Compare to Chondrichthyes Difference in skeletal system

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Bony fish

    1. Compare to Chondrichthyes

      1. Difference in skeletal system (bone vs. cartilage)

      2. Swim bladder vs. oil in liver

    2. First appeared near the end of the Silurian Period

    3. But Devonian Period is known as the age of fishes

    4. Major radiation within this period

    5. By mid-Devonian, two major lineages diverged (SubClasses)

      1. Actinopterygii (ray-finned fishes)

      2. Sarcopterygii (lobe-finned fishes; gave rise to tetrapods)

        1. Lungfish

        2. Coelocanths

  1. Major characteristics of bony fish (shared, derived characters = synapomorphies)

    1. Unique pattern of dermal head bones, including mouth bones with rooted teeth

    2. Bony fin rays supporting fins

    3. Differentiation of branchial muscles

    4. Shared, derived characteristics (= synapomorphies) of Sarcopterygii

      1. Fleshy pelvic and pectoral fins with

        1. Single basal skeletal element

        2. Central supporting elements

        3. Muscular lobes

      2. Differences in hard materials of scales and teeth

      3. Unique characteristics of jaws, gill supports, etc.

    5. Shared, derived characteristics (= synapomorphies) of Actinopterygii

      1. Pectoral fin

        1. Multiple enlarged basal elements

        2. Elements supporting fin rays don’t extend into fin

        3. Single dorsal fin

        4. Unique arrangement of scales

  1. General features of Osteichthyes (does not matter whether primitive or derived)

    1. Fully calcified body skeleton

    2. Dermal armor is reduced to relatively thin, interlocking scales

      1. Usually of elasmoid type (lamellar bone only)

      2. But also ganoid (gars) with lamellar bone and a form of enamel called ganoine

      3. Cosmoid (Sarcopterygii) with two bony layers plus dentine and enamel

    3. Bony operculum covers single gill opening

    4. Lung or swim bladder derived from the gut present

  1. Distribution and diversity

    1. Sarcopterygii has seven living species

      1. Seven living species of lungfish

        1. Size range from 17 inches to 6.5 feet

        2. Strictly freshwater, found in Africa (5 spp), South America (1sp), Australia (1 sp)

          1. Gondwanan distribution

          2. Best explained by continental drift

        3. In African and SA species, gills reduced; breath air only through lungs (though some transfer at gills); Australian species retains functional gills

        4. African and SA species live in shallow waters, and can aestivate in burrows for long periods during dry season

        5. Australian species lives in more open waters and can only survive limited periods of moderate habitat desiccation

      2. Coelocanth (Latimeria chalumnae)

        1. Considered a 400 million year old living fossil

        2. Found off South Africa, Mozambique, Madagascar; recently one taken from Indonesia

        3. Seem to prefer relatively deep, cold waters with rocky, steep shores

        4. Grow to about 6', 140 lbs

        5. Ovoviviparous, with 20-65 developing eggs and 5-26 young born after gestation period of about 13 months

        6. Note combination of low reproductive rate and narrow habitat preferences make them vulnerable to over-exploitation

        7. Once thought to have gone extinct with the dinosaurs 65 million years ago, the Coelacanth was "discovered" alive and well in 1938

          1. Fishermen brought one to the surface in 1938 off the coast of Africa in the Indian Ocean

          2. It was buried beneath the rest of the catch (sharks and rays), but someone noticed the unusual blue fin

          3. A knowledgeable observer preserved it, but all innards thrown away

          4. Didn’t see another one until 1952, even though had people looking in deep sea and rewards posted around all local villages

          5. Local fisherman caught one on a hand line (5 feet) and notified the local scientists

          6. Everything was preserved and scientists published the account in journals

          7. The fish actually didn’t inhabit the deep oceanic water that people thought – much shallower

          8. In 1998, another find in Indonesia – appears to be a new species based on DNA evidence

    1. Actinopterygii

      1. Bichirs & reedfish = 11 living species; African fresh-water

      2. Sturgeons (27 species)

        1. Fresh and coastal marine waters of Europe, Asia, NA; many anadromous

        2. Bottom feeders (but not scavengers), with fleshy barbels below jaw to help search bottom sediments for food

        3. Unique rows of bony plates (5) along body

        4. Largest fresh-water fish = beluga sturgeon of SE Europe, said to reach length of 8 m and wt. of 2,865 lbs – most famous of caviar sturgeons

