Download Fish Biology

Fish Biology
Fish shapes
• Cold-blooded aquatic
animals with
backbones, gills, and
fins
• Most are torpedoshaped (fusiform) for
efficient travel through
water, but they may be
flattened and rounded
(flounder), and vertical
and angular (sea
horses)
Fish Size
• Fish range in size:
• the pygmy goby, which
reaches only 12mm
long and 1.5g in
weight; sexually
mature at 6mm
• The whale shark grows
to 18m and weighs
over 20 tons
•
“The tiny coral reef-dwelling fish
called the pygmy goby has taken
the record as the shortest-lived
vertebrate. The pygmy goby lives
an average of 59 days, pipping the
previous record holder, an African
fish which lives for just over twoand-a-half months.” (BBC News)
Fish Distribution
• Found throughout the world
• Altitudes of more than
5000m to depths of about
10km
• Some inhabit hot springs,
such as Cyprinodon, where
water may reach 45°C
• Others are found in the
Antarctic seas, such as
Chaenocephalus, where it
may be less than 0°C
• 107 species are distributed
worldwide in tropical and
subtropical waters, but
many species have limited
ranges
Fish Distribution
•
•
•
•
There are 20 000 or more fish species
60% live in marine waters
40% are found in fresh water
Most of the world’s fish are continental either in freshwater on land, or in the sea
close to the coast
• Coasts are good for fish as they are rich in
nutrients such as nitrates and phosphates –
from rivers, upwelling, aeration from the surf
and tide, and the sunlight
Fish Anatomy
• Three classes:
• Agnatha (jawless fishes) that consists
of hagfish and lampreys
• Chondrichthyes (cartilaginous –
skeleton) that consists of sharks and
rays
• Osteichthyes (bony-skeleton) – all
other fish
Skeletons
• Skeletons of the three groups are very
different
• Hagfish and lampreys have a notochord, a
rod-like structure composed of unique tissue
Skeletons
• Sharks and rays have a notochord that is
surrounded and constricted by the
vertebrae, to form a backbone. The
remainder of their skeleton is composed of
cartilage, not bone (but it can be hardened
by calcareous salts)
• Primitive bony fishes have vertebrae that
are mostly cartilaginous, but advanced fish
have bony vertebrae united to form a
backbone, with no notochord
Fins
• Fins are either median or paired
• Median fins are along the centerline of the
body, at the top, bottom, and the end
• Dorsal fin (top) may be one or several fins
(one behind the other), and may include a
fleshy fin (adipose) near the tail
• Bottom (anal) fin is located on the belly
behind the anus
• End fin is called the tail, or caudal fin
Fins
• Pectoral fins are at the front of the
body, behind the gill openings and
usually provide maneuverability
• Pelvic fins (ventral fins) are along the
bottom of the body but can vary in their
placement (can be in the middle of the
belly, below the pectorals, or in front of
the pectorals.) Can provide
maneuverability
Scales
• Scales are colorless
• Coloring of the fish comes from the structures
beneath or associated with the scales
• Not all species of fish have scales, or they can
be so tiny it would appear that they do not have
any
• Scales may only be present on small areas of
the body
• Arranged in imbricate (overlap like shingles) or
mosaic (fitting closely together or barely
separated)
Four Basic Scale Types:
• 1. Placoid scales (dermal denticles):
– are on sharks and rays, and are tooth-like
in structure (enlarged ones are actual
teeth in sharks)
– Scales do not increase in size, so new
scales must be added as the shark grows
• 2. Cosmoid scales:
– Coelacanth have
them
– Also in lungfishes
(only single-layered)
– Four-layered bony
scale
• 3. Ganoid scales:
– Found on gars
– Typically squarish
– Single bony layer
• 4. Leptoid scales:
– Derived from ganoid scales by the loss of
the ganoin layer
– Single layer of bone
– Found on the higher bony fishes and
occur in two forms: cycloid (circular) and
ctenoid (toothed)
Fish Circulation
• Blood transports oxygen, nutrients,
and wastes
• Single circuit: heart-gills-body-heart
• Fish heart is two-chambered, with an
upper atrium and lower ventricle
• Other organisms may have three or
four-chambered hearts
Fish Respiration
• Fish must extract oxygen from the water
and transfer it to their bloodstream
• This is done by gills, lungs, specialized
chambers, or skin
• More difficult than extracting oxygen from air
• Some fish can extract as much as 80% of
the oxygen in the water passing over the
gills whereas humans can only extract about
25% of the oxygen from the air taken into
lungs
Gills are efficient because:
• Large surface area – gills have 10 to 60
times more than body surface area
• Short distance for oxygen to diffuse – blood
in the gills is close to the water
• Countercurrent circulation – blood flows
forwards while the water flows the other so
that there is always less oxygen in the blood
than in the water
