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Chapter   6 - The Major Radiation of Fishes

CLASS OSTEICHTHYES

Carp and  Burrfish----photographs © 2001by Dr. Allan H. Chaney,  used  with permission

Characteristics

1. internal skeleton ossified (i.e., endochondral bone)
2. swim bladder or lung present
3. bony scales (ganoid, cycloid, ctenoid, or cosmoid)
4. gill slits covered by an operculum (single external gill opening)
5. late Silurian to Recent

Taxa

• 24,000 species of living bony fish include the ray-finned (Actinopterygii) and lobe-finned (Sarcopterygii) fishes [Table 6.1]

• bony fishes from SeaWorld

SUBCLASS ACTINOPTERYGII --- ray-finned fish

• Learn  more about ray-finned fish from the UCMP or from the Tree of Life.
• Learn about the anatomy of bony fishes from the Florida Museum of Natural History

Characteristics 

1. fins with multiple parallel endochondral supports [fin rays]
2. fins controlled by muscles in body wall
3. caudal fin primitively heterocercal with no epaxial lobe
4. hyostylic jaw support
5. internal nostrils absent
6. large eyes (primitively)
7. scales ganoid, cycloid or none
8. middle Devonian to Recent

Taxa

• the ray-finned fish are the majority of Recent vertebrates (around 24,000 species)

INFRACLASS CHONDROSTEI

• A paraphyletic group of primitive actinopterygians including the sturgeons and reedfish

Characteristics

1. vertebral centra not ossified
2. heterocercal caudal fin
3. large maxilla joining preoperculum
4. non-overlapping ganoid scales, usually rhombic in shape, connected by peg and socket joints
5.  heterocercal tail.

ORDER PALAEONISCIFORMES

1. extinct, mainly Paleozoic fishes such as Moythomasia [fig. 6-1e]
2. heavy ganoid scales
3. long maxilla integrated with cheek
4. strong heterocercal tail

ORDER POLYPTERIFORMES

1. 11 living species of reed fishes and bichirs, e.g., Polypterus [Fig. 6-6a] known from Africa
2. freshwater
3. elongate forms
4. dorsal fins with anterior spine run the length of the body
5. symmetrical caudal fin
6. ganoid scales
7. paired lungs
8. fleshy pectoral fin
9. the most primitive of living actinopterygians [contradicted by some molecular data]
10. a brief introduction from the Fort Worth Zoo
11. more information is available from Robinson Research World of Knowledge

ORDER ACIPENSERFORMES Cretaceous-Recent--25 living species northern hemisphere-freshwater and coastal scales reduced--in sturgeons (Acipenser) to 5 rows of bony scutes, in paddlefish (Polyodon) to a few at base of tail heterocercal tail mainly cartilaginous endoskeleton

Acipenser--note the bony scales and heterocercal tail

INFRACLASS NEOPTERYGII

1. separation of maxilla from cheek;  short jaws with a specialized support
2. the lower jaw articulates with the vertical quadrate [fig 6-5]
3. near symmetrical caudal fin
4. vertebral centra ossified

Taxa

• the paraphyletic holosteans and the teleosts

DIVISION HOLOSTEI

• Holosteans are a paraphyletic group including the gars, the bowfins.. They represent a grade of evolution characterized by a mobile maxilla that is hinged in front and freed from the crescent-shaped preoperculum; abbreviated heterocercal or externally symmetrical [but lacking hypurals] tail for more efficient forward drive; scales generally retain ganoin

ORDER LEPISOSTEIFORMES Characteristics gars--7 living species, e.g., Lepisosteus [fig 6-6d] heterocercal caudal fin  ganoid scales long snout with many teeth, voracious predators on small fish restricted to North America

ORDER AMIIFORMES

Characteristics

1. bowfins (Amia) [fig 6-6e] have a specialized double jaw joint involving the symplectic and the lower jaw, as well as the quadrate and articular
2. Cycloid scales cover body
3. Predator on smaller fish
4. Mississippi drainage of North America

DIVISION TELEOSTEI

Characteristics

1. 23,800 living species in 24 orders
2. ganoid scales absent, cycloid or ctenoid scales present
3. homocercal caudal fin with hypurals [expanded neural spines that make the tail symmetrical] and epurals
4. maxilla without teeth, mobile; often excluded by premaxillary from border of mouth
5. vertebral centra well ossified.

