The effect of periphyton and supplemental feeding

on the production of the indigenous carps

Tor khudree and Labeo fimbriatus

P. Keshavanath a, B. Gangadhar a, T.J. Ramesh a, A.A. van Dam b,*,M.C.M. Beveridge c, M.C.J. Verdegem b

aCollege of Fisheries, University of Agricultural Sciences, Bangalore, P.B. 527,

Mangalore 575 002, Karnataka, IndiabFish Culture and Fisheries Group, Department of Animal Sciences, Wageningen Institute of Animal Sciences,

Wageningen University, P.O. Box 338, 6700 AH Wageningen, The NetherlandscInstitute of Aquaculture, University of Stirling, Stirling FK 9 4 LA, Scotland, UK

Received 16 December 2000; received in revised form 17 January 2002; accepted 21 January 2002

Abstract

Two experiments were conducted, one with the herbivorous mahseer Tor khudree and another

with the fringe-lipped carp Labeo fimbriatus to study the effect of feeding and periphyton on their

growth and production. Twelve tanks (25 m2) with mud bottoms and 0 (control), 98 (low density)

or 196 (high density) bamboo poles tank� 1 were used. Mahseer (initial wt. 3.5 g) and fringe-

lipped carp (initial wt. 0.73 g) stocked at 25 fish tank� 1 were reared for 90 and 60 days,

respectively. Fish in half of the tanks received a pelleted feed (35% protein) at a ration of 5% body

weight day� 1. Water was monitored daily for dissolved oxygen, pH, temperature, and Secchi disc

visibility, and weekly for ammonia, nitrate, phosphate, and alkalinity. Periphyton dry matter, ash,

and chlorophyll content were quantified fortnightly. Periphyton biomass, measured as total

pigment (chlorophyll-a + pheophytin), decreased with time in both experiments indicating effective

grazing by the fish. In the control treatment (without supplemental feed and substrates), mahseer

grew to a final weight of 30.8F 0.9 g and fringe-lipped carp to 19.1F1.1 g (meanF S.D.).

Supplemental feeding alone resulted in higher final mean weight of mahseer and fringe-lipped carp

of 38.3F 0.6 and 22.9F 1.2 g, respectively. The provision of substrates resulted in final mean

weights of mahseer of 36.0F 5.7 and 36.1F1.3 while that of fringe-lipped carp were 22.8F 1.2

and 22.5F 1.9 (low and high density, respectively). Net production of mahseer with substrates was

0044-8486/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.

PII: S0044 -8486 (02 )00034 -0

* Corresponding author. Tel.: +31-317-484625; fax: +31-317-483937.

E-mail address: anne.vandam@alg.venv.wag-ur.nl (A.A. van Dam).

www.elsevier.com/locate/aqua-online

Aquaculture 213 (2002) 207–218

41% and 51% higher, and that of fringe-lipped carp was 43% and 75% higher than in the control

(low and high density, respectively). The combination of substrates and supplemental feed resulted

in mean final weights of mahseer of 40.3F 0.4 and 39.7F 1.2, and of fringe-lipped carp of

23.6F 1.4 and 25.5F 0.1 (low and high substrate density, respectively). Production of mahseer

with a combination of substrates and feeding was 71% and 54% higher, and of fringe-lipped carp,

it was 85% and 87% higher than in the control (low and high density, respectively). It is

concluded that the provision of substrates can reduce the need for artificial feed and can be an

alternative to feeding in the culture of herbivorous fish.

D 2002 Elsevier Science B.V. All rights reserved.

Keywords: Periphyton; Tropical aquaculture; Tor khudree; Labeo fimbriatus; India

1. Introduction

In India, the major carps catla (Catla catla), rohu (Labeo rohita), and mrigal (Cirrhinus

mrigala) are the mainstay of freshwater aquaculture. They are usually cultured in manured

ponds, but there is a trend towards intensification and greater reliance on supplemental

feeding. High feed costs (Veerina et al., 1993) may exclude subsistence farmers from

adopting this approach to increase production. An alternative approach is to provide ponds

with substrates for the growth of periphyton that can be eaten by herbivorous fish.

