Feeding ecology of common carp (Cyprinus carpio L.)in a rice–fish culture system of the Apatani plateau(Arunachal Pradesh, India)

S. K. Saikia Æ D. N. Das

Received: 4 August 2007 / Accepted: 3 March 2008 / Published online: 14 March 2008

� Springer Science+Business Media B.V. 2008

Abstract For two years (2002, 2003) selective

feeding ecology of the common carp (Cyprinus

carpio L.) has been studied in carp-integrated rice

fields in Apatani Plateau of Arunachal Pradesh

(India). Sampling strategy was based on the water

depths in the fields and on the flood phases: early

flood phase (June–July), mid flood phase (July–

August), and late flood phase (September–October).

In 2003 the water level was higher and therefore

periphyton availability was better. This resulted in

larger gut contents and better growth of the carp

compared with 2002 when the water levels were

lower. Gut contents analyses revealed a total of 60 food

items of which 22 belonged to the Chlorophycea, 12 to

the Cyanobacteria, 10 to the Bacillariophycea and 16

to several zooplankton taxa. With the progress of

flood phases, the fish increased its feeding on

periphyton food items; simultaneously, feeding on

plankton items gradually declined. This was caused

by the increasing periphyton availability on the

rice-stems. Selective feeding on plankton and periph-

yton taxa was studied, selectivity changed with the

flood phases. Periphytic Chlorophycea and Cyano-

bacteria, especially, were strongly positively selected.

Generally, periphyton was the most important

resource for the common carp in the rice fields.

Keywords Rice–fish integration �Periphytophagous � Gut content � Niche breadth �Food selection

Introduction

The common carp (Cyprinus carpio L.) is probably

the first fish species whose distribution was widely

extended by human introduction, since its introduc-

tion by the Romans from the River Danube

throughout Europe (Balon 1995). It is the third most

frequently introduced world-wide species (Welcom-

me 1992). It also accounts for the world’s second

highest farm fish production, mainly from Asia

(Milstein 1992) and for the production of ornamental

varieties with monetary value (Balon 1995).

Despite the common carp’s ubiquity and economic

importance, little is known of its feeding ecology in

natural systems (Crivelli 1981). The functional mor-

phology of its feeding apparatus (Sibbing 1988) and

the impact of this cyprinid species on macrophytes

and water quality (Richardson et al. 1990; Wilcox

and Hornbach 1991; Lougheed et al. 1998) have been

well documented. Yet most of the studies on diet

have been done on fish culture ponds (Crivelli 1981;

Sibbing 1982; Michel and Oberdorff 1995) with a

S. K. Saikia (&) � D. N. Das

Department of Zoology, Rajiv Gandhi University,

Rono Hills, Itanagar, Arunachal Pradesh, India

e-mail: sksaikai@yahoo.com

D. N. Das

e-mail: dndas321@rediffmail.com

123

Aquat Ecol (2009) 43:559–568

DOI 10.1007/s10452-008-9174-y

very preliminary report from rice fields (Chapman

and Fernando 1994).

Fernando (1993) reported the rice field environ-

ment as the richest habitat of aquatic organisms. The

increasing popularity of rice–fish culture in South-east

Asia (Halwart 1998), in turn, is explained by its

potential both ecologically and economically. Besides

all planktonic forms in the rice field environment,

periphyton growing particularly on submerged rice

stems and other submerged objects available in the

field contributes significantly to primary production

(Moss 1998).

Apatani Farmers in Arunachal Pradesh, India have

been using the underwater resources (preferably

periphyton) in their indigenous practice of rice–fish

culture for many decades. Their fields are stocked

with fry (3–5cm) of common carp (Cyprinus carpio

L.) at the density of 2500 numbers ha-1 in late May

just after transplanting rice. The final harvest of fish

performed in late October or early November offers

farmers an average gain of fish of 250–500 kgha-1 in

addition to the main crop i.e. rice at the rate of 1.5–3.0

t ha-1season-1 (Saikia and Das 2004). During the

period of rice–fish farming in these fields no agro-

chemicals (e.g. pesticides, fertilizers, lime etc.) and

supplementary feeds are supplied. In addition to cow

dung as organic manure, sometimes organic wastes

from kitchens, poultry, or pig houses are also supple-

mented in the field during field preparation for rice

cultivation. Thus the fish thrives mainly on natural

food available in the water column of the rice fields

(Saikia and Das 2004). In this study we tried to gain

more insight into the selective feeding of the common

carp in rice field and the factors regulating its gut

fullness and growth.