SUBDIVISION OSTEOGLOSSOMORPHA  [fig 6-7]

SUBDIVISION ELOPOMORPHA [fig 6-8a, b]

leptocephalus larva (6-8b); anguilliforms (true eels), tarpons

SUBDIVISION CLUPEOMORPHA [fig 6-8c]

herrings and allies
specialized for feeding on plankton

SUBDIVISION EUTELEOSTI

17,000 species in 375 families

Superorder Ostariophysi [fig 6-9]

• carp, minnows, catfish
• 80% of all freshwater fish
• specialized hearing system of modified cervical vertebrae, ribs and neural arches [Weberian apparatus, Fig. 6-9a]

Neoteleosts [Fig. 6-10]

Superorder Acanthopterygii

• the most successful fish, includes 15,000 species in 300 families in 13 orders, the most diverse is the Order Perciformes: there are 150 families and 7000 species of perch-like fish
• Protrusible mouth and suction feeding [Fig. 6-5]: maxillary completely excluded from jaw border, able to protrude their mouth in 5-10 milliseconds.
• pelvic fins are moved anteriorly, ventral to pectoral fins [prevents lifting as pectorals brake]
• swim bladder ductless.

SUBCLASS SARCOPTERYGII

• Learn  more about lobe-finned fish from the UCMP or from the Tree of Life.
• David Atkins, professor emeritus, George Washington University, chordate biology page on lobe-finned fish

Characteristics

1. paired fins that are fleshy, with muscular lobes at base and with only a single element articulating with girdles)
2. forearm with a single proximal element (humerus), followed by the homologs of the radius and ulna.
3. cosmine on scales and skull roof bones (cosmoid scales support a complex electrosensory system)
4. true enamel on teeth

Taxa

• the lobe-finned fish include the Dipnoi (lungfish), coelacanths (Actinistia), the extinct rhipidistian fish, and their descendants, the tetrapods

ORDER ACTINISTIA (Middle Devonian to Recent)

Characteristics

1. internal nares absent
2. numerous paired snout bones
3. vertebral column unossified
4. maxilla absent

Taxa

• Coelacanths (Fig. 6-3)
• Two living species are recognized.
• This group was thought to have gone extinct in the Cretaceous until a living coelacanth (Latimeria chalumnae) from the depths of the Indian Ocean off east coast of Africa was recognized in 1939. A second species has been found near Sulewesi in Indonesia.
• About 200 specimens have since been collected. The "coelacanth" gets up to 2 m. in length and lives at the bottom in 100-400 m of water. Coelacanths may have a well developed electric sense that is associated their predatory behavior.   They have recently been studied from a submersible and have been observed orienting with head down and tail up..
• The Coelacanth Rescue Mission presents: The Fish Out of Time
• Information about the original discovery by Majorie Courtney-Latimer from the Australian Museum Fish site.

SUBCLASS CHOANATA

Characteristics

external nostrils connected by a continuous passage to the internal nares (choana)

Taxa

lungfish, rhipidistians, and tetrapods

 

DIVISION RHIPIDISTIA (Devonian to Permian)

Characteristics

skull roof bones homologous with skull of tetrapods

proximal paired fin bones homologous with limbs of tetrapods

labyrinthodont teeth typically present

Taxa

includes two orders of lobe-finned fish close to the ancestry of the tetrapods - the Orders Osteolepidoidea (including Eusthenopteron) and Elpistostegida (=Panderichthyida) - and the tetrapods.

