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The Fishes
Phylum Chordata
Subphylum Vertebrata
Classification has changed in the last few years (and will probably continue to do so); we will use classification that our book uses – see p. 540 (124)
See p. 509 (93) for “Traditional Linnean Classification”; you will see some of these names used as synonyms in other books.
Below are some terms commonly used (some used to be names of superclasses or some kind of taxonomic groupings) (see also cladogram of fishes on p. 517 (101) and also cladogram of living members of Phylum Chordata on p. 499 (83):
Chordata = animals with notochord at some stage in the life cycle
Euchordata = chordates that retain an axial skeleton throughout life
Craniata = Euchordates with a cranium = Vertebrates
Gnathostomata = Craniata with jaws
Agnatha = fish with no jaws (jawless)
Teleostomi = bony fishes + tetrapods
Tetrapoda = four-limbed vertebrates
Osteichthyes = bony fishes
Amniota = tetrapods with embryos having extraembryonic membranes
Protochordata = includes the Subphylum Urochordata and Subphylum Cephalochordata
1. Agnatha (jawless) - lampreys, hagfishes
- no jaws, lack scales; notochord persists (is cartilaginous - it does not become bone); paired fins absent, median fins only (2 dorsal, 1 ventral); gill apertures or openings (pharyngeal gill slits); skeleton is cartilaginous
- ammocoete larva= eel-like larval stage of lamprey which lives in streams and burrows in a sand/mud bottom and filter feeds on minute food particles
- both ectoparasitic and free-living species
- heart has 1 atrium, 1 ventricle (hagfish has 3 accessary hearts)
- digestive system without stomach; intestine has spiral valve and cilia (in lampreys only)
- reproduction - external fertilization; both kinds of gonads are in each animal, but only 1 set works (so they are not considered hermaphroditic)
- kidneys - mesonephric kidney in lampreys; pronephric kidney anteriorly and mesonephric kidney posteriorly in hagfishes
- have single median nostril
Superclass Myxinomorphi
1. Class Myxini (hagfishes) – hagfishes are an entirely marine groups that feeds on annelids, molluscs, crustaceans, and dead/dying fish, etc.; so they are predators or scavengers, NOT parasitic like some lamprey species; isosmotic to sea water like marine invertebrates; they have the ability to secrete copious amounts of mucus; biology is still largely unknown; characteristics are on p. 519 (103)
Superclass Petromyzontomorphi
2. Class Petromyzontida (old Class = Cephalaspidomorphi ) (lampreys) - many are parasitic; they attach to a fish by their suckerlike mouth, then rasp a hole in the fish and suck the body fluids of the fish; sea lampreys caused much damage to the fish populations in the Great Lakes after the Welland Ship Canal was put in (in 1829) and deepened between 1913 and 1918, but serious problems with sea lampreys were not evident until about the 1940's-1950's
- marine forms are anadromous , i.e., they leave the sea where they spend their adult lives and go up freshwater rivers and streams to spawn; characteristics are on p. 520 (104)
Superclass Gnathostomata - have jaws; have paired limbs or fins
1. Class Chondrichthyes - cartilaginous skeletons; characteristics are on p. 522 (106)
a. Subclass Elasmobranchii - sharks, skates, rays; they retain urea and nitrogenous wastes to prevent water from being drawn out
- know shark structures and functions from lab
South Africa - they have found more since then; they are usually in deep water and don't come into contact with humans that often
coelacanth - has an important evolutionary position; the lobe-finned fishes had lungs and gills (an advantage in the Devonian - when they had alternating droughts and floods) - they used their strong lobed fins to get from pool to pool of water
2) Lungfishes - 3 genera alive today
a) Neoceratodus sp. - Australian lungfish - can survive in stagnant, oxygen-poor water by coming to the surface and gulping air into their single lung - can't live long out of water; normally relies on gill breathing
b) Lepidosiren sp. - South American lungfish - can live outside of water for long periods of time
c) Protopterus sp. - African lungfish; burrows down at the approach of the dry season - secretes slime - mixes it with mud to make a hard cocoon - then animal estivates until it rains
Structural and Functional Adaptations of Fishes
1. Locomotion in Water
- zigzag muscle bands (called myomeres)- muscles contract on one side of the fish, then on the other; sort of like "serpentine movement"
- swimming is most economical form of animal locomotion
- fish create virtually no turbulence (slime layer, texture of their surface, and body bend all contribute)
2. Neutral Buoyancy and the Swim Bladder
a. sharks - most species must keep swimming in order not to sink; sharks have no swim bladder, but they don't sink to the bottom and stay there because of the following features:
- heterocercal tail gives uplift to tail; broad head and flat pectoral fins provide head lift; they also have large livers with a special fatty hydrocarbon called squalene - has density of only 0.86 - so the liver acts like a large sack of buoyant oil
b. bony fish - most have a swim bladder; it arose from paired lungs of primitive Devonian freshwater bony fishes (most of which probably had lungs)
- swim bladder is absent in flounders, sculpins (bottom dwellers)
- swim bladder - must be able to adjust volume of air
- less specialized fish (e.g., trout) - have pneumatic duct which connects the swim bladder to the esophagus; these fish can gulp air at the surface
- some fish species have lost the pneumatic duct - they get gas from blood; they have a gas gland (gg) which secretes gas into the bladder; they have have a resorptive area or "ovale" that can remove gas from bladder
- gg has rete mirabile (rm) - means "marvelous net" - it is a capillary bed that transfers gas (especially oxygen) from blood to swim bladder
- how system works: gg secretes lactic acid into the blood; the high localized acidity in rm forces hemoglobin to release oxygen; rm picks up oxygen; oxygen pressure increases and oxygen diffuses into swim bladder 3. Respiration - fish have gill lamellae and operculum
- pathway of water: mouth--> gills--> operculum
- countercurrent flow - flow of water is opposite to the
- water tends to go into fish and salt is lost by diffusion outward; freshwater fish are hyperosmotic regulators - excess water is pumped out with mesonephric kidney which forms very dilute urine; also have a special salt-absorbing cells in gill epithelium which move salt ions (mainly Na+, Cl-) from water to blood
b. in marine fish:
- marine fish tend to lose water and gain salt (they are called hypoosmotic regulators ); to compensate, they drink salt water (to get water), then excrete the salt out with special salt-secretory cells in the gills; some salt goes out with feces, some by kidney, also 7. Feeding Behavior
- most fish are carnivorous; some are herbivores, some filter feeders (e.g., herring, anchovies); some scavengers, omnivores
Know kinds of tails and examples of fish that have them (Fig. 24-16); same for kinds of scales (Fig. 24-17).
