Larval rearing of the Asian Catfish, Pangasius bocourti (Siluroidei, Pangasiidae): alternative feeds...

Larval rearing of the Asian Catfish, Pangasius

bocourti (Siluroidei, Pangasiidae): alternative feeds

and weaning time

Le Thanh Hung a,b, Nguyen Anh Tuan c, Philippe Cacot a,Jerome Lazard a,*

aCentre de Cooperation Internationale en Recherche Agronomique pour le Developpement, Departement

Elevage et Medecine Veterinaire/Groupe Aquaculture Continentale Mediterraneenne et Tropicale

(CIRAD–EMVT/GAMET), TA 30/01, 34398 Montpellier cedex 5, FrancebUniversity of Agriculture and Forestry (UAF), Thu Duc, Ho Chi Minh City, Viet Nam

cCan Tho University (CTU), Can Tho City, Viet Nam

Received 25 November 1999; received in revised form 1 July 2001; accepted 7 July 2001

Abstract

Three experiments were carried out to evaluate Pangasius bocourti larval rearing with different

feeding regimes. In the first experiment, survival rates of larvae fed on Artemia nauplii, cladocereans

(Moina sp.), or red-blood worms (Tubifex) were not significantly different, 91–93%. However,

Artemia nauplii and Tubifex gave similar growth rates (35–36% day� 1) while Moina sp. resulted in

lower growth. Commercial trout-starter feed resulted in the lowest survival (67%) and growth rates

(20% day� 1) when compared to live feed.

In the second experiment, feeding dry feed based on yeast and beef liver or feeding decapsulated

Artemia cysts improved survival rates. These were 90% and 87%, respectively, not significantly

different from Artemia nauplii. Regarding growth, dry feed and decapsulated Artemia cysts resulted

in lower growth rates than Artemia nauplii. These were 23% and 29%, respectively. Stomach content

analysis showed that reduced growth in decapsulated-cyst fed larvae compared to live Artemia

reflected a difference in feed ingestion and preference rather than a difference in nutritional quality of

the feed.

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

PII: S0044 -8486 (01 )00737 -2

* Corresponding author.

E-mail address: [email protected] (J. Lazard).

www.elsevier.com/locate/aqua-online

Aquaculture 212 (2002) 115–127

In the third experiment, it was shown that larvae require 3-day feeding on Artemia nauplii before

weaning them on to trout-starter feed to prevent negative effects on growth. Three days after initial

feeding, fish stomach attains its biological and physiological functions.

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

Keywords: Larval rearing; Pangasius bocourti; Weaning time; Dry diet; Live feed

1. Introduction

The Asian catfish, Pangasius bocourti Sauvage 1880, is cultured in cages in the

Mekong delta, Vietnam, and annual production is around 27,000 tonnes (Phuong, 1996).

The seed supply has been dependent on catching fry in natural waters. Artificial

propagation and larval rearing represent the major bottleneck for the production and cage

culture of the species. Induced spawning of the species was successfully carried out for the

first time in 1995 (Cacot, 1998). Currently, information on the larval rearing of this species

is lacking.

Brine shrimp nauplii (Artemia sp.) are widely recognized to be an excellent starter feed

for freshwater and marine fish species (Leger et al., 1986), but cyst price is high.

Successful rearing of fish larvae using live zooplankton has been reported for several

species (Watanabe and Fujita, 1983). Among the various species of zooplankton, the genus

Moina (cladocereans) is known to be suitable as an initial feed for Chanos chanos

(Villegas, 1990) and Clarias macrocephalus (Fermin and Bolivar, 1991). Red-blood

worms, Tubifex, have also been used successfully for European catfish (Silurus glanis)

larval rearing (Ronyai and Ruttkay, 1990). The use of decapsulated Artemia cysts rather

than live nauplii, has several advantages: eliminating the inconvenience of producing live

food (Pector et al., 1994), decapsulated cysts are disinfected and have a higher dry weight

and energy content (Vanhaecke et al., 1983). Moreover, they do not leach nutrients into the

water like formulated feed, and their particle size is appropriate for many fish species. As a

consequence, they have been considered as a reference diet for the nutritional study of C.

gariepinus (Verreth et al., 1987). It has also been reported that some freshwater fish

species can be exclusively reared on artificial diets from the start of exogenous feeding.