        5. Sturgeons are source of caviar, but also used for meat, oil, swim bladder used to produce a product (sheet of almost pure gelatin used for glues, waterproofing, and clarifying white wine)

      3. Paddlefishes

        1. 2 living species, one NA (mostly Mississippi river system) and Chinese

        2. Largely scaleless

        3. Elongate snouts make up 36 - 52% of total length

        4. Snout covered with electroreceptors used to detect swarms of zooplankton, upon which it filter feeds

      4. Bowfin: 1 species, from large rivers of E. NA

Short heterocercal caudal fin. , Long dorsal fin base with about 48 dorsal rays. , Swim bladder capable of respiratory function. , About 90 cm maximum length.

      1. Gars: 7 species; mostly freshwater from eastern NA south to about Costa Rica, but sometimes found in brackish coastal waters

        1. Uniquely elongated snout: elongation is between eyes and nose (rather than in front of nose, as in paddlefish and other beak fish), so nostrils at tip of “beak”

        2. Lurking ambush predators, with dorsal and anal fins displaced posteriorly to increase thrust

        3. Ganoid scales not found in many/any other groups

      2. Teleost fish

        1. Approximately 20,800 species

        2. Worldwide, in virtually every type of aquatic habitat

        3. Two largest groups

          1. Catfish & minnows: just over 6,000 species

          2. Perches: ~ 7,800 species

    1. Convergent evolution that makes this group extremely successful

      1. Increased locomotor efficiency

        1. Swim bladder provides precise buoyancy regulation

        2. Symmetrical, more flexible caudal fin provides better forward thrust and maneuverability

        3. Fins released from need to control lift (because of a and b)

          1. Can be folded to body during rapid locomotion, reducing drag

          2. Can be modified to serve a variety of other functions

        4. Reduction in dermal armor to thin scales reduces weight, increases flexibility of body, fins, etc.

      2. Increased complexity and efficiency of feeding apparatus (face, jaws, skull and associated musculature)

        1. Increase in the number of mobile joints between the bones of the jaws, face, etc

        2. Increase in both subdivision of muscles (to control increased number of joints, greater precision of movement) and size (and, therefore, strength) of jaw-closing muscles

        3. Mobile, tooth-bearing pharyngeal jaws

        4. Results include

          1. Highly protrusible jaws provide very strong , directional suction for feeding from a variety of places relative to fish’s mouth (i.e., above, in front, below, to side, etc.)

          2. Flexibility of joints permits mouth to close while buccal cavity still expanded to trap prey inside mouth

          3. Pharyngeal jaws help trap food in mouth, and provide very strong grinding surfaces for dealing with a wide range of food types

          4. Mobile jaws with fine motor control permit delicate movements and manipulation of environment (for feeding and for other functions – jaws become like our hands)

        5. Net result has been huge radiation into numerous ecological niches and virtually every aquatic habitat

    1. Example of adaptability of bony fish – deep sea fishes

      1. Epipelagic zone = upper waters where photosynthesis takes place

      2. Mesopelagic zone = waters between 100 - 1000 m

      3. Bathypelagic zone = waters below 1000 m

      4. Most important feature of deep-sea environment is lack of food

        1. Water is too deep for light to penetrate (no photosynthesis)

        2. Only food is detritus “rain” from surface waters; this declines rapidly with depth

        3. Productivity (and therefore species diversity) in deep-sea environments is greatest in tropical regions in areas of upwelling

