Phylum Chordata: Fishes

-Icthyology
- True fish is different from jellyfish, starfish, shellfish, etc.
- True fish is a gill-breathing, ectothermic, aquatic vertebrate that has fins, skin with scales in most cases
- They dominate the sea.
- Jawless fish such as hagfish & lampreys
- jawed fish are either cartilaginous or bony
-vertebral column replaced the notochord
-cranium enclose brain & spinal cord
-specialized sense organs with 3 portions of brain
-jaw with teeth
-pectoral & pelvic fins
-gills are most efficient respiratory structure in animal kingdom.
-excellent olfactory & visual senses.




Superclass Agnatha: Jawless fishes: Class myxini: hagfishes:

-Body eel-like, slender, naked skin
-no dorsal fin
- caudal fin extend anterioly along the dorsal surface
-heart with one atrium & one ventricle
-entirly marine feed in dead or dying fishes, annelids, molluscs, crustaceans
-Not parasitic nor predaceous
-No stomach, but have intestine
-almost completely blind, strong sense of smell & touch.
-generate great amount of slime
- development is direct
-Kidneys balance the blood to be isosmotic with sea water
-sexes are separate, external fertilization





Class Cephalaspidomorphi: (Petromyzontes): lampreys

-family Petromyzontidae
-Petromyzon marinus the destructive marine
-Not all of them are Parasitic.
-All lampreys ascend freshwater river or streams to breed.
-The marine forms are anadromous: means
-male build nest & fertilize the eggs in that nest.
-The adults die soon after spawning.
-larva resemble amphioxus
-3 to 7 years later they become adult.
-anticoagulant into the wound
-eel-like body
- skin instead no scales
-fibrous & cartilaginous skeleton
-tongue has teeth, well developed sucker
-seven pairs of gills.
-no stomach & there is intestine
-larva called ammocoete, external fertilization, sexes are separate.
S

uperclass Gnathostomata

Class Chondrichthyes: Cartilaginous fishes:

-

some calcification
-Not too diverse only 850 species. only 25 lives in freshwater
-well-developed sense organs
-Powerful jaws
- swimming musculative
- predaceous habits

Subclass Elasmobranchii: Sharks, Skates, & rays.

-carnivores
- dogshark order Squaliformes
-dangerous sharks: order Lamniforms.
-Carcharodon great white shark
-Isurus mako shark
-Galeocerdo tiger shark
- Australia than any other part of the world
-rostrum in front of mouth.
-heterocercal tail
-pectoral & pelvic fin
- dorsal & caudal fin
-clasper in male in pelvic fin
-five gill slits
-leathery skin covered with tooth-like placoid scales
-less accurate vision than other fishes
-great sense of smell
-neuromast are sensitive to vibrations
-The receptors, the ampullary organs of Lorenzini are in head
-Both upper & lower jaws have triangular teeth
-mouth ---> pharynx ---> open into separate gill slits
---> esophagus is short ---> j-shape stomach
---> intestine ---> rectum
-Chambers of heart are tandem






-fertilization internal
-gestation period up to 2 years the longest at any vertebrae
-ovoviviparous = embryos remain in shark's oviduct
-viviparous: placenta give the food to the fetus
-oviparous = when lay eggs after fertilization
-Parental care end after offspring is born
-Elasmobranchs retain nitrogenous compounds in blood to maintain their osmostic balance with sea water

Order

Rajiformes:


-Rays are specialized for benthic
-Large pectoral fins that are fused to head
-gill opening are under side of head
- mouth have teeth for crushing prey
- Electric rays have large electric organ on each side of the head


-Each organ is made up of disc like cells connected so when all of cells are discharged simultaneously a high current is produced.
-voltage is low output maybe several kilowatts
-used by ancient Egyptians

Subclass Holocephali:

-ratfish, rabbitfish, spookfish, ghostfish, these diverced from sharks lineage
-Antomically chimaeras is something between shark & bonyfish
-No tooth on jaw but plates
- upper jaw attached to cranium very unusual for fishes.
-omnivores



Class osteichthyes: bony fish

-

Bony fishes probably evolved from acanthodians
- operculum over the gill slits
-had lungs as accessory breathing
-Pectoral fins
-Pelvic fins smaller
- dorsal & anal median fins















