Ichthyology – Introduction to Fishes

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WFB 232 Ichthyology

Ichthyology – Introduction to Fishes
Vertebrate classes: # species % of vertebrates

Agnatha 85 <1%

Chondrichthyes 850 2% > 50% of all vertebrates are fishes

Osteichthyes 23,000 50%

Amphibia 2,600 6%

Reptilia 6,500 14%

Aves 8,600 19%

Mammalia 4,100 9%

physiological and sensory modalities in fish that are not present in other taxa


buoyancy control

respiration (air and water)

mechanosensory – lateral line


electric generation

light production

Characteristics and constraints of the aquatic environment

salinity - must deal constantly with osmoregulation - into or out of body

temperature - water has high thermal capacity, 4x that of air

motion - from still water, with little oxygen exchange, to torrential currents

gas saturation - water contains (relative to air) very little oxygen; methods for withdrawal must be specialized;

too little, fish must achieve oxygen elsewhere; too much results in gas bubble diseases

pressure - increases 1 atm for every 33’ of depth (= 10 m)

consequence for buoyancy and gas bladders

few fish are neutrally buoyant – use air or fat to compensate

fish need much less skeletal support than terrestrial animals, due to support surrounding body

viscosity - much higher effort required to swim in water than air

fastest swimming speed (tuna) - 21m/s in short bursts; killer whale does 15m/s

little effort required to prevent sinking

light - attenuates rapidly with depth; thus deep-sea fish may create own light

sound - propagates rapidly in water (400x as well as in air)

provides medium of communication by vibration, but with little directionality

Distribution of aquatic habitats

Salt water Fresh water

oceans 97.10% ice, snow 2.2%

salt lakes 0.01 groundwater 0.6

lakes 0.01

atmosphere 0.001

rivers 0.0001

Total 97.11 2.81

Fish distribution in habitat:

freshwater 41%

saltwater 58%

move between (anadromous, catadromous) 1%


Learn how species are defined and named; understand how taxonomic nomenclature is used

Begin to know the classes, orders, and representative families and species in each order of fishes

Learn to ‘read’ taxonomic descriptions

Recognize primitive (older) versus advanced (recent) traits in fishes
Classification = hierarchical grouping of organisms (i.e. a process, an operation)

Systematics = the study of relationships

Taxonomy = the science of biological nomenclature (formal rules for use)
Taxonomic hierarchy: (note standardized endings)

Phylum: Chordata

Subphylum: Vertebrata

Superclass: Gnathostomata

Class: Actinopterygii (formerly Osteichthyes)

Order: Cypriniformes

Suborder: Cyprinoides

Family: Cyprinidae

Subfamily: Cyprininae

Genus: Cyprinus

Species: carpio
standardized endings (well-established in ichthyology)

Order: -formes

Suborder: -oides

Family: -idae

Subfamily: -inae

Tribe: -ini

Only genus and species are underlined or italicized with only the generic term capitalized.
phylogenetic systematics – objective is to make the classifications non-arbitrary, and informative about evolutionary relationships

cladograms: each branch represents monophyletic group - all from common ancestor

if polyphyletic, then subsequent categories based on false assumption

all members share one or more derived characters

problem is to determine whether a given character is homologous or convergent

plesiomorphies – primitive character states

apomorphies – advanced character states

autoapomorphies – specialization unique to one taxon

synapomorphies – shared specializations

Taxonomic relationships defined on the basis of

morphometrics - usually measurements as ratio against SL, to account for absolute size

meristics - counts, with ranges - may vary with environment

anatomical traits - shape, presence/absence of structures

color patterns - highly variable, change with maturity, subjective, fade in preservative

karyotypes - changes in number and shape of chromosomes

biochemical methods - look directly at genetic material
Authorship of scientific names

In original genus: Amia calva Linnaeus – usually followed by date

In new genus: Lepisosteus osseus (Linnaeus)

right of priority – given to first full written description, usually with type specimen from a type locality

the description makes it a nominal species

original species name must not be changed, even if genus is changed

- unless previously used for another animal (nomen praeoccupatum)