Materials and methods

Study locations and farmers

The study area, the Apatani plateau (Fig. 1), is

geographically placed at a height of 5,000 feet above

mean sea level and is located at 26�500–98�210Nlatitude and 92�400 and 94�210E longitude. The

plateau covers an area of 10,135 km2. Of the total

terrace wet cropping area of 715.7 ha, rice–fish

culture covers approximately 592.0 ha. Average

rainfall is 108.1 cm and temperature covers a range

from maximum 31.6�C in summer to minimum 1.1�C

in winter. The relative humidity varies from 36.5% to

82.8%. This study was performed in rice fields of

seven villages (Fig. 2). Each year these fields were

selected randomly (Table 1).

Unlike other tribes of this mountainous state of

northeast India, the Apatani tribe is the only agrarian

tribe practising settled agriculture with rainfed and

streamfed irrigation facilities. The average water

levels of fields studied are shown in Fig. 3. Rice is

the principal crop in addition to millet and other grain

CHINA

EAST KAMENG

ASSAM

UPPER SUBANSIRI

Rive field

International Boundary

National Boundary

District BoundaryBlock Boundary

Drainage

Index

2010 0 10 30 Km

N

L O W E R

S U B A N S I R I

Ziro

Hapoli

APATANI PLATEAU

Fig. 1 Map of Apatani

Plateau (Arunachal Pradesh,

India) showing the study

area

560 Aquat Ecol (2009) 43:559–568

123

RICE FIELD

VILLAGE

HILLY PLOT

RIVER

STREAMROAD

N

HAPOLI

ZIRO

HIJA-1

HIJA-2

MUDANG

SURULIA

PAKIN

SALAIA

HARI

INDEX (MAP NOT TO SCALE)

Fig. 2 Map of the study

sites (seven villages) of

Apatani Plateau (Arunachal

Pradesh, India)

Table 1 Summary of the major survey reports of rice–fish

culture fields from Apatani Plateau, Arunachal Pradesh, India

Year Villages Average

field

size (m2)

Maximum

water

level (cm)

Crop yield

Rice

(t ha-1)

Fish

(kg ha-1)

2002 Hija1 1,200 30 2–3 230–350

2002 Hija2 1,900 34 3–4 300–500

2002 Mudang 1,536 40 3–4 300–450

2003 Surulia 1,781 42 3–4 300–500

2003 Hari 2,335 45 3–4 300–500

2003 Pakin 1,230 32 3–4 350–500

2003 Salaia 1,866 30 3–4 350–500

0

5

10

15

20

25

30

2003

2002

July August September October

Wat

er d

epth

(cm

)

June

Fig. 3 Average water levels (cm) in the rice fields of Apatani

Plateau during June-October in 2002 and 2003

Aquat Ecol (2009) 43:559–568 561

123

crops in their homestead plots. The cropping pattern

of the area includes mono-cropping of wet rice once a

year in their wet plots associated with year-round

sequential production of various vegetables on field

dykes and in their homestead plots.

Periphyton and phytoplankton sampling

For periphyton study, rice stems were collected from

the local cultivar three times in a month starting from

June till the end of the cropping seasons i.e. October

of both 2002 and 2003. Individual rice plants usually

reach up to 4–4.5 feet in height and one-third of its

length remains under water for at least three months,

especially in August, September, and October. Rice

stems were collected from a depth of 7.0–8.0 cm

from field water surface and 5.0 cm above the field

bottom, at a constant length of 5.0 cm. These were

then preserved in 4% formalin.

Plankton collection

Water sampling for plankton and periphyton, and fish

gut sampling, were performed on the same day.

Plankton was sampled by pouring 50 l of water

through a 0.20-lm plankton net and was preserved in

4% formalin. In the laboratory, each preserved sample

was centrifuged at 1,500 rpm for 10 min continuously

and the volume was reduced to 10 ml and stored.

Sampling strategy was based on the water depths in

the fields and on the flood phases: early flood phase

(June–July), mid flood phase (July–August), and late

flood phase (September–October).

