Earthworm

Earthworm (Perionyx excavatus) as a main protein source for growing zig-zag eel (Mastacembelus armatus) in small-household aquaculture-based farming systems in the Mekong river delta

Department of Aquaculture, Faculty of Agriculture and Natural Resources, Angiang University,
25, Vo Thi Sau street, Long Xuyen city, Angiang, Vietnam
pploan@agu.edu.vn

The purpose of the present study was to show: (i) that Zig-zag eels can live and grow well in captive culture in artificial conditions such as plastic containers; and (ii) that earthworms produced from live stock manure can be a good protein source and can replace the natural feed sources for growing zig-zag eels in artificial culture. Perionyx excavatus were cultured on fresh cow manure in wooden boxes, which were surrounded by plastic sheets. The area of each frame was 2 x 2 x 0.4m. Earthworm seed was put into the boxes with density of 2 kg per m². Biomass production of earthworms was determined after 60 days and yielded 3.5kg adult earthworm/m². Temperature, pH and DO were within the normal range for fish culture. Growing Zig-zag eels were fed small shrimps as a control treatment (SS), or earthworms (EW) or commercial pellet feed (CP).

Daily weight gain (DWG), specific growth rate (SGR), and survival rate (SR) were measured. Growth rate of the Zig-zag eels was best for EW, followed by SS with the poorest performance on CP, which was not consumed such that the fish lost weight on this treatment. There was no effect of feed source on fish survival rate. It was concluded that earthworms are a valuable source of protein for growing Zig-zag eel fish.

Zig-zag eel (Mastacembelus armatus) (Fishbase 2007) lives in fresh or brackish water. Preferred water conditions are pH 6.5 to 7.5 and temperature 22-28⁰C. In nature, zig-zag eel is widely distributed from Pakistan to Vietnam and Indonesia. They often bury their body under sand and look for feed. For this species the main feed is of animal origin. The zigzag eel has the habit of searching for food during the night. Their food comprises worms, larvae of zoobenthos, mature zoobenthos, shrimp, young fish and detritus (Pethiyagoda 1991; Rainboth 1996). This fish species can grow to a length of 90 cm and about 1 kg in weight). The flesh is of high quality and has a high economic value. In natural conditions, they are exploited strongly by fishermen (Truong Thu Khoa and Tran Thi Thu Huong 1993; Mai Đinh Yen 1992; Pethiyagoda 1991; Nelson 1994; Binh Thuan aquaculture office 2007).

The earthworm (Perionyx excavatus) is a species which lives on manure and decomposing organic matter. There are reports that they are cultivated in Philippines, Australia and other countries (Gurrero 1983; Edwards 1983). The mature worms are from 10 to 15 cm in length, and consist of 15 – 20% solid substance. In the solids portion they contain 68-70% protein, 7-8% lipids, 12-14% carbohydrate and 1–12% ash (An Phu farm2010).

The objective of this study was to evaluate the feeding of earthworms as an alternative protein source for zig-zag eels raised in a captive culture system.

Materials and Methods

Location

The experiment was conducted from March to June, 2008 in a farm of Angiang University (AGU), located in My Khanh Commune, Long Xuyen city, An Giang Province.

Fish fingerlings and stocking density

Zig-zag eel fingerlings (Photo 1) with a range of live weight of 29.9 to 32.7g, and length of 20.4 to 21.6cm were distributed at random to 9 plastic tanks (Photo 2), with volume of 1m³and 80 cm height of water body inside. The density was 30 fingerlings in each tank. One third of the water surface of the water in each tank was covered with water hyacinth so that the fish could shelter under it.

Experimental design and treatments

The treatments were allocated in three blocks according to a randomized block design (Table 1).

The small shrimps were bought in the local market, having been collected from the field or in natural water bodies. Commercial pellet feed was a donation from the UP (Uni-President) Company. It had a protein level of 33%. The earthworms were cultured on cow manure in the AGU experimental farm.

After 3 days of adaptation to the tanks with no feed, the fish subsequently were fed twice a day, with amounts of between 5 and 7% of body weight (DM basis). One fifth of the feed was given in the morning at 7-8 am and the remainder in the afternoon at 5-6 p.m. The following morning before the first meal, all refusals were siphoned off. The water was changed at weekly intervals at the rate of 50% of total water volume.

Culturing earthworms

The earthworms used to start the culture were bought from farms around Long Xuyen city. They were laid on the floor of three wooden boxes (2 x 2 x 0.4m) at a density of 2 kg worms/m². The boxes were surrounded by plastic sheet ,and covered with a black net to control the humidity of the substrate in the boxes, and prevent insects and animal predators getting access to the worms. The feed for the earthworms was fresh cow manure added twice weekly to the boxes in amounts determined according to earthworm demand. Water was sprayed over the manure to keep a humid environment inside the boxes (about 80% humidity). After 60 days from the first addition of substrate; the adult worms were ready to be harvested.

Data collection and analysis

Water quality (temperature, pH and dissolved oxygen [DO] was recorded every 3 days at 6.00am and 14.00pm. Temperatures were measured by thermometer, and pH and DO using the "Aqua" test kit. Every 15 days, at least 10 fish per tank were sampled for measurement of weight and length. The following criteria were calculated:

Statistical analysis

The data were subjected to the analysis of variance (ANOVA) procedure for Randomized Complete Block designs using the general linear model (GLM) in SPSS version 15.0 for Windows. Pair wise comparisons with a confidence level of 95% were used to identify differences among dietary treatments.