These include C. gariepinus, Cyprinus carpio and Heterobranchus longifilis (Appelbaum

and Van Damme, 1988; Charlon et al., 1986; Legendre et al., 1995).

The aim of this study was to evaluate different types of live feed, artificial diet and

decapsulated Artemia cysts in term of acceptability, growth and survival rate of P. bocourti

larvae and to determine the optimal weaning time. The development of the digestive canal

of P. bocourti larvae was also considered.

2. Material and methods

Broodfish was induced to spawn by treatment with Human Chorionic Gonadotropin

hormone (HCG). Twenty-four hours after hatching, 500 larvae were placed into each of the

twelve 50-l aquaria. Feeding started from 48 h post-hatching when the yolk sac was not

L.T. Hung et al. / Aquaculture 212 (2002) 115–127116

completely absorbed.Weight and total length at that time ranged from 3.7 to 4.0mg and from

8.7 to 9.0 mm, respectively.

Water flow through the aquaria was maintained constant at 0.4–0.5 l.min � 1 and

aeration was provided. Dissolved oxygen and pH were measured twice a week with a DO

meter (YSI model 518) and a pH meter (Hana HI 8424). Ammonia and nitrite were

measured by colorimetry (Aquaquant 14423, 14424). Temperature, monitored twice a day

at 0800 and 1500 h, ranged from 28 to 30 jC. Dissolved oxygen concentration was always

higher than 5 mg l � 1. The pH level varied from 7.0 to 7.5. Ammonia and nitrite value

ranges were 0.1–0.3 and 0.01–0.04 mg l � 1, respectively.

Three experiments were carried out to evaluate different feeds on growth and survival

rates in P. bocourti larvae and the weaning time was determined using a trout-starter feed.

Each treatment had three replications.

1. The first experiment tested four diets: Artemia nauplii, Tubifex, Moina sp. and trout-

starter feed.

2. The second experiment tested three diets: Artemia nauplii, decapsulated Artemia

cysts and a dry diet based on beef liver and yeast.

3. The third experiment was designed to determine the most suitable weaning time for

early juvenile P. bocourti. These were eight treatments: 0, 1, 2, 3, 4, 5, 6 and A. The

numbers (1, 2, 3. . ., etc.) stand for number of days that larvae were fed with Artemia

nauplii before shifting directly to trout-starter feed. In treatment 0 and A, the larvae were

fed exclusively on dry diet or Artemia nauplii, respectively.

The San Francisco Bay strain Artemia cysts were incubated in 10 ppt saline water for 24

h at 30 jC. The newly hatched Artemia were kept in aerated saline water and used within 12h. The nauplii were 146–250 Am in width and 411–450 Am in total length. Moina were

cultured in earthen ponds fertilized with pig manure. They were collected daily and treated

with formalin (50 ppm) for 1–2 min to eliminate pathogens. They were still alive and

moved actively after treatment. Some other zooplankton organisms were recorded in the

Moina collection, including Eucyclops. Cladocereans were mostlyMoina sp., 288–300 Amwidth and 850–900 Am length. T. tubifex were collected on riverbanks. They were treated

with formalin (50 ppm) for 1–2 min and then chopped into small pieces of 800–900 Amwidth and 900–1000 Am length. Artemia cysts were decapsulated in 25% hypochloride

solution for 5–10 min and then washed in freshwater until the chlorine odor disappeared.

Decapsulated cysts were then kept at 10 jC for daily feeding. The trout-starter diet

(Aqualim, France) used in the first experiment and weaning time trial, had a proximate

analysis of 55% proteins, 18% lipids and 8% minerals. The size of feed particles was 0.2–

0.4 mm. Another dry diet was used in order to improve the survival and growth rates using

beef-liver and yeast with the component and proximate analysis presented in Table 1.

Fish were fed six times a day at 0800, 1200, 1600, 2000, 2400 and 0400 h. Live feed

such as Artemia nauplii, Moina and Tubifex were fed at 160% fish biomass (wet feed

basis), on the basis of fish weight registered every 3 days. The dry diet was distributed at

20% fish biomass and adjusted every 3 days after weighing.

