2. WHAT EXACTLY ARE PLANKTON?
1. Plankton are weakly swimming or drifting organisms
2. “Plankton” is not a single species but a large group of
organisms that fall into two primary categories:
• Phytoplankton (plants)
• Zooplankton (animals)
3. Many are microscopic, some visible to the naked eye
3. WHY ARE PLANKTON IMPORTANT?
Important part of global carbon cycle
Food source (basis of the food web)
Producer of oxygen (photosynthesis)
4. LINK IN THE FOOD CHAIN
There are several other fishes and mammals in the sea
whose life is linked with phytoplankton. Each species has its
own period of growth and the growth intensity depends on
many external factors such as temperature, salinity,
nutrients and the physiological state. These factors are
influenced by season and climate.
The largest fish-the basking shark, is also a planktonic
feeder, mainly feeding on the copepod Calanus which
survives on the phytoplankton. The fishery for oil sardine
and mackerel are entirely dependent on the bloom of
phytoplankton along the west coast of India.
5. FISH PLANKTON RELATIONSHIP
The plankton occupies the first trophic level in the food
chain and hence its contribution to the subsequent higher
level of energy transfer is of great importance to the fishery
biologist. Both herbivorous and carnivorous fishes do
depend upon the plankton as their source of food and
ultimately as their source of energy.
The relationship between plankton and fish are manifold in
the aquatic environment.
6. THE REMARKABLE RELATIONSHIP OF PLANKTON AND FISH
Plankton as food of fishes
Plankton as an index of fish abundance
Mutual relationship
Host parasitic relationship
Plankton as a causative agent of fish
mortality
7. PLANKTON AS FOOD OF FISHES
Young stages of many bottom living fish feed on plankton. It is thus
clear that their abundance and their distribution are directly linked to
the plankton. Plankton is thus of fundamental important to the
fisheries through a shorter or longer food chain according to the type
of food the fish eat.
Adult fish living on the bottom are also dependent on the plankton,
not so directly as the larvae and the pelagic fish,
Rotifers are of substantial importance to freshwater fishes. For many
fishes, rotifers are the basic food in the earlier stage of life history.
The crustaceans are one of the most important groups of plankton
population in relation to fish particularly in respect of their food.
Crustaceans are eaten largely by majority of fishes. The copepods,
chiefly Calanus, constitute the main portion of food of herring.
Although herring will take other foods when necessary, they prefer
Calanus if available in sufficient quantity
8. PLANKTON AS AN INDEX OF FISH ABUNDANCE
The region rich in nutrient usually develops a rich plankton
population and many fishes accumulate there. Of particular
importance to the life of fishes are phosphate and nitrate
because the presence of these compounds particularly
favors the development of organic lives in the water.
It in noteworthy that the numbers of young of certain marine
commercial fishes are in close dependence upon the zone
of maximum plankton production. The adaptive nutritional
significance of the shoal is most strongly expressed in
pelagic shoaling fishes.
9. MUTUAL RELATIONSHIP
At the time of photosynthesis, the phytoplankton uses co2 and
release o2. during respiration the fish use the o2 and liberate co2 which in
turn can be utilized by the phytoplankton during photosynthesis. thus,
both the organisms are benefited through the gas exchange between
them.
Sun
Solar
energ
y
Autotrophs
(primary
producers)
Plant/animal
energy sources
(carbohydrates)
Heterotrophs
(consumers)
10. HOST – PARASITE RELATIONSHIP
Many planktonic copepods act as intermediate hosts and
help in the transmission of certain diseases of fishes. For
example, the life cycle of Bass tapeworm could not be
completed unless the eggs of the Proteocephalus
ambloplitis are eaten by the copepod plankton. Again, this
copepod plankton is eaten by the fish and thus the fish
becomes infected with the disease
11. PLANKTON AS A CAUSATIVE AGENT OF FISH MORTALITY
The extensive literature dealing with the
problem of sudden fish mortality reveals that the
heavy bloom of phytoplankton may be
responsible for the death of fish due to the
reasons as follows:
Accumulation and decay of thick algal
population
Secretion of toxic substances by phytoplankton
Depletion of oxygen
