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Rearing of Fabrea salina Henneguy (Ciliophora, Heterotrichida) with three unicellular feeds
[Influence du régime alimentaire sur la croissance en culture d'un cilié extrêmophile Fabrea salina Henneguy (1889)]
Comptes Rendus. Biologies, Volume 331 (2008) no. 1, pp. 56-63.

Résumés

The growth rate of the ciliate Fabrea salina was studied in batch cultures in the presence of three feeds, tested separately from each other: the Prymnesiophyceae, Isochrysis galbana obtained from pure culture, the Chlorophyceae Dunaliella salina, and the commercially available yeast Saccharomyces cerevisiae. F. salina, and D. salina were harvested below the surface from the first evaporation pond and the crystallizer pond, respectively in multi-pond salterns (Sfax, Tunisia). The highest density of Fabrea was recorded with I. galbana (26 ind ml−1). However, the greatest length (243 μm) was recorded with Fabrea fed with D. salina. The lowest density, length and biovolume values were recorded with Fabrea fed with S. cerevisiae. The ANOVA test showed that density (F=18, d.f.=57), length (F=33, d.f.=57), and biovolume (F=19, d.f.=57) of Fabrea fed with yeast were significantly different (p<0.001) from those when Fabrea was fed with D. salina and I. galbana. The ciliate Fabrea encountered in the Sfax saltern (Tunisia) might be a valuable food source for Tunisian marine fish hatcheries.

L'influence du régime alimentaire sur la croissance en culture d'un cilié extrêmophile, Fabrea salina, a été étudiée en culture batch en utilisant trois nourritures différentes, constituées par une culture pure de la Prymnésiophycée, