Biology experiment
Group members: Chan Wai Lan (2)
Class :6B
Ma King Man (6)
Cheung Wai Tong (12)
Topic: The study of the tolerance of freshwater fish to salinity and diet of the
freshwater fish
Aim
To find out the endurance of freshwater fish to salinity in water and to study the diet
of the freshwater fish.
Basic principle
To find out the changes in the behavior of fishes by increasing the salinity of the water.
We increased the percentage of the salinity of the water by 10% each two days by
adding certain amount of salt.
By observing the experimental fish and recording the times of their deaths, so that
survival time can be considered in relation to the salinity.
Details of the freshwater fish
Family: minnow
Common name: Golden tiger barb
Scientific name: Capoeta tetrazona
Feeding Habits
Fresh spinach, zucchini, peas and lettuce. Live blood worms, glass worms, brine shrimp
and tubifex worms. Frozen vegetable diet, daphnia, plankton, beef heart, brine shrimp,
glass worms and blood worms. Flake and freeze dried foods also accepted.
Compatibility
Extremely active schooling fish that will harass smaller fish and slow moving fish.
Recommended for the active aquarium only.
Habitat
Indonesia-Borneo: Moderately decorated with rocks, live plants and driftwood. Live plants
may be nibbled on.
Breeding
Adult males display more red coloration in their fins and nose area.
Additional Comments
There is a misconception that all the members of the Barb Family are aggressive towards
other tank mates. Tiger Barbs are very active fish and if kept in schools of five or more
they usually stick to themselves, and not bother the other fish in the aquarium as often as
one or two Tiger Barbs would.
Family: Tetraodontidae
Common name: Green Puffer
Scientific name: Tetraodon fluviatilis
Physical description:
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Size: up to 6 inches (15 cm).
Strata: bottom, middle.
pH range: 7.5 to 8.5.
Temparature: 75 to 82F (24 -28C).
Color: white underbelly and yellow/green top covered in black spots, this top
coloring ranging from dark green to fluorescent green to yellow.
Very thick set and shaped, protruding eyes and very broad forehead.
Fan shaped Caudal fin and no Ventral fins.
The body covered with small spines and leathery texture skin.
General information:
Puffers are of the family Tetraodontidae, meaning four toothed. They have a club-shaped
and unarmored body. Green Puffer is a freshwater to light brackish species inhabiting
rivers, lakes and flood plains. It is mostly carnivorous (mollusks, crustaceans, invertebrates)
and also will eat vegetation. Generally a peaceful fish, but as it gets older it can get more
aggressive, especially, when harassed by potential predators and a notorious fin-nipper.
Green puffer with a smooth belly is very popular, it is often confused wity t. nigroviridis,
and also t. schoutedeni, which are more club-shaped. The green puffer exhibits a torpedo
shaped body, with a longer sloping head and back region.
T. fluviatilis
T. nigroviridis
Special anatomical, physiological
or behavioral adaptations:
The pufferfishes are unique in that they are able to inflate predators, making them at least
twice as big. They do this by sucking in and retaining water or air in their bodies. Puffers
have a pair of sharp front teeth which resemble a parrot's beak, and enable them to crush
the shellfish and crabs they usually feed on. Pufferfishes themselves should not be eaten
for they often contain a virulent toxin in their tissues.
Comments about the Green Puffer of the Fort Worth Zoo:
Usually seen at aquarium when they are small, they can grow to 4-6 inches and do some
serious damage to most fish. Therefore, these fish should be keep in small groups. The
female lays a clutch of 150-200 eggs onto a flat surface and the male guards them until
hatched.
Data and results
Salinity in sea water:
35g in 1000ml(measured by a salinity meter used in fish shop)
Calculation:
*total amount of salt added / total amount of water *100%=percentage of salinity of sea
water.
 The percentage of the salinity of the world’s seawater is 3.5%
# percentage of salinity of water/percentage of salinity in sea water *100%=
concentration of salinity in the freshwater when compared with sea water.