Thirty larvae were randomly sampled every 3 days from each replicate and placed on

paper towels to absorb water and weighed for each replicate as a batch to 0.1 mg

(Kerdchuen and Legendre, 1994). At the end of the experiment, 50 fish were sampled per

aquarium. On each sampling day, five supplementary larvae were also caught 30 min after

L.T. Hung et al. / Aquaculture 212 (2002) 115–127 117

feeding and fixed in formalin solution (10%) for gut content analysis and mouth size

measurement.

Mouth height was the distance from lower jaw to upper jaw in larvae with the mouth

opening at 45j or 90j (Shirota, 1970). Mouth width was taken as the width of the lower

jaw. Measurement was performed under a binocular lens with an accuracy of 0.01 mm.

Survival rates were calculated by taking into account the remaining and discarded larvae.

Dead larvae were removed from aquarium twice a day at 1000 and 2000 h. Cannibalism

rates were defined by

Cannibalism rate ð%Þ ¼ 100� ½Survival rate ð%Þ þ Observed mortality ð%Þ�

The development of the alimentary canal was studied in larvae fed exclusively with

Artemia nauplii. The larvae for this study (10 per samples) were collected at 0, 24, 36, and

48 h post-hatching and on the 3rd, 4th, 5th, 7th and 10th days after hatching. The sample

was fixed in buffered formalin. Hollande–Bouin solution was also used to fix samples for

PAS (Periodic Acid Schiff) staining (Humason, 1972). The samples were then dehydrated,

embedded in paraffin wax and were sectioned at 5–10 Am. Sections was stained with

either Hematoxycline–Eosine or PAS, which is used to identify the mucous materials in

tissues (Humason, 1972). The pH level of gastric fluid was measured by injecting

indicators into the digestive gut: Methyl red acting at the pH range of 4.2–4.6 (color

changed from yellow to red) and Congo red acting at the pH range of 3.3–3.5 (color

changed from orange to red).

Mean weight, specific growth rates and survival rates were subjected to one-way

ANOVA, followed by Duncan’s Multiple Range to test the 95% significant difference

among treatments. Data of survival and cannibalism rates were transformed to arcsine�before ANOVA analysis to have homogeneity of variance.

3. Results

3.1. Comparison between Artemia nauplii, Tubifex, Moina sp. and trout-starter feed

Gut content analysis showed that feeding 48 h after hatching at a temperature of 28–30

jC. At this stage the yolk sac was not completely absorbed. At first feeding, the mouth

height at 45j and 90j was 0.55 and 0.95 mm, respectively. The width of the lower jaw was

1.00 mm (Table 2). It showed that the larvae have mouth size large enough to ingest

different types of natural diets including Moina and Tubifex.

Table 1

Component and proximate analysis of artificial diet based on beef liver and yeast

Component of the diet Proximate composition (dry basis)

‘‘Protibel’’ yeast powder 50% Moisture 7.8%

Beef liver 35% Crude proteins 35.7%

Soybean oil 5% Crude lipids 10.9%

Vitamin premix 5% Ash (minerals) 11.7%

Mineral premix 5% Fiber 6.8%


Mean weight, specific growth rates (SGR) and survival rates at the end of the first

experiment indicated that Artemia nauplii and Tubifex are better diets than Moina and trout

starter (P < 0.05) (Table 3). During the first 3 days of feeding, Artemia nauplii led to the

highest growth performances. Nevertheless, by the 8th day the Tubifex fed larvae caught

up with the growth of larvae fed on Artemia nauplii (Fig. 1).

The survival and cannibalism rates of larvae fed with live feed were not significantly

different. The larvae reared on trout starter had the lowest survival rate (67.5%) and the

highest rates of cannibalism (10.4%). Cumulative mortality (Fig. 2) indicated that larvae

fed on live feed, had high mortality during the first 3 days of feeding (2nd to 5th days),

when compared to later days (from 5th to 11th days). By contrast, artificial feed caused an

increased mortality until the end of the experiment. However, the mortality of larvae fed

with the artificial diet tended to diminish after the 5th day.

