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

• Endotherms-

– High metabolic

rate

– Insulation (large

quantities)

hair/feathers

– Minimize heat

exchange F

I

S

H

Modern Fish:

Agnatha: Jawless fish (primitive)

ex:

Chondrichthyes: cartilaginous fish

ex:

Osteichthyes: bony fish

ex:

Lamprey and Hagfish

Sharks

Perch, salmon …

External Anatomy

Dorsal Fins

Pectoral

Fin

Caudal

Fin

Anal finPelvic fin

Operculum

SCALES

Figure 24.18

Tale of Tails

• A) - Heterocercal, (B) - Protocercal,

(C) - Homocercal, (D) - Diphycercal

Sharks

Perch

Lungfish

Coelacanth

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

• 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

Physoclistous Fish

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 esphogusstomachintestines

• 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