Ch: 24 - Fishes

Chordates

deuterostome coelomates, 4 features - nerve cord, notochord, pharyngeal slits, postanal tail, can be divided into 3 clades: Urochordata, cephalochordata (nonvertebrates), craniata (vertebrates)

Urochordates

tunicates

Urochordates characteristics

larvae are tadpolelike and have notochord and nerve cord - free swimming but do not feed, adults typically lose the tail and notochord, are immobile filter-feeders, many secrete a tunic (cellulose sac) that surrounds the animal

Cephalochordat

lancelets

Cephalochordata characteristics

scaleless chordates, notochord persists throughout animal’s life, have no distinguishable head, feed on plankton using cilia-generated currents, closest relatives to vertebrates

Craniata

animals with a cranium

Myzinoidea

hagfishes

Myzinoidea characteristics

60 species, all marine, maintain same internal salt concentration as seawater, degenerate eyes, no vertebrae, feed on dead and dying fish, produce slime as defense; can tie themselves in a knot to clean slime off, leathery skin used to make various products

Subphylum vertebrata characteristics

neural crest: a unique group of embryonic cells tha forms many vertebrate structures, internal organs: liver, kidneys, endocrine glands, heart and closed circulatory system, endoskeleton: made of cartilage or bone, makes possible great size and extraordinary movement

Petromyzontoidea

lampreys

Petromyzontoidea characteristics

some anadromous, some exclusively fresh, some predatory (parasitic), other not, spawning occurs in streams over shallow riffles, 2-3 years larval stage; feed on detritus small inverts, etc., then metamorphose into adult stage. susceptible to lampricide chemical, adults move out into larger body of water

Fishes characteristics

vertebral column, jaws and paired appendages, internal gills (heart > gills > body > ), nutritional deficiencies

Class Chondrichthyes

cartilaginous fishes - sharks, rays, chimaeras, etc.

Holocephali

chimaeras (ratfish)

Holocephali characteristics

pelvic and cephalic claspers in males, scaleless skin, bulky head with sensory canals, single gill opening, spine in dorsal fin, large tooth plates for crushing

Elasmobranchii

sharks, skates, rays and sawfish

Elasmobranchii (shark) characteristics

placoid scales, claspers on male, heterocercal tail, multiple rows of teeth in mouth, conspicuous gill slits, variety of feeding habits: planktivory to cookie cutters

Elasmobranchii (rajiformes - skates and rays) characteristics

flattened bodies, enlarged pectoral fins used for rajiform swimming, spines in dorsal side and caudal peduncle, generally flat teeth for crushing, some with specialized electric organs

Fish characteristics

gills are efficient at extracting oxygen from water that has 1/20 the oxygen of air, lateral line system detects water currents and vibrations, a sense of “distant touch”, the aquatic environment has shaped and constrained evolution - myriad adaptations

Bony fishes lineages:

ray-finned fishes and lobe-finned fishes

Bony fishes and tetrapod uniting features

endochondral bone replaces cartilage during development, lung or swim bladder is present - evolved as an extension of gut, have several cranial and dental characters unique to clade

Class Sarcopterygii

lobe-finned fishes - lungfishes and coelacanths

Class Sarcopterygii characteristics

ancestor of tetrapod, pair lobed fins, coelacanths: ossified swim bladder, long muscular lobed fins that move similarly to the limbs of bladder. lungfish: some rely on gill respiration and cannot survive long out of water and others can live out of water for long periods of time

Class Actinopterygii

ray-finned fishes - sturgeons, paddlefish, etc.

Actinopterygii characteristics

have a neutral buoyancy and a swim bladder - gas filled space and is the most efficient flotation device, as fish descends the bladder is compressed and as a fish ascends the bladder expands making the fish lighter, they detect sounds as vibrations in the inner ear, fish gills are filaments with thin membranes folded into plate-like lamellae, gills are inside the pharyngeal cavity and covered with a movable flap - the operculum, the operculum protects delicate gill filaments and streamlines body, pumping action by operculum move water through gills, water flow is opposite to the blood flow, fish devote most of their time searching for food to eat and eating, most fish are carnivores, most fish do not chew food - it would block water flow across the gills, many plankton feeders swim in large schools and using gill rakers to strain food, digestion follows the vertebrate plan, intestine tends to be shorter in carnivores and long and coiled in herbivores, stomach primarily stores food, intestine digests and absorbs nutrients, most fishes are dioecious with external fertilization and external development,

Oxygen uptake methods

countercurrent exchange - maximizes exchange of gases

ram ventilation: forward movement is sufficient to force water across gills