3.2. Comparison between Artemia nauplii, decapsulated Artemia cysts, and dry yeast and

beef liver diet

In the second experiment, the SGR of larvae fed Artemia nauplii was 35.4% day� 1

higher than that obtained with decapsulated cysts (28.7% day � 1) or dry diet (22.7%

day � 1). However, the survival rates of fish fed on decapsulated cysts or the dry diet, were

90.4% and 86.6%, respectively, which were not significantly different to those fed on

Artemia nauplii (90.5%). Cannibalism rates were not significantly different among the

three treatments (Table 4 and Fig. 3).

Table 3

Mean weight, specific growth rate and survival rate of P. bocourti larvae fed on artificial diet or live feed (Artemia

nauplii, Moina sp., Tubifex) after 9 days of nursing from D2 to D11

Feeding treatments Artemia nauplii Moina sp. Tubifex Trout starter

Initial weight at D2 (mg) 3.7 3.7 3.7 3.7

Weight at D5 (mg) 13.3F 1.7a 9.9F 1.2b 11.0F 0.4b 7.2F 0.4c

Weight at D8 (mg) 41.5F 4.6a 22.9F 0.7b 37.6F 1.3a 14.6F 1.3c

Final weight at D11 (mg) 100.7F 0.7a 60.8F 5.1b 101.5F 11.7a 24.3F 1.7c

SGR (% day� 1) 36.0F 0.4a 31.0F 0.9b 36.7F 1.3a 20.8F 0.8c

Survival rate (%) 91.7F 5.2a 93.7F 2.4a 92.7F 2.1a 67.5F 13.6b

Cannibalism rate (%) 3.9F 1.5a 1.6F 2.4a 2.6F 1.4a 10.40F 2.6b

Figures in the same line having same superscripts are not significantly different by Duncan’s multiple range test

( P< 0.05). MeanF S.D. (based on three replicates).

SGR= 100� (ln(W2)� ln(W1))/(T2�T1).

Table 2

Mouth size of P. bocourti larvae at first feeding. (48 h post-hatching)

Age from Total length Mouth size (mm)hatching (mm)

Opening

at 45jOpening

at 90jWidth of

lower jaw

48 h (D2) 8.72 0.55 0.95 1.00

72 h (D3) 9.65 0.71 1.19 1.28

96 h (D4) 10.60 0.80 1.25 1.31

Distance from the lower to upper jaw was measured for mouth opening at 45j or 90j.


3.3. Weaning time and digestive tract development

3.3.1. Weaning time

In the third experiment, the growth of larvae fed on Artemia nauplii were not

significantly different from those weaned to dry feed after 4–6 days Artemia feeding

Fig. 2. Cumulative mortality of P. bocourti larvae in response to live feed or trout-starter feed. Feeding started

48 h post-hatching (D2). Vertical bars = S.D.

Fig. 1. Growth curve of P. bocourti larvae fed on live Artemia nauplii, Moina sp., Tubifex and a trout-starter feed

in the first experiment. Feeding started 48 h post-hatching (D2).


(Fig. 4). However, weaning after 2 days Artemia feeding led to a reduced growth and

fish fed exclusively on dry diets have the lowest growth. In general, the final weight

illustrated a reduced trend if fish were weaned earlier than 3 days Artemia feeding

(Fig. 4).

Concerning survival rates, larvae fed exclusively on a commercial trout diet had the

lowest survival rate (67.2%). Nevertheless, weaning after 1 or 2 days, Artemia feeding

resulted in improving the survival rate (78.0% and 76.0%, respectively). Starting from 3

Fig. 3. Growth curve of P. bocourti larvae fed on Artemia nauplii, decapsulated Artemia cysts or dry diet based on

yeast and beef liver (dry diet 2) in the second experiment. Vertical bars = S.D.