For Golden tiger barb
Table showing the salinity of the water
Date
Volume of
water(ml)
Amount of salt
added (g)
Total amount of
salt in water (g)
Percentage of
salinity of
water (%)*
6.11.2006
3000
0
0
7.11.2006
3000
8.25
8.25
0.275
9.11.2006
3000
8.25
16.5
0.55
13.11.2006
4000
16.5
33
0.825
20.11.2006
3000
8.25
33
1.1
22.11.2006
3000
8.25
41.25
1.375
24.11.2006
3000
8.25
49.5
1.65
0
Table showing any changes in the behavior of fishes in saline solution of different
concentration
Date
7.11.2006
Changes in fishes
3 fises are take part in the experiment.
They are healthy and swim very quickly
8.11.2006
The color of their back turns brick red
9.11.2006
Same as before
10.11.2006
Same as before
13.11.2006
The water was changed. Same as before. Another small fish was
added ,water was changed
14.11.2006
The 3 old fishes were the same as before. The color of the small fish’s
back turns brick red, and swam quickly.
15.11.2006
Same as before
20.11.2006
The water was changed, fishes were healthy although no food supply
for 4 days (holidays).
21.11.2006
Same as before
22.11.2006
Same as before
23.11.2006
3 big fishes were healthy; the small fish did not eat.
24.11.2006
3 big fishes were healthy; the small fish did not eat.
25.11.2006
3 big fishes were healthy; the small fish died, the area near its gill
turned from golden yellow to red.
27.11.2006
3 big fishes died as well.
Table showing no. of survival date and concentration of salinity
Date
concentration of salinity in
the freshwater when
compared with sea
water.(%)#
Number of Number of fish present
accumulated
survival
date
6.11.2006
0
0
3 elder fish
7.11.2006
(0.275/3.5*100%)7.86
1
3 elder fish
9.11.2006
15.71
3
3 elder fish
13.11.2006
23.57
7
3 elder fish+1 younger fish
20.11.2006
31.43
14
3 elder fish+1 younger fish
22.11.2006
39.29
16
3 elder fish+1 younger fish
24.11.2006
47.14
18
3 elder fish+1 younger fish
25.11.2006
47.14
19
3 elder fish
27.11.2006
47.14
21
0
After all the fishes died, we disectd the 3 big fishes. We find out that one of the fishes
is a female because we find some eggs inside its abdominal cavity. One of the fishes
is a male because no eggs were there. However, the eyes of one of the fishes turned
milky and some yellow mucus was flowed out of its mouth and it smelled nasty. Also,
its abdominal cavity becomes brown in color, it was hard to distinguish the structure
of its tissues.
Table showing the salinity of the water
Date
Volume of
Amount of salt
Total amount of
Percentage of
water(ml)
added (g)
salt in water (g)
salinity of
water (%)
20.11.2006
2000
0
0
21.11.2006
2000
16.5
16.5
0.825
22.11.2006
2000
16.5
33
1.65
24.11.2006
2000
5.5
38.5
1.925
7.12.2006
2000
5.5
44
11.12.2006
2000
5.5
49.5
2.475
13.12.2006
2000
5.5
55
2.75
14.12.2006
2000
5.5
60.5
3.025
18.12.2006
2000
5.5
66
20.12.2006
2000
5.5
71.5
0
2.2
3.3
3.575
Table showing any changes in the behavior of fishes in saline solution of different
concentration.
Date
Changes in fishes
20.11.2006
4puffer fishes took place in this experiment
21.11.2006
4 puffer fishes were healthy
22.11.2006
Same as before
23.11.2006
The eyes of one of the puffer fishes became milky, the tails of three of
the puffer fishes are beaten off by the biggest puffer fish
.24.11.2006 2 puffer fishes were eaten by the biggest one.
27.11.2006
The remaining 2 fishes still alive, but the fin of one of the fish was
eaten by the biggest one.
