Ensiling of Golden Apple snails (Pomacea canaliculata) and growth performance of African catfish (Clarias gariepinus) fingerlings fed diets with raw and ensiled Golden Apple snails as protein source

O Phonekhampheng, L T Hung* and J E Lindberg**

Department of Livestock and Fisheries, Faculty of Agriculture, National University of Lao, Vientiane, Lao PDR
*Faculty of Fisheries, Nong Lam University, Ho Chi Minh City, Vietnam
**Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, P.O. Box 7024, SE-750 07 Uppsala, Sweden
jan-eric.lindberg@huv.slu.se

Abstract

The influence of ensiling Golden Apple snails (GAS) on nutritional and biochemical traits, and the growth performance of African catfish (Clarias gariepinus) fingerlings fed diets where fish meal was replaced with raw or ensiled GAS as protein source was studied.

Raw GAS was ensiled without (control) and with addition of citric acid or sugar cane molasses. The dry matter (DM) content in ensiled GAS decreased (P<0.05), and the pH value and ammonia nitrogen content increased (P<0.05), with time of ensiling on all treatments with the largest effects in the control and in the treatments with lowest inclusion of citric acid and sugar-cane molasses. Crude protein content decreased numerically with time of ensiling on all treatments. It was only the treatments with high addition of sugar cane molasses (>15 % in DM) that maintained a brownish-yellow colour and a nice smell for the whole ensiling (28 d) period.

A control diet with fish meal and three experimental diets, where fish meal was replaced with raw or ensiled GAS, were formulated and fed to African catfish fingerlings. GAS was ensiled with 5 % citric acid or 20 % sugar cane molasses. The growth performance and feed consumption was recorded for a period of 6 weeks. There were no differences (P>0.05) in growth performance, feed and protein utilization, and whole body composition between treatments.

In conclusion, protein from raw and ensiled GAS can completely replace fish meal in diets for African catfish fingerlings under tropical conditions without negative effects on growth performance and feed utilization.

Key words: catfish, Golden Apple snail, growth performance, silage

Introduction

The traditional practice in small-scale African catfish (Clarias gariepinus) production in Laos, as in many other parts of Southeast Asia, is based on fertilizing the fishponds to culture natural food organisms before stocking the fish. However, by using supplement feed it should be possible to double the stocking density and also harvest marketable sized fish up to one month earlier than without supplementary feeding (DLF 1999). It has been estimated that feed costs constitute about 50–80 % of the total production cost for semi-intensive and intensive catfish farming (Branch and Tilley 1991). Therefore, the future development of small-scale aquaculture systems in Laos will depend on available feed resources (Phonekhampheng et al 2008a), in particular protein-rich feedstuffs.

Different conventional and non-conventional feedstuffs have been used in Southeast Asia to formulate catfish diets (Santiago et al 1986; Natividad 1982; Phonekhampheng et al 2008b). Among the non-conventional feedstuffs, the Golden Apple snail (GAS; Pomacea canaliculata) is of particular interest due to its high protein and fat content (Kaensombath 2003; Phonekhampheng et al 2008b), making it potentially useful as a replacement for fish meal in catfish diets. However, the availability of the GAS is irregular during the year and it is therefore necessary to find ways to preserve a temporal abundance. Sun-drying is a cheap and simple option in tropical countries during the dry season but is not applicable throughout the year. As an alternative, the fermentation technology is an affordable low-level preservation technique ideally suitable for tropical developing countries (Lee 1990; Han-Ching et al 1992). This technology is more weather independent and has previously been successfully applied to fish and shrimp offal (Fagbenro 1996; Ngoan et al 2000).

The present experiment was performed to evaluate the influence of ensiling of GAS on nutritional and biochemical traits, and to evaluate the growth performance of African catfish (Clarias gariepinus) fingerlings fed diets where fish meal was replaced with raw or ensiled GAS as protein source.

Material and methods  

Location and climate

The present study was carried out in facilities of the faculty of Fisheries at the Nong Lam University, Ho Chi Minh city, Vietnam. The mean ambient temperature was 31 °C in the middle of the day during the trial, which started in May 2007.

