Fish Morphology

Chondrichtyes vs Osteichthyes

Osteichthyans v.s. Chondrichthyes

OsteichthyansChondrichthye

s

Has cycloid scales.

Presence of dermal bone

Operculum covers the gills

Has placoid scales

No Bones in their body

Gill Slits are exposed (Naked)

Bony fish have a bony opeculumCartilaginous fish have gill slits

Skeleton

The Chondrichthyeso cartilage, composed of chondrocytes

suspended in a protein matrix.

Osteichthyeso composed of cartilage and bone.

scale Scales serve as protection for the fish. Reduces drag during swimming.

Scales Chondricthyes

o large scales called placoid scales• Scales have a bone like base embedded in

the skin and a backward projecting enamel covered dentine spine.

Osteichtyeso Have cycloid or ctenoid scales.• Cycloid scales are smooth, flat and round• Ctenoid scales posses a comb-like

extensions (ctenii)

Types of Scales

Scales – thin bony plates that overlap each other and provide protection.

Glands on the scales produce a slimy mucus, which protects them from bacteria.

Types of Scales There are four types of scales: 1. Placoid – type of scales on sharks 2. Ganoid – scales are connected to each other

(like armor). Ex. Is a Gar

Scales 3. Cycloid – have smooth

surfaces and edges. 4. Ctenoid – are like cycloid

scales, but have sharp/rough edges that stick out.

Cycloid Scales

Ctenoid Scales

Placoid Scales

Ganoid Scales

Homocoercal tail (caudal fin

Maneuverability (steering) and propulsion

Dorsal fin The main purpose of the dorsal fin is to stabilize

the animal against rolling and to assist in sudden turns.

Anal fino Stabilize the fish while swimming.

Pectoral fin The paired pectoral fins are located on each

side, usually just behind the operculum, and are homologous to the forelimbs of tetrapods.

It assists in maintaining depth as the fish swims.

Pelvic fin The paired pelvic or ventral fins are located

ventrally below the pectoral fins. They are homologous to the hindlimbs of tetrapods. The pelvic fin assists the fish in going up or down through the water, turning sharply, and stopping quickly.

FROG FISH

Lateral line The lateral line is a sense organ used to detect

movement and vibration (mechanoreceptors) in the surrounding water. In most species, it consists of a line of receptors running along each side of the fish.

Lateral Line

NOSTRILS The nostrils of fish do not open into the back of

the mouth as do those of mammals, and are not, therefore, for breathing.

They lead into organs of smell which are as a rule, very sensitive, so that a fish can detect the presence of food in the water at considerable distances.

EYES Fish see through their eyes and can detect color. The eyes are rounder in fish than mammals

because of the refractive index of water and focus is achieved by moving the lens in and out, not distorting it as in mammals.

GILLS

Gills• Gills are the main site of gas exchange in almost all fishes. The gills consist of bony or stiffened arches (cartilage) that anchor pairs of gill filaments.

Numerous lamellae protrude from both sides of each filament and are the primary sites of gas exchange.

Microscopic gill structure: showing gill filament and lamellae (Red blood cells evident.)

Respiration Most terrestrial vertebrates have internal lungs

that must be ventilated through bidirectional movement of air to replenish the oxygen (O2) supply

Most fish have external gills that are ventilated by a unidirectional flow of water, by pumping or swimming

Fine sieve structure of gills very efficiently extracts O2 from water.

Efficient O2 uptake is vital to fish because of its low water solubility.

Oxygen is ROUGHLY 20x more abundant in the air than in the water.

Respiration

Solubility decreases with increased temperature & salinity!

Respiration

Oxygen solubility determined by temperature

Temp (C) O2 con. at sat. (mg/l) – Fresh

O2 con. at sat. (mg/l) – Salt

0 10.3 8.0

10 8.0 6.3

20 6.5 5.3

30 5.6 4.6

Also, metabolic rate (demand for O2 ) increases as temperature rises. (How does this affect nutrition?)

Respiration

Also, metabolic rate (demand for O2 ) increases as temperature rises. (How does this affect nutrition?)

What does this mean to fish??

Respiration

In warm water...fish need to extract MORE O2 from LESS!

How can fish remove 80 - 90% of O2 available from

water?

Short diffusion distance at gill site

Large surface area for diffusion at gill site

Counter current exchange of gases at gill site

Large volume of water passes over gills

Oxygen Exchange in Fish

Fish employ the countercurrent system to extract O2 from the water.

This system moves water flowing across the gills, in an opposite direction to the blood flow creating the maximum efficiency of gas exchange.

Branchial vs. Ram Ventilation

Ram Uses same parts, but not the pumping energy

required. Sharks primarily. Once swimming speed is achieved...no need to actively vent buccal cavity. However, this can only be used consistently by strong swimmers (sharks, tuna).

