Genotype-environment interaction in Tilapia (Oreochromis nilotica) fed duckweed (Lemna minor) or commercial feed

Tick Nouanthavong and T R Preston¹

Living Aquatic Resources Research Center, Vientiane Lao PDR
ticknv_15@hotmail.com
¹ Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia

Abstract

The hypothesis to be tested in this study was that Tilapia fingerlings from brood-stock raised in open ponds and fed duckweed would be more productive and would adapt better to the local farmer conditions than when they are from brood-stock that have been raised intensively on commercial feed. The experiment was arranged in two stages.

In stage 1, there were two treatments applied during the raising of Tilapia brood stock: DW: Duckweed (27% crude protein) fed ad libitum; CF: Commercial feed (32% crude protein) fed at 3% of the live weight of the fish. Each treatment was replicated 5 times (ponds) in a completely randomized design. Measurements of growth were done every 30 days over a total period of 180 days.

After 210 days the fish were separated into males and females for a further period of 30 days at the end of which males and females were put together in the same pond for breeding. During this preparation-breeding stage (180 to 270 days) the original feeding treatments were continued. Fingerlings produced during the breeding phase were put in separate ponds (according the treatments of the parents). When they reached approximately 7g they were distributed into the two feeding treatments: CF and DW with 2 replicates (ponds) on each treatment. After they reached on average 10g live weight, the numbers were reduced to 25 per pond (5 fingerlings/m²).

In stage 2, there were thus four treatments, applied to the progeny from stage 1, arranged as a 2*2 factorial with 2 replications (ponds) in a completely randomized design. DW-DW: Progeny of DW brood-stock were fed duckweed; DW-CF: Progeny of DW brood-stock were fed commercial feed; CF-DW: Progeny of CF brood-stock were fed duckweed; CF-CF: Progeny of CF brood-stock were fed commercial feed. Measurements of growth in weight and length were made every 30 days over a total growth period of 180 days.

In stage 1, the Tilapia derived from natural ponds in rural areas grew faster when they were fed a commercial concentrate (32% protein) than when they were fed duckweed (27% crude protein in DM). In contrast, in stage 2, the fingerlings derived from parents raised on duckweed grew faster than those from parents raised on concentrate feed. This advantage was manifested irrespective of the diet of the offspring.

Key words: breeding, chicken manure, fingerlings, natural feed, rural areas

Introduction

In fish hatcheries used to produce Tilapia (Latin name) fingerlings for sale to farmers, the brood-stock are usually selected and maintained in an intensive system in cages or in open ponds and are fed commercial fish feed. This may be appropriate when the fingerlings are to be raised in similar “intensive” production systems. However, in the rural areas in Lao PDR, Tilapia are usually raised in open ponds or in the rice field using only the natural feed of plankton and detritus, and occasionally rice bran and waste food from the household. For these conditions, fingerlings from brood-stock raised intensively with commercial feed may not be the most appropriate.

The concepts of genotype-interaction have been debated for many years (eg: Bowman and Powell 1964). It is now well established that animals in a population that have been selected for high production efficiency are more at risk for behavioral, physiological and immunological problems (Rauw and Gomez-Raya 2015). Thus it has been recommended that future breeding stock should be selected within environmental conditions comparable to where candidate animals are intended to perform (Hammami et al 2009)

The culture of tilapia in ponds is expanding and has become the most popular method of growing tilapia. However, the high cost of production inputs particularly on feeds is a major obstacle to sustain the interest of these farmers to continue their operation. This has been a major problem to tilapia farmers. To address this problem, the Bureau of Fisheries and Aquatic Resources in Lao PDR has deemed it necessary to introduce and promote a technology on the use of duckweeds as an alternative food for tilapia. The rationale for the use of this technology based on the successful introduction and application of this system in Bangladesh by Skillicorn et al (1993).

Duckweeds are small free floating plants with reported crude protein in dry matter (DM) content of 18 to 40 % depending on the nutrients added in the culture media (Tu et al 2012).

Leng et al (1995) showed that the yield of Tilapia could be as high as 10 tonnes/ha/year. According to Hillman and Culley (1978) duckweed protein has a better array of essential amino acids than most vegetable proteins and more closely resembles animal protein.

