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ZZOOOOPPLLAANNKKTTOONNSS

Dr. Subhendu Datta

Sr. Scientist

Kolkata, India

The zooplnktons are exclusively of animal origin. In ponds, they mainly comprise protozoans,

rotifers, cladocerans, copepods and their larval forms. In older classification, Protista, a

kingdom into which all organisms of simple biological organization were classified. In

modern classification, it has been replaced by the Protoctista. Protoctista is a kingdom

consisting of unicellular or simple multicellular organisms that posses nuclei and cannot be

classified as animals, plants or fungi. Protoctista includes protozoa, algae, dinoflagellate,

oomycota and slime moulds. Common freshwater zooplanktons are described here with their

identifying characters.

Protozoa (Greek, Protos-first; zoon- animal)

Characteristics: Single celled or in colonies of like cells (no tissues); symmetry-spherical,

bilateral or none. Size usually microscopic. 30000 species present.

Paramecium: Older classification New classification

Kingdom-Protista Kingdom-Protoctista

Phylum- Protozoa Phylum- Ciliophora

Class- Ciliata Class- Ciliata

Order- Holotricha (or, Holotrichida) (rest is same)

Family- Paramecidae

Genus- Paramecium

Microscopic, unicellular organisms, body slipper shaped, posterior end pointed, body covered

with small cilia. Two contractile vacuoles, one in front and another in rear half of cell.

Protozoa

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Amoeba: Older classification New classification

Kingdom-Protista Kingdom-Protoctista

Phylum- Protozoa Phylum- Rhizopoda

Class- Sarconida (Rhizopoda) Class- Lobosa

Order- Amoebaea (or, Amoebina) (rest is same)

Family- Chaosidae, Mayorellidae, Hartmannellidae, Hyalodiscidae

Genus- Amoeba

The amoeba appears to be the simplest possible living animals, an independent cell with

nucleus and cytoplasm but no permanent organelles. Movement by forming and extending

temporary fingerlike extensions or pseudopodia (pseudo-false; pods- foot). Contractile fluid

filled vacuole and food vacuoles are present. Pseudopodia lobose, fingerlike.

Rotifera (Rotatoria- wheel animalcules)

A phylum of microscopic (0.04 – 2.00 mm), pseudocoelomate aquatic animals characterized

by a crown of cilia at the head end. These are used in locomotion and in some species for

feeding the crown (corona), resemble a rotating wheel when the cilia are beating. Rotifers

posses jaws and are covered with a layer of chitin (the lorica). There is no circulatory system

and gas exchange occurs across the body surface. Some rotifers reproduce by

parthenogenesis. On the anterior end is a retractile disc or corona (often double) rimmed with

cilia. Most of the common aquatic bdelloid rotifers can usually be recognized at a glance

under low power because of the characteristics “2-wheeled” appearance when swimming or

feeding, or by the method of crawling on the substrate. Most of the bdelloids may crawl in

inchworm or leech fusion on surfaces with the corona withdrawn.

Classification: Old classification

Phylum- Aschelminthes (Trochelminthes)

Class- Rotatoria

New classification

Phylum- Rotifera

Class- Monogononta, (freshwater rotifers, 1 ovary, Bdelloidea- 2 ovaries)

Seisonidae (marine rotifers)

A. Order- Ploima

(i). Family- Brachionidae

Sub-family- Brachioninae Examples of genera: Keratella, Kellicottia, Brachionus etc.

(ii). Family- Asplanchnidae Example of genera: Asplanchna

(iii) Family- Synchaetidae Example of genera: Polyartha

B. Order- Flosculariaceae

(i). Family- Testudinellidae Example of genera: Filinia

1. Keratella: Conical in shape, outer covering or lorica box-like with polygonal facets. Four

to six spines at anterior margins while 1-2 at posterior (spine are symmetric although not

necessarily equal).

2. Kellicottia: Body enclosed in a transparent box or lorica; anterior spines asymmetrically

unequal in length.

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3. Brachionus: Inhabit wide range of water bodies such as freshwater, backwater, saltlakes

and brackishwater. Size 120-250µ. Body enclosed in dumble shaped lorica, even number

(generally six) of spines projecting at anterior margin, foot annulated and retractile.