The average application of cow manure was 7 kg twice weekly. Thus after 56 days the total amount was 112kg. The total harvest of earthworms at this time (56 days) was on average 3.55 kg. The increase in worm biomass was therefore 3.55-2.00 = 1.55 kg. Thus the culture of 1 kg earthworms required 112/1.55 = 72 kg of fresh cow manure. In each 1 kg of earthworm biomass there were from 1,100 to 1,200 worms.

Table 2. Mean values (with SE) and range for water quality parameters in tanks used to raise zigzag eel fish on small shrimp, earthworms or commercial feed
	Small shrimps	Commercial feed	Earthworms
Temperature, °C
Mean	29.6 ± 1.46	29.7 ± 1.39	29.7 ± 1.35
Range	26.5 – 33	26.5 – 33	27 – 33
DO, ppm
Mean	4.60 ± 0.60	4.49 ± 0.58	4.58 ± 0.53
Range	3.5 – 5.9	3.5 – 5.8	2.8 – 5.8
pH
Mean	7.7 ± 0.60	7.56 ± 0.56	7.61 ± 0.54
Range	6.6 – 9.3	6.5 – 9.0	6.7 – 8.8

Water quality parameters (Table 2) were within the normal range for captive fish culture (Boyd 1990) and did not differ among treatments.

Feed composition

There were major differences in the composition of the feeds (Table 3). Crude protein content was highest in the earthworms which were twice as rich in this element as the commercial feed, Ether extract was highest in the small shrimp and lowest in the commercial feed. Ash content was lowest in the earthworms with less than half the amount found in the trash fish and the commercial feed.

Table 3. The chemical composition of the feeds
Ingredients, (%)	Small shrimp	Commercial feed	Earthworms
DM, %	16.9	89.0	16.8
As % of DM
Crude protein	54.3	33.0	64.0
Lipid	14.5	4.00	9.70
Ash	16.5	16.0	6.37

Feed consumption

There were no feed refusals in the case of the earth worm and small shrimp diets (Table 4). Small amounts of commercial feed were offered but the eel fish did not eat it.

Growth and feed conversion

The eel fish fed earth worms grew 23% faster than those fed the small shrimp (Table 5; Figure 1). By contrast, the fish fed the small shrimp grew more in length than those fed earth worms. As a result the weight length ratio was higher for the fish fed earthworms than for those fed small shrimp (Table 5; Figure 2) which indicates that the flesh to bone ratio would be higher for fish fed the earth worm diet. Feed conversion data could not be analysed because all the tanks in each treatment were supplied with the same quantities of feed. However, because the eel fish grew faster when fed earthworms compared with small shrimp, they required 27% less DM per unit gain in weight.

Table . .Mean values for changes in weight and length, and in survival, of zigzag eel fish fed trash fish, earthworms or commercial feed (90 days of experiment)
	Small shrimp	Commercial feed	Earthworms	SEM	P
Weight, g
Initial	29.9^a	30.0^a	32.7^a	1.92	0.498
Final	55.1^b	20.7^a	61.6^c	1.13	0.0001
Daily gain	0.283^b	-0.117^a	0.347^c	0.018	0.0001
SGR, %/day	0.679^b	-0.412^a	0.704^b	0.0066	0.0001
Length, cm
Initial	20.3^a	21.5^b	21.6^b	0.17	0.0001
Final	26.3^b	21.8^a	26.9^c	0.156	0.0001
Gain	5.84^c	1.14^a	5.32^b	0.0034	0.0001
Weight/length	2.09	#	2.28	0.041	0.001
DM feed conversion	1.23	#	0.97
Survival, %	100	100	100
^a,b,c Means with different superscripts within rows are significantly different (p<0.05) # The fish did not eat the commercial feed and lost weight during the experiment

Survival rate

All the fish survived even on the commercial feed treatment where they lost weight. This proved that the Zig-zag eels can grow well in plastic tanks, in standing water.

Conclusions

Acknowledgements

The authors wish to acknowledge the Swedish International Development Authority (Sida) for financial support of this study. We also would like to thank the Faculty of Agriculture and Natural Resources, Angiang University, for allowing us to use their facilities, and in particular Mr Tuan, Mr Nhan for their excellent assistances during the course of experiment.

References

Boyd C E 1990 Water quality in ponds for aquaculture. Alabama agriculture experiment station, Auburn University. Birmingham Publishing Co. Birmingham, Alabama. First printing 5M, December 1990

Edwards C A. 1983. Earthworms. Organic waste and feed. Span, Le progress en agriculture 26,3 p.106 – 108.

Guerro R D 1983 The culture and use of Perionyx excavatus as a protein resources in the Philippines. In: Satchell, J., E (Eds.), Earthworm Ecology from Darwin to vermiculture. Chapman and Hall, London, p. 310.

Mai Đinh Yen 1992 Classification freshwater fish in the South of Vietnam. Science & Technology Publishing House.

Rainboth W J 1996 Fishes of the Cambodian Mekong. Feed and Agriculture Organization of the United Nations

Truong Thu Khoa and Tran Thi Thu Huong 1993 Classification fresh water fish in Mekong Delta. Faculty of Aquaculture, Can Tho University.

Table 4. Amounts of earth worms and small shrimp that were offered and consumed
	Small shrimp	Commercial feed	Earthworms
Feed DM offered, g/fish/day	0.346	0.0183	0.311
Feed DM intake, g/fish/day	0.346	0	0.311

Table 1. The layout of the experiment
Block 1	Block 2	Block 3
EW	SS	CP
SS	CP	EW
CP	EW	SS


Figure 1. Changes in weight of zigzag eel fish fed small shrimp (SS), earthworms (EW) or commercial feed (CP)	Figure 2. Changes in weight: length ratio of zigzag eel fish fed small shrimp (SS), earthworms (EW) or commercial feed (CP)