Table 4

Mean weight, specific growth rate and survival rate of P. bocourti larvae fed on Artemia nauplii, decapsulated

Artemia cysts or dry diet based on yeast and beef liver after 9 days of nursing from D2 to D11

Feeding treatments Artemia

nauplii

Decapsulated

Artemia cysts

Dry diet based on

yeast and beef liver

Initial weight (mg) 3.7 3.7 3.7

Final weight (mg) 97.6F 10.7a 53.0F 3.8b 30.9F 2.6c

SGR (% day� 1) 35.3F 2.2a 28.7F 0.8b 22.7F 0.2c

Survival rates (%) 90.5F 4.7a 90.4F 7.4a 86.6F 1.5a

Cannibalism rates (%) 3.2F 4.2a 5.5F 4.8a 7.0F 1.4a

Figures in the same line having same superscripts are not significantly different by Duncan’s multiple range test

( P< 0.05). MeanF S.D. (based on three replicates).

SGR= 100� (ln(W2)� ln(W1))/(T2�T1).


days Artemia feeding survival rates were consistently high and varied between 88.1% and

96.2%, and they were not significantly different from those fed exclusively on Artemia

nauplii.

3.3.2. Digestive tract development in P. bocourti

The digestive tube is rudimentary and undifferentiated at hatching, and lies on its

yolk sac. Twenty-four hours later, the pancreas and liver differentiated as a clump of

cells in the posterior part of the digestive tract (Fig. 5). At initiation of exogenous

feeding (day 2), the stomach became enlarged with isometric epithelium cells, which are

different from the elongated cells in the intestinal part. Also, at that time, zymogens

were detected in the pancreas, but gastric glands were not yet found in the stomach. Up

to 4 days post-hatching (day 4) these glands were found beneath the gastric epithelium.

On day 5, the section stained with PAS, indicated that the stomach starts secreting

mucopolysaccharides (Fig. 6). Also at that time, the gastric pH level fell to 3.3 by

Fig. 4. Mean weights (mg) and survival rates in P. bocourti larvae weaned to dry diet at different days post-

hatching. Fish were fed either on Artemia nauplii and then shifted directly to a commercial trout-starter feed. The

number (0, 1, 2. . .) in horizontal axis stands for the days that larvae were fed with Artemia nauplii before shifting

directly to trout-starter feed. Treatment ‘‘0’’ and ‘‘A’’ indicate that larvae were fed exclusively on dry diet or

Artemia nauplii, respectively.


Fig. 5. The digestive tube (A) is rudimentary and undifferentiated at hatching, and lies on its yolk sac (C).

Pancreas and liver (B) are present as a clump of cells in the posterior part of the digestive tract. HE� 60.

Fig. 6. Longitudinal section of a digestive tube of P. bocourti larvae 5 days post-hatching, illustrates liver (A),

intestine (B) and a stomach that is well-performed (C). PAS� 100.


changing color of Congo red indicator. All these observations indicated that the stomach

then attained its morphological and probably functional completeness.

4. Discussion

4.1. Growth performances and survival rates

In the first and second experiments, Artemia nauplii proved to be an excellent feed in

terms of growth and survival rates. Nevertheless, the survival rate of larvae fed on

Artemia was not significantly different from that fed on Moina or Tubifex, suggesting

that live feeds other than Artemia can be used to rear P. bocourti larvae. Larvae fed on

Moina had lower growth than those fed on Artemia nauplii and Tubifex. The same

conclusion was reported in H. longifilis (Kerdchuen and Legendre, 1994) and in C.

macrocephalus (Fermin and Bolivar, 1991). However, Adeyemo et al. (1994) showed

the opposite for two other catfish, H. bidorsalis and C. gariepinus. Fish fed on M. dubia

had higher growth and survival rates than those fed on Artemia nauplii. In their

experiments the SGRs for Artemia treatment were surprisingly low, 5.1 and 6.1%

day � 1 for a 7-day duration for H. bidorsalis and C. gariepinus, respectively. Numerous

ephippial eggs found in larval stomach content analysis may explain, at least in part, the

lower growth in P. bocourti larvae as ephippial eggs are resistant to digestion in many

fish species (Mellors, 1975). Tubifex have been used economically as a live feed for

nursing European catfish (S. glanis) on large scale in Hungary (Horvath et al., 1981),

but many fish larvae cannot ingest such large prey. Fortunately P. bocourti larvae at

exogenous feeding have a mouth opening large enough permitting the ingestion of

chopped Tubifex, and their growth and survival rates were not different from those fed

on Artemia. Hence, the study confirmed the feasibility of completely replacing Artemia

with Tubifex to nurse P. bocourti larvae.