Fish capture and collection of stomach content

The fishes ([15g body weight) were collected from

trenches of the rice fields after plankton and periph-

yton sampling. These are collected by draining the

fields temporarily. Fish from the larger rice fields

were caught with drag nets from the trenches. The

samples were taken three times a day i.e. in the

morning, at noon, and in the evening and all samples

of a particular time were pooled. All the captured fish

(individual weight range 5-450 g) were individually

weighed using a standard balance. They were

preserved in 10% buffered formalin. The anterior

portion of the digestive tract lying between the

esophagus and the first major bend of the small

intestine was dissected out to obtain identifiable food

items ingested by the fish (Haroon and Pittman 1997).

Each stomach along with the content was blotted

uniformly with tissue paper and weighed. Guts were

cut longitudinally and the fullness was estimated

(fullness index according to Haroon 1998). Only

those guts with fullness greater than 0.25 were

analysed.

Identification and quantification of samples

Samples of periphyton and plankton were identified

under a compound microscope using 400 or 6009

magnification. All organisms were identified up to

genus level (Prescott 1984; Edmondson 1992). Uniden-

tifiable materials of animal origin were recorded as

‘‘unidentifiable animal matter’’ and counted separately

from detritus. After vigorous shaking of the preserved

sample, ten drops of the sample were put on a glass slide

and analysed (ten drops = 1 ml). Plankton, periphyton,

and gut contents were counted by following the Lackeys

(1938) drop count method. To avoid calculation error,

the plankton under the whole cover slip was counted.

For quantification of periphyton, the area of rice

stem was calculated by use of the formula:

A = Pr2h

where A = area in cm2, r = radius of stem in cm,

h = length of stem in cm. Densities of periphyton

were expressed as numbers cm-2.

Food composition and food selection

Relative food composition (Pfi/Tfi) was expressed as

a proportion according to Haroon and Pittman (2000),

where Pfi is the number of a particular food item in

the gut and Tfi is the total number of all food items

combined in the gut.

Diet breadth (B) is a measure of how selectively

the fish utilizes its food resources in the environment

(Levins 1968):

Bx ¼ 1=XðPxiÞ

2

where Pxi = the proportions of food category i in

predator species x. B values vary from 1.0, when the

fish population uses one resource state exclusively

562 Aquat Ecol (2009) 43:559–568

123

and equals 0 when the population uses all resource

states.

Selective feeding was estimated using the model

developed by Haroon and Pittman (1999). It is based

on prey-specific electivity abundance instead of prey

specific abundance as proposed in Amundsen et al.

(1996) and frequency of occurrence of a given food

category or prey type. Ivlev’s (1961) electivity index

was used to measure the selection of available food

organisms by fish:

Ei = Sti � Pi/Sti + Pi

where Ei = electivity index for species I, Sti = rel-

ative proportion of species i in the diet, Pi = relative

proportion of species i in the environment. E values

vary from -1 to +1, values around 0 indicate no

selection, a value of +1.0 indicates strong positive

selection, and -1.0 indicates strong avoidance. Since

Ivlev’s electivity (E) values are sensitive to the

relative densities of the food types in the environment

(Jacobs 1974), food selection was analyzed by

plotting the E values of the food items against their

relative proportion in the environment.

Results

Feeding activity

A plot of weight of gut content against body weight at

different flooding phases revealed significant corre-

lation (Fig. 4). It shows the growth of the fish along

with the gradual progress of the flood phases. Food

intake and fish growth was much larger in 2003 than

in 2002.

Planktonic and periphytic abundance

The food organisms eaten by the common carp were

diverse and included phytoplankton, periphyton

(Chlorophyceae, Cyanobacteria, Bacillariophyceae),

and animal food (Cladocera, Rotifera). In 2002,

Oedogonium was abundant as plankton in all phases.

Cosmarium and Scenedesmus, respectively, were the

next most abundant planktonic genera to Oedogonium.

The periphyton Oedogonium and Cosmarium were

abundant in flood periods other than June–July. In

July–August, maximum periphytic abundances were

shown by Cosmarium, Oedogonium, Scenedesmus,

Tetraspora, Melosira, and Navicula. Navicula was

abundant as plankton in June–July, August–September,

and September–October but its periphytic form was

very abundant in July–August. Melosira abundance

was moderate as plankton and highest as periphyton.

Unlike 2002, in 2003 Oedogonium was abundant

as plankton in all phases and as periphyton except in

June–July. Among the other planktonic forms,

Cyclotella, Melosira, Gleocapsa, Closterium, and

Cymbella were the more or less abundant genera in

the rice fields in June–July and July–August and

declined gradually towards the end of the season. Of

course, except September–October, the periphytic

forms of Oedogonium were highly abundant followed

by Cosmarium, Navicula, and Closterium. Anabaena,

however, was comparatively less abundant in

August–September of this season.