Ensiling of Golden Apple snails (GAS)

GAS (Pomacea canaliculata) was purchased from farmers in the Mekong delta. To prepare the GAS for ensiling, the shell was broken and removed, and the remaining cover and flesh cleaned with water before chopping and grinding.

The ground material was cleaned then mixed with additives (citric acid or molasses) in the raw form and placed in sealed plastic containers for ensiling for a total of 28 days. Citric acid (CA) was added at 1 (CA1) and 5 (CA5) % of dry matter (DM). Sugar cane molasses (M) was added at 5 (M5), 10 (M10), 15 (M15) and 20 (M20) % of DM. The experiment was arranged as a completely randomized design with three replications per treatment. Samples for pH determination and chemical analysis were taken at the start (0), and after 7, 14, 21 and 28 days of storage.  

Growth performance of African catfish fingerlings

Diets and experimental design

A control diet (C), composed of fish meal, rice bran, vitamins and minerals, and a binder (carboxy-methyl cellulose) was formulated (Table 1).

In addition, three experimental diets where fish meal was replaced with GAS were formulated. Fish meal was replaced with GAS ensiled with 5 % citric acid (diet GAS-CA5), with GAS ensiled with 20 % molasses (diet GAS-M20) and with raw GAS (diet GAS-Raw).

African catfish (Clarias gariepinus) fingerlings (360 in total) with an average body weight of 15 ± 0.4 g were randomly allocated to 12 net-cages (0.5 m x 2 m x 2 m) with three cages (replicates) per treatment. Each cage was stocked with 30 fingerlings. They were acclimatized to the experimental conditions and cultured in the net-cages to be familiar with artificial feed for at least 15 days before starting the experiment. The growth performance and feed consumption was recorded for a period of 6 weeks. The daily feed allowance was 5 % of the average fish body weight, which was fed in two equal meals twice a day.

Water in the pond were the net-cages were kept was supplied from the near Dat lake.  Dissolved oxygen (DO) and pH in the pond water were monitored every day and was in the range 4 to 5 mg/l and 7.4 to 7.8, respectively, during the experiment. Total ammonia was monitored twice a week, and was 0.2 mg/l at the start and 0.5 mg/l at the end of the experiment. The air temperature was recorded daily and varied between 27 to 31^oC during the experiment.

Preparation of diets

The feedstuffs used in the basal diet were purchased from the local market. GAS was purchased from farmers in the Mekong delta. To prepare the raw GAS, the shell was broken and removed, and the remaining cover and flesh cleaned with water before chopping and grinding. The same procedure was followed for the preparation of raw and ensiled GAS. The ensiled GAS was ensiled with 5% of citric acid and 20 % sugar-cane molasses (in DM) and was allowed to ferment for 14 days before use.

The test diets were prepared by mixing the raw and ensiled GAS with the other feed ingredients (Table 1). After mixing the dietary ingredients the feed was cold pelleted using a 5 mm dye and then dried at 60°C for 24 hours before use.

Sampling

At the start of the experiment fish were weighed and randomly distributed in the concrete tanks. Every two weeks the fish were weighed to evaluate their weigh gain. To minimize stress during weighing MS222 (3-aminobenzoic acid ethyl ester) was used to anaesthetize the fish.

Calculations

The following calculations were made on collected data to describe and evaluate fish performance: 

(i) Mean weight gain (MWG) = Wf -Wi 

Where, Wf is the mean final fish weight and Wi the mean initial fish weight. 

(ii) Percentage body weight gain (PWG) = (MWG x 100)/Wi
(iii) Specific growth rate (SGR, %) (Brown 1957)  = [(log Wf – log Wi) x 100)]/D

(iv) Protein efficiency ratio (PER) = MWG/protein consumed

(v) Net Protein Utilization (NPU, %) = 100 x (Fish protein gain/protein consumed)

(vi) Feed conversion ratio (FCR) = feed consumed (dry weight)/fish weight gain

Chemical analyses

Dry matter (DM), ash, crude protein (CP), crude fat (EE), crude fiber (CF) and NH₃-N were analyzed according to standard methods of AOAC (1990).

Statistical analysis

The data were subjected to analysis of variance (ANOVA) by using the General Linear Model (GLM) procedure of Minitab version 14 (2000). When the F test was significant (p<0.05) the Turkey’s test for paired comparisons was used to compare means.

