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Fishes. Chapter 24. Diversity. “Fish” has many usages extending beyond what are actually considered fishes today (e.g., starfish, etc.). Fishes do not form a monophyletic group. In an evolutionary sense, can be defined as all vertebrates that are not tetrapods.

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fishes

Fishes

Chapter 24

diversity
Diversity
  • “Fish” has many usages extending beyond what are actually considered fishes today (e.g., starfish, etc.).
  • Fishes do not form a monophyletic group.
    • In an evolutionary sense, can be defined as all vertebrates that are not tetrapods.
    • Common ancestor of fishes is also an ancestor of land vertebrates.
      • Therefore in pure cladistics, would make land vertebrates “fish.
      • Approximately 24,600 living species.
    • Adapted to live in medium 800 times denser than air.
    • Can adjust to the salt and water balance of their environment.
diversity3
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
Ancestry of Fishes
  • Fishes have descended from an unknown free-swimming protochordate ancestor.
    • Agnathans including ostracoderms.
    • Gnathostomes derived from one group of ostracoderms.
      • Four groups of gnathostomes flourished during the Devonian, two survive today.
fossils of early vertebrates
Fossils of Early Vertebrates
  • Armored, jawless vertebrates called ostracoderms had defensive plates of bone on their skin.
    • One group of ostracoderms led to the gnathostomes.
fossils of early vertebrates7
Fossils of Early Vertebrates
  • Placoderms, one group of early jawed fishes, died out during the Carboniferous.
    • Left no descendents.
fossils of early vertebrates8
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.
    • Possible sister group of the bony fishes.
fossils of early vertebrates9
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 vertebrates10
Fossils of Early Vertebrates
  • The last group, the bony fishes, are the dominant fishes today.
    • Ray-finned fishes include most modern bony fishes.
    • Lobe-finned fishes contain few living species.
      • Includes sister group of tetrapods.
      • Lung fishes & coelacanths.
origins of bone and teeth
Origins of Bone and Teeth
  • Mineralization appears to have originated with vertebrate mouthparts.
  • The vertebrate endoskeleton became fully mineralized much later.
agnathans
Agnathans
  • The least derived vertebrate lineages that still survives are class Myxini, the hagfishes and class Petromyzontida, the lampreys.
    • They lack: jaws, internal ossification, scales, and paired fins.
    • Pore-like gill openings along the side of the body.
class myxini hagfish
Class Myxini - Hagfish
  • Entirely marine.
  • Feeds on annelids, molluscs, crustaceans, & dead or dying fishes.
    • Predators or scavengers.
class myxini hagfish14
Class Myxini - Hagfish
  • Hagfishes are jawless marine vertebrates that have a cartilaginous skull and axial rod of cartilage derived from the notochord.
    • They lack vertebrae.
class myxini hagfish15
Class Myxini - 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
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.
class petromyzontida lampreys17
Class Petromyzontida - Lampreys
  • All ascend freshwater streams to breed.
    • Marine forms are anadromous.
    • Freshwater forms move between lakes & streams.
class petromyzontida lampreys18
Class Petromyzontida - Lampreys
  • Lamprey larvae are called ammocoetes.
    • Larvae look much like amphioxus.
    • Possess basic chordate characteristics in simplified form.
    • Suspension feeders.
class petromyzontida lampreys19
Class Petromyzontida - Lampreys
  • Many are parasitic as adults.
    • Those that are not, do not feed as adults.
derived characters of gnathostomes
Derived Characters of Gnathostomes
  • Gnathostomes have jaws that evolved from skeletal supports of the pharyngeal slits.
derived characters of gnathostomes21
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
Fossil Gnathostomes
  • The earliest gnathostomes in the fossil record are an extinct lineage of armored vertebrates called placoderms.
fossil gnathostomes23
Fossil Gnathostomes
  • Another group of jawed vertebrates called acanthodians radiated during the Devonian period.
    • Closely related to the ancestors of osteichthyans (bony fishes).
class chondrichthyes
Class Chondrichthyes
  • Members of class Chondrichthyes have a skeleton that is composed primarily of cartilage.
  • The cartilaginous skeleton evolved secondarily from an ancestral mineralized skeleton.
subclass elasmobranchii
Subclass Elasmobranchii
  • The largest and most diverse subclass of Chondrichthyes, Elasmobranchii, includes the sharks and rays.
subclass elasmobranchii26
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.
    • Placoid scales.
    • The upper & lower jaws have a front, functional row of teeth and several developing rows growing behind as replacements.
subclass elasmobranchii27
Subclass Elasmobranchii
  • Spiral valve in intestine slows passage of food and increases absorptive area.
  • Large fatty liver aids in buoyancy.
subclass elasmobranchii acute senses
Subclass Elasmobranchii– Acute Senses
  • 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 elasmobranchii29
Subclass Elasmobranchii
  • All chondrichthyans have internal fertilization.
  • Oviparous 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 elasmobranchii30