Hypothesis

The hypothesis that was tested in this study was that Tilapia fingerlings from brood-stock raised in open ponds and fed duckweed would be more productive and would adapt better to the local farmer conditions than when they were produced from brood-stock that had been raised intensively on commercial feed.

Materials and methods

Location and climate of the study area

The experiment was carried out from July 2014 to February to 2016 at the Nongtang station of the Living Aquatic Resource Research Center (LARReC), located 15 km from .Vientiane Capital, Lao PDR.

The average temperature in Vientiane is 25.9 degrees, with April the warmest month having a mean temperature of 28.5 degrees. Laos is at 17°57'N, 102°33'E, 171 m above sea level.

Vientiane has a tropical wet and dry climate with a pronounced dry season According to the Holdridge life zones system of bioclimatic classification Vientiane is situated in or near the subtropical moist forest biome (http://www.vientiane.climatemps.com/).

Experimental design

The experiment was arranged in two stages.

Stage 1:

There were two dietary treatments applied during the raising of Tilapia brood stock:

DW: Duckweed

CF: Commercial feed

Each treatment was replicated 5 times (ponds) in a completely randomized design. The experiment lasted for 180 days.

Stage 2:

There were four treatments (Figure 1), applied to the progeny from stage 1, arranged as a 2*2 factorial with 2 replications (ponds) in a completely randomized design.

DW-DW: Progeny of DW brood-stock were fed duckweed

DW-CF: Progeny of DW brood-stock were fed Commercial feed

CF-DW: Progeny of CF brood-stock were fed duckweed

CF-CF: Progeny of CF brood-stock were fed Commercial feed

Figure 1. Arrangement of the treatments in stages 1 and 2

Stage 1:

Source of Tilapia fingerlings

Tilapia fingerlings (about 5 g in weight) were collected from a farmer’s pond in Hodsaifong district, Vientiane Capital, and transported to Nongtang station. At the station they were stocked in two open ponds and fed either fresh duckweed or commercial feed. When they reached an average weight of 45 g fingerlings from each of the DW and CF groups were allocated to the experimental ponds (5 ponds per treatment) at a density of 25 fingerlings/pond (5 fingerlings/m²).

Preparation of the ponds

The ponds were 2m x 2.5m x 1m (depth), with water exchange by pumping four times per week. Lime was applied at the rate of 100 mg/m² per day for ten days to eliminate parasites and adjust the pH. Dry chicken manure (500g/m²⁾ was then applied to stimulate growth of plankton. Netting was used to cover each pond (Photo 1).

Photo 1. Layout of the ponds

Source of duckweed

Duckweed was collected from natural sources and cultivated in 3 ponds each 4.0*2.5m area and 0.5m deep. Chicken manure was applied to each pond at the rate of 8 kg per pond every 3 weeks. The duckweed was harvested daily (approximately one third of the surface area per day) and applied immediately to the Tilapia ponds receiving treatment DW.

Feeding

Fish in the DW treatments were fed duckweed ad libitum, the amounts offered being adjusted according to the rate of consumption by the fish. The commercial feed (CF) was purchased in the market and fed at the rate of 3% of the live weight of the fish.

Measurements

The duckweed and commercial feed were analyzed for DM, crude protein and crude fiber following AOAC (1990) procedures (Table 1).

The weight and length of random samples (n=10) of the fish were recorded every 30 days.

Stage 2:

Breeding

After 210 days the males and females were separated to individual ponds according to each treatment. They continued to receive the experimental diets for a further 30 days after which the males and females were mixed together for breeding. During the following 30 days the fingerlings were collected, put in separate ponds and fed according to their origin (ie: those from brood-stock DW were fed DW; those from brood-stock CF were fed CF. At the end of this period the fingerlings were allocated to the experimental diets according to the plan for phase 2. There were two replicates of the four treatments: DW-DW, DW-CF, CF-DW, CF-CF.

When the fingerlings reached a weight of approximately 10 g the numbers in each pond were reduced to 10 to give a stocking density of 5 fish/m² From this point the feeding and management system for CF and DW were the same as in Stage 1.

