Ecology of fishes

1. ECOLOGY OF FISHES
1). FRESH WATER FISHES:
• Fresh water means, the tropical fresh water of
Lakes and Streams.
• There are three main factors such as Physical.
Chemical and Biological that determines the
distribution, population/ abundance and
specialization in feeding and reproduction
among the species of fishes in waters of
tropical Lakes and Streams.

2. • Among all three main factors, Biological factors
are more important in determining the fish
distribution, abundance/ population and diversity
of fishes.
• Climatic temperature has a great influence for
multiple generations of these fishes.
• Tropical rivers provide a large base for the
breeding of fresh water species, e.g. Amazon
River in south America drains about 30% of the
total freshwater fish species in the world.

3. • A) PHYSICAL FACTORS: This include the temperature,
Water level fluctuations, gradient and stream order
and turbidity of water.
• B) CHEMICAL FACTORS: This include the
• i) White water: It is characterized by high turbidity
caused by suspended materials, pH of water which
should be around 7 at neutrality, moderate level of
dissolved oxygen and high nutrient level.

4. • ii) Clear water: Clear waters are the transparent
jungle/ forest stream water with moderate to low
gradients, pH rages from 5.5 to 7.8 slightly acidic
with high level of dissolved O2 that support
abundant fish life.

5. • iii) Black water. This is a water of streams of big
forests which is black brown in color, but
transparent and it appears black from distance,
because of high dissolved organic matter.
• Black water are extremely acidic with pH lower
than 4.5 and contain no dissolved nutrients.
• The decay organic matter reduces the amount of
dissolved O2, thus less conducive for supporting
the fish life.

6. • C) BIOLOGICAL FACTORS: These factors include
• I) Predators prey relationship: Predatory fishes seems
to exert a stronger influence on the community
structure of tropical fishes and predation is the
ultimate cause of death in most of these fishes.
• Ii) Competition: Food resources competition is an
important factor both for tropical and temperate
waters for the survival and livings of fish types.
• Studies have shown that certain kinds of food ,
segregation among fish species and their population
are regulated by random environmental events.

7. • Symbiosis: This means the dependence of
tropical water fish species as a part of their
food live on other fish body parts such as fins,
scales and gills.
• For example, the South American cat fishes
enter the gill chamber of large fishes where
the feed on gill filaments and the blood etc.

8. • 2. BRACKISH WATER FISHES/ ESTUARIES
• Brackish water / Estuaries are traditional environments
between fresh water and salty water. Basically, the
estuaries are the Bays
• ( where the rivers and ocean meet together) whose
waters are significantly diluted by flowing river waters.
( Distt. Thatta in Pakistan).
• Estuaries fishes are therefore, a the mixture of
tolerant species of fishes of both marine and fresh
water environments which include the fish species
migrating from one environment to another and a
small no. of resident/ local fish species.

9. • The fluctuating physical and chemical environments
limits the no. of fish species in estuaries.
• But the abundance of nutrients allow the estuaries to
support large concentration of individual fish species.
• These individuals often belong to economically
important species which are the major source of food
supply.
• According to an estimate 8% 0f the total commercial
mature species catch come from estuaries.

10. • Unfortunately, the estuaries are located near big
urban centers, like New york, Mumbai and
Karachi etc.
• Huge amount of garbage and sewerage water is
added in these estuaries on daily basis, therefore
the water really becomes brackish in these areas.
• However, fortunately, the fish species adjust
themselves in such environment of estuaries and
live under such conditions.
• Following topics will be discussed concerning the
estuaries species of fishes.

11. 1) CHARACTERISTICS OF ESTUARIES:
• The characteristics of estuaries depends upon its
size, shape, geological history, location, amount
of fresh water flow and nature of surrounding
land.
• However, no estuary have a common
characteristics, but provide a good food source in
the form of gradient for fish population.
• Amount of fresh water flow from rivers and back
through of ocean water during storms in the form
of huge waves effect the fish population.

12. • The fluctuating nature of estuaries
environment means the fishes have to spent a
considerable amount of energy for their
adjustment in changing conditions.
• Further more, the large amounts of pollutants
in the form of chemicals, heavy metals and
garbage from cities are very dangerous for fish
population and also toxic for humans/ animals
if used for drinking.

13. • II) TYPES OF ESTUARIES FISHES:
• Broadly, speaking the estuaries fish specie are of five
main types.
• Typically, an estuary has the representatives of all five
type of fishes and their abundance varies from season
to season and locality to locality.
• a) Fresh water fishes: These may complete their entire
life cycle in upper reaches of estuaries and invade low
reaches in response to decreasing salinities.
• Most true, the fresh water fishes are not found at
salinities higher than 3-5ppt and most tolerant species
up to 10-15ppt.