Diflugia, Epistylis, Arcella, Monostyla, Colurella,

and Bdelloid were available planktonic organisms of

animal origin. Of these Arcella and Diflugia were

dominant as both plankton and periphyton in 2002.

In 2003, Diflugia and Epistylis were abundant as

y = 1.8015Ln(x) - 6.3458R2 = 0.2962, n=100

-5

0

5

10

15

0 50 100 150 200 250 300 350 400 450

y = 4.0206Ln(x) - 8.5542R2 = 0.5031, n=275

-5

0

5

10

15

20

25

0 50 100 150 200 250 300 350 400 450 500

Gut

con

tent

(m

g)G

ut c

onte

nt (

mg)

B

A

Body weight (g)

Body weight (g)

2002

2003

Fig. 4 Regression of gut content (mg) against body weight (g)

of common carp (Cyprinus carpio L.) during three flood phases

of 2002 (a) and 2003 (b) from rice fields of Apatani Plateau.

The three flood phases were: filled diamonds = early flood

phase (June–July), empty triangles = mid flood phase (July–

August), and empty diamonds = late flood phase (September–

October). Fish with a gut fullness \0.25 were not included in

the analysis

Aquat Ecol (2009) 43:559–568 563

123

plankton. In this season Diflugia, Arcella, and Lecane

were also abundant as periphyton.

Diet composition

In total, 60 available food items were recorded in the

gut (Table 2). The fraction of these food items used

by the fish showed great variation. During June–July

of 2002 the fish mostly preferred organisms of animal

origin and detritus matter; however, it gradually

extended the resource limit towards Cyanobacteria

preferring Anabaena (fraction used 0.0865 and

0.0734) and reduced to a moderate level during

September–October (fraction used 0.0429). Nostoc

shared a fraction of 0.0769 during July–August

and ended up moderate in September–October

(fraction used 0.0474). Hapalosiphon was common

but showed smaller fractions. Other Cyanobacteria

members like Microcystis or Phormidium were

occasional food appearing in smaller fractions in fish

gut. Again, with the progress of the flood phases it

was inclined further to the Chlorophycean group,

trapping Oedogonium and Cosmarium moderately

during both 2002 and 2003. In September–October of

2002, zooplankton, especially the naupli of Clado-

cera, were consumed extensively (fraction used

0.1084) following Bdelloid, Colurella, Bosminopsis,

Bosmina, Diflugia and Monostyla. In 2003, food

items of animal origin were Moina, Lecane, Polyar-

thra, Diflugia, Brachionus, naupli of Cladocera, and

Epistylis. However, except Lecane and Monostyla,

others did not regularly appear in the fish gut. Most of

them disappeared from the gut during June–July in

both years. In the case of Bacillariophyceae, Navicula

and Melosira frequently appeared, with considerable

fractions during both 2002 and 2003 in comparison

with other members of the group. Detritus appeared

in a variable range throughout the season of both

years. However, in June–July and July–August its

fractions were higher than in August–September and

September–October during both years.

Niche breadth

The Levins niche breadth was compared for two

different resource types, plankton and periphyton, in

the rice field with a view to drawing a more

meaningful conclusion about food accessibility to

the common carp. The lower niche breadth for

plankton in comparison with periphyton indicated

grazing of the fish on periphyton biomass (Table 3).

Table 2 List of food organisms of the common carp (Cypri-nus carpio L.) in rice fields of Apatani Plateau

Chlorophyceae Cyanobacteria Zooplankton

Ankistrodesmusa Anabaenab Diflugiaa,b

Bulbochaeteb Aphanocapsa Copepod nauplii

Closteriopsis Aulosira Arcellaa,b

Closteriuma,b Chroococcus Polyarthra

Cosmariumb Gleocapsa Colurella

Desmidium Gleothece Bdelloid

Euastruma Hapalosiphon Bosmina

Geminella Microcystis Bosminopsis

Gonatozygonb Nostocb Brachionus

Hormidium Phormidium Epistylis

Mesotaenium Spirulina Filinia

Microspora Stegonema Lecane

Oedogoniuma,b Bacillariophyceae Moina

Pediastrum Amphora Monostyla

Penium Cyclotellaa Trichocerca

Pleurotaenium Cymbella Testudinella

Scenedesmusa,b Fragillaria

Spirogyra Gomphonema

Staurastrum Melosirab

Tetraspora Naviculaa,b

Ulothrix Nitzschia

Zygnema Pinnularia

Tabellaria

a Abundantly available as planktonb Abundantly available as periphyton

Table 3 Levins niche breadth (Bx) of common carp (Cyprinuscarpio L.) for two resource types (phytoplankton, periphyton)

during three flood phases in 2002 and 2003 in the rice fields of

Apatani Plateau (Arunachal Pradesh)