28.11.2006
All the fins of the wounded fish were beaten, so it cannot balance its
body, it was thrown to the rubbish bin. The fish was fed with brine
shrimp.
6.12.2006
The last puffer fish was healthy.
7.12.2006
Same as before. Water was changed .
11.12.2006
The last puffer fish was healthy.
12.12.2006
Same as before. Water was changed
13.12.2006
The last puffer fish was healthy.
14.12.2006
The last puffer fish was healthy.
15.12.2006
Same as before. Water was changed
18.12.2006
The last puffer fish was healthy.
19.12.2006
The last puffer fish was healthy.
20.12.2006
Same as before. Water was changed
2.1.2007
The fish was died and the reason is unknown.
Table showing no. of survival date and concentration of salinity
Date
Concentration of salinity in
the freshwater when
compared with sea
water.(%)#
Number of Number of fish present
accumulated
survival
date
20.11.2006
0
0
4 puffer fishes
21.11.2006
23.57
1
4 puffer fishes
22.11.2006
47.14
2
4 puffer fishes
23.11.2006
47.14
3
4 puffer fishes
24.11.2006
55.00
4
2 puffer fishes
27.11.2006
55.00
7
2 puffer fishes
28.11.2006
55.00
8
1 puffer fish
7.12.2006
62.86
17
1 puffer fish
11.12.2006
70.71
21
1 puffer fish
13.12.2006
78.57
23
1 puffer fish
14.12.2006
86.43
24
1 puffer fish
15.12.2006
86.43
25
1 puffer fish
18.12.2006
94.29
28
1 puffer fish
19.12.2006
94.29
29
1 puffer fish
20.12.2006
102.14
30
1 puffer fish
2.1.2007
102.14
43
0
Analysis of the results:
(Background information:
Osmoregulatory mechanism
Fresh water fish live in water with little or no salinity. However, their internal salinity
(body fluid) is 0.9%—just like ours. To complicate matters, a fish must exchange water
with its environment for respiration and nutrition through its gills and its digestive tract, so
it needs a mechanism to prevent its internal salinity from being lost through its gills and
gut to the low concentration in the pond, and correspondingly gaining water. Fish
accomplish this by a mechanism called osmoregulation. One of the main guardians of
salinity is the kidney. As lots of water enter through gills and gut, the kidney retains the
salt and produces huge amounts of very dilute urine.
Differences in osmoregulatory mechanism between freshwater fishes and marine fishes:
Freshwater fish (teleosts) .Their body fluids (1/3 the concentration of sea water) have
a greater concentration than their surrounding environment (hyperosmotic). As a
result they are constantly taking on water by diffusion through their skin and, to a
much larger extent, through the thin membranes of their gills. Therefore, to maintain
the high concentration of their body fluids, they must continuously excrete the excess
water they have absorbed. This is accomplished by highly efficient kidneys which
produce a very dilute urine (Moyle and Cech, 1982). The only problem with such a
high rate of urine production is that a loss of salts and other solutes is unavoidable.
Salts, mostly Na+ and Cl-, are also lost by diffusion through gill membranes. Some of
these can be replaced by ions contained in food but by far the most common method
is through the movement of a substance against an osmotic gradient through the use of
energy. This usually involves the exchange of one substance for another. In the case of
freshwater fish, Na+ ions are taken from the water and ammonia ions are taken from
the fish and they are exchanged. This effectively rids the fish of ammonia. Chloride
ions are exchanged for carbonate ions which helps in maintaining the pH of the body
fluids.
Marine fish (teleosts) .Their body fluids are, again, 1/3 of that of sea water but this
time they are in sea water so their body fluids are hypoosmotic to their environment.