Increased yields of fish and prawn species, such as the tilapias Sarotherodon melanotheron

(Hem and Avit, 1994) and Oreochromis mossambicus (Shankar et al., 1998), the carps L.

calbasu and L. rohita (Wahab et al., 1999a,b), and the freshwater prawn Macrobrachium

rosenbergii (Tidwell et al., 2000) have been reported using such methods.

A need for diversification of farmed fish species has been identified (NACA/FAO,

2000), and mahseer, Tor khudree and fringe-lipped carp, L. fimbriatus seem to be good

candidates for farming in India (Bazaz and Keshavanath, 1993; Basavaraju et al., 1995).

Mahseer feeds on plants, insects, shrimps, and molluscs (Talwar and Jhingran, 1992;

Froese and Pauly, 1999), whereas the fringe-lipped carp grazes on diatoms and algae that

grow on submerged rocks and twigs (Bhatnagar and Karamachandani, 1970). In an earlier

experiment, mahseer showed better growth and production with bamboo poles than with

PVC pipes, both used at 196 poles/25 m2 as substrate for periphyton (Keshavanath et al.,

2001). Because of the high cost of bamboo, in the present study, we investigate the effect

of lowering the bamboo density on fish production and compare the effect of substrates

with that of supplemental feeding.

2. Materials and methods

2.1. Experimental design

Experiments were conducted at the College of Fisheries, Mangalore, India, between 17

May 1999 and 24 August 1999 (Experiment 1, mahseer) and 28 October 1999 and 1

P. Keshavanath et al. / Aquaculture 213 (2002) 207–218208

January 2000 (Experiment 2, fringe-lipped carp). Twelve concrete tanks (5� 5� 1 m)

with a 15-cm sandy loam soil bottom were used for each experiment and water depth was

maintained at 80F 2 cm (tank wall surface exposed to water ca. 16 m2). The tanks were

dried, quicklime applied at 300 kg ha� 1, and poultry manure (2000 kg ha� 1) was added

as fertilizer. Bamboo poles, purchased from a local market, were cut into 1.5-m lengths,

and were then placed in four tanks at 98 poles tank � 1 (low density treatment) and in four

tanks at 196 poles tank � 1 (high density treatment). The total surface area available for

colonization by periphyton was 34.5 m2 in the low-density treatment (16 m2 tank

wall + 18.5 m2 bamboo), and 53 m2 (16 + 37 m2) in the high-density treatment tanks.

The remaining four tanks had no additional substrate and served as controls.

Tanks were filled with water and evaporative losses were replenished weekly. Juvenile

T. khudree (average wt. 3.50F 0.16 g) or L. fimbriatus (average wt. 0.73F 0.11 g) were

stocked at 25 fish tank � 1 (Day 0), 7 days after manuring.

2.2. Feeding

The feed was prepared by mixing about 800 ml of water with 1 kg of the ingredients by

hand to form a dough, which was cooked at 80 jC for 30 min and then cooled, mixed with

the vitamin–mineral mixture (Supplevite-M, manufactured by Sarabhai Chemicals,

Baroda, India), and pelletized (size: 3 mm). Pellets were then dried at 50 jC to a moisture

content of less than 10%.

Fish in half of the tanks in each treatment were fed (Table 1) at a ration of 5% body

weight day � 1. The feed was applied daily at 1000 h in one corner of the tanks. Feed

amount was adjusted fortnightly based on sample weights of at least 50% of the fish

stocked (in the substrate treatments, it was impossible to catch all the fish for weighing).

The duration of the experiment was 90 days with T. khudree and 60 days with L.

fimbriatus.

Table 1

Ingredient proportion and proximate composition of the diet

Ingredient % Proximate compositiona %

Fish meal 31 moisture 5.2

Rice bran 41 crude protein 33.9

Groundnut cake 17 fat 7.7

Tapioca flour 10 ash 13.4

Vitamin and mineral mixtureb 1 crude fibre 10.1

NFE 24.8

energy (kJ g� 1) 14.1

a % Fresh weight.b Composition per 250 g: Vit. A—500,000 IU; Vit. D3—100,000 IU; Vit. B2—0.2 g; Vit. E—75 U; Vit.