Results 

Ensiling of GAS

Chemical composition and pH

The DM content in ensiled GAS decreased with time in all treatments (P<0.05) (Table 2).

The decrease in DM content was most marked in the control and in treatments CA1 and M5. With the highest inclusion of citric acid (CA5), and with inclusion of more than 10 % sugar-cane molasses (treatment M10, M15 and M20), the DM content showed only a small decrease (less than 2 %-units) with time of ensiling.

The pH values increased markedly (P<0.05) with time of ensiling in the control, and in the citric acid treatments (CA1 and CA5) (Table 2). However, the pH value in treatment CA5 was markedly lower (P<0.05) than in the control from day 7 and onwards. In the sugar-cane molasses treatments, pH values were lower than in the control from day 7 and onwards with inclusion of 10 % or more. 

Crude protein (CP) content showed only minor changes with time of ensiling on all treatments (Table 3).

The content of ammonia nitrogen (A-N) increased with time of ensiling on all treatments (Table 3). The increase in A-N was marked in the control, and in the treatments with lowest inclusion of citric acid (CA1) and sugar-cane molasses (M5). For all other treatments, the A-N content increased to a similar level with time of ensiling.

Physical characteristics

For all treatments, there were only small changes in color during the first 7 days and all had a smell of fish paste. Already at day 14, the control treatment had become black in color and had a stinky smell.

At day 14, the color was dark yellow and silages had a smell of fish paste in treatments CA1 and CA5. At day 21, treatment CA1 had turned dark in color and had a stinky smell. In contrast, at day 21 treatment CA5 was still dark yellow in color and had a smell of fish paste. At day 28, also treatment CA5 was black in color and had a stinky smell. At day 14, the treatments M5 and M10 were brown in color and had a smell of fish paste. At day 21, the color had changed from brown to black and it had got a stinky smell. For treatment M15 and M20, the brown color and the fish paste smell remained until day 21. At day 28, the color was brown to brownish-yellow and the silage maintained a smell of fish paste.

Growth performance of African catfish fingerlings

No mortalities or health problems were encountered during the experimental period and fish regained their appetite shortly after the adaptation period.

There were no differences (P>0.05) in growth performance of African catfish fingerlings, expressed as specific growth rate (SGR) or percentage body weight gain (PWG), between the control diet and the diets with ensiled and raw GAS (Table 4).

Moreover, feed utilization, expressed as the feed conversion ratio (FCR), was similar (P>0.05) between diets. The dietary protein utilization, expressed as the protein efficiency ratio (PER) and as net protein utilization (NPU), were numerically higher on diets with GAS inclusion than on the control diet. However, these differences were not significantly different.

There were no treatment differences (P>0.05) in whole body moisture content and in chemical composition on a fresh weight basis (Table 4). However, whole body protein content on a dry matter basis was lower (P<0.05) in fish fed diet GAS-Raw (41.2 %) than the other diets (50.9-52.2 %).

Discussion 

The results from the current study indicate that it is necessary to include an additive to raw GAS in order to get biochemically acceptable silage. The GAS ensiled without any additive deteriorated rapidly, as reflected in a rise in pH and ammonia-N content, a marked drop in DM, a darkening in colour and an unpleasant smell. A similar development was found for the ensiled GAS with the low inclusion of citric acid and molasses. In contrast, addition of 15 to 20 % sugar cane molasses resulted in biochemically acceptable silage that maintained a brown to brownish-yellow colour and had a pleasant smell.

Earlier studies have shown that GAS can be successfully ensiled with addition of rice bran and molasses, with a reduction in pH from 6.6 to 4.7 after 7 days of ensiling (Kaensombath 2003), and the silage remained stable during storage for 56 days. Rattanaporn et al (2001) showed that addition of molasses to minced GAS (5, 10 or 15 % per kg fresh-matter) resulted in a rapid drop in pH that maintained at a low level for 10 days of storage. However, the lowest level of molasses addition could not prevent autolysis of the material, as reflected in increasing levels of free amino acids. Moreover, studies on ensiling of shrimp head offal with addition of molasses (Fagbenro and Bello-Olusoji 1997; Ngoan et al 2000; Nwanna 2003), cassava starch (Fagbenro and Bello-Olusoji 1997) and cassava root meal (Ngoan et al 2000) have shown a marked drop in pH shortly after the start of the ensiling process and a reasonable stability in pH and ammonia-N during storage.