The lower growth and survival rates of larvae fed on commercial trout-starter feed are

in agreement with findings in other catfish. When fed on trout-starter feed, H. longifilis

larvae (Kerdchuen and Legendre, 1994) and C. gariepinus larvae (Hogendoorn, 1980)

had low survival rates; 32% and 12%, respectively. This may be related to the feed

quality and the digestibility or to the primary development of digestive systems at first

feeding. In the study, P. bocourti apparently showed a better survival rate; 67.5% when

compared to 32% and 12% in the two catfish. That indicates this species has a high

potential to feed on artificial diet. Moreover, yeast and beef-liver dry diet proved

comparable to Artemia nauplii in term of survival rates. The same result was reported in

H. longifilis (Kerdchuen and Legendre, 1994) and in C. gariepinus (Appelbaum and Van

Dame, 1988). The improved survival of dry feed based on yeast and liver could be

attributed to better digestibility of protein. Inactive yeast is roasted at high temperature

during the manufacturing process, thereby, denaturing the proteins to a significant

degree, which in turn facilitates its digestion (Hecht, 1996). Cannibalism was reported in

most larval rearing. Hecht and Appelbaum (1987) demonstrated that cannibalism in C.

gariepinus contributed greater to larval mortality than natural mortality. In C. macro-

cephalus, Fermin and Bolivar (1991) observed a high cannibalism rate in a dry diet


treatment (21.7%), higher than in combination of Artemia with dry diet (9.7%). In the

study the larvae fed trout-starter feed resulted in a higher cannibalism rate (10.4%) than

live food (1.6–4.7%).

Verreth et al. (1987) proposed decapsulated Artemia cysts as a reference diet in larval

nutritional studies. In this study live Artemia nauplii resulted in a higher growth rate than

Artemia cysts. Several workers confirmed a highly nutritional value of decapsulated cysts:

30–50% higher energy than freshly hatched nauplii (Vanhaecke et al., 1983). It is clear

that the nutritive value of feeds does not account for the growth difference observed in

body gain of larvae fed on live Artemia nauplii and on decapsulated cysts. The study

showed P. bocourti larvae ingested more live Artemia nauplii than decapsulated cysts

(Fig. 7). This may be linked to movements of live nauplii and quick sedimentation of

decapsulated cysts, which consequently become less available for the larvae. The stomach

analysis elucidates the reason for reduced growth in larvae fed on decapsulated cysts. In

brief, the difference in growth reflects a difference in feed ingestion and preference rather

than in nutritional quality of the feed.

4.2. Weaning time and digestive tract development

The study indicates that P. bocourti larvae require 3 days Artemia feeding before

shifting directly to trout-starter feed. When compared to other freshwater species, P.

bocourti larvae can be weaned earlier. Verreth and Van Tongeren (1989) indicated that

C. gariepinus could be weaned at 4.1 and 1.8 days in respect to growth and survival.

Fig. 7. Amount of Artemia nauplii or decapsulated cysts found in stomach of P. bocourti larvae 30 min post-

feeding.


Fermin and Bolivar (1991) reported the weaning time of Asian catfish (C. macro-

cephalus) to be 4 days after live zooplankton feeding. This study shows that P. bocourti

larvae develop a functional stomach earlier than C. gariepinus, which is a possible

reason why the larvae of the species may be weaned onto day feed earlier than other

Siluroidei larvae. Yet, little research has paid attention to the fact that the larval

preference of live feed rather than dry diet is due to the movement of live prey. As a

result, feed intake of the dry diet feeding is constantly lower than that obtained in live

feeding, especially during the initial feeding when larval fins are not yet well developed.

This is possibly an important reason for the unsuitability of the dry diet for larval rearing

in many fish species.

Acknowledgements

CIRAD and IRD supported this work in a co-operative project with Vietnam. The

authors are grateful to Dr. Marc Legendre (IRD), Dr. Pierre Bergot (INRA) for critical

comments on the manuscript.

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Larval rearing of the Asian Catfish, Pangasius bocourti (Siluroidei, Pangasiidae): alternative feeds...

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