K—0.1 g; calcium pantothenate—0.25 g; nicotinamide—1.0 g; Vit. B12—0.6 mg; choline chloride—15 g;

calcium—75 g; manganese—2.75 g; iodine—0.1g; iron—0.75 g; zinc—1.5 g; copper—0.2 g; and cobalt—

0.0045 g.

P. Keshavanath et al. / Aquaculture 213 (2002) 207–218 209

P. Keshavanath et al. / Aquaculture 213 (2002) 207–218210

Fig. 1. Surface temperature (A), dissolved oxygen concentration (B), Secchi visibility (C), alkalinity (D), total

ammonia nitrogen (E), nitrate nitrogen (F), and phosphate–phosphorous (G) in tanks with bamboo substrates at

different densities (0 (control), 98 (low density) and 196 poles/25 m2), stocked with T. khudree (Experiment 1) and

L. fimbriatus (Experiment 2). Bars indicate standard error (n= 4). For clarity, only error bars for the treatments

without substrate are given.

P. Keshavanath et al. / Aquaculture 213 (2002) 207–218 211

2.3. Water-quality monitoring

Samples for water-quality measurement were taken between 0900 and 1000 h. Surface

and bottom temperatures, dissolved oxygen, pH, and water transparency (Secchi disc

depth) were measured daily. Total alkalinity, ammonia, nitrate, and phosphate concen-

trations were measured weekly, starting on Day 7. Temperature and pH were measured by

dipping a water-quality analyser directly in the tank water (Horiba, Japan; model U10),

and dissolved oxygen, total alkalinity, ammonia, nitrate, and phosphate were measured

using standard methods (APHA, 1992).

2.4. Biological measurements

From Day 15 onwards, periphyton biomass, ash (APHA, 1992), chlorophyll-a, and

pheophytin (Stirling, 1985) were estimated fortnightly according to the following

procedure. Three bamboo poles were removed from each tank and samples for estimation

of chlorophyll-a and pheophytin were collected by scraping a 2-cm-wide band of

periphyton from around the circumference of each pole. Periphyton was then removed

from the remaining pole surface for estimation of dry matter, by drying at 100 jC to

constant weight. Ash content was determined by heating dried samples in a muffle furnace

(4 h at 550 jC) and ash-free dry matter (AFDM) was then estimated. Poles were replaced

in their respective tanks and marked to avoid being resampled.

At the end of the experiment, fish were counted and weighed, and the following

parameters are calculated for each tank:

where Wstock and Wharv are the mean individual wet fish weight and Nstock and Nharv are the

number of fish at stocking and harvest, respectively.

2.5. Statistical analyses

Mean values of final fish weight, survival, and production were compared by two-way

ANOVA with substrate density (three levels) and feeding (two levels) as factors and two

replicate tanks per treatment. All periphyton and water-quality parameters were subjected

to repeated measures ANOVA with substrate density and feeding as main factors and

sampling date as subfactor (Gomez and Gomez, 1984), again with two tank replicates.

When a main effect was significant, pairwise comparison of treatment means was done by

Tukey HSD test. All analyses were done using the ANOVA procedure of SAS version

6.12 (SAS Institute, Cary, NC 27513, USA) and all tests were done at a probability level of

5%.

Survival (%) 100(Nharv�Nstock)/Nstock

Net production (g tank� 1) (Wharv�Nharv)� (Wstock�Nstock)

Food conversion ratio, FCR (� ) g feed dry matter given/g wet weight gain

P. Keshavanath et al. / Aquaculture 213 (2002) 207–218212

3. Results

3.1. Water quality

There was no significant effect of feeding on any of the water-quality parameters,

except for an increase in ammonia concentration in Experiment 2. Mean values of water-

quality parameters for each substrate density are presented in Fig. 1. Apart from a higher

nitrate concentration in the treatments with substrate in Experiment 2, there were no

differences between substrate densities in ammonia, nitrate, and phosphate concentrations

or in alkalinity and Secchi visibility.

Fig. 2. Ash-free dry matter (AFDM; A), total pigment content (chlorophyll a and pheophytin; B), and ash (C) of

periphyton growing on bamboo substrates in tanks with T. khudree (Experiment 1) and L. fimbriatus (Experiment

2), with and without feeding. Bars indicate standard error (n= 4).