Flood phases 2002 2003

Periphyton Plankton Periphyton Plankton

June–July 0.07211 0.01255 0.98468 0.01255

July–August 0.31165 0.02314 1.07961 0.00302

August–

September

0.98268 0.00175 1.11422 0.00250

September–

October

0.10754 0.00522 0.14058 0.00580

Niche measure values[0.60 are shown in bold and are considered

to be biologically significant (Zaret and Randell 1971)

564 Aquat Ecol (2009) 43:559–568

123

In June 2002, the niche breadth of common carp had

an approximately fivefold greater value when periph-

yton was treated as food source. This difference

widens with the progress of the season reaching a

maximum niche breadth during August–September in

2002 and September–October in 2003.

Selective feeding

Both positive and negative selection of food items

was observed (Fig. 5, 6). In 2002, the fish rejected

most of the planktonic Chlorophyceae during June–

July, but showed moderate to strong affinity towards

periphytic Chlorophyceae. The planktonic form of

Oedogonium was preferred by the fish only in July–

August and August–September. In the periphytic

form it was strongly rejected in all flood phases. The

fish exhibited moderate to high selectivity toward

planktonic feed resources, for example Hapalosiphon

in June–July, Melosira, Scenedesmus, and Cosmari-

um in July–August, Anabaena, Oedogonium, and

Lecane in August–September, and Monostyla in

September–October. The strong planktonic candi-

dates for fish food were Pediastrum, Microspora,

Bulbochaete, and Ankistrodesmus in June–July, July–

August, August–September, and September–October,

respectively. They were less abundant but highly

preferred by the fish. However, strong food selectiv-

ity for periphytic organisms was observed for

Bulbochaete and Nostoc in June–July, Closterium in

July–August, Penium in August–September, and

Aanabaena and Staurastrum in September–October.

The moderate to high periphytic choices were Arcella

in June–July, Chroococcus in July–August, Diflugia

and Spirulina in August–September, and Euastrum

and Melosira in September–October.

In 2003, Oedogonium was strongly rejected by the

fish as planktonic feed. Navicula was also mildly

rejected. The strongly selected planktonic feeds were

Ankistrodesmus in June–July and August–September,

and Desmidium and Closterium in July–August

and September–October, respectively. However,

moderate selectivity was shown to Closterium in

June–July, Testudinella and Closterium in July–

August, Diflugia and Spirulina in August–September,

and Gomphonema in September–October. The strong

periphytic candidates were Hormidium and Closteri-

um in June–July, Cyclotella in July–August, Penium,

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

AnkistrodesmusBulbochaete MicrosporaPediastrum Oedogonium

2002

Nostoc

Anabaena Lecane

OedogoniumClosterium

Hapalosiphon

Scenedesmus Unid

CosmariumMelosira

Melosiraentified zoo Monostyla

Cosmariumus

ClosteriumDiflugia, Lecane Arcella

MicrocystisDiflugiaNaviculaNaupliaArcellaTrichocerca

-1

E F G H

A B C D

Oedogonium

Nauplia MonostylaNavicula

Pinnularia

Pediastrum

Oedogonium Scenedesmus

BrachionusScenedesmus

EuastrumStaurastrumAnabaenaBulbochaete

Penium DetritusDiflugiaSpirulina

GomphonemaEuastrum

ClosteriumNostoc

Arcella Chroococcus MelosiraDiflugia

Unidentified zoo

OedogoniumSpirogyra

Navicula

GomphonemaUnidentified zoo

CosmariumPediastrum

Lecane AmphoraScenedesmusAnkistrodesmus Oedogonium

CosmariumMelosira

OedogoniumCosmarium Navicula Aulosira

Cosmarium ScenedsmusDiflugia AnkistrodesmusAphanocapsa

Oedogonium TetrasporaClosterium

Brachion

Euastrum

2927252321191715131197531 -1 2927252321191715131197531 -1 2927252321191715131197531 -1 2927252321191715131197531