• Water flows one direction only over the gills
Fish Body Temperature
• Cold-blooded – body temperature varies
with external temperature
• Blood passing through the gills loses heat to
the water so that a fish’s body temperature
is usually within a degree of the water
temperature
• There are some warm-blooded fish (tuna,
mackeral sharks) – they have a
countercurrent circulatory network that
keeps their bodies 5 to 12 degrees warmer
than the water
Fish Water Balance
• Blood of freshwater fish is more salty than
the water in which they live
• Osmotic pressure causes water to diffuse
into the fish’s body through the gills, mouth
membranes and intestines
• Must eliminate excess water so they
produce very dilute urine (ex. Lampreys
may create an amount of urine up to 36% of
their body weight per day)
• A gain in water means a loss in salt, so they
absorb salt from the water with their gills
• Marine bony fishes have blood that is
less salty than sea water, so they lose
water and absorb salt
• So they drink seawater and produce
little urine
• Excrete excess through gills or anus
• Hagfish have a salt concentration
equal to that of seawater
• Sharks retain the excess salt to keep
the sharks’ blood at a higher salt
concentration than seawater
Fish Gas Bladder
• Reducing body weight is important to fish so
they expend less energy to keep at a given
depth
• Total body density equal to that of water
would be weightless, not floating or sinking
• Fat is less dense than water, so some fish
have up to 1/3rd of their weight in fat (such
as deep sea sharks that have large livers
that contain squalene)
• Many fishes have a gas-filled bladder
• The amount of body volume that it takes up
will depend on whether the fish is freshwater
or marine
• Freshwater is less dense and is less
buoyant, so they need a larger gas bladder
to keep from sinking
• -Gas bladders can be 7-11% of body
volume in freshwater fish, and 4-6% in
marine fish
• Gas levels within the bladder must be
adjustable, or the fish would always
remain at the same depth
• In some fish, air is gained through
gulping fresh air, and expelling it
through the mouth and gills; in others
the gas is exchanged through the
blood system
Fish Lateral Line System
• This is sensitive to differences in water
pressure
• Can be due to changes in depth or waves
• Consists of a neuromast, which is a bundle
of sensory and supporting cells that have
hairs that are enclosed in a gelatin
• Neuromasts send out nerve impulses and
when pressure causes the hairs to move,
the nerve impulses will increase or decrease
• Neuromasts may be single, in small groups (pit
organs), or in rows (lateral line system)
• Lateral line system runs along the sides of the body
onto the head, where it divides into three branches
– two to the snout and one to the lower jaw
• Another fish swimming will cause a pressure wave
in the water that can be detected by the lateral lines
of other fish
• When a fish is swimming towards something, the
pressure waves will change around its body, which
will tell the fish to swerve to avoid the object
Fish Reproduction
• Most are egg-layers
• Some bear live young
• Live-bearing fish are either ovoviviparous
(eggs hatch within the female) or viviparous
(unborn are supplied with nutrients from the
mother’s tissues)
• Live bearing and some egg-layers have
internal fertilization and they have modified
structures that will introduce sperm into the
female’s body
• Three modes of reproduction:
– Heterosexual (most popular)
– Hermaphroditic
– Parthenogenetic
Heterosexual
• In some live-bearing fishes the female
may be able to store the sperm for up
to 10 months and is used to fertilize
new batches of eggs as they develop
• Some females may carry sperm from
multiple males
Hermaphroditic
• Single fish could be both male and
female, produce eggs and sperm
(either at the same time or at different
times) and will mate with another
hermaphrodite
• External self-fertilization can occur, or
internal self-fertilization
• Some fish will switch their sex as they
age
Parthenogenetic
• Unfertilized eggs develop
into embryos – known to
one fish species, Poecilia
formosa, of the Amazon
River
• Development will continue
without fertilization, but
mating with a male is still
required to stimulate egg
development
Parental Care
• Some fish form huge schools of males
and females, release their eggs and
sperm, and then leave
• Other fish build nests and care for
eggs and newly hatched young
• Others will carry the eggs with them in
such places as their mouths, gill
cavities or other cavities
“The most fascinating thing about the Arrowana is
that it is a mouthbrooder,capable of carrying
hundreds of eggs in its mouth and even after they
hatch, the little fish live in their mother's mouth till
the time they learn the ways of the world”
http://hubpages.com/hub/The-Mouthbrooder-Dragon-Fish-Arowana