Fishes Chapter 24
What is a fish? • “Fish” has many usages extending beyond what are actually considered fishes today (e.g., starfish, cuttlefish etc.). • Fishes do not form a monophyletic group. • One group of fishes contains the ancestor to the land vertebrates (tetrapods) • In an evolutionary sense, fish can be defined as all vertebrates that are not tetrapods.
Fish Definition • Aquatic vertebrates with Gills, Fins and usually skin with Scales. • Dominate Seas, Lakes and Streams • Around 28,000 species • Adaptations: • Ability to move or remain motionless in a medium that is 800Xdenser than air (cartilage/swim bladder) • Salt and water exchange (kidneys) • Sensory System excellent (lateral line) • Respiratory System efficient (gills)
Taxonomy • Fishes are in Phylum Chordata • Bilateral Symmetry • Notochord (skeletal rod) present • Dorsal Nerve Cord; Anterior end usually brain • Pharyngeal pouches present at some time in life • Postanal tail at some life stage • Segmentation
Diversity • Evolution in an aquatic environment both shaped and constrained its evolution. • “Fish” refers to one or more individuals of one species. • “Fishes” refers to more than one species.
Ancestry of Fishes • Fishes have descended from an unknown free-swimming protochordate ancestor (like lancelet). • Agnathans (jawless)including ostracoderms. • Hagfishes and Lampreys • Gnathostomes (jawed)derived from one group of ostracoderms. • Four groups of gnathostomes flourished during the Devonian, two survive today. • Classes Chondrichthyes and Osteichthyes
Fossils of Early Vertebrates • First: • Armored, jawless vertebrates called ostracodermshad defensive plates of bone on their skin. • One group of ostracoderms led to the gnathostomes.
Fossils of Early Vertebrates • Placoderms (plated heads), one group of early jawed fishes, died out during the Carboniferous. • Left no descendents.
Fossils of Early Vertebrates • Another group, the acanthodians, were common during the Devonian, but became extinct during the Permian. • They were distinguished by having heavy spines on all fins except the caudal (tail) fin.
Fossils of Early Vertebrates • A third group of gnathostomes, the cartilaginous fishes (Class Chondrichthyes) lost the dermal armor and uses cartilage rather than bone for the skeleton. • Sharks, skates, rays, chimaeras.
Fossils of Early Vertebrates • The last group, the bony fishes (Class Osteichthyes), are the dominant fishes today. • Ray-finned fishes (95%) include most modern bony fishes. • Lobe-finned fishes contain few living species. • Includes sister group of tetrapods. • Lung fishes & coelacanths.
Agnathans • The least derived (simplest!) vertebrate lineages that still survives are class Myxini, the hagfishes and class Petromyzontida, the lampreys. • They lack: jaws, internal ossification, scales, and paired fins. Eel-like body • Pore-like gill openings along the side of the body.
Class Myxini - Hagfish • Entirelymarine. • Feeds on annelids, molluscs, crustaceans, & dead or dying fishes. • Predators or scavengers. • Use 2-toothed keratinized tongue to rasp bits of flesh from prey
Hagfish • Hagfishes are jawless marine vertebrates that have a cartilaginous skull and axial rod of cartilage derived from the notochord. • They lack vertebrae.
Hagfish • A hagfish can tie itself in knots to increase leverage when burrowing into a dead fish. • Produces large amounts of slime.
Class Petromyzontida - Lampreys • Lampreys(Class Petromyzontida) are found in fresh and saltwater. • Lampreys have cartilaginous segments surrounding the notochord and arching partly over the nerve cord. They have a vertebrae! • Also have cerebellum and eye muscles (unlike hagfish)
Lampreys • All ascend freshwater streams to breed. • Marine forms are anadromous. (swim upstream to spawn) • Freshwater forms move between lakes & streams.
Sea Lamprey • Life Cycle • Adults leave sea • Males build nest • Females join in • Spawn- female positions over nest, male attaches to dorsal side of female’s head • Eggs shed into nest, then male fertilizes the eggs • Adult dies • Eggs hatch in 2 weeks • Ammocoetes (do not resemble adult) • Leave nest for 3-7 years • Quick metamorphosis- turns to adult
Lampreys • Lamprey larvae are called ammocoetes. • Larvae look much like amphioxus (lancelet). • Possess basic chordate characteristics in simplified form. • Suspension feeders as Larvae.