As a result they will tend to lose water by osmosis to the environment through their
skin but mostly through their gills. Consequently, they have developed mechanisms
and behaviour to compensate for this water loss. Firstly, the kidneys of marine teleosts
are modified in such a way that very little water is extracted from the blood, some
species even lack certain kidney structures and can't eliminate water (Gordon, 1977;
Moyle and Cech, 1982). This results in a reduction in the loss of water by the
production of urine. However, water is still being lost by the gills and this cannot be
stopped, so the only method left is to somehow replace the water as quickly as it is
lost. Marine teleosts accomplish this by actually drinking water, the most reliable
drinking rates reported in the literature range from 3-10 ml/(kg hr) (Gordon, 1977).
However, drinking water by itself cannot solve the problem, a complex series of
events must first occur in the digestive tract. These events are not yet well understood
but it is known that most of the water is absorbed as are the monovalent ions Na+ and
Cl- (they are, after all, drinking salt water!), while the divalent ions (such as
magnesium and sulfates) are excreted by the kidneys (Gordon, 1977). Sodium (Na+)
and chloride (Cl-) also move by diffusion into the body through the gills. Therefore,
Na+ and Cl- ions will accumulate in the body of the fish and must be eliminated, this
is accomplished by special cells in the gills called chloride cells, which me these ions
out of the body by active transport
Golden Tiger Barbs do not require any special attention and are rather hardy. They need their
water to be between 68 and 79 degrees Fahrenheit. Golden Tiger Barbs do best in slightly
acidic water, with a pH in the range of six to seven.)
In this experiment, the small golden tiger barb live for 11 days and then die.The
actual reason is unknown,but it didn’t eat for a few days.We guessed it couldn’t
adapt to the change in environment,i.e.change in salinity in water, so it became ill
and finally died.After the small fish died,the other 3 golden tiger barbs died and
they had lived for 21 days.They died suddenly because they were still healthy on
25.11.2006,maybe the small fish got illness and inflect the other fishes.
The osmoregulatory mechanism in freshwater fish is to absorb water
continuously from water to dilute their body fluid.However, as the salinity in the
experimental fish tank increases, the concentration of mineral salts in the water
is higher than that in their body, so water will diffuse out from their body.Since it
is the opposite way of osmoregulation in their body,i.e. initailly,they absorb water
but now,they lose water,so their body may not br adaptable to the change and
affect their health.Marine fishes have the osmoregulatory mechanism to
compensate the loss of water from their body while freshwater fishes do not, so
freshwater fishes cannot live in sea water.
For Pufferfish,they often sold as freshwater fish, but this species actually thrives
in brackish water and may even requires saltwater when reaches adulthood.
Therefore, the puffer fish can live for 43 days in this experiment, which is much
more than that of the golden tiger barb. Initially ,4 puffer fishes are introduced
in the experiment, but as time passed,the stronger fish eat the other fishes.This is
because puffer fish is very aggressive and they eat meat,so they will kill each
others.One thing special is that the strongest puffer fish only beat off the fins of
the other fishes,but not their body.We guess this is due to the presence of toxins
in puffer fish.On the 43 days,the strongest fish died,we don’t know the reason,
and as we left the fish in the laboratory in Christmas holiday(13 days),we don’t
know the actual time when the fish died.The reason for the puffer to die maybe
lack of food.As the fish didn’t die when the concentration of salinity in water is
94.29%,we guess it will not die if the concentration increased to 102.14%.
However, in this experiment,only one type of freshwater fish is analysed and
after the fishes died,we didn’t carry out the same experiment again.Therefore,the
data is not reliable.We should carry out the experiment for a few times and use
different types of fishes in the experiment.
Conclusion for the first part of the experiment:
Freshwater fishes cannot live in sea water because freshwater fishes do not have
the osmoregulatory mechanism to absorb water to compensate the loss of water
into the environment.However, it will not die suddenly, it will get sick and refuse
to eat and finally die.
Topic : The Dissection of two fishes
Aim
The objective of the experiment is to compare the kinds of food obtained by them by
extracting the substances in the stomach and comparing the appearance of their
stomach.