It appears likely, that the successful ensiling of GAS was due to lactic acid fermentation in the material (McDonald et al 1991). In contrast, the deteriorated and poor-quality GAS silage was most likely associated with contamination with enterobacteria. They are classified as facultative anaerobes, and consequently compete with the lactic acid bacteria for the water soluble carbohydrates. In addition, they have a pH optimum for growth of about 7.0 and are therefore usually active at the early stages of fermentation, when pH is favorable for their growth (McDonald et al 1991). 

Replacement of fish meal with raw or ensiled GAS did not negatively affect the growth performance, feed utilization and protein utilization of African catfish fingerlings. This indicates that GAS has a high nutritive value and could be used to completely replace fish meal in African catfish production. In accordance with the current findings, it was recently reported by Sogbesan et al (2006) that African catfish (Clarias gariepinus) fingerlings (2.8 g initial body weight) had a similar or improved growth performance on diets where fish meal was replaced by garden snail (Limicolaria aurora) meal. Moreover, dietary protein utilization (PER) remained unchanged or was even slightly improved at an inclusion level of 25 %, while the feed conversion (FCR) was slightly lower at 100 % replacement of fish meal in the diet.

The recorded water temperature (23-26 °C) and water quality parameters (DO 4.0-6.2, pH 6.0-6.8) in the current study were in the range of those recommended (temperature 22-28 °C , DO minimum 0.5 mg/L, pH 6.0-8.0) for growing African catfish by Akinwole and Faturoti (2007). Channel catfish are considered to have an optimal growth in water temperatures ranging from 28°C to 30°C (Chapman 1992).

It has previously been shown (Hogendoorn et al 1983; Henken et al 1986) that African catfish fingerlings raised in an intensive culture system in the BW range used in the current study may exhibit a maximal SGR of 5-6 % at a feeding level of 5 % of BW and with a water temperature of 25-30°C. The SGR in the current study was 1.5 %, which is well below maximum values and could be due to the low dietary CP content (Henken et al 1986). The CP intake in the current study was approximately 2 g d^{-1 kg BW -0.8} which was estimated by Henken et al (1986) to result in a FCR of 2.5 and a PER of 2.4. The latter values indicate that the feed and protein utilization recorded in the present study was poorer than what could be anticipated. In contrast, Degani et al (1989) reported a SGR of 0.8-1.3 %, a FCR of 2.3-3.8 and a PER of 1.05-1.44 in two months old African catfish fingerlings fed diets with 23-30 % CP at a feeding level of 4 % of BW and at a water temperature of 27°C. These results were inferior to those in the present study.

Body composition remained unchanged by the dietary treatments, with the exception of a reduced CP content on the diet with raw GAS. This could possibly indicate an impaired protein value linked to this feed resource. Body moisture content was comparable to previously reported values (Degani et al 1989), while body protein content was lower (Degani et al 1989) and body lipid higher (Henken et al 1986). This could be due to the low dietary CP content in the current study, as both protein and lipid accretion is closely linked to the dietary protein content. A reduction in CP content in the diet of African catfish will result in lower accretion of body protein and a higher accretion of body lipids (Henken et al 1986), and thus a change in body composition.

Conclusions 

• The present study demonstrates that African catfish (C. gariepinus) fingerlings are able to efficiently utilize GAS protein and convert it into fish biomass.

  
  

• Moreover, the data show that protein from ensiled GAS can completely replace fish meal in diets for African catfish fingerlings under tropical conditions without negative effects on growth performance and feed utilization.
   

Acknowledgments 

The authors are grateful to the Swedish International Development Authority (Sida/SAREC) for funding this study and the faculty of Agriculture, National University of Lao for allowing the first author to carry out this study. Thanks are also due to the Feed Analysis Laboratory of the Department of Livestock and Fisheries of the Ministry of Agriculture and Forestry.

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Received 18 September 2008; Accepted 9 November 2008; Published 1 February 2009

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