4. Asplanchna: Body large sac-like, lorica absent, spines absent, foot absent.

5. Filinia: Two to three very long movable appendages extends from anterior side, body

shape indefinite, foot absent (appendages are setiform extensions of cuticle).

Filinia

Brachionus

Keratella

Kellicottia

Asplanchna

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Arthropoda

With paired, joint appendages on a body nearly always segmented (segmentation is obscured

in some crustacea, especially smaller ones).

Crustacea (a sub-phylum under the phylum arthropoda): Two pairs of antennae, respiration by

gills or body surface.

The segmented body usually has a distinct head (bearing compound eyes, two pairs of

antennae and various mouthparts), thorax and abdomen and is protected by a shell-like

carapace. Each body segment may bear a pair of biramous appendages used for locomotion,

as gills and for filtering food particales from the water. Appendages in the head region are

modified to form jaws and in the abdominal region are modified to form jaws and in the

abdominal region are often reduced or absent. Typically, the eggs hatch to produce a free-

swimming nauplius larva. This develops either by a series of moults or undergoes

metamorphosis to the adult form.

Euchlanis

Gastropus

Plyartha

Testudinella

Macrotrochella

Trichotria

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Nauplius larva: It has an unsegmented body with a single eye at the front (the nauplius eye),

mandibles, antennae and three pairs of limbs. Free-swimming larvae of crustacea.

Cyclops Nauplii

Class- Copepoda: Usually 0.5 to 2 mm long and lack both a carapace and compound eyes.

Five or six pairs of thoracic appendages, first 4 pairs being biramous, body small, cylindrical

and divided into a metasome (sometime called cephalothorax. It is the body segment of

copepods composed of the head and thorax) and a urosome (include the genital segment and

succeeding abdominal segments). Parasitic forms are greatly modified. Example- Cyclops,

Diaptomus, Canthocamptus.

Class- Branchiopoda (phyllopods):- Many pairs of flattened appendages on thorax serving for

both locomotion and respiration.

Order: Cladocera (water fleas): Four to 6 pairs of thoracic appendages; body compressed, all

except head usually enclosed within a bivalve carapace. Second antennae used for

locomotion, single compound eye.

Cyclops: Phylum- Arthropoda

Sub-phylum

(or, super-class)- Crustacea

Class- Copepoda

Order- Cyclopodia

Family- Cyclopoidae

Genus- Cyclops

Free living copepoda. Body elongated, head and thorax united, antennae shorter than

cephalothorax, a pair of branched swimming feet in genital segment, female carries a pair egg

sacs laterally. Abdomen without appendages. Freeliving, have single median eye.

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Diaptomus: Phylum- Arthropoda

Sub-phylum- Crustacea

Class- Copepoda

Order- Calanoida

Family- Diaptomidae

Genus- Diaptomus

Free living copepoda. Body long and pear shaped

but without shell like covering. Four or 5 branched

feet. One egg sac carried medially in case of female.

Antennae as long as body (urosome), 23-25 segments.

Canthocamptus: Phylum- Arthropoda

Sub-phylum- Crustacea

Class- Copepoda

Order- Harpacticoida

Family- Canthocamptidae

Genus- Canthocamptus

Free living copepoda. Body linear, cylindrical, completely

segmented, usually carried one egg sac laterally.

Antenna smaller than cyclopoid, 8 segmented,

Cephalothorax not sharply differtiated, last thoracic

segment included in the urosome.

Daphnia: Phylum- Arthropoda

Sub-phylum- Crustacea

Class- Branchiopoda

Order- Cladocera

Family- Daphnidae

Genus- Daphnia

Daphnia species have a transparent carapace and a protruding head with a pair of highly

branched antennae for swimming and a single median compound eye. No transverse suture on

neck, shell with polygonal marks and with posterior sharp spine, 5 pairs of thoracic

appendages form an efficient filter-feeding mechanism. Rostrum present, cervical sinus

absent.

Cyclops

Diaptomus

Female Diaptomus – Side view

Canthocamptus

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Daphnia

Ceriodaphnia: Phylum- Arthropoda

Sub-phylum- Crustacea

Class- Branchiopoda

Order- Cladocera

Family- Daphnidae

Genus- Ceriodaphnia

Head without a beak, small and depressed, antennules small,

first antenna short, valves oval or rounded ending in a

sharp short dorsal spine. Rostrum absent, cervical

spine present.