P. Keshavanath et al. / Aquaculture 213 (2002) 207–218 213

Substrate density had a significant effect on temperature and dissolved oxygen

concentration in both experiments, with lower temperatures and oxygen concentrations

in the higher substrate density.

3.2. Periphyton growth

No significant effect of substrate density on periphyton AFDM, pigment, or ash content

was seen in either experiments. There were some small differences between low-substrate

density and high-substrate density tanks, but no trends were readily apparent. Mean

periphyton AFDM, total pigment concentration, and ash for tanks with and without

feeding are presented in Fig. 2.

In Experiment 1, feeding had a significant effect on periphyton AFDM, but not on the

other periphyton parameters. In Experiment 2, feeding had no significant effect on any of

the periphyton parameters. Mean AFDM and ash were higher in the tanks with feeding in

Experiment 1 (0.53–0.54 vs. 0.26–0.28 mg dry matter cm � 2). These differences were

much smaller in Experiment 2. In both experiments, the difference in pigment concen-

tration between fed and nonfed tanks was negligible.

Sampling date had a significant effect on AFDM and ash in both experiments: they

increased with time in Experiment 1, while they both decreased in Experiment 2 (Fig. 2).

Table 2

Analysis of variance (ANOVA) comparing the periphyton biomass parameters (ash-free dry matter: AFDM; total

pigment: chlorophyll-a+ pheophytin) in Experiments 1 and 2 between treatments with and without supplemental

feeding and with different substrate densities

Species Effect df AFDM Total pigment Ash

MS F P MS F P MS F P

T. khudree Feed (F) 1 0.5338 21.14 0.0100 2.7807 0.36 0.5805 0.0661 3.12 0.1523

(Experiment 1) Substrate

density (S)

1 0.0001 0.00 0.9622 2.9316 0.38 0.5709 0.0007 0.03 0.8627

F� S 1 0.0000 0.00 0.9783 1.3145 0.17 0.7009 0.0005 0.02 0.8859

Error 1 4 0.0252 7.7107 0.0212

Date (D) 6 0.1369 5.87 0.0004 5.6898 2.17 0.0737 0.0223 2.57 0.0396

D� F 6 0.0801 3.43 0.0107 3.8225 1.46 0.2252 0.0081 0.93 0.4879

D� S 6 0.0535 2.29 0.0613 2.6204 1.00 0.4427 0.0077 0.88 0.5186

Error 2 30 0.0233 2.6169 0.0087

Total 55

L. fimbriatus Feed (F) 1 0.0000 0.01 0.9238 2.9863 0.95 0.3859 0.0003 0.33 0.5968

(Experiment 2) Substrate

density (S)

1 0.0002 0.09 0.7748 6.0014 1.90 0.2401 0.0003 0.33 0.5968

F� S 1 0.0062 3.81 0.1225 3.9044 1.24 0.3285 0.0007 0.65 0.4645

Error 1 4 0.0016 3.1573 0.0010

Date (D) 3 0.0144 19.66 0.0001 4.7927 2.94 0.0670 0.0022 3.32 0.0488

D� F 3 0.0036 4.87 0.0147 1.0666 0.65 0.5923 0.0002 0.37 0.7770

D� S 3 0.0007 1.01 0.4165 1.9581 1.20 0.3428 0.0002 0.27 0.8468

Error 2 15 0.0007 1.6286 0.0007

Total 31

Significant effects ( P< 0.05) are printed bold.

P. Keshavanath et al. / Aquaculture 213 (2002) 207–218214

Periphyton biomass was generally higher in Experiment 1 than in Experiment 2. Pigment

concentrations decreased with time in both experiments (Fig. 2). This time, effect on total

pigment content was marginally significant in both experiments (P < 0.08; Table 2).

Table 3

Fish production parameters of Experiment 1 (T. khudree) and Experiment 2 (L. fimbriatus)a

Species Feeding Substrate

(poles/25 m2)

Final weight

(g)

Survival

(%)

Net yield

(g/25 m2)

FCRd

(g feed/g fish)

MeanF S.D. MeanF S.D. MeanF S.D. MeanF S.D.