Subclass Elasmobranchii
  • Ovoviviparous species retain developing young in the uterus while they are being nourished by the yolk.
subclass elasmobranchii31
Subclass Elasmobranchii
  • In viviparous species, young receive nourishment from the maternal bloodstream through a placenta, or from nutritional secretions produced by the mother.
    • Some receive additional nutrition by eating eggs & siblings.
  • Parental care ends as soon as eggs are laid or young are born.
subclass elasmobranchii32
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 elasmobranchii33
Subclass Elasmobranchii
  • Stingrays have a slender whip-like tail with one or more saw-edged spines with venom glands at the base.
  • Electric rays have large electric organs that can discharge high-amperage, low voltage current into the surrounding water.
subclass holocephali
Subclass Holocephali
  • A second subclass is composed of a few dozen species of chimaeras, or ratfishes.
    • Flat plates instead of teeth.
    • Upper jaw fused to cranium.
osteichthyes
Osteichthyes
  • Osteichthyes are the bony fishes.
    • Bone replaces the cartilage during development.
    • A swim bladder is present for controlling buoyancy and respiration in some.
    • Not a monophyletic group.
osteichthyes36
Osteichthyes
  • Fishes breathe by drawing water over four or five pairs of gills located in chambers covered by a protective bony flap called the operculum.
class actinopterygii
Class Actinopterygii
  • Ray-finned fishes (class Actinopterygii) contain all the familiar bony fishes – more than 23,600 species.
class actinopterygii38
Class Actinopterygii
  • The fins, supported mainly by long, flexible rays are modified for maneuvering, defense, and other functions.
class actinopterygii39
Class Actinopterygii
  • Two main groups of ray-finned fishes.
    • Chondrosteans (e.g. sturgeons) have heterocercal tails and ganoid scales.
class actinopterygii40
Class Actinopterygii
  • Neopterygians – one lineage of early neopterygians led to the modern bony fishes (teleosts).
  • Early type neopterygians include the bowfin and gars.
class actinopterygii41
Class Actinopterygii
  • The major lineage of neopterygians are teleosts, the modern bony fishes.
    • Changes in fins increased maneuverability and speed.
    • Symmetrical, homocercal, tail allows increased speed.
teleosts
Teleosts
  • Thinner, lighter cycloid and ctenoid scales replace the heavy dermal armor of primitive ray-finned fishes. Some (e.g. eels) lack scales.
teleosts43
Teleosts
  • Fins diversified for a variety of functions: camouflage, communication, complex movements, streamlining, etc.
teleosts44
Teleosts
  • The swim bladder shifted purpose from primarily respiratory to buoyancy.
  • Gill arches in many diversified into pharyngeal jaws for chewing, grinding, and crushing.
class sarcopterygii
Class Sarcopterygii
  • Lobed-finned fishes (class Sarcopterygii) include 2 species of coelacanths and 6 species of lungfishes.
    • This group was much more abundant during the Devonian.
    • Rhipidistians are an extinct group of sarcopterygians that led to tetrapods.
class sarcopterygii46
Class Sarcopterygii
  • All early sarcopterygians had lungs as well as gills and a heterocercal tail.
    • Later sarcopterygians have a continuous flexible fin around the tail.
  • They have fleshy, paired lobed fins that may have been used like legs to scuttle along the bottom.
class sarcopterygii47
Class Sarcopterygii
  • Some lungfishes can live out of the water for long periods of time.
    • During long dry seasons, the African lungfish can burrow down into the mud and secrete lots of slime forming a hard cocoon where they will estivate until the rains return.
class sarcopterygii48
Class Sarcopterygii
  • Coelocanths arose during the Devonian and peaked (max. species) in the Mesozoic.
    • One genus, two species currently.
    • Believed to be extinct for 70 million years, rediscovered in 1938.
      • The second species was discovered in 1998.
locomotion in water
Locomotion in Water
  • Fishes use trunk and tail musculature to propel them through the water.
  • Musculature is composed of zigzag bands called myomeres.
locomotion in water50
Locomotion in Water
  • Flexible fishes like eels use a serpentine movement.
    • Not very efficient for high speed.
  • Fast swimmers are less flexible.
    • Body undulations limited to caudal region.
locomotion in water51
Locomotion in Water
  • Many fast swimmers are streamlined with grooves so their fins can lie flat.
buoyancy
Buoyancy
  • Sharks must move constantly to avoid sinking.
    • The heterocercal tail provides lift as it moves from side to side.
    • Broad head and angled, stiff fins add lift.
    • Their large livers with fatty hydrocarbons aid in buoyancy as well.
      • Liver is like a large sack of buoyant oil.
buoyancy53
Buoyancy
  • Bony fishes use a gas-filled space to regulate buoyancy – the swim bladder.
    • Derived from a pair of lungs.
    • Swim bladders are absent in tunas, abyssal fishes, many bottom dwellers.
    • Bony fishes will sink without the swim bladder because they are denser than water.
buoyancy54
Buoyancy
  • Fishes must be able to regulate gas inside the swim bladder.
    • At depth, the gas will compress and the fish will sink.
    • As it rises to the surface, the gas will expand and the fish will rise faster.
  • Gas may be removed in two ways.
buoyancy55
Buoyancy
