Cuvier and Valenciennes compiled and classified fish and conducted anatomical studies, which improved the understanding of fish interrelationships.
• In Histoire Naturelle des Poissons (1828), Cuvier provided an early history of ichthyology.
• French Revolution cut short Bernard Germain de Lacepede's studies (1756-1826), and he composed his five-volume work on fishes largely from memory and rough notes.
• Successors corrected the errors he made.
• Samuel L. Mitchill (1764-1831) wrote the first major work for North America, The Fishes of New York (1815).
• Constantine Rafinesque (1783-1840) wrote the most detailed of the early accounts, Ichthyologia Ohiensis (1820).
• Sir John Richardson (1787-1865) first described Pacific coast fishes of North America in his Fauna Boreali-Americana (1836).
• Louis Agassiz (1807-1873) wrote his first major work in 1829 titled Another Treatise on the Fishes of Brazil Agassiz classified the fishes collected by Johann Baptiste von Spix (1781-1826), who had died after spending three years in the rivers and streams of the Brazilian jungle.
• In 1846, Agassiz moved to Harvard University, convinced the American public of the importance of science, and made contributions to ichthyology.
• Johannes Müller (1801-1858) revised Agassiz's ideas to produce a fish classification system.
• Major groups recognized by scientists today were improved through the work of Ernst Haeckel (1834-1919), Thomas H. Huxley (1825-1895), Edward D. Cope (1840-1897), and Theodore Gill (1837-1914).
• The theory of Charles Darwin greatly influenced them.
• Albert Günther (1830-1914) of the British Museum produced the eight-volume Catalogue of the Fishes in the British Museum.
• David Starr Jordan (1851-1931) turned down curatorship at the British museum to continue his career, becoming the founding president of Stanford University.
• Jordan was known for his work Fishes of North and Middle America (four volumes, 1896-1900).and also authored the standard ichthyology text Guide to the Study of Fishes (1905).
• As the twentieth century progressed, ichthyology became more diverse with evolution and systematics linking these areas.
• Charles T. Regan (1878-1943), Leo S. Berg (1876-1950), and Carl L. Hubbs (1894-1979) made major contributions.
• Regan's work on teleost anatomy and classification is the foundation for contemporary systems.
• Berg described information on fish fauna of Russia and nearby areas.
• Hubbs worked with fishes of North and Central America, developing on Jordan's work.
• Regional works on fish have proliferated, with guides in states, provinces, and countries.
• A new compilation of fish species of the world was produced by William N. Eschmeyer (1998) and colleagues, which used modern computers.