DIVISION TETRAPODA

tetrapods are weird lobe-finned fish that are adapted to life on land

Taxa

AMPHIBIA

AMNIOTA (mammals, reptiles, and birds)

ADAPTATIONS OF BONY FISHES

FISH LOCOMOTION

1. fish fins and locomotion
   1. anterior to posterior sequential contractions along one side of the body with simultaneous relaxation along other side [fig 6-11]
   2. propulsion from other fins than just the body [fig 6-13]
2. Functional Morphology of Fishes [fig. 6-13, 6-14]
   1. body shape and fin location highly variable
   2. body design for high speed swimming
      1. minimize surface area exposed to fluid: sphere
      2. minimize cross-sectional area pencil shape
      3. minimize retarding force: teardrop (torpedo) shaped = tuna
      4. also inset eyes and slime reduce friction
      5. small scales or scaleless
   3. forward thrust [Fig. 6-12]
      1. pitch - tilt up and down (around z axis)
         1. resisted by paired fins pectoral and/or pelvic;
      2. side to side
         1. roll (around x axis - long axis) and yaw (around y axis)
         2. resisted by dorsal, anal, and caudal
   4. undulatory and oscillatory motions of body and fins
      1. elongate undulating body of eels induces drag
      2. rapidly swimming fishes are proportionately shorter and less flexible
         1. force from anterior muscle segments is transferred from anterior muscle segments to caudal peduncle and tail
      3. caudal fin: heterocercal, homocercal
      4. aspect ratio [fig. ]
         1. AR = (caudal fin height)²/caudal fin area
         2. broad surface area powerful thrust; but high frictional drag
         3. high aspect ratio (and narrow caudal peduncle): rapid sustained propulsion
   5. pectoral and pelvic fins
      1. oscillatory motion; precise maneuverability, braking and turning
   6. dorsal and anal fins: can undulate for slow forward propulsion
   7. locomotor strategies [fig. 6-11; 6-13]
      1. cruising
         1. high aspect ratio; elongate, torpedo shape; high beat frequency; tuna cover large territory, encounter many prey; but with low success 15-20%
         2. red muscle: myoglobin, sustained activity, cruisers
      2. maneuverability
         1. slow moving; low aspect ratio; use paired fins for locomotion; pelvic anterior to pectoral
      3. acceleration
         1. moderately low aspect; use undulatory motion for rapid starts; torpedo shape; few prey available, 70-80% capture success
         2. white muscle: rapid contraction, easily fatigued, lungers
      4. generalists
         1. range of locomotive style; intermediate (40-50%) success

LIFE HISTORIES--extremely varied

1. Desert pupfish - live in isolated permanent springs in Western U.S. deserts.
2. migrators
   1. reproduction and food finding; cod swim upcurrent to deposit eggs;
      1. anadromous [salmon]: spawns in streams; spend most of their life in marine
      2. catadromous [Anguilla eels]: adults in freshwater, breed in the Sargasso sea
3. schooling
   1. common in many species
   2. vision and lateral line systems; reproduction, safety from predators
4. deep-sea species of bony fish [Figs. 6-17]
   1. Midwater (mesopelagic) Fish [Dysphotic and Aphotic Zones 100-1000m],
      1. small size, large mouths and teeth; 100 X more light sensitive than humans, large eyes; 80% with photophores (light producing organs), bioluminescence: produced by bacteria; ascend closer to surface at night [fig 6-18] to feed; vast schools of small fish provide food for tuna, dolphins, etc.
   2. bathyl & abyssalpellagic: 
      1. 75% of ocean, many blind, mainly small predaceous fish; bizarre fish w/warning devices, long teeth, expandable stomachs [fig 6-20]. angler fishes with parasitic males.
5. Antarctic ice fish - lives in water so cold that it does not need hemoglobin to bind oxygen.
6. Fishes in Coral Reef Communities [Fig. 6-21]

Bioluminescence

1. luciferin and luciferase
2. produce light with 99% efficiency
3. bacteria, dinoflagellates & organisms that feed on them (ctenophores, jellyfish)
4. photophores (light producing organs)

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