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View the document Feeding Value Of Fresh Perennial Leguminous Shrub Leaves To Nile Tilapia (Oreochromis Niloticus L.)

Feeding Value Of Fresh Perennial Leguminous Shrub Leaves To Nile Tilapia (Oreochromis Niloticus L.)

M.A.G. Castanares,¹ D.C. Litile,¹ A. Yakupitiyage,¹

P. Edwards,¹ And L.L. Lovshin²

¹Division of Agricultural and Food Engineering, Asian Institute of

Technology

Bangkok, Ihailand

²Department of Fisheries and Allied Aquaculture, Auburn University

Auburn, Alabama

Abstract

The feeding value of fresh pigeon pea (Cajanus cajan), leucaena (Leucaena leucocephala), gliricidia (Gliricidia septum), and sesbania (Sesbania grandifloraJ leaves to Nile tilapia (Oreochromis niloticus) was evaluated in an outdoor recirculating water system comprising 15 5 m³ concrete tanks for 56 days. Commercial catfish pelleted feed was used as a control diet. The protein content of all green fodder was within the limits of the required dietary protein level for Nile tilapia. Average green fodder intake of fish fed ad libitum ranged from 0.2 to 0.4% body weight/day, but fish lost weight during the experiment. Results of this experiment indicate that there is no value in feeding the leguminous fodders tested here to fish.

Introduction

Legume fodder is considered cheap nutritious feed for terrestrial farm animals (NRC 1984). Pigeon pea, gliricidia, leucaena, and sesbania are four common perennial forage legumes that are often used by Asian farmers as animal feed or as green manure for conventional crops. Although some perennial legume fodders have been found to have deleterious effect to farm animals, gliricidia, leucaena, and sesbania are frequently used as ruminant feed in the tropics (Williamson and Payne 1978). Pigeon pea, which is also a food crop for humans, is usually cut 50-75 cm from the ground for forage when the pods begin to ripen (Bogdan 1977).

The nutritive value of these fodders as nonconventional feed for livestock suggests that they are a potential source of herbivorous fish feed for small-scale fish farmers. There have been several studies, especially on the inclusion of leucaena leaf meal in the diet of finfish (Jackson et al. 1982, Ferraris et al. 1986, Wee and Wang 1987a) and Penaeus monodon (Vogt et al. 1986, Penaflorida 1989). However, there is no information on the nutritive value of the fresh leaves of these plants as the major nutritional source for fish.

The present study was, therefore, designed to evaluate the potential use of these fresh legume leaves as the main dietary source for Nile tilapia. This species is primarily a microphagous feeder (Colman and Edwards 1985), but it is also known to ingest plant leaves.

Materials and Methods

This study was conducted at the Asian Institute of Technology (AIT), Bangkok, Thailand, from March 28 to May 23, 1991. A completely randomized design (CRD) with five treatments, in triplicate, was utilized. Treatments consisted of fish fed the four different legumes and a control diet. The feeding trial was conducted in a recirculating system that consisted of 15 outdoor concrete tanks (2 x 2 x 1.2 m) and a biofilter. A flow rate of recirculating water was maintained to provide sufficient oxygen and to circulate the total volume of water through the biofilter unit at least once a day. A rotating octahedron plastic net cage was placed in each tank. The cage had a frame of painted steel and wood and the sides of the cage were covered with a black plastic net (2 cm mesh size). Each cage unit was rotated daily to expose the submerged half to the air to minimize fouling. The experimental cages were stocked with sex-reversed male Nile tilapia (Oreochromis niloticus) with an initial weight of approximately 25 g, at a density of 15 fish per cage.

Pigeon pea, gliricidia, leucaena, and sesbania were cultivated on the AIT campus. Fresh leaves of the four legumes were collected daily from the field and a known weight of fodder was presented to the fish once a day to feed to satiation. A bundle of fodder was tied to a floating PVC frame (0.5 x 0.5 m) in each cage at 0900 hr and the uneaten materials were collected 24 hr after. The dry matter content of offered and uneaten fodder from each tank was determined for two successive days, at biweekly intervals, to obtain the average daily dry matter intake by the fish. A commercial catfish pellet (Charoen Pokphand Company Ltd., Thailand) was the control diet, fed at 3% body weight per day.