- if previously described, later description becomes junior synonym

hybrids denoted with an x - Rutilus rutilus x Abramis brama

Nomenclature (International Code of Zoological Nomenclature)


ch = k (e.g., ichthyology) – there is no ‘k’ in Latin

initial c = s (e.g., Cyprinidae)

genus and species always italicized; genus is always capitalized, species name is not capitalized

Neogobius melanostomus
genus and subspecies can be abbreviated after they have been mentioned once in a text

N. melanostomus

N. m. caspia
subgenus is usually in parentheses

Dreissena (Pontodreissena) polymorpha

Characteristics of the classes of extant fishes

Character Primitive Advanced

skeleton cartilaginous ossified (calcified bone) - may be lost

paired fins absent present

gill arches absent present

gill arches not joined to brain case firmly joined to brain case

nostril(s) 1, median paired

jaws absent present

fins with spines absent (trout) present (perches) - but may be lost (killifish)

pectoral fins horiz. base low on vert. base high on body (basses)

body (minnows)

pelvic fins far back on belly (pikes) forward, attached to pectoral girdle (sculpins)

tail heterocercal symmetrical

scales cycloid (herring) ctenoid (sunfish) - absence is specialization

mouth front of head (trout) up- or down-turned (suckers, killifish)

Taxonomy of Fishes

Kingdom Animalia

Phylum Chordata

Subphylum Vertebrata


Class Myxini

Order Myxiniformes (hagfishes)

Class Cephalaspidomorphi

Order Petromyzontiformes (lamprey)


Class (Placodermi)

Class (Acanthodii)

Class Chondrichthyes

Subclass Holocephali

Order Chimaeriformes (chimaeras)

Subclass Elasmobranchii

9 orders (sharks, rays, skates)

Class Sarcopterygii

Subclass Coelacanthimorpha

Order Coelacanthiformes (coelacanths)

Subclass Dipnoi

Order Ceratodontiformes (Australian lungfish)

Order Lepidosireniformes (S. American, African lungfish)

Class Actinopterygii - (rayfins, higher bony fishes)

Subclass Chondrostei

Order Polypteriformes (birchirs, reedfish)

Order Acipenseriformes (sturgeons, paddlefishes)

Subclass Neopterygii

Order Semionotoformes (Lepisosteiformes) (gars)

Order Amiiformes (bowfin)

Division Teleostei

35-38 orders (modern body fishes)

Example of a taxonomic description (adapted from Berg, 1949)

Round goby, Neogobius melanostomus (Pallas, 1811). D1 VI (V VII); D2 I + 14 16 (13 16); A I + 11 13 (11 14); P 18 19 (17 20). [ = the anterior dorsal fin has 5 7 spines, usually 6, and the posterior dorsal fin has one spine and 13 16 soft rays. The anal fin has one spine and 11 14 soft rays, and the pectoral fins have 17 20 soft rays.] Scaled on the parietal region, nape, back (all), throat (all or most), abdomen, pectoral fin peduncles, and one quarter of the gill covers. Scales on the middle and anterior nape are cycloid. Head is as wide as or wider than deep; depth is 0.9 1.2 times the width. Head length 4.2 4.5 of total body length. Angle of the jaw below the anterior quarter of the eye. Lower jaw not prominent. Snout 1.1 1.4 times the orbit diameter. Upper lip narrows slightly to the rear. Usually 6, rarely 7, transverse suborbital series of pit organs. Ventral fins reach or almost reach the vent. Pelvic disk is 0.6 0.8 times the abdomen length. If present, the anterior membrane width is very shallow, with rounded, lateral lobes. Caudal peduncle depth is about two thirds its length. Lacks a gas bladder and chemoreceptors.
Fish Anatomy
Objectives: become acquainted with the general external and internal structures of fishes, and how they vary functionally and taxonomically

become familiar with parts of fish and associated terminology

learn to recognize fishes by similarities and differences in structure

External anatomy



mouth position – superior, terminal, sub-terminal, inferior

teeth types and locations;

mostly on mandible (lower jaw), premaxilla and maxilla (upper jaw) – Bond Fig. 2-20

generally protrusible in derived bony fishes

frenum - bridge of skin binding lips to snout or chin in non-protrusible jaw

additional (or seasonal) structures include barbels, tubercules, kype, cirri

sensory pores

Body shapes – which taxa have each, what are the advantages of each type?






