Download Fish Anatomy I: External Anatomy

Class Osteichthyes
Bony Fish
General Characteristics of Class
• internal skeleton ossified (turned to bone)
• Paired fins made of rays and spines, or
lobed fins
• swim bladder or lung present
• bony scales (ganoid, cycloid, ctenoid)
• gill slits covered by an operculum (single
external gill opening)
• 2 chambered heart
Actinopterygii VS Sarcopterygii
• Ray-finned
• fins with multiple
parallel supports
• fins controlled by
muscles in body
wall
• Lobe-finned
– Have lungs as well
as gills
– Can live periods
outside of water
• Ex: lung-fish
coelacanth
Modern Fishes
• Great Diversity
– 27,000 species
– Representing 96% of all living fishes or about
½ the vertebrates
– Thought to be 5-10,000 undescribed species
• Diverse Habitat
– Highest mountains to 8,000m below surface
– Hot springs (44ºC) to polar seas (-2ºC)
– Freshwater to extreme salt concentrations
The Aquatic Environment: Life in the Water
• Water has a high specific heat
– Endothermy is not needed
• Less O2 in water 
– efficient gills required
• Water is dense
– bony skeleton not needed (but Osteichthyes does)
• Water will conduct electricity, air does not
– Can use this to help detect predators or prey
• Water is more viscous than air
– Develop methods to propel self
Ectothermy vs. Endothermy
• Ectotherms– Low metabolic
rates
– Little insulation
– Rapid heat
exchange
F
I
S
H
• Endotherms– High metabolic
rate
– Insulation (large
quantities)
hair/feathers
– Minimize heat
exchange
Modern Fish:
Agnatha: Jawless fish (primitive)
ex: Lamprey and Hagfish
Chondrichthyes: cartilaginous fish
ex:
Sharks
Osteichthyes: bony fish
ex: Perch, salmon …
External Anatomy
Operculum
Dorsal Fins
Caudal
Fin
Pectoral
Fin
Pelvic fin
Anal fin
SCALES
Figure 24.18
Tale of Tails
• A) - Heterocercal, (B) - Protocercal,
(C) - Homocercal, (D) - Diphycercal
Sharks
Lungfish
Coelacanth
Perch
Swim Bladder
• Arose from the paired lungs
• Needed to achieve neutral buoyancy
• Secreting gas into the bladder as it swims
up, and removing gas as it swims down.
Types of gas bladders
• 1. Physostomous Fish
• Pneumatic duct connect swim bladder to
esophagus  used for air removal
• 2. Physoclistous Fish
• No tube - gas in blood used to fill bladder
How Swim Bladder Works
Physoclistous Fish
• Ovale
– a vascularized area of the swim bladder
– Used to get air out of the swim bladder
• Rete mirabile
– moves gas from the blood into the swim
bladder
Flow of water is opposite the flow of blood
Maximal Oxygen uptake
This is called: Counter-current Exchange System
Ventilation in Fish: The Gill
• Gills:
– thin filaments/ covered epidermal membrane
• These membranes fold into lamellae.
– Richly supplied with blood
– Covered by operculum
• (protection and pumping system)
• Mouth gills out operculum
Osmotic Regulation
• Freshwater (fish are hyperosmotic regulators)
– Low salt – so water tends to enter the
bodies osmotically and salt is lost by
diffusion outward.
– Body has mucous covering to try to
prevent this, but most exchange occurs
in the gills
• Defense against this
– Excess water pumped out by kidneys which create very
dilute urine
– Salt absorbing cells – move salt from water to blood.
Osmotic Regulation
• Marine (fish are hyposmotic regulators)
– High salt – so fish need to lose water
and gain salt. (risk: fish can dry-out)
– To compensate for water loss – a
marine fish drinks seawater.
• Salt is carried by the blood to the gills where they
are secreted by salt-secretory cells.
Integument
• Live cells next to environment
• Mucous layer (to get rid of bacteria?)
• Scales evolved from armor for protection:
– A. Cycloid (perfectly smooth)
– B. Ctenoid (comb-like)
Pigment cells-Under Neural Control
• 1. Chromatophores-contain true pigments
– A. carotenoids
– B. erythrophores
– C. melanocytes
• 2. Iridocytes-contain waste products
(guanin) helps to reflect light
Digestion
• Buccal cavity esphogusstomachintestines
• Some species don’t have a stomach (minnows) possess
a pyloric caecae
Food swallowed whole
Primitive teeth
Gill rakers and gill filaments screen objects exchange air
Generalized feeders
Pharyngeal teeth: last arch in back, help to tear