The details of the two fishes
There are two fishes included in the experiment. They are perch(鱸魚) and crucian
crap(鯽魚) respectively.
Perch(鱸魚)
Labrax japonicus
Morthology:
Perch have "rough" or ctenoid scales.. On the dorsal side of the fish, there consists a
upper maxilla and lower mandible for the mouth, a pair of nostrils, and two lidless
eyes. On the posterior sides are the operculum, which are used to protect the gills.
They have a pair of pectoral and pelvic fins. On the anterior end of the fish, there are
two dorsal fins. The first one is spiny and the second is soft. There is also an anal fin,
which is also considered spiny, and a caudal fin. Also there is a cloacal opening right
behind the anal fin.
Crucian crap(鯽魚)
Carassius carassius
The crucian is a medium-sized cyprinid, which rarely exceeds a weight of over 3.3
pounds (1.5 kg). They usually have a dark green back, golden sides, and reddish fins,
although other colour variations exist.
Results
The table showing the difference between the two fishes
Perch
Crucian crap
The size of body(cm)
26.7
25.9
Presence of teeth
present
Absent
The lenght of stomach(cm)
5.1
2.6
The shape of stomach
The stomach of the
The stomach of the
perch is larger and its
crap is slightly conical
thickness is more than
the that of its intestine.
Thus it is easy to
distingish the stomach
and intestine.
and its shape is similar
to its intestine. As the
shape of them are
similar, it is difficult
to recognise the
stomach.
The substance in the stomach
nothing
nothing
The length of intestine
29.0
37.5
The positon of mouth
anterior mouths
inferior mouths
The analysis of the result
Unfortunately, there is nothing can be found in the stomach of both fishes. The fishes
used in the dissection were bought from market, so the fishes may be starved for few
days before we bought them and the food obtained were digested and absorbed.
However, the difference between the size of their stomach can be seen easily.
1. By the presence of teeth and the lenght of intestine, we can know which type of fish
are they. (Carnivorous fishes, herbivorous fishes and omnivorous fishes)
In order to digest and absorb the food efficiently, the intestines of different fish which feed
on different kinds of food developed to its optimum shape during the evolution. For
example herbivores have long intestine and the stomach are short(some the herbivorous
fishes do not have stomach), it can lengthen the time of plant food stay in the digestive
system as the food is difficult to digest. Omnivorous or meat-eating fish have much shorter
intestines and larger stomach, which can suit to their easily digested diet which is rich in
protein.
The intestines run in several coils through the body. The intestines of meat-eating fish are
short and straight, whereas those of plant-eating fish are long and twisting.
As the food resource of herbivorous fishes can be the aqueous plants or algae which
can be ingested without chewing, the presence of teeth is not important of them.
Oppositely, the carnivorous fishes have to chew the solid food(e.g. smaller
fishes),they must have a set of teeth.
2. By the position of mouth, we can also know that the habitats of the fishes
Fish with anterior mouths have horizontal mouths pointing forwards and a body
equally curved at the top and bottom (it is perch in this experiment). These fish live in
the middle water levels and feed there.
Fish with inferior mouths(it is crucian crap in this experiment) usually have bearded
mouths, sloping downwards and a body which curves upwards, with a relatively flat
belly line (e.g. armoured catfish, loaches). These fish feed on the floor, searching for
the food in the deeper sea
There are many intermediate forms between superior fishes and anterior fishes. Fish
from the middle water levels will look for food on the surface of the water and surface
fish will look at lower levels. However, ground feeding fish(fishes with interior
mouths) are reluctant to leave their "realm" to look for food in open water.
The conclusion of this part of the experiment
Although we could not compare the food eaten by the perch and the crucian crap, by
the presence of teeth, the characteristics of their digestive systems, the position of the
mouth, we know that perch is carnivorous fish and live near the surface of the water
and crucian crap is herbivorous fish and live in the deeper of the water.