Fig. 5 Selective feeding of the common carp (Cyprinus carpioL.) in the rice fields of Apatani Plateau during 2002. Electivity

index (on y axis) plotted against relative occurrence of food

organisms (on x axis). Top row: Plankton, (a) = June–July;

(b) = July–August; (c) = August–September; (d) = Septem-

ber–October). Bottom row: Periphyton, (e) = June–July;

(f) = July–August; (g) = August–September; (h) = Septem-

ber–October

Aquat Ecol (2009) 43:559–568 565

123

Ankistrodesmus, and Polyarthra in August–September,

and Staurastrum, Epistylis, Lecane, and Euastrum in

September–October. In June–July and July–August

Desmidium was preferred moderately as periphytic

feed. However, Closterium and Gomphonema were

strongly rejected as periphytic members in August–

September and September–October. In July–August,

the feeding preferences for Diflugia and Spirulina of

periphytic forms were congruent with their plank-

tonic forms. The moderate preferred periphytic

candidate in September–October was Melosira. The

frequency of positive selection of planktonic feeds

decreased toward the late flood phase of each year.

During this decreased feeding on plankton more

periphytic food was selected in both years.

Discussion

Gut fullness and growth

Common carp showed much better growth in 2003,

when the water was deep, than in 2002, when it was

shallow. This is a direct effect of an increase in the

amount of available periphyton with increasing water

depth in rice fields. A similar effect was observed by

Evans and Stockner (1972).

Diet of common carp

Common carp is reported to be an omnivorous fish

that feeds on chironomids, tubificids, zooplankton,

and zooperiphyton (Sibbing 1988). The occurrence of

algal feed in the stomach revealed the planktivorous

nature of feeding of common carp in the rice–fish

system. Such shifting of feed intake by the fish

might have been influenced by limited availability of

organisms of higher trophic level (i.e. zooplankton

macrozoobenthos, etc.) in the rice field of the Apatani

Plateau. The Chlorophycean members, especially,

were seen constantly dominating the other counter-

parts of algal origin in the gut. Shroeder (1980)

opined that fish prefer to feed at lower trophic levels

if their usual feeds become limited. The initial

preference towards Chlorophycea and Cyanobacteria

clearly explains such selective preference of common

carp. Rieradevall (1991) also observed a shift of feed

items of common carp to amphipod and phantom

ridge larvae from chironomids and molluscs due to

their higher availability in lake systems. The irregular

Ankistrodesmu

PachycladusArcella

Closterium

Cosmarium

Colurella

Melosira

Epistylis

Scenedesmu

A

Desmidium

Testudinella

Closterium

NaviculaCymbella

Gleocapsa

Scenedesmus

B

Closterium

Gomphonema

Navicula

MelosiraNostoc

OedogoniumCosmarium

Ankistrodesmus

D

Hormidium Closterium Desmidium

Diflugia

Scenedesmus

GleocapsaMesotaenium

GonatozygonGeminella

E

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

-1 2927252321191715131197531

Staurastrum, Epistylis, LecaneEuastrum

Melosira

CosmariumNavicula

Spirogyra Oedogonium

Ankistrodesmus

H-1 2927252321191715131197531

Gomphonema

Spirulina

Diflugia

AnkistrodesmusPolyarthra

Gomphonema

Amphora Navicula Oedogonium

Closterium

AphanocapsaStaurastrum

G-1 2927252321191715131197531

Penium Cyclotella

Unidentified zoo

Desmidium

Scenedesmus

GleocapsaCymbella

NaviculaClosterium

ArcellaStaurastrum

F-1 2927252321191715131197531

Diflugia

Ankistrodesmu

Cosmarium

Diflugia

Oedogonium

Amphora

Staurastrum NaviculaNauplia

PolyarthraAmphora

C

Spirulina

Fig. 6 Selective feeding of the common carp (Cyprinus carpioL.) in the rice field of Apatani Plateau during 2003. Electivity

index (on y axis) plotted against relative occurrence of food

organisms (on x axis). Top row: Plankton, (a) = June–July;

(b) = July–August; (c) = August–September; (d) = Septem-

ber–October). Bottom row: Periphyton, (e) = June–July;

(f) = July–August; (g) = August–September; (h) = Septem-

ber–October

566 Aquat Ecol (2009) 43:559–568

123

occurrence of variable fractions of animal feed in the

fish gut during mid flood and late flood phases could

be an attempt to resurrect the omnivorous nature of

common carp. The gradual increase in size or body

weight with progress of time might have some

influence on such food-selection tendencies. Haroon

and Pittman (1997, 2000) observed that large Bar-

bodes gonionotus fed on aquatic macrophytes,

whereas, small ones mostly preferred aquatic insects.