Experimental fish were sampled biweekly to record their survival and batch weight, and the feed ration of commercial pellets was adjusted accordingly. All fish were counted and weighed individually at the end of the experiment. Samples of initial and final experimental fish were sacrificed and dried in an oven at 100°C for 24 hours. Green fodder, commercial catfish pellets, and fish carcasses were analyzed for moisture, crude protein, crude lipid, and ash. The crude fiber content of experimental feeds was also determined (AOAC 1975).

Results

The average approximate compositions of the four green fodder types and the commercial pellets are presented in Table 1. The mean body weights of the experimental fish during the feeding trial are shown in Figure 1. The mean final body weights of the fish fed the four legumes decreased compared to their initial mean body weights (Table 2). However, the fish fed commercial pellets grew from approximately 24 g to 93 g during the feeding trial.


FIGURE 1. Growth in average weight (gram) of Nile tilapia during the experimental period; (a) treatments with green fodder and pellet; (b) treatment with only green fodder

More than half (approximately 60%) of the experimental fish fed leucaena fodder developed eye cataracts. Gross morphological disorders were not observed in the other treatments.

TABLE 1 Average Proximate Composition of Green Fodder and Commercial Pelleted Feed

   

Percent, Dry Matter Basis

 

Feed

Dry Matter

Crude Protein

Crude Lipid

Crude Fiber

Ash

Nitrogen Free Extract

Pigeon pea

34.4

24.2

3.6

19.4

9.0

43.1

Gliricidia

20.3

27.3

3.0

12.8

8.8

48.1

Leucaena

28.2

32.5

1.9

12.5

6.3

46.9

Sesbania

20.5

26.3

2.6

12.1

10.5

48.7

Pellet

90.6

36.0

3.2

8.0

10.5

42.4

The dry matter intake of fish fed the experimental fodders was markedly low throughout the experimental period Cl able 3). The body lipid contents of experimental fish fed fodder were extremely low compared to their initial body lipid contents and that of the fish fed the control diet (Table 4).

Discussion

Chemical analysis of the tested fodders indicated that their protein contents were within acceptable limits for Nile tilapia (Tacon 1987). Crude protein contents ranged from 24.2 to 32.5% on a dry matter basis, with pigeon pea the lowest and leucaena the highest. In contrast, the crude lipid contents were relatively low. The crude fiber contents of the fodders was relatively high, ranging from 12.1% for sesbania to 19.4% for pigeon pea. The low lipid and high fiber content of these plants may pose a problem for their use as fish feed.

There was a reduction in the body weight of fodder-fed tilapia. Low feed intake indicated the unpalatability of the tested fodders since the highest estimated total dry matter consumption among the fodders was only 5.5 g for gliricidia-fed fish in 56 days. The corresponding protein intake of fish fed gliricidia was therefore only 1.5 g, which may not be sufficient to maintain the nitrogen balance of the fish. However, fish fed commercial pellets containing 36% crude protein at 3% body weight/day grew by 75.1 g within 56 days. This resulted from 27 g of protein ingested over the same period.

It can be concluded, therefore, that fish growth was hindered by poor fodder intake by the fish. Direct feeding on these fodders could not supply sufficient nutrition for normal growth of Nile tilapia. The relatively low body lipid content of the fodder-fed fish reflects the utilization of stored body fat as an energy source for metabolism during the experimental period, which resulted in weight loss.

The observed low dry matter intake of fodder-fed fish may be attributed to the presence of potential anti-nutritional factors in leguminous fodder. However, a gross morphological disorder resulting from an anti-nutritional factor was only detected among leucaena-fed fish, i.e., eye cataracts.

TABLE 2 Growth Performance of Nile Tilapia Fed with Leaves of Four Legume Species and Commercial Catfish Pelleted Feed for 56 Days + 1 Standard Error)

 

Initial Weight

Final Weight

Weight Gain

Relative Growth

Percent

Feed

(g)

(g)

(g)

Rate (mg/g/day)

Mortality

Pigeon pea

25.3

23.1

-2.2

-1.6

4.4

 

±0.3

± 1.4

±0.6

±0.4

 

Gliricidia

24.1

21.4

-2.7

-2.0

2.2

 

±0.4

± 1.4

±0.4

±0.3

 

Leucaena

24.4

21.8

-2.5

-1.8

4.4

 

±0.1

± 1.1

±0.5

±0.4

 