Fins – what are each used for? how does their presence or location vary among taxa?

paired fins: pelvic – some modified to disk (gobies) or claspers (sharks)

placement may be abdominal, subabdominal, jugular, mental (under chin)


single fins: dorsal - one or two; rarely three; may be modified to disk

(medial) anal – may be modified to intromittent organ (gonopodium)

caudal – rounded, lobed, truncate, emarginated, forked; homocercal or heterocercal

adipose – in only a few orders

peduncles (base of fin or tail where they attach to body)

supporting structures:

ceratotrichia – cartilaginous elements in elasmobranch fins

lepidotrichia – rays (double, segmented elements) sometimes modified to spines (ossified, single)

Skin and scales – which are more advanced, or primitive?

presence, absence, or partial covering of scales

functions of scales

types of scales: placoid, ganoid, cycloid, ctenoid, scutes

skin pigmentation: melanophores

Internal anatomy

Internal organs

GI tract (stomach, intestine, pyloric caecae), reproductive organs, kidneys, liver, gall bladder, spleen

gas bladder may be present or absent, connected or not to other organs

physoclistous – closed gas bladder

physostomus – gas bladder has open connected to esophagus

Body musculature

hypaxial muscles

epaxial muscles




premaxilla, maxilla, dentary, palatine may all have teeth attached

operculum: opercle, subopercle, preopercle, interopercle

otoliths – ear bones

branchial arches - usually 5 pairs - bear gill rakers on inner surface

fifth arch may be modified to pharyngeal teeth

breathing apparatus (see diagrams in Bond)
Vertebral column

Vertebrae composed of centrum, with neural spine, neural arch, neural canal

zygopophysis, basapophysis – small locking projections add rigidity, connection with ribs

hemal spine, hemal arch (only near tail), hemal canal

dorsal ribs, or epipleurals, project from pleurals
Caudal skeleton

urostyle – last vertebra, modified into plate

hypurals - modified from hemal arch, connected to end of vertebral column and caudal elements

epurals – remnant from hemal spine, one or more free bones above hypurals

Appendicular skeleton

pterygiophores articulate with fin rays

pectoral girdle – cleithrum, scapula, coracoid bones

pelvic girdle – simple system to support fins

Orders of fishes, with selected families
Number of Representative Common # species

Class/subclass Order Families families names in order

Myxini Myxiniformes 1 Myxinidae hagfish 43

Cephalaspidomorphi Petromyzontiformes 1 Petromyzontidae lamprey 41


Holocephali Chimaeriformes 3 Chimaeridae chimaeras 31

Elasmobranchii Heterodontiformes 1 Heterodontidae bullhead sharks 8

Orectolobiformes 7 Rhincodontidae whale sharks 31

Carchiniformes 7 ground sharks 208

Lamniformes 7 Cetorhinidae basking sharks 16

Hexanchiformes 2 Hexanchidae cow sharks 5

Squaliformes 3 Squalidae dogfish 74

Squantiniformes 1 Squantinidae angel sharks 12

Pristiophoriormes 1 Pristiophoridae saw sharks 5

Rajiiformes 9 Rajidae skates, rays 456


Coelocanthimorpha Coelacanthiformes 1 Latimeriidae coelacanth 1

Dipnoi Ceratodontiformes 1 Ceratodontidae Australian lungfish 1

Lepidosireniformes 2 Lepidosirenidae S. Am., African lungfish 5


Chondrostei Polypteriformes 1 Polypteridae birchirs, reedfish 10

Acipenseriformes 2 Acipenseridae sturgeons, paddlefish 26

Neopterygii Semionotoformes 1 Lepisosteidae gars 5

Amiiformes 1 Amiidae bowfin 1
Div. Teleostei Osteoglossiformes 6 Hiodontidae mooneye 217