T. khudree no 0 30.8F 0.9 66.0F 2.8 419.5F 7.2 –

(Experiment 1)b 98 36.0F 5.7 76.0F 5.7 593.0F 57.2 –

196 36.1F1.3 80.0F 0.0 634.3F 25.7 –

yes 0 38.3F 0.6 66.0F 2.8 543.3F 17.6 2.0F 0.1

98 40.3F 0.4 80.0F 0.0 717.5F 7.1 1.5F 0.0

196 39.7F 1.2 74.0F 8.5 647.9F 106.4 1.7F 0.3

L. fimbriatus no 0 19.1F1.1 65.0F 7.1 297.5F 58.6 –

(Experiment 2)c 98 22.8F 1.2 77.5F 10.6 425.8F 25.4 –

196 22.5F 1.9 95.0F 7.1 522.0F 78.1 –

yes 0 22.9F 1.2 85.0F 7.1 472.5F 21.9 1.1F 0.1

98 23.6F 1.4 95.0F 7.1 550.1F 67.4 0.9F 0.1

196 25.5F 0.1 90.0F 7.1 555.2F 55.8 0.9F 0.1

a Figures are meansF S.D. of two replicate tanks.b Mean stocking weight is 3.50F 0.16 g, duration of 90 days.c Mean stocking weight is 0.73F 0.11 g, duration of 60 days.d Total amount of feed given (g)/net fish production (g).

Table 4

Analysis of variance (ANOVA) comparing the fish production parameters in Experiments 1 and 2 between

treatments with and without supplemental feeding and with different substrate densities

Species Effect df Final weight Survival Net yield

MS F P MS F P MS F P

T. khudree Feed (F) 1 78.18 12.77 0.0117 1.33 0.07 0.8049 22,875.22 8.76 0.0253

(Experiment 1) Substrate

density (S)

2 16.55 2.70 0.1456 177.33 8.87 0.0162 37,270.34 14.27 0.0052

F� S 2 4.40 0.72 0.5249 25.33 1.27 0.3476 4081.26 1.56 0.2842

Error 6 6.12 20.00 2611.54

Total 11

L. fimbriatus Feed (F) 1 19.53 11.89 0.0137 352.08 5.83 0.0523 36,850.98 12.08 0.0132

(Experiment 2) Substrate

density (S)

2 9.75 5.93 0.0379 314.58 5.21 0.0488 24,519.55 8.04 0.0201

F� S 2 2.44 1.49 0.2988 189.58 3.14 0.1168 5159.57 1.69 0.2616

Error 6 1.64 60.42 3051.39

Total 11

Significant effects ( P< 0.05) are printed bold.

P. Keshavanath et al. / Aquaculture 213 (2002) 207–218 215

3.3. Fish growth, survival, and production

Feeding had a significant effect on mean final weight and production of mahseer. Mean

individual weight was greater with feeding (38.3 against 30.8 g without feeding). Feed had

no significant effect on survival and resulted in a higher production (543 g tank � 1, against

420 without feed in tanks without substrate) (Tables 3 and 4). A similar effect of feeding

on weight and production was observed with fringe-lipped carp, while the effect on

survival was marginally significant (P= 0.052, Table 4). Mean final weight of fringe-

lipped carp in fed tanks was 22.89 g compared with 19.07 g in nonfed tanks, and

production was 473 against 298 g tank� 1 (Table 3).

Substrate density had no significant effect on mean final weight of mahseer. Survival

and production, however, were significantly higher in tanks with substrate. Production

with substrates was 593 and 634 g (for low and high density, respectively) in tanks without

feeding and 718 and 648 g in tanks with feeding (Table 3). FCR values were lower in tanks

with substrate. In fringe-lipped carp, substrate density had a significant effect on final

weight, survival, and production. In tanks with substrate, production was 426 and 522 g

(for low and high density, respectively) without feeding, and 550 and 555 g with feeding.

Again, improved FCR values were observed in treatments with substrate.

4. Discussion

Feeding had a significant effect on the production of both species, resulting in net

production that was 30–59% greater than that of fish in nonfed tanks without substrate.