The following notes are NOT REVISED as of 22 January 2009
The Fishes (Student Handout) Updated 2/26/98 -1- Subphylum Vertebrata
1. Superclass Agnatha (jawless) - lampreys, hagfishes
- no jaws, lack scales; notochord persists (is cartilaginous- it does not become bone); paired fins absent, median fins only (2 dorsal, 1 ventral); gill apertures or openings (pharyngeal gill slits); skeleton is cartilaginous
- ammocoete larva- eel-like larval stage of lamprey which lives in streams and burrows in a sand/mud bottom and filter feeds on minute food particles
- both ectoparasitic and free-living species
- heart has 1 atrium, 1 ventricle (hagfish has 3 accessary hearts)
- digestive system without stomach; intestine has spiral valve and cilia (in lampreys only)
- reproduction - external fertilization; both kinds of gonads are in each animal, but only 1 set works (so they are not considered hermaphroditic)
coelacanth - has an important evolutionary position; the lobe-finned fishes had lungs and gills (an advantage in the Devonian - when they had alternating droughts and floods) - they used their strong lobed fins to get from pool to pool of water
- Lungfishes - 3 genera alive today 1) Neoceratodus sp. - Australian lungfish - can survive in stagnant, oxygen-poor water by coming to the surface and gulping air into their single lung - can't live out of water 2) Lepidosiren sp. - South American lungfish - can live outside of water for long periods of time 3) Protopterus sp. - African lungfish; burrows down at the approach of the dry season - secretes slime - mixes it with mud to make a hard cocoon - then animal estivates until it rains
b. Subclass Actinopterygii - "ray-finned" fishes
- about 24,600 species - teleost fish (Division Teleostei) -modern bony fishes
- cycloid or ctenoid (comblike ridges on exposed edge) scales; some lack scales
- most have homoceral tail
- lungs of primitive forms have been transformed into swim bladder
- many have spines
- know yellow perch structures and -3- functions from lab (Fig. 27-15)
**Structural and Functional Adaptations of Fishes
- Locomotion in Water**
- zigzag muscle bands (called myomeres)- muscles contract on one side of the fish, then on the other; sort of like "serpentine movement"
- swimming is most economical form of animal locomotion
- fish create virtually no turbulence (slime layer, texture of their surface, and body bend all contribute) 2. Neutral Buoyancy and the Swim Bladder a. sharks - most species must keep swimming in order not to sink; sharks have no swim bladder, but they don't sink to the bottom and stay there because of the following features:
heterocercal tail gives uplift to tail; broad head and flat pectoral fins provide head lift; they also have large livers with a special fatty hydrocarbon called squalene - has density of only 0.86 - so the liver acts like a large sack of buoyant oil
b. bony fish - most have a swim bladder; it arose from paired lungs of primitive Devonian freshwater bony fishes (most of which probably had lungs)
- swim bladder is absent in flounders, sculpins (bottom dwellers)
- swim bladder - must be able to adjust volume of air
- less specialized fish (e.g., trout) - have pneumatic duct which connects the swim bladder to the esophagus; these fish can gulp air at the surface
- some fish species have lost the pneumatic duct - they get gas from blood; they have a gas gland (gg) which secretes gas into the bladder; they have have a resorptive area or "ovale" that can remove gas from bladder
- gg has rete mirabile (rm) - means "marvelous net" - it is a capillary bed that transfers gas (especially oxygen) from blood to swim bladder
- how system works: gg secretes lactic acid into the blood; the high localized acidity in rm forces hemoglobin to release oxygen; rm picks up oxygen; oxygen pressure increases and oxygen diffuses into swim bladder 3. Respiration - fish have gill lamellae and operculum
- pathway of water: mouth--> gills--> operculum -4-
- countercurrent flow - flow of water is opposite to the direction of the blood flow; some fish can extract up to 85% of the oxygen passing over gills
- ram ventilation - very active fishes (e.g., mackerel, herring) have to swim continuously to force water into the mouth 4. Migration
- eel -- read in book; eels are catadromous , i.e., they spend most of their lives in freshwater, then migrate to the sea to spawn
- homing salmon - anadromous (adults live at sea but return to freshwater to spawn)
- Atlantic salmon and steelhead trout -- can spawn for several years
- Pacific salmon (e,g., king, sockeye, silver, humpback, chum, Japanese masu) - make 1 spawning run then die
- salmon seem to imprint on odors of parent stream, but they are not sure how they get from open areas back to coast; maybe they use currents, temperature gradients, food availability) 5. Reproduction and Growth
- some species are dioecious (separate sexes), have external fertilization, external development, i.e., oviparous (egg-producing)
- ovoviparous - (live egg-producing) - guppies, mollies -