-ray-finned fishes (Actinopterygii) includes modern bony fishes, largest radiation in vertebrate
-Fleshy-finned fishes (Sarcopterygii) includes lungfishes, & Coelacanth the ancestors of the tetrapods.
-Their tail is homocercal










-Skin has much gland with dermal scales & some without scale




-3 types of scales: ganoid, cycloid, ctenoid, no placoid









-mouth has teeth, some are toothless
-Red blood cells have nucleus
-Fertilization external
-larva may be different from adult

Subclass Actinopterygii:

Ray-finned Fishes:


- teleost
-extended mouth & a heterocercal tail
-more primitive forms have ganoid scales
-more primitive form have been replaced by right, thin cycloid & ctenoid scales
-These 2 look alike except that ctenoid scales have comblike ridges
- maybe adaptation to reduce friction
-All teleosts have homocercal tail
-Some teleosts have stout, sharp spines for defense mechanisms.
- telost are most diverse group of fishes

Subclass Sarcopterygii: Fleshy-finned fishes:

-only seven species.
-All of early sarcopterygians had lungs as well as gills, heterocercal tail
-diphycercal tail
-scales had dentine-like material called cosmine civered by enamel
-They took gulp of air by coming to top of water
-They lack internal nostril

Special characteristic of Fishes for being so successful:

locomotion in water:

-Larger the fish faster they can move.
-myomeres
-swimming is the most economical form of animal locomotion.
-energy cost per kilogram of:
1Kmsalmon0.39 Kcal
1Kmflyiny gull1.45 Kcal
1Km ground squirrel 5.43 Kcal

The Buoyancy & Swim Bladder:

-Shark must always move in order not to sink.
-Sharks also have large liver that have a lot of fat.

-

Swim bladder is gas-filled space.
-fishes that come to the surface (trout) have pneumatic duct that connects the swim bladder to esophagus.


Respiration:

-gills are cover by lamellae.
-operculum covers the gills.
-water moves from mouth to gills & out thru operculum.
-In elasmobranchs have gill slits instead of operculum.
-ram ventilation
-freshwater eel when make trips to the land use their skin as a source of respiration.

Osmoregulatory mechanisms:

-Salt concentration in freshwater is .001M to .005 M per liter
-Blood concentration in freshwater fishes is 0.2 to 0.3 M
- hyperosmotic
-So urine is very dilute
-There are salt absorbing cells in the gill more Na & Cl from water into the blood
-glomerulus actively reabsorb NaCl.
-In marine fish; gills secrete NaCl & get rid of MgSO4 magnesium sulfate from feces
- hyoosmotic regulator
- blood concentreation 0.3 to 0.4 M
- salt water about 1M
-glomerulus is reduced in size & excrete MgSO4 in urea & urea has little water
- They tend to lose water & gain salt
-In marine fish NaCl is filtered thru gills & move out thru gills.

Digestion & absorption:


-The number of fishes that eat plankton are most abundant.
-The food chain.
-Herbivores - omnivores - carnivores
- Scavenger - parasites - suspension feeders
-digestion & absorption
-Some have Pyloric ceca






Reproduction:

-Eels are catadromoussea
-Young eels are called elvers
-Salmon are anadromous
-They die after they spawn.
-Most fishes are dioecious with external fertilization.
-oviparous "egg producing"
-ovoviviparous "live egg-producing"
-viviparous "alive-producing"
-freshwater fishes produce fewer & larger eggs to increase chance of survival
-fish in temprate zone grow during summer & stop growing in winter
-some have annual rings in scale
-After they become adult they still grow in size







Evolution:

-Fishes descended from unknown free-swimming protochordate ancestor
-The earliest fishlike vertebrate branched to jawless aganthans & the jawed gnathostomes
-All other vertebrae came from one of these two group
-jawless group include ostracoderms extinct, hagfishes living, lampreyes living.
-agnathans have no vertebrae but they have cranium & many other homologies.
-The jawed fish are either cartilaginous or bony fishes.
-Cartilaginous fishes such as sharks, rays, & chimaeras lost heavy dermal armor & adopted to cartilage instead of bone.
-Bony fishes are dominating fish today.
-Two distinct lineages of bony fishes
A. ray-finned fishes subclass Actinopterygii
B.fleshy-finned fishes subclass Sarcopterygii sister group of tetrapods.
eg. lungfishes & coelacanth