Elopiformes 2 Megalopidae tarpon 8

Albuliformes 3 Albulidae bonefish 29

Anguilliformes 19 Anguillidae eels 738

Saccopharyngiformes 4 swallowers, gulpers 26

Clupeiformes 4 Clupeidae herrings 357

Gonorynchiformes 4 milkfish 35

Cypriniformes 6 Cyprinidae carp, shiners 2,662

Catostomidae suckers

Characiformes 10 Characidae hatchetfish 1,343

Siluriformes 31 Ictaluridae catfish 2,405

Gymnotiformes 6 knifefish 62

Esociformes 2 Esocidae pikes 5

Umbridae mudminnows 5

Osmeriformes 13 Osmeridae smelt 236

Salmoniformes 1 Salmonidae salmon, trout, ciscoes 66

whitefish, chubs

Stomiiformes 9 lightfish, dragonfish 321

Ateleopodiformes 1 Ateleopodidae jellynose fish 12

Aulopiformes 12 lizardfish 219

Myctophiformes 2 lanternfish 241

Lampridiformes 7 ribbonfish, oarfish 19

Polymixiiformes 1 Polymixiidae beardfish 5

Percopsiformes 3 Percopsidae trout-perch 9

Ophidiiformes 4 cusk-eels 355

Gadiformes 12 Gadidae cod, hake 482

Batrachoidiformes 17 Batrachoididae toadfish 69

Lophiiformes 16 Lophidae anglerfish 297

Ogvocephalidae batfish

Mugiliformes 1 Mugilidae mullets 80

Atheriniformes 5 silversides, grunion 285

Beloniformes 5 needlefish, flying fish 191

Cyprinodontiformes 13 Cyprinodontidae livebearers 807

Poeciliidae guppies

Stephanoberyciformes 9 whalefish 86

Beryciformes 14 squirrelfishes 123

Zeiformes 6 John Dories 39

Gasterosteiformes 11 Gasterosteidae sticklebacks 257

Pegasidae seamoths

Syngnathidae pipefish, seahorses

Indostomidae I. paradoxus

Synbranchiformes 3 Synbranchidae swamp eels 87

Scorpaeniformes 20 Cottidae scorpionfish, sculpin 1,271

Dactylopteridae flying gunards

Perciformes 128 Percichthyidae temperate bass 9,293

Centrarchidae sunfish

Percidae perch, bass

Sciaenidae drum

Mullidae goatfishes

Cichlidae cichlids

Mugilidae mullets

Gobiidae gobies

(also: bluefishes, remoras, blennies, mackerels,

dolphins, snappers, tunas, swordfish)

Pleuronectiformes 6 Pleuronectidae flounder, flatfishes 570

Tetraodontiformes 9 Balistidae triggerfishes 339

Ostraciidae cowfish, boxfish

Tetraodontidae puffers

Molidae molas (ocean sunfish)

Totals: 5 classes 57 orders 478 families ~26,000 species



Understand the physical characteristics of water that affect the ability to swim

Understand the various modes of fish propulsion, factors that affect their efficiency, and representative species that use them

physical properties of water

density – 830 x more than air

viscosity – 70 x more than air

boundary layer

Reynolds number (Re) (dimensionless variable)

Re = LVr/m

L = length of object

V = velocity of object

r = density of fluid

m = viscosity of fluid

Examples of Re:

animal speed Re

whale 10 m/s 300,000,000

tuna 10 m/s 30,000,000

copepod 20 cm/s 300

sea urchin sperm 0.2 mm/s 0.03
unavoidable issues when swimming:

flow changes to turbulent at Re ~ 2,000

boundary layer changes to turbulent as Re goes from 5x105-5x106

turbulent flow is a consequence of

decreasing viscosity

increasing density of liquid

increasing speed

increasing length

for efficient swimming

avoid separation of boundary layer from surface

maximize laminar flow in boundary layer

minimize turbulent flow in wake


streamline body (tapering)

aspect ratio of about 0.25

max. thickness of body 1/3 back

drag reduction - keep body rigid

slime layer to reduce frictional drag

rough surface (cteni) keeps boundary layer attached
Swimming modes

“kick and glide”

active - sustained for hours or days

burst - only for up to 30 secs

large fishes have greater difference between burst and active than small fishes

active swimming accomplished using red muscle along sides of fish

- high myoglobin and mitochondrial enzymes

burst swimming with white muscle

  • great contractile speeds, low endurance

Body/caudal fin propulsion

Medial/paired fin propulsion

non-swimming locomotion





walking on bottom vics




passive drift

jet propulsion

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