The effect of feed on growth of fish was partly indirect, via higher periphyton biomass in

fed tanks with substrate. Periphyton alone enhanced fish production by 41–75%, which is

comparable to the effect of feeding. Provision of substrates can thus reduce the need for

artificial feed and can be considered as an alternative to feeding in the culture of

herbivorous fish.

The combination of feeding and periphyton resulted in a 54–87% greater production

compared to the control treatment. Whether combining periphyton with feeding is

worthwhile will depend on the cost of substrates and feeds and on the choice of fish

species. In both experiments, pigment concentration decreased with time (Fig. 2B) due to

grazing by mahseer and fringe-lipped carp. Periphyton dry matter, however, increased in the

fed tanks in Experiment 1 while it decreased slightly in Experiment 2 (see Fig. 2A).

Due to the higher initial weight of mahseer, total feed input in Experiment 1 was more than

double compared to Experiment 2. This led to higher fish production and also to more

suspended organic material (mostly faeces, and possibly some uneaten feed), as shown by

the lower Secchi disc values in Experiment 1 (Fig. 1C). Since manuring was done only

initially, the increase in periphyton dry matter was caused mainly by entrapment of

suspended faecal and feed material in the periphyton layer. Experimental studies in rivers

show that external adhesion of suspended particles on freshwater plants can influence the

analytical results of aquatic biota considerably (Sansone et al., 1998). Microbial organisms

and meio- and macrofauna growths in the periphyton may also be utilized by fish.

Periphyton prevents detritus from sinking to the oxygen-poor sediment where decom-

P. Keshavanath et al. / Aquaculture 213 (2002) 207–218216

position is slow and fish avoid grazing. Trapped in the periphyton layer, detritus is

decomposed more rapidly and is more accessible to grazers. In this way, periphyton

enhances the cycling of nutrients.

FCR improved with substrate density. However, these values are not very meaningful

because they concern a supplemental feed. The ‘‘net’’ FCR values (based on the difference

between the fish production in the nonfed tanks and that in the fed tanks with the same

substrate density) do say something about the interaction between substrates and feeding.

Net FCR values were considerably higher in the high substrate density treatment (mahseer:

78.6 in high-density substrate vs. 8.6 in no substrate and low density substrate; fringe-

lipped carp: 14.9 vs. 2.8 and 4.0). This shows that the efficiency of supplemental feed was

drastically reduced with high substrate density.

No differences in periphyton biomass per unit surface area were observed between the

two substrate densities. Halving the substrate density in the pond implies halving of the

periphyton biomass, provided that no other factor, e.g. light or nutrients, is limiting.

However, periphyton biomass alone gives no indication of productivity. With higher fish

density, periphyton biomass will be lower, self-shading will be reduced, and as a result,

periphyton productivity can be expected to be higher. There is an optimal ratio between

fish stocking density and periphyton substrate density. In the present experiments,

reducing the substrate density had no effect on fish production, probably because fish

density remained below the carrying capacity of the system. This is confirmed by the

generally high level of dissolved oxygen in both experiments. With increased fish density,

reducing the substrate density may not be possible without affecting fish production.

Only minor differences in water quality were observed between the treatments.

Generally, the water quality was acceptable for fish production and substrates did not

have positive or negative effects on water quality at these stocking densities. Substrate

density had a small but clear effect on dissolved oxygen concentration and temperature

(Fig. 1), probably due to the shading effect of the bamboo poles.

Provision of substrate increased fish survival in both the experiments. In addition to

increasing food supply, the presence of substrate appears to reduce stress by acting as a

shelter or hiding place. Higher survival of mahseer was observed in our earlier study with

periphyton (Keshavanath et al., 2001) and in studies in Bangladesh (Wahab et al.,

1999a,b), making periphyton-based systems particularly worthy of consideration for fry

and fingerling production.

Acknowledgements

This research was funded through the European Commission (grant INCO-DC

IC18CT970196), and consists of a cooperation between partners in South Asia (India and

Bangladesh) and Europe (UK and The Netherlands).

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P. Keshavanath et al. / Aquaculture 213 (2002) 207–218218