Ceriodaphnia

Moina: Phylum- Arthropoda

Sub-phylum- Crustacea

Class- Branchiopoda

Order- Cladocera

Family- Daphnidae

Genus- Moina Moina

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Body heavy with rounded abdomen, head large, rounded in front with depression above eye.

Antennules long and freely movable, abdominal setae very long.

Moinodaphnia: Phylum- Arthropoda

Sub-phylum- Crustacea

Class- Branchiopoda

Order- Cladocera

Family- Daphnidae

Genus- Moinodaphnia

Valves elliptical, head small, antennules on ventral surface of head, Moina (Small)

minute spines on ventral margins, sharp angle but no spine at

junction of dorsal and ventral side.

Simocephalus – female & developing young

Simocephalus: Phylum- Arthropoda

Sub-phylum- Crustacea

Class- Branchiopoda

Order- Cladocera

Family- Daphnidae

Genus- Simocephalus

Cervical sinus present, no crest. Head and rostrum

small, valves large and somewhat quadrate and Simocephalus - mother and young

without posterior spine, markings of transverse

lines over lorica.

Bosmina: Phylum- Arthropoda

Sub-phylum- Crustacea

Class- Branchiopoda

Order- Cladocera

Family- Bosminidae

Genus- Bosmina

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Antennules large, fixed to head and parallel. Post abdomen quadrate, 6 pairs of feet.

Bosmina – Female (Single) Number of Bosmina Female

Macrothrix: Phylum- Arthropoda

Sub-phylum- Crustacea

Class- Branchiopoda

Order- Cladocera

Family- Bosminidae (?)

Genus- Macrothrix

Head large, its dorsal margin rounded over abruptly

into anterior margin, first antennule long and freely

moving, valves reticulate, 6 pairs of feet, abdominal

setae present.

Sida: Phylum- Arthropoda

Sub-phylum- Crustacea

Class- Branchiopoda

Order- Cladocera Macrothrix

Family- Sididae

Genus- Sida

Head large and separated from the body by a depression, rostrum pointed and forms beak, a

large cervical gland on head. First antennae one jointed with long terminal flagellum. Cervical

sinus present, rostrum present dorsal ramus of antenna 3-jointed.

Sida

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Diaphanosoma: Phylum- Arthropoda

Sub-phylum- Crustacea

Class- Branchiopoda

Order- Cladocera

Family- Sididae

Genus- Diaphanosoma

Head more depressed, dorsal more arched, rostrum absent, antennules small, attached to basal

part with setae on each side and long slender flagellum. No anal spines on post abdomen,

claws with 3 basal spines.

Diaphanosoma

How to Identify a Zooplankton?

To identify zooplankton requires use of a compound microscope. A dissecting

microscope is also handy for sorting and counting. Specimens are mounted on glass

slides and examined at 25-100X magnification. Comparison of your animal with an

image, whether a photo (this web site) or line drawings (in taxonomic keys), is only a

first step to identification. In order to identify your animal to species requires that you

consult one or more of the above-cited sources, learn some anatomical terminology,

and follow the keys. However, you can develop an eye for certain characteristics

useful for discriminating species by examining your animal under the microscope

(best) and by referring to photos in this web site. In particular, consider the following

traits. What is the general body shape? (Try drawing the outline of the body.) What is

the color? Opaque or translucent? Examine the relative length of appendages (e.g.

antennae, legs) and setae (hair-like processes). Notice presence and relative size of

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spines. For more-detailed descriptions of taxonomically-useful anatomy, please

consult any good text book (Edmondson, 1959; Thorp and Covich, 1991).

Also notice the size of your animal. Taxonomic keys often include questions

about size. Determining size may seem tricky at first, but it is basically like using a

ruler in everyday life. You need to know the scale of your ruler and then match it with

items of interest. The standard ruler for a microscope is called an "ocular

micrometer", which is fitted into the eyepiece of your microscope. In lieu of a

micrometer, you can use the diameter of the field. Each of these methods requires

that you first standardize your microscope against a ruler of known length; at low

magnification, this standard could be a transparent office ruler, but at higher

magnifications a stage micrometer is needed. Be aware that different microscopes

are not exactly the same and the size goes down with increased magnification. For

example, a microscope at 100X has a field diameter of about 1,500 µm, but at 250X

this diameter is 450 µm.