Measurements

The duckweed and commercial feed were analyzed for DM, crude protein and crude fiber following AOAC (1990) procedures (Table 1).

The weight and length of random samples (n=10) of the fish were recorded every 30 days.

Statistical analysis

The data on growth, feed intake and conversion were analyzed by the general linear model in the ANOVA program of the Minitab software (Minitab 2000).

Results and discussion

Stage 1.

The fish grew faster and had a better weight: length ratio when they were fed commercial feed rather than duckweed (Table 2) reflecting the greater intake of DM on the CF than on the DW treatment. DM feed conversion was similar on both treatments.

Parameters of water quality (Table 3) showed that all values were within the normal range for Tilapia (Boyd 1995).

Stage 2:

The Tilapia fingerlings derived from brood-stock raised on duckweed grew faster than those from parents raised on concentrate feed. This advantage was manifested irrespective of the diet of the offspring (Table 4; Figure 2). However, there was a significant interaction between parent and offspring treatments such that the improvement in growth rate as a result of parental feeding on duckweed was much greater when the progeny were also fed on duckweed (Figure 2). This advantage was manifested equally in growth in length as in weight (Figure 3).

Figure 2. Growth of Tilapia fingerlings derived from brood-stock raised on duckweed (DW) or commercial feed (CF) and fed either duckweed or commercial feed.	Figure 3. Increase in length of Tilapia fingerlings derived from brood-stock raised on duckweed (DW) or commercial feed (CF) and fed either duckweed or commercial feed.

This example of genotype-environment interaction, although well known for other farm animals (Rauw and Gomez-Raya 2015) does not appear to have been reported for fish. The implications are that in hatcheries that produce Tilapia fingerlings for farmers in rural areas the feeding of the Tilapia brood-stock should be with natural feeds such as duckweed, which is the most widely distributed and most suitable natural food available in rural areas.

Conclusions

• Tilapia derived from natural ponds in rural areas grew faster when they were fed a commercial concentrate (32% protein) than when they were fed duckweed (27% crude protein in DM) fertilized with chicken manure.
  
  
• In contrast, the fingerlings derived from parents raised on duckweed grew faster than those from parents raised on concentrate feed. This advantage was manifested irrespective of the diet of the offspring.

Acknowledgements

This research is part of the requirement by the senior author for the degree of PhD at Nong Lam University. The support from the MEKARN II project, financed by Sida, is gratefully acknowledged,

Refererences

AOAC 1990 Official Methods of Analysis Association of Official Analytical Chemists 15th Edition (K Helrick editor) Arlington pp 1230

Bowman J C and Powell J C 1964 The effect of different levels of management on the assessment D of differences between varieties of chicken, II. Animal Production 6, pp5-20

Boyd C E 1995 Pond aquaculture water quality management.www.springer.com/la/book/9780412071812

Hammami Hedi, Rekik Boulbaba and Gengler Nicolas 2009 Genotype by environment interaction in dairy cattle. Biotechnol. Agron. Soc. Environ 13(1), 155-164

Leng R A, Stambolie J H and Bell R 1995 Duckweed - a potential high-protein feed resource for domestic animals and fish. Livestock Research for Rural Development. (7) 1: http://www.lrrd.org/lrrd/7/1/3.htm

Minitab 2000 MinMinitab reference Manual release 13.31. User’s guide to statistics. Minitab Inc, USA.

Rauw W M and Gomez-Raya L 2015 Genotype by environment interaction and breeding for robustness in livestock. Frontiers in genetics. 6:310

Skillicorn P, Spira W and Journey W 1993 "Duckweed Aquaculture - A New Aquatic Farming System for Developing Countries", The World Bank.76pp. Washington DC

Tu D T M, Dong N T K and Preston T R 2012 Effect on composition of duckweed (Lemna minor) of different levels of biodigester effluent in the growth medium and of transferring nutrient-rich duckweed to nutrient-free water. Livestock Research for Rural Development. Volume 24, Article #71. http://www.lrrd.org/lrrd24/4/mytu24071.htm

Received 25 September 2016; Accepted 13 October 2016; Published 1 December 2016

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