Download Name: Lab Section_______________ Introduction Today in lab, we

Lab 4 : Fish Systems
Introduction
Today in lab, we will be examining the many organ systems of the
Atlantic herring (Clupea harengus). We will look at Reproduction,
Respiration/Circulation, Feeding/Digestion and Locomotion. The lab will
introduce new concepts, as well as reviewing some older ones.
The Atlantic herring is a pelagic schooling fish found in great abundance
in the North Atlantic Ocean. In Nova Scotia, the Atlantic herring is fished during
the fall for roe (eggs) which is shipped primarily to a Japanese market. Herring
are also used for lobster bait. Herring eat plankton and must filter the small
organisms out of the water.
External Morphology
Morphology refers to the external shape and features of an
object/organism. Anatomy is used to refer to the internal location and
arrangement of organs and features.
Morphology
Examine the fish that you and your partner share. When trying to
identify fish to species level, the overall body shape, fins, jaw and eye placement
are important. Identify the different structures of your herring.
Figure 1. Typical Fish Fins and Features
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Median
Paired
1 – Operculum
2 – Lateral Line
3 – Dorsal Fin
4- Cloaca (Anus)
5– Caudal Peduncle
6- Caudal Fin
7-- Anal Fin
9—Pelvic Fin
10—Pectoral Fin
Graham Bould. July 2006. Hector’s
Lampfish. Wikimedia Commons.
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Lab Section__________________
Internal Anatomy
Reproduction
Atlantic Herring, like most fish, use external fertilization, where eggs or
sperm are released through the cloaca into the water. Find the cloaca of the
herring. Shallowly cut the skin from the cloaca to the pectoral girdle. The first
thing you will notice are paired gonads, in the females they will be reddish, in
the males white. The female gonads contain thousands of small eggs (20 000 to
200 000 depending on size), or roe. The male gonads contain sperm in a milky
substance, referred to as milt. Fish do not have separate exits for these
reproductive cells, they are released in the cloaca where the intestines also
empty. Before removing the gonads, see if you can follow the path the eggs or
milt will follow through the cloaca into the water.
Hdahlmo. December 2005. Wikimedia Commons.
1 – Liver
2 – Swim bladder
3 – Gonad
(female)
4 – Pyloric caeca
5 – Stomach
6 – Intestine
Figure 2. Internal Anatomy of a Fish
After tracing this path, you may remove the gonads from the fish to allow
you better view of the other organs.
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Lab Section__________________
Circulation and Gas Exchange
Fish have a single loop closed circulatory system. The blood goes from
the heart to the gills where it is oxygenated, then goes via the dorsal aorta to the
body and returns to the heart through the postcardinal vein.
Main artery
Main vein
Gills –
counter current
Heart
Figure 3. Typical Fish Circulatory System
Florida Center for Instructional Technology
http://etc.usf.edu/clipart"
Gas exchange takes place in fish via their gills. The gills are located on
both sides of their mouths and are hidden by the gill operculum which protects
the delicate structures from damage. The operculum is also used to ventilate the
gills when fish are not moving. Find the gill operculum on your herring. Tap it
to see how strong it is. Lift it and note the gills underneath. You should be able
to count how many gill arches there
are, each gill arch has gill rakers on
one side and gill filaments on the
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other. The lamellae on the filaments
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are the functional respiratory
elements. The filaments are usually a
deep red colour because they are
highly vascularized with networks of
Figure 4. Gill Arch (1-filaments and 2-rakers)
capillaries since this is the primary site
of gas exchange.
Fish allow water to flow through their mouths and out their opercula. As
the water flows over their gills, they absorb oxygen into their blood through a
counter-current exchange system. The oxygen-depleted water continues out
through the gill operculum. Cut off the first gill arch and examine it. Identify
the gill filaments, lamellae and the extra long gill rakers. There are a few
dissecting scopes set up for you to examine the filaments, under higher power?
If you continue your cut through the pectoral girdle towards the anterior
end you should be able to find the triangle shaped heart of the herring.
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Lab Section__________________
Digestion
Herring primarily eat zooplankton; do they have teeth? Imagine that you
are a piece of plankton, starting in the mouth, use a blunt probe to follow the
path the food would take. Take care to identify the various components of the
feeding and digestive systems: a) mouth and gill rakers; b) esophagus
c) stomach – site of primary digestion
d) pyloric caeca – the finger-like organ contains many enzymes and assists in digestion
of proteins and sugars
e) liver – secretes fat digesting enzymes, and stores fat
f) intestines – completes nutrient absorption
g) anus/cloaca – location of waste release
You may cut open the stomach if you wish to try and identify stomach contents.
Figure 5:
Source: The Visual Dictionary http://www.infovisual.info. Reproduction rights reserved and strictly limited.
Locomotory System
Using primarily the blunt probe, carefully remove the skin from one side
of the fish. Examine the muscle structure. You should see very distinctive blocks
of muscles. These blocks are myotomes, they are divided by myosepta. Fish
have both red and white muscle, as you learned in the video in class. Cut a
cross-section through the tail behind the anus, identify sections of red and white
muscle in this section. What are the functions of the different types of muscle? What
type of fibres make up each colour of muscle?
You also learned in the video that most fish have gas-filled swimbladders
which help them maintain buoyancy in the water. Some fish have only a gas
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gland which produces gas that fills the bladder (physoclistous). Other fish,
including herring, get gas into their swim bladders by “gulping” air into the gut
which then enters the swim bladder via a pneumatic duct (physostomous). Try
and find the pneumatic duct between the intestine and the swimbladder.
Swimming
Movement and Gait Changes
Many fish propel themselves by generating backward moving waves of
contraction on their bodies that extend to the caudal fin. This type of swimming
(or gait) is called Body or Caudal Fin (BCF) locomotion, and is powered by the
red and white muscles forming most of the body of the fish. Fish can also use
their median and/or paired fins to propel themselves and this is called MPF
locomotion. These are powered by separate muscles operating the fins. Many
fish use one form of locomotion at one speed and change ‘gaits’ to another form
as the speed changes. The burst and coast gait is used by many fish to reduce the
cost of locomotion when moving over long distances.
Observation of Swimming
Observe the different swimming gaits used by the live fish in the
aquarium at the back of the lab. You should be able to see fish using all the gaits
in the chart below. Students should not do this all at the same time. Complete at
any point during the lab.
Swimming Gait
(BCF or MPF)
Fins used
Station holding
-remain in same location
‘Saunter’
-move slowly
Sprint
-move quickly
Burst and coast
-sprint followed by a glide
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Name:___________________
Lab Section__________________
Assignment - Hand in at the end of lab.
Locomotion
1. From your observations of the fins and body undulations used during the
burst and coast gait, hypothesize why it is often used by fish to reduce the cost of
locomotion.
Circulation and Gas Exchange
2. What circulatory or gas exchange adaptations (at least 3 points) might you
expect between an active pelagic fish, such as herring, but not in a more
sedentary bottom-dwelling fish such as a sculpin?
Digestion – one sentence answers only.
3. Why do herring have such long gill rakers?
4. What benefits (other than enzyme secretion) might the pyloric caeca provide in
terms of digestive abilities?
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