Sesbania

24.9

21.2

-3.6

-2.7

2.2

 

±0.6

±5.6

±2.7

±2.0

 

Pellet

24.0

93.2

69.3

51.5

2.2

 

±0.3

±5.7

±2.9

± 1.4

 

No feed

23.8

21.6

-2.1

-1.6

0.0

 

Sallmann et al. (1959) reported that a reduction of the mitotic index in lens epithelial cells of rats fed leucaena indicated a mimosine induced eye cataract. However, inclusion of leucaena leaf meal (LLM) in the diet of Nile tilapia, with or without pretreatment by soaking, did not cause eye cataracts in previous nutritional studies, although there was growth retardation with an increased inclusion of LLM in the ration (Wee and Wang 1987a, Santiago et al. 1988). The results of the present experiment indicate that it may be necessary to pretreat fresh leucaena leaves to reduce the detrimental effect of mimosine to Nile tilapia. Pretreatment of leucaena fresh leaves by soaking at room temperature for 48 hr has been reported to reduce the mimosine content (Wee and Wang 1987b).

Recirculated water in the tanks had a brown color, probably due to the diffusion of tannins and other pigments from the leaves. Krishnamurthy et al. (1972) and Rao and Mariappan (1972) reported that tannin as low as 6.5 mg/l is lethal to freshwater fish, and that 320 mg/l of tannin was toxic to Catla catla, respectively. However, direct toxicity by water soluble tannins could not be a major influencing factor in the present study because water was recirculated through all five treatments, including the control treatment wherein fish grew at 1.3 g/day. Further research on tannin toxicity is required. It may be possible to reduce the water soluble fraction of tannin in a pretreatment by submerging the fodder in water for a longer duration.

In addition to tannins, pigeon pea fodder was possibly deleterious to fish due to the presence of other toxic factors. Pigeon pea leaves, like the pods, may also contain haemaglutinins, protease inhibitors, cyanogen, and physic acid, which depresses appetite (IDRC/ICAR 1988).

TABLE 3 Feed Utilization Indexes of Nile Tilapia Fed with Four Legume Leaves and Commercial

Catfish Pellet for 56 Days

Feed

Average Total Dry Matter (g)

Average Feeding Consumed Per Fish (% Body Weight) per Day

Pigeon pea

3.0

0.2

 

± 0.3

±0.0

Gliricidia

5.5

0.4

 

±0.1

±0.0

Leucaena

4.2

0.3

 

±0.3

±0.0

Sesbania

2.6

0.1

 

±0.3

±0.0

Pellet

75.1

3.0

 

±2.0

±0.0

 

The results of the present experiment suggest that it is not possible to use the four tested leguminous fodders as direct feed for Nile tilapia. If toxic components were the major factors affecting low dry matter intake, it is highly unlikely that other more voracious macrophagous fish such as grass carp (Ctenopharyngodon idella), giant gourami (Osphronemus goramy), and silver barb (Puntius gonionotus) would be able to utilize these fodders efficiently. It is known that non-ruminants have a lower toxicity tolerance to mimosine and other toxic factors than ruminants (IDRC/ICAR 1988).

TABLE 4 Initial and Final Carcass Composition of Experimental Fish

 

Percent

Percent, Dry Matter Basis

Treatment

Dry Matter

Crude Protein

Crude Lipid

Ash

Initial Fish Sample

24.1

60.8

20.9

14.2

Pigeon pea

13.6

64.4

2.2

29.3

Gliricidia

12.8

61.6

3.4

31.0

Leucaena

12.2

61.2

3.3

25.9

Sesbania

13.5

63.5

2.4

28.3

Pellet

20.9

64.2

21.3

12.6

No feeding

10.7

63.5

2.7

30.4

 

However, before generalizations are made, further research should be conducted to verify the

feeding value of these fodders for other herbivorous species. Identification of the anti-nutritional

factors and the development of a cheap pretreatment for these fodder may be necessary to improve their potential as fish feed. As an alternative, however, the relatively high nitrogen content of legume leaves suggests that they may have potential as green manure and serve as a source of nitrogen for fertilizing fish ponds.

Acknowledgments

The authors thank the Office of Research, USAID, for funding grant number 493-5600-9-44

0075-00, the network meeting, and the publication of this paper. Peter Edwards and David Little are

seconded to AIT by the Overseas Development Administration (ODA), London.

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