Plankton Analysis

Information on the abundance and variations of natural fish food organisms is necessary for

proper fishery management. Methods of plankton analysis include collection of plankton

samples and analysis of the samples both quantitatively and qualitatively.

A. Collection of samples

In fish ponds plankton samples are generally collected using a truncated cone shaped net by

filtering known volume of water (normally 50 or 100 1). The plankton sieving net is the

common equipment used and is made of bolting silk cloth No. 25 (# 0.064 mm mesh size) for

phytoplankton and No. 13 (# 0.112 mm mesh size) for zooplankton.

The plankton cloth is cut based on the following calculations.

Using 1+X as radius, lay off the arc C on a piece of paper. At Centre h, lay off angle a by

means of a protractor and draw lines he and hf. With x as radius, draw arc C of smaller circle.

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Leaving 1 cm all along the sides, the cloth may be cut and stitched and fitted onto a brass

frame having wooden handle.

For he and hf, mark points at 90 + 53.3 = 143.3° and 90 - 53.3 = 36.7°

Usually about 50–100 1 of water is filtered through the plankton net and the sample is

preserved in 5% formaldehyde. In the laboratory, the preserved plankton samples are analysed

for quantitative and qualitative aspects.

B. Quantitative analysis of total plankton:

Settling volume:

Transfer the sample to a graduated cylinder or centrifuge tube and allow sufficient time (at

least 6–8 hours) for plankton to settle at the bottom and record its volume and express the

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volume as ml of plankton/1 or ml of plankton/m3. Centrifuge of the samples may also be

resorted to, for quicker analysis.

Wet weight:

The plankton sample is filtered through bolting silk cloth, excess water is blotted out and the

residual material is weighed. The wet weight is expressed as mg/1 or g/m3 water.

Dry weight:

After taking the wet weight, dry the plankton samples in a hot-air oven at 60–80°C for about

six hours and take the weight on a sensitive balance. Express the weight as mg/1 or g/m3.

Numerical count:

Dilute the filtered sample to a known volume, say 10 ml, and take for counting under

microscope. Shake well the diluted plankton sample and take one drop for counting on a

glass slide and cover with a cover slip or take 1 ml of plankton suspension in the Sedgewick-

Rafter counting cell having a capacity of 1 ml with its area divided into 1 000 equal squares.

Count the number of plankters under microscope with 10x and 10x lenses. If 100 squares at

random are counted, and 100 1 water had been filtered, the number per litre will be given by

X × 10 × 10÷100, where X is the number of plankters. While only the larger plankters are

counted in the “survey count” method, all the plankters are counted in the “total count”

method.

C. Qualitative analysis of plankters:

The “differential count” method is usually followed which requires enumeration of some or

all kinds of plankters, distinguishing them qualitatively into species or genera of

phytoplankton and zooplankton. Shake well the diluted plankton sample and take 1 ml of

plankton suspension in Sedgewick-Rafter counting cell or one drop on a glass slide and cover

with cover slip and count following the method described for numerical count. Instead of

counting the total number of plankton, count important groups of phytoplankton and

zooplankton separately. Important groups of phytoplankton usually encountered are green

algae (chlorophyceae), diatoms (Bacillariophyceae), blue-green algae (Cydnophyceae),

dinoflagellates (Dinophyceae) and chrysomonads (Chrysophyceae). Zooplankton in ponds

mainly comprise protozoans, rotifers, cladocerans, calanoid and cyclopoid copepods and their

larval forms and occasionally nematodes and ostracods.

Based upon the total counts, percentage composition of the different forms as well as

phytoplankton and zooplankton as a whole may be calculated with their seasonal variations.

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Literatures

1. Edmondson, W.T. (ed.). 1959. Freshwater biology. Wiley.

2. Thorp, J.H., and A.P. Covich. (eds.). 1991. Ecology and classification of North American

freshwater invertebrates. Academic Press, San Diego.

3. Kumar, D. 1992. Fish culture in undrainable ponds. A manual for extension. FAO Fisheries Technical Paper No. 325. Rome, 239 p.