14. • The fish species live in upper reaches of North
American estuaries are white cat fish, mosquito
fish, sun fish and common carp fishes.
• b) Diadromous fish: These are found in large
number within estuaries and they pass through
on their way to either fresh or salt water.
• The estuaries for these fishes act as staging areas
and may remain in them for several days or
weeks before finally moving upstream.
• The fish species in this group include, the
Salmons and Shads.

15. • iii) True estuarine fishes: These are those fish
species that spend entire life cycle of their life in
estuaries and these are abundant of species
world wide.
• The fish species in this group include the gobies,
anchovies, mullets, cockers and other resident
fishes of estuarine ecosystem.
• Iv) Non Dependent Marine Fishes: These are
commonly found in the lower reaches of
estuaries

16. • But do not depend on them to complete their
life cycle.
• These species may be an important part of
estuaries ecosystem, but they also are a part
of shallow water marine environment.
• Two main species of fish in this category
include the stag horn Scalping and Shiner
perch.

17. • V) Depend Marine Fishes: These fishes usually
spend one stage of their life in estuaries using
them as spawning ground as nurseries for the
young and feeding ground for adults.
• The fish species in this group are Mangroves
which serve as a nursery area for adults.

18. • It also depend upon the oxygen level, marsh
vegetation, predation, interspecific competition
and invasion etc.
• Iv) FOOD WEBS: Food predominantly in the form
of detritus ( Debris, mixture etc.) which is
abundant in estuaries.
• But the availability of a particular food show
considerable fluctuations even over a short
period of time.
• Therefore, most of the estuaries fishes are not
specialized feeders.

19. • 3). FACTORS THAT AFFECT THE DISTRIBUTION
• The distribution and abundance of estuaries
fishes are determined primarily by physical and
chemical factors and secondly by biological
factors reason being that most of estuaries fishes
are part time residents as these fishes move from
fresh water to sea water and vice versa in search
of food.
• The seasonality of estuarine fish population
seems to be created primarily by their responses
to temperature and salinity.

20. • 5). FISH SPECIES: The fish species that make up
estuarine fish communities are usually consistent
and predictable.
• The composition of fish community in a given
• circumstances is dependent on the season of the
year, temperature, salinity and gradient etc.
• 6) LESSONS FROM ESTUARIES SPECIES: Despite,
the high variability of estuarine conditions,
estuaries species typically have predictable
patterns of distribution and abundance.

21. • On broader scale, the no. of species using
estuaries increases from temperate to tropical
areas.
• The estuarine fish population can change
dramatically in response to disturbances as a
result of human activities.

22. MARINE FISHES
• CHARACTRISTIC: Generally speaking, the fishes in
this group are capable of living both in fresh and
marine waters. The fishes are cool blooded
covered with scales and equipped with a pair of
fins to swim in the water.
• Marine fishes are also called salt water fishes that
can live and swim alone or in a large group
together.

23. • Marine life or sea life or the ocean life is the
plants, animals and other organism that live in a
salt water of the sea.
• Marine fishes range in a size from the
microscopic to the biggest size as the whales,
including the phytoplankton which can be a part
of food for other fishes.
• These phytoplankton lack the cellular structure
which is generally considered necessary for life.

24. • Marine/Sea/ocean life is the plants, animals
and other organism that live in salty water of
the sea.
• Marine species of fishes range in size from the
microscopic including the phytoplankton
which can be a part of for all other fishes.
• These phytoplankton's lack the cellular
structure which is generally considered
necessary for life

25. • Marie/ Salt fishes have small scales than fresh
water fishes who have large scales.
• Marine fishes are vertebrates having 5-7 gills
which directly open in to the sea water.
• According to an estimate world oceans have
more than 20.000 species of fishes and marine
fishes are available in all shapes, size, color
and drastically live in different depths and
extreme temperature conditions.

26. • Most of the marine fishes live on different
continents and regions.
• A large number of marine fish species have a
variant and complex habitats within the open
nature of coastal ecosystem.
• While studying the ecology of marine fishes,
three aspects are kept in mind.
• Firstly, the marine fishes prefer to live/ tied to the
bottom.
• 2ndly, the marine fishes can survive/thrive into
constantly changing/ fluctuating ocean graphic

27. • Conditions such as big storms, pollution and
variable temperatures.
• Thirdly, the fish population is connected/
dependent to the larvae movements with
current waves of water and active
movements by adult fishes in response to the
change of oceanographic conditions.