The occurrence of detritus matter in the gut of

common carp also disclosed a similar explanation

regarding the shifting of food choice. Waterlogged

rice fields usually accumulate high detritus material

when inundated (Fernando 1995). Chapman and

Fernando (1994) reported high detritus content in

the stomach of common carp in a lowland rice field.

The detritivorous character of the fish at a later stage

might be due to its foraging nature. Haroon et al.

(1998) reported similar results on Oreochromis spp.

in the rice fields of Bangladesh.

The zooplankton taxa, Arcella, Diflugia, Colurella,

Bosminopsis, Bosmina, and small rotifers (Lecane

and Monostyla) were predominantly observed during

the initial stage of the flood phase. Of these, some are

abundant as both plankton and periphyton and others

were rarely observed in the rice fields. The large

zooplankton (Cladocera) are consumed at a later

stage of the flood phase. Sibbing et al. (1986)

reported that smaller carp retain smaller zooplankton

and detritus matter in the branchial sieve. However,

this retention capacity for small items decreases with

the growth of the fish (Sibbing 1988). Thus, the

growth of the carp in the rice fields influenced the

size-selective feeding of this species.

Niche breadth of carp

Two types of food, i.e. plankton and periphyton, in

the rice field ecosystem were available for the fish.

The fish showed overall narrow niche breadth in the

first resource type throughout all the flood phases.

The greater the niche breadth, the more selective the

fish is feeding. A smaller niche breadth is an

indication of either resource partitioning (Haroon

and Pittman 2000) or less affinity of the fish for the

resource type on which niche breadth was measured.

With progress of the flood phases, the niche breadth

of the fish increased for periphytic food items,

indicating its tendency to browse on the attached

organisms. Simultaneously, feeding on plankton grad-

ually declined. This was probably caused by increasing

periphyton availability on the rice-stems. The mid-

flood phase is productive with sufficient depth of water

and light (Fernando 1993). During this period periph-

yton reached its highest biomass on the rice stems and

the fish consumed it in large amounts.

Selective feeding

We observed that the decrease in preferred planktonic

food items coincided with a gradual increase in

preferred periphytic food items (Figs. 5, 6g, h). Diet

shifts from plankton toward specific periphyton items

occurred as the flood phases progressed. A similar

dietary shift for particular periphyton was observed for

Oreochromis spp. (Haroon et al. 1998) with change of

habitat from pond to rice field. The feeding strategy

plots showed strong selection for periphytic members

of Chlorophyceae and Cyanobacteria. For some peri-

phytic forms, for example Closterium, Anabaena,

Melosira, Gomphonema, and Diflugia selection was

in proportion to the availability of periphyton in the

environment. Strong preference toward periphytic

Bacillariophycean microalgae especially Melosira

and Gomphonema could be due to the additional

nature of attachment of microalgae over periphytic

filamentous macroalgae (van Dam et al. 2002). Guirel

et al. (1993) and Konan-Brou and Guirel (1994)

observed Melosira and Nitzschia to exhibit similar

nature of attachment in ponds. The avoidance of

abundant larger algae like Oedogonium and Spirogyra

evident from the lower corner of the plot can also be

best explained by this nature of the microalgae. These

organisms are present abundantly but avoided by the

fish. Navicula was moderately avoided both as plank-

ton and periphyton. In most cases its avoidance range

was 0 to -0.2 in periphyton to -0.2 to -0.4 in

plankton. All these indicated the benthic and periph-

yton feeding habit of the fish either as browser or

surface grazer. Similarly, the fish strongly selected

most Chlorophyceaen members of rare occurrence.

Rare but strongly preferred Cyanobacteria members

were Nostoc, Spirulina, Anabaena, and Chroococcus.

Our study showed that periphyton is the most

important resource for common carp in rice fields.

This feeding is far from random—periphytic Chlo-

rophyceae and Cyanobacteria were especially

strongly positively selected.

Aquat Ecol (2009) 43:559–568 567

123

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