Lampreys • Many are parasitic as adults. • Those that are not, do not feed as adults. • Attach to mouth via sucker, using sharp keratinized teeth, rasp thru the flesh of prey and suck out body fluids
Great Lakes and Lampreys • No lampreys in Great Lakes until: • Canal @Niagara Falls deepened from 1913-1918 • Lampreys devastated trout population an other species • 1960’s reached peak abundance then • Declined due to depletion of food and larvacides applied • Restocking trout and finally recovering
Gnathostomes (pgs. 525-530) • Class Chondrichthyes • Cartilaginous Fishes
Derived Characters of Gnathostomes • Gnathostomes have JAWS that evolved from skeletal supports of the pharyngeal slits.
Derived Characters of Gnathostomes • Other characters common to gnathostomes include: • Enhanced sensory systems, including the lateral line system. • An extensively mineralized endoskeleton. • Paired appendages.
Fossil Gnathostomes • The earliest gnathostomes in the fossil record are an extinct lineage of armored vertebrates called _______________.
Fossil Gnathostomes • Another group of jawed vertebrates called _____________________radiated during the Devonian period. • Closely related to the ancestors of osteichthyans (bony fishes).
Class Chondrichthyes • Members of class Chondrichthyes have a skeleton that is composed primarily of ______________________. • The cartilaginous skeleton evolved secondarily from an ancestral mineralized skeleton.
Subclass Elasmobranchii • The largest and most diverse subclass of Chondrichthyes, Elasmobranchii, includes the sharks and rays.
Subclass Elasmobranchii • Most sharks have a streamlined body and are swift swimmers. • Heterocercal tail – the upper lobe of the tail is longer than the lower. • Placoidscales. • The upper & lower jaws have a front, functional row of teeth and several developing rows growing behind as replacements.
Subclass Elasmobranchii • Spiral valve in intestine slows passage of food and increases absorptive area. • Large fatty liver aids in__________________.
Subclass Elasmobranchii– Acute Senses (Equipped for Predatory Life) • Prey is initially detected using large olfactory organs. • Mechanorecptors in the lateral line system sense low-frequency vibrations from far away. • Vision is important at close range. • Bioelectric fields surrounding their prey can be detected using electroreceptors in the ampullae of Lorenzini on the shark’s head.
Subclass Elasmobranchii • All chondrichthyans have internal fertilization. • ________________species lay large yolky eggs soon after fertilization. • Some lay eggs in a capsule called a “mermaid’s purse” that often have tendrils to attach it to a some object.
Subclass Elasmobranchii • ___________________ species retain developing young in the uterus while they are being nourished by the yolk.
Subclass Elasmobranchii • In __________________ species, young receive nourishment from the maternal bloodstream through a placenta, produced by the mother. (LIKE US!) • Some receive additional nutrition by eating eggs & siblings. • Parental care ends as soon as eggs are laid or young are born.
Subclass Elasmobranchii • Skates and rays are specialized for bottom dwelling with a flattened body and enlarged pectoral fins. • Gill openings on ventral surface. • Water enters through spiracles on dorsal surface.
Subclass Elasmobranchii • __________________ have a slender whip-like tail with one or more saw-edged spines with venom glands at the base. • __________________have large electric organs that can discharge high-amperage, low voltage current into the surrounding water.
Subclass Holocephali • A second subclass is composed of a few dozen species of chimaeras, or ___________. • Flat plates instead of teeth. • Upper jaw fused to cranium.
Class Osteichthyes: Bony Fishes • Osteichthyes are the bony fishes. • Bone skeleton replaces the cartilage during development. • A swim bladder is present for controlling buoyancy and respiration in some.
Evolutionary Position • Devonian Period: Age of Fishes
Osteichthyes- Respiration • Fishes breathe by drawing water over four or five pairs of gills located in chambers covered by a protective bony flap called the operculum.
SubClass Actinopterygii • Ray-finned fishes (class Actinopterygii)contain all the familiar bony fishes – more than 23,600 species.
SubClass Actinopterygii • The fins, supported mainly by long, flexible rays are modified for maneuvering, defense, and other functions.
SubClass Actinopterygii • Two main groups of ray-finned fishes. 1. Chondrosteans(nonteleosts)(e.g. sturgeons) have heterocercaltails and ganoid (like diamonds) scales.
SubClass Actinopterygii 2. Neopterygians – one lineage of early neopterygians led to the modern bony fishes (teleosts). • Early type neopterygians include the bowfin and gars.