1. Fill mouth cavity (open mouth, expand volume of mouth, expand volume of gill chamber with operculum closed)

2. Fill gill cavity (close mouth, squeeze mouth cavity, expand gill cavity, with operculum closed)

Branchial

3. Expel water from gill cavity (squeeze mouth and gill cavities, open operculum)

4. Reset for next cycle

Branchial

Branchial MouthPharynxOperculumBranchial Arches (gill arches)

Osmoregulation & Excretion

A Balancing Act

Physiological systems of fishes operate in an internal fluid environment that may not match their external fluid environment

Relative concentrations of water and solutes internally must be maintained within fairly narrow limits

Internal environment influenced by external environment

Osmoregulation & Excretion

Osmoregulationo Regulates solute concentrations and balances the

gain and loss of water

Excretiono Gets rid of nitrogenous metabolites and other waste

products

Freshwater fishes in different environments show adaptations that regulate uptake and conservation of both water and solutes

Osmoregulation & Excretion

Osmoregulation & Excretion

Osmoregulation is based largely on controlled movement of solutes between internal fluids and the external environment

Osmosis and Osmolarity

Cells require a balance between uptake and loss of water

Osmolarity, the solute concentration of a solution, determines the movement of water across a selectively permeable membrane

If two solutions are isoosmotic, the movement of water is equal in both directions

If two solutions differ in osmolarity, the net flow of water is from the hypoosmotic to the hyperosmotic solution

Osmotic Challenges

Osmoconformers, consisting only of some marine animals, are isoosmotic with their surroundings and do not regulate their osmolarity

Osmoregulators expend energy to control water uptake and loss in a hyperosmotic or hypoosmotic environment

Hagfishes

Osmoconformers Only vertebrate that is isotonic to

seawater - much like marine invertebrates

Osmoregulators

Aquatic vertebrates - gills are chief organs of excretion/osmoregulation

Kidneys first evolved as osmoregulatory organs in fishes to remove water (freshwater) or conserve water (marine)

Marine Animals

Most marine vertebrates are osmoregulators

Marine bony fishes are hypoosmotic to sea water

They lose water by osmosis and gain salt by diffusion and from food

They balance water loss by drinking seawater and excreting salts

(a) Osmoregulation in a marine fish

Gain of waterand salt ionsfrom food

Excretionof salt ionsfrom gills

Osmotic waterloss through gillsand other partsof body surface

Gain of waterand salt ionsfrom drinkingseawater

Excretion of salt ions andsmall amounts of water inscanty urine from kidneys

Key

Water

Salt

Freshwater Animals

A different form of osmoregulator Freshwater animals constantly take in

water by osmosis from their hypoosmotic environment

They lose salts by diffusion and maintain water balance by excreting large amounts of dilute urine

Salts lost by diffusion are replaced in foods and by uptake across the gills

(b) Osmoregulation in a freshwater fish

Gain of waterand some ionsin food

Uptake ofsalt ionsby gills

Osmotic watergain throughgills and otherparts of bodysurface

Excretion of salt ions andlarge amounts of water indilute urine from kidneys

Key

Water

Salt

Kidneys-Fish nitrogenous wastes

The type and quantity of an animal’s waste products may greatly affect its water balance

Among the most significant wastes are nitrogenous breakdown products of proteins and nucleic acids

Fish typically produce toxic ammonia (NH3) rather then less toxic compounds

Abundance of water to dilute toxic materials

Proteins Nucleic acids

Aminoacids

Nitrogenousbases

—NH2

Amino groups

Most aquaticanimals, includingmost bony fishes

Mammals, mostamphibians, sharks,

some bony fishes

Many reptiles(including birds),

insects, land snails

Ammonia Urea Uric acid

CapillaryFiltration

Excretorytubule

Reabsorption

Secretion

Excretion

Filtra

teU

rine

2

1

3

4

Animal Inflow/Outflow Urine

Freshwaterfish. Lives inwater lessconcentratedthan body fluids; fishtends to gainwater, lose salt

Does not drink waterSalt in(active trans-port by gills)

H2O inLarge volume of urine

Urine is lessconcentratedthan bodyfluids

Salt out

Animal Inflow/Outflow Urine

Marine bony fish. Lives inwater moreconcentratedthan bodyfluids; fishtends to losewater, gain salt

Drinks waterSalt in H2O out

Salt out (activetransport by gills)

Small volumeof urine

Urine isslightly lessconcentratedthan bodyfluids

Osmoregulation in different environments

Each species has a range of environmental osmotic conditions in which it can function:o stenohaline - tolerate a narrow range of salinities in

external environment o euryhaline - tolerate a wide range of salinities in external

environment

• short term changes: estuarine - 10 - 32 ppt, intertidal - 25 - 40• long term changes: diadromous fishes

(salmon)

o organisms like salmon:

o In sea, they drink sea water and discharge salt through their gills

o In freshwater, they stop drinking and produce large volumes of dilute urine, gills take up salt

Euryhaline

Anadromous: Most of life spent in salt water, returning to rivers or other freshwater to spawn.

Amphidromous: migrate between salt and freshwater at some point in the life cycle, but well before final maturation and spawning

Catadromous: Most of life spent in freshwater, returning to ocean to spawn.

Diadromous: Blanket category referring to any migration between salt and fresh water or vice versa

o Shark tissue contains a high concentration of ureao To prevent urea from damaging other organic

molecules in the tissues, they have trimethyl amine oxide (TMAO)

o Because of high solute concentration in tissue, water enters the cells (sharks don’t drink)

o Produce concentrated urine

Marine cartilaginous fishes: