Vertebrate zoology (03 bony fishes, student version)

STRUCTURAL AND FUNCTIONAL ADAPTATIONS OF FISHES Neutral Buoyancy and the Swim Bladder All ﬁshes are slightly heavier than water To keep from sinking, sharks must always keep moving forw

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STRUCTURAL AND FUNCTIONAL

ADAPTATIONS OF FISHES

Neutral Buoyancy and the Swim Bladder

All ﬁshes are slightly heavier than water

To keep from sinking, sharks must always keep moving forward in the water

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The asymmetrical

tail create lift

when sweeping

Broad head and

ﬂat pectoral ﬁns

act as angled

planes to provide

additional lift

Sharks have very large livers containing a special fatty hydrocarbon called

squalene with a density of only 0.86 gr/mm

The liver acts like a large sack of buoyant oil that helps to compensate the

shark’s heavy body  reduces shark’s specific weight!

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Swim bladders are present in most pelagic bony ﬁshes but are absent in

tunas, most abyssal ﬁshes, and most bottom dwellers (ﬂounders,

sculpins)

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Two types of swim bladder:

+ The more primitive physostomous

(Gr., phys, bladder, stoma, mouth) ﬁshes

have a pneumatic duct that connects the

swim bladder to the esophagus, through

which they may expel air

+ More derived teleosts exhibit the

physoclistous (Gr., phys, bladder, clist,

closed) condition in which the

pneumatic duct is lost in adults

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+ Gas is secreted into the swim bladder by the

gas gland Gas from the blood is moved into

the gas gland by the rete mirabile, a complex

array of tightly-packed capillaries that act as a

countercurrent multiplier to increase oxygen

concentration

+ To release gas during ascent, a muscular

valve opens, allowing gas to enter the ovale

from which the gas is removed by diffusion into

the blood

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Osmotic Regulation

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Osmoregulators control the concentrations of salt and water in their bodies

- In fresh water, an animal is usually hyperosmotic to the medium, and the

osmotic gradient leads to an influx of excess water

- In salt water, most vertebrates are hyposmotic; therefore, water tends to flow

from their bodies into the surrounding environment

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- Excess water is pumped out by

the opisthonephric kidneys, which

are capable of forming very

dilute urine

- Special salt absorbing cells

located in the gill epithelium

actively move salt ions,

principally sodium (Na+) and

chloride (Cl-), from water to the

blood

Together with salt present in the

ﬁsh’s food, these absorption

replaces diffusive salt loss.

A freshwater ﬁsh maintains osmotic and ionic

To compensate for water

loss, a marine teleost drinks

seawater Excess salt

accompanying the seawater is

disposed in multiple ways

+ Major sea salt ions (sodium,

chloride, and potassium) are

carried by the blood to the gills

where they are secreted outward

by special salt-secretory cells.

+ The remaining sea salt ions,

mostly magnesium, sulfate, and A marine ﬁsh maintains osmotic and ionic.

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Migration (HUGH DINGLE AND V ALISTAIR DRAKE, BioScience • February

2007 / Vol 57 No 2):

(1) a type of locomotory activity that is notably persistent, undistracted, and

straightened out;

(2) a relocation of the animal that is on a much greater scale, and involves

movement of much longer duration, than those arising in its normal daily

activities;

(3) a seasonal to-and-fro movement of populations between regions where

conditions are alternately favorable or unfavorable (including one region in

which breeding occurs);

(4) movements leading to redistribution within a spatially extended population

Migration of Freshwater Eels

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Eels are catadromous (Gr kata, down, dromos, running), meaning that they

spend most of their lives in freshwater but migrate to the sea to spawn

Adult eels leave the coastal rivers of

Europe and North America, they swim

steadily and apparently at great depth

for 1 to 2 months until they reach the

Sargasso Sea, a vast area of warm

oceanic water southeast of Bermuda

At depths of 300 m or more, the eels

spawn and die

Minute larvae - leptocephali (Gr

leptos, slender, kephal - e, head) begin

an incredible journey back to the

streams of Europe and North America

Migration of Salmon

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Salmon are anadromous (Gr anadromos, running upward); they spend their

adult lives at sea but return to freshwater to spawn

7 species:

+ Atlantic salmon, Salmo salar (L salmo, salmon, al, salt): make repeated

upstream spawning runs

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After migrating downstream as a smolt, (a

juvenile stage) a salmon ranges many

hundreds of miles over the Paciﬁc for 2

- 4 years and then returns almost

unerringly to spawn in the headwaters of

its parent stream

- Salmons imprinted with the distinctive odor of the stream, which is

apparently a mosaic of compounds released by the characteristic vegetation and

soil in the watershed of the parent stream

- They also imprint on odors of other streams they pass while migrating

downriver

Use these odors in reverse sequence as a map during the upriver migration as

returning adults

From the open ocean to the mouth of a coastal

river:

- Some fish (e.g Salmon) (like birds) can

navigate by orienting to the position of the sun

- Fish also appear able to detect and to

navigate to the earth’s magnetic ﬁeld

- Fish use ocean currents, temperature

gradients, and food availability to reach the

general coastal area where “their” river is

located

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Locomotion in water

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Hearing and Weberian Ossicles

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(Hickman, 2008, p 532-533; Kardong, 2008, p 693-694)

Respiration

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Feeding Behavior

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Reproduction and Growth

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