ISOLATION AND SELECTION OF TETRASELMIS STRAINS FOR FEEDING GEO-DUCK LARVAE AT VANDON, QUANG NINH

ISOLATION AND SELECTION OF TETRASELMIS STRAINS FOR FEEDING GEO-DUCK LARVAE AT VANDON, QUANG NINH Nguyen Thi Hoai Ha1, Le Thi Phuong Hoa2, Pham Thi Bich Dao1, Lưu Thị Thùy Giang1 , Tran

ISOLATION AND SELECTION OF TETRASELMIS STRAINS FOR FEEDING

GEO-DUCK LARVAE AT VANDON, QUANG NINH

Nguyen Thi Hoai Ha1, Le Thi Phuong Hoa2, Pham Thi Bich Dao1, Lưu Thị Thùy Giang1

, Tran Thi Diep1

1

Institute of Microbiology and Biotechnology, Vietnam National University, Hanoi

2

Faculty of Biology, Hanoi National University of Education

Abstract

Tetraselmis species are widely used as food for aquatic animals such crustaceans, bivalves and fish especially in their larvae stage Three Tetraselmis strains were

successfully isolated from the shrimp farming at Vandon, Quangninh Among them,

Tetraselmis strain T1 showed best growth Medium f/2 was selected as best medium for its growth Fatty acid profile of Tetraselmis strain T1 consisted of C16 and C18

acids as most abundant, which is typical for most green algae Essential fatty acids,

-linolenic acid and linoleic acid accounted for 34.2% of total fatty acids, half of total unsaturated fatty acids Eicosapentaenoic acid (EPA) was also in high concentration The result suggested the high quality of as food for aquatic animals like geo-duck On

the way to apply Tetraselmis strain T1 in feeding geo-duck, outline for its biomass

production was structured

Key words: microalage, Tetraselmis, geo-duck, EPA

1 Introduction

Microalgae are the base of the entire aquatic food chain which has an important role in the aquaculture They are major source of nutrients for all stages of bivalves, for larval stages

of crustaceans and fish, and as food for zooplankton which are fed to late larval and juvenile

fish and crustaceans [10, 11] Among them, many Tetraselmis species are widely used

especially at the larval stage of aquatic animals [11]

Geo-duck is a bivalve species, which inhabits commonly in Quang Ninh and is served

as a specialty with high nutrition [3] However, geo-duck resource is decreasing seriously In a

way to find suitable food for sustainable development and conservation of this resource we

carried out the research “Isolation and selection of Tetraselmis strains for feeding Geo-Duck larvae at Vandon, Quangninh”

2 Materials and methods

2.1 Isolation and classification of Tetraselmis strains

Seawater was collected from the shrimp farming at Vandon, Quangninh Tetraselmis strains were isolated based on their morphological properties using micropipettes [5,9] Algal

strains were grown at room temperature and illuminated under neon light (Philips daylight tubes) on 10: 14 h light: dark cycles

2.2 Selection conditions and nutrition component analysis

Media f/2 [5, 13], ASW (artificial sea water) and ESM (modified Erd-Schreiber's and Schreiber's medium) were used to select culture medium for the growth and development of each strain Cells were cultured in 250-ml conical flask and harvested every two days Cell density was determined with a Neubauer haemocytometer in three replicates In order to

survey the influence of temperature on photosynthetic system of Tetraselmis strains,

florescence indexes were measured using Plant Efficiency Analyser (PEA), Hansatech Intruments Ltd., Englanh, from which Fv/Fm ratio was calculated [1,2]

Fatty acid composition was determined according to Krienitz et al [8] by gas chromatography (Finnigan Trace GC) using an ultra-column BPX70 Fatty acids were identified by comparing retention times with those of a calibration standard solution

3 Results and discussion

3.1 Isolation of Tetraselmis strains

Tetraselmis strains were isolated from the seawater at the shrimp farming in Vandon,

Quangninh and signified as T1, T2, T3 They were grown in non-aerated f/2 medium Cell density was determined every 2 days until 6 days of cultivation Data were shown in Figure 1

Among selected Tetraselmis species, T1 showed best growth, especially at 6-day culture and

would be used in following experiments

0 20 40 60 80 100 120

Time (days)

culture day 2 culture day 4 culture day 6

Figure 1 The growth of three Tetraselmis strains T1, T2, T3

3.2 Taxanomic properties of Tetraselmis T1 species

Observation on the morphology of Tetraselmis T1 species (Fig 2) showed Tetraselmis

cells are usually solitary, free-swimming, thecate cells with four flagella and approximately 12-20 micrometers long The four flagella are slightly shorter than the cell body Each cell contains a single pyrenoid, located more or less in the middle of the cell

Division: Prasinophyta

Class: Prasinophyceae

Order: Dunalliellales

Family: Polyblepharidaceae

Genus: Tetraselmis

Figure 2 Morphology of

Tetraselmis strain T1 3.3 Selection of culture medium

Tetraselmis strains are photoautotrophic microorganisms However, the biophysical

properties of microalgae may vary with respect to the alteration of environment [10,11] Therefore, the selection of suitable culture medium is essential for the optimal development of

Table 1 Cell density of Tetraselmis

T1 grown on different media

Culture

time

(days)

Cell density (104/ ml)

f/2

medium

ESM medium

ASW medium

0 12,5 12,5 12,5

6 100 87,5 12,5

8 122 115 6,3

12.5 44 75 100 122

100 89

12.5 37.5

75 87.5

115 107

87

12.5 22 31

12.5 6.3

0 20 40 60 80 100 120 140

Time (days)

F/2 medium ESM medium ASW medium

Figure 3 The growth of Tetraselmis T1 on

different media

Data showed the population density of Tetraselmis T1 increase steadily on f/2 medium

and reach the maximum (122x104 cells/ml) on the eighth day of culture In the meantime, the value was lower in case of ESM medium and much lower for ASW medium (Table 1, Fig 3)

It is suggested that f/2 is the most suitable for culturing Tetraselmis strain T1 and can be

applied for biomass production in aquaculture

3.4 The effect of temperature on photosystem II of Tetraselmis T1

Temperature has effects on the structure and function of photosystems in microalgae and higher plants, thereby on the photosynthesis productivity and their growth In this study,

we investigated the change of Fv/Fm ratio according to the temperature (Fig 4)

The data suggested low heat-tolerance ability of Tetraselmis T1 Fv/Fm ratio was

reduced immediately when the temperature increased 1oC and more seriously when it is over

34oC and especially 40oC However, Tetraselmis T1 microalgae grown on f/2 medium seemed

to be most stable

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

25 26 28 30 32 34 36 38 40 42 44 46

Temperature (oC)

ESM ASW

Figure 4 Variation of Fv/Fm ratio related to temperature on different media

3.5 Analysis of fatty acid components of Tetraselmis T1

Lipid has its own specificity in each species of living organisms Fatty acids are mostly located in the cell membrane, which is much enough to apply to taxonomic characterization Furthermore, most animals cannot synthesize essential fatty acids (linoleic and linolenic acid)

thus have to depend on the diet [4,6] Fatty acid components of Tetraselmis strain T1 were

analysed

The fatty acid profile of Tetraselmis strain T1 (Table 2) consisted of huge range of fatty

acids from 12C to 23C with C16 and C18 being most abundant This distribution is typical of most green algae [6, 10] The unsaturated fatty acids accounted for 68.5%, among which C18 polyunsaturated fatty acids (PUFA) were the major

Alpha-linolenic acid was found in highest concentration (27.1%) and higher Tetraselmis

sp (-linolenic acid 16.7%) which have been reported by Pratoomyot [7] Linoleic acid and  -linoleic acid are essential fatty acids that can be converted into long-chain PUFA in algae, which many marine animals showed limited ability [8] Furthermore, oleic acid and eicosapentaenoic acid (EPA) have remarkably high content 13.2% and 9.3%, respectively which was comparable to

previous reports for which was comparable to previous reports for T suecica with small amount of

EPA (4.5%)[15] EPA of the membrane phospholipids is a precursor in prostaglandin synthesis, which leads to synthesis of a number of other tissue hormones [6,8] However, this microalgae

was deficient of DHA which was similar to T chui and T suecica but contrasts to Tetraselmis spp [7] This result suggested high quality of Tetraselmis T1, which can be applied in aquatic food

webs such as for feeding geo-duck

Table 2 Percentage composition of fatty acids in Tetraselmis strain T1

C:20:4 n6 Arachidonic acid (ARA or AA) 0.4

C:20:5 n3 Eicosapentaenoic Acid (EPA) 9.3

C:22:6 n3 DocosahexaenoicAcid (DHA) 0

3.6 Biomass collecting of Tetraselmis strain T1

In order to collect biomass from Tetraselmis strain T1 for feeding geoduck larvae 8 day age, Tetraselmis strain T1 was cultured in f/2 medium, grown at room temperature and

illuminated under neon light (Philips daylight tubes) 4000 - 5000 Lux as the following scheme with illustrated pictures

Microalgae volume was used depending on geo-duck larvae density in the container At Van Don, Quang Ninh, we have been fed geoduck larvae with 120 – 180 liters microalage with cell density 12.2-12.5 105 cells/ml for one tank about 2.5105 – 16.6105 geo duck larvae/m3 per day

Stock culture

cells/ml

2-6 litre flask

After 5-7 days, cell density

30–60 litre plastic bag

cells/ml after 4-6 days

160 litre tank

After 4-6 days, cell density

10 litre container

After 2-3 days, cell density

4 Conclusions

Three Tetraselmis strains were successfully isolated from the shrimp farming at Vandon, Quangninh and annotated as T1, T2, T3 Among them, Tetraselmis strain T1 showed best growth and well cultured in f/2 medium

Fatty acid composition of Tetraselmis strain T1 was typical of most green algae with

high content of C16 and C18 acids Approximately 68.5% of total fatty acids were unsaturated, among which -linolenic acid and linoleic acid were major components There was also high content of EPA (9.3%), a precursor in prostaglandin synthesis The data suggested the

signification of using Tetraselmis strain T1 in feeding geo- duck as high quality food The outline of biomass production of Tetraselmis strain T1 for aquaculture of geo-duck larvae in

Van Don, Quang Ninh was established

Acknowledgements

The authors wish to thank the Asia Research Center, Vietnam National University, Hanoi for

suport Many thanks also to go the Center of Aquaculture Breeding farm, Vandon district for supplying marine microalgae

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