  • Physostomous fishes (more primitive, e.g. trout) have a pneumatic duct that connects the swim bladder and the esophagus.
    • Air can be expelled through the duct.
    • Gas must be secreted into the swim bladder from the blood, although some species can gulp air to fill the swim bladder.
buoyancy56
Buoyancy
  • Physoclistous fishes (more derived, e.g. advanced teleosts) the pneumatic duct has been lost. Gas must be absorbed by blood from the highly vascularized ovale.
    • Gas is secreted into the swim bladder from the blood at the gas gland.
hearing
Hearing
  • The bodies of fishes are nearly the same density as water.
    • Makes hearing difficult.
  • Weberian ossicles, found in minnows, suckers, & catfish, improves hearing.
  • Sound detection starts in swim bladder (sound vibrates easily in air) and is transmitted to the inner ear by Weberian ossicles.
respiration
Respiration
  • Fish gills are composed of thin filaments covered with an epidermal membrane that is folded into lamellae.
    • Richly supplied with blood vessels.
    • Located inside the pharyngeal cavity.
    • Covered with an operculum in bony fishes.
    • Elasmobranchs have gill slits.
respiration59
Respiration
  • Water must be continuously pumped over the gills.
  • A countercurrent system is found where the flow of water is opposite to the flow of blood.
    • Deoxygenated blood encounters the freshest water with the highest oxygen content.
osmotic regulation
Osmotic Regulation
  • Freshwater fishes (hyperosmotic regulators) must have a way to get rid of water that enters their bodies by diffusion through the gills.
    • Water enters the body, salts are lost by diffusion.
    • Water is pumped out by the opisthonephric kidney which can form very dilute urine.
    • Salt absorbing cells in the gill actively move salt from the water into the blood.
osmotic regulation62
Osmotic Regulation
  • Saltwater fishes (hypoosmotic regulators) have a lower blood salt concentration than the seawater.
    • Tend to lose water and gain salts.
    • Marine teleosts drink seawater.
    • Salts are carried by the blood to the gills where they are secreted out by salt-secretory cells.
    • Other salts are voided with feces or excreted by the kidney.
feeding behavior
Feeding Behavior
  • Most fishes are carnivores and prey on everything from zooplankton to large vertebrates.
    • Some deep-sea fishes can eat victims twice their size – an adaptation to scarce food.
    • Most fishes can’t chew with their jaws (this would block water flow over the gills), many have pharyngeal teeth in their throats.
    • Large-mouthed predators can suck prey in by suddenly opening their mouths.
feeding behavior64
Feeding Behavior
  • Herbivorous fishes eat plants and micro-algae.
    • Most common on coral reefs – parrotfishes, damselfishes, surgeonfishes.
    • And tropical freshwater habitats – minnows, characins, catfishes.
feeding behavior65
Feeding Behavior
  • Suspension feeders filter microorganisms from the water using gill rakers.
    • Herring-like fishes are common – menhaden, herring, anchovies etc.
    • Many larval fishes.
    • Basking sharks.
  • Most are pelagic fishes that travel in large schools.
feeding behavior66
Feeding Behavior
  • Other groups are scavengers that eat dead and dying animals,
  • Detritivores that consume fine particulate organic matter,
  • Parasites that consume parts of other live fishes.
migration
Migration
  • Freshwater eels are catadromous, they enter the ocean as adults, migrate to a spawning area where they spawn & then die.
  • Larvae make their way back to the streams – only females enter the streams.
migration68
Migration
  • Anadromous salmon spend their lives at sea, returning to freshwater to spawn.
    • Die after spawning.
  • Strong homing instinct brings them to their parent stream.
    • Guided by odor of parent stream.
reproduction
Reproduction
  • Most fishes are dioecious with external fertilization and external development – oviparity.
  • Ovoviviparous species (guppies, mollies, surfperches) bear live young after development in the ovarian cavity of the female.
reproduction70
Reproduction
  • Fertilized eggs may be pelagic and hatch into pelagic larvae.
  • Large yolky benthic eggs are often attached to vegetation or deposited in nests, buried, or even carried in the mouth.
    • Many benthic spawners guard their eggs.
      • Usually the male.
reproduction71
Reproduction
  • In some species, males defend nest sites and perform courtship rituals to entice females to lay their eggs in his nest. Sometimes, several females will lay eggs in a nest.
    • The male will guard the eggs from predators and will also fan them with his fins to aerate them.
growth
Growth
  • Larvae may depend on the yolk sac until their mouths and digestive systems are fully developed.
    • Larvae then forage for their own food.
growth73
Growth
  • Larvae metamorphose into juveniles with body shape & color patterns usually similar to the adults.
    • Some species have different color patterns in juveniles.

French Angelfishes (Pomacanthus paru) juvenile (left) and adult (right).

growth74
Growth
  • Growth is temperature dependent.
    • Fish grow faster in summer when the temperature is warm and food is plentiful.
    • Growth may nearly cease during the winter.
    • Annual rings in scales, otoliths, and other bony parts reflect seasonal growth.
    • Fish continue to grow throughout life.
      • Larger fishes produce more gametes.