      5. Adaptations of deep-sea fish

        1. Five orders of fish have species adapted to deep-sea environments

        2. In general, as depth increases, get decrease in size, abundance, and diversity of fish

          1. 800 species of mesopelagic fish

          2. 150 species of bathypelagic fish

        3. Because food is limited, many adaptations of deep-sea fish are related to obtaining and conserving energy

          1. Species generally adopt “low energy” habits – e.g., little long-distance movement, sit-and-wait predation

          2. Because locomotion is limited, axial skeleton and muscle mass are both reduced

          3. Because no light (or very limited light) is present, most have bioluminescence produced by photophore organs; this can serve to

            1. Lure prey

            2. Identify species and gender (very important when densities are low)

          4. Jaws are generally very large relative to body size and gut is hugely distensible

          5. Allows individuals to take and store whatever prey they encounter

    1. Conservation

      1. Fresh-water fish

        1. 40% of fish species live in fresh water habitats

        2. Nearly all have been affected by habitat alteration, degradation (including introduction of exotic species), and loss

        3. In US alone, 20% of 800 species of native freshwater fish are currently facing some significant threat

        4. Worldwide scope of the problem is probably greater

      2. Marine fish

        1. Biggest problem that we know about (for obvious reasons!) is with commercially valuable fish

        2. One major problem is that it’s hard to predict future stock size based on current stock size (abundant juveniles may not produce abundant adults; sometimes a small breeding population can produce a relatively large adult population) – so managing commercial fisheries well is difficult

        3. Overfishing is a huge problem, partly because of difficulty in managing stocks and partly because of socioeconomic issues

          1. See in many species of swordfish, which led to a boycott by elite restaurants and chefs 4 years ago

          2. Also see in orange ruffy

            1. One of most desired fish in most restaurants

            2. Light and delicate flavor

            3. Problem is that don’t reproduce until 20-25 years old

            4. Can live to 100 years old

            5. Very low reproduction

            6. And attain full growth before reproduce

            7. So many taken before reproduce

      3. Coral reef fish

        1. Confined to warm, shallow tropical waters) are the most diverse group of vertebrates on earth

        2. Diversity depends on the structural integrity of coral reef systems

        3. Problem is that coral reefs are

          1. Being destroyed directly by human activity (mined for limestone, broken up for harvest, blown up by people collecting for the exotic pet trade, etc.)

          2. Dying for other reasons – e.g., increasing water temperature has caused large-scale deaths of some reefs world wide


Refers to physiological behaviors that:

  • ensures the survival of portions of the eggs so that young can carry on the species;

  • involves the number of eggs produced and treatment of the eggs themselves - i.e. whether the eggs are placed in a nest or retained within the female;

  • physiological behaviors are taimed to lay eggs at the optimal time for survival

Most bony fishes are dioecious - separate male and female individuals
Some may be monoecious or hermaphroditic - individuals with both male and female gonads.
May be:
Synchronous - where the individual has ripe ovaries and testes at the same time
Consecutive hermaphrodites - first one sex and become the other with age or time

  • - protandrous: male first and then develop functional ovaries

  • - protogynous: female first

Most bony fishes internal fertilization but some do have internal fertilization by way of a gonopodium (intromittent organ)

Most species are oviparous but some are viviparous (~1%) or ovoviviparous

those that are viviparous are primarily guppies, top minnows, gambusia
eggs are mesolecithal (moderate amount of yolk) or megalecithel (heavily yolked) and

  • pelagic: float in H2O

  • dermersal: have a density greater than H2O and sink when released from female

The number of eggs produced is directly related to parental care - those with maximum parental care produce very few eggs

  • free-floating pelagic: ocean sunfish - 2.8 million eggs

  • bury but don’t guard: salmon - 5,000 eggs

  • builds nest and guards: stickleback - 60 eggs

Eggs may be laid under a number of situations:
nonguarders: eggs laid are not guarded by the parents

guarders: one or both parents tend the eggs once they are laid; will guard against predation and aerate the developing eggs

  • substratum choosers - don’t construct a nest but choose a substrate and guard the eggs

  • nest spawners - make a nest and guard the eggs


  • external bearers - mouth or pouch brooders

  • internal bearers - have internal fertilization; ovoviviparous or viviparous

Basic reproductive development:
anadromous: live at sea and swim upstream to spawn
catadromous: live in fresh water and spawn at sea


Greatest depth and width about 1/3 back from mouth
Mouth shape and position highly variable
Operculum (bony flap) covers gills - water enters mouth, passes through pharynx and across gills, exits through opercular opening
Tail terminates with bony or cartilaginous rays
Fins represented by single median caudal, dorsal (1-3), anal and adipose fins; paired pectoral and pelvic fins - fin location, size, and shape highly variable
Jaws developed from 1st and 2nd gill arches

  • 1st gill arch jaw arch; opening retained as spiracle in sharks, eustacean tubes in higher vertebrates

  • 2nd gill arch hyomandibular arch or tongue support

Chondrychthyes have non-overlapping dermal scales of modified bone

  • Placoid scales: plate-like; develop similarly to teeth with dentine covering - very hard and somewhat crystalline

Bony fishes carry a variety of overlapping scale types

  • Ganoid scales: rhomboidal scales coated with enameloid material secreted by epidermal cells - gars, ganoin absent on sturgeons

  • Ctenoid scales: posterior margin of the scale is toothed or comblike - spiny-rayed bony fishes

  • Cycloid scales: smooth, disc-like and more or less circular in outline - soft-rayed fishes

Simple two-chambered heart: sinus venosus leads into single atrium and ventricle
Heart pumps blood forward through ventral aorta into gill region and then through body
Single directional heart - blood only flows in one direction through heart and associated blood vessels
Afferent arteries - branch from ventral aorta through gill network
Efferent arteries - branch in both directions from gills to head and body: forward through internal carotids and back through dorsal aorta


Gills form pouches in Agnathans but lie in bands in chondrychthyes and bony fishes; supported by gill bars branching from expanded pharynx through to outside operculum
accessory breathing organs include:

  • developed lungs (lungfish): usually paired with reduced gills

  • others with complete and functional swim bladder (freshwater fish only): highly partitioned pouch off gut used to hold extra air when more active and water O2 content reduced - gulp air at surface

  • vascularized skin allows variable amounts of gas transport - up to 30% in some eels

  • gills can exchange gases for a limited period from air as long as they remain moist

Teleosts with pharyngeal diverticulum - long sacs from the head into the body which act similarly to lungs

  • gut also used as air absorbing mechanism by gulping air

  • some species gulp air from the immediate surface - tends to be better oxygenated

  • air transferred to various organs where oxygen uptake can occur

Swim/gas bladder located in the dorsal body cavity above all viscera except kidney, may be loose (catfish, carp) or firmly attached (perch-like fish)

  • advanced fish loose connection with pharynx with age

  • acts primarily as a hydrostatic organ to maintain the body at various levels in the water

  • may also function in sound reception or production

Sensory systems include taste, smell, sight, sound, and touch

touch through tactile receptors on body surface

taste and smell both by molecular receptors in mouth, nasal epithelium

  • choane secondary pouches on each side of the face not associate with the pharynx

  • acoustical/lateral line system receptor system with asymmetrical hair like protrusions - inhibition or stimulus of nerve endings dependent on direction of movement of hair cell capsule; very sensitive to fluid movement

hearing dependent upon membranous labyrinth

  • thin membranous tubes and sacs in rough 3-planar arrangement of semicircular canals which sense motion and maintain balance

  • Webberian ossicles associated with middle ear used to maintain balance - serves as  an indicator of age

sight well developed with size of eye directly related to  depth and loss of light intensity

  • deep sea fishes often with chemoluminescent organs to generate their own light

  • lens with bulge for better forward and upward vision

  • also with increased refractive index for increased light gathering capabilities

  • limited accommodation by moving the lens closer to or away from retina

  • some species with partitioning of the lens to vary direction/observation such as air/water

  • tapetum lucidum present behind retina of sharks to function like a mirror

electric organs modified muscle cells capable of creating electric potential, electric current discharge or light impulse to stun prey or scare away predators - Ampullae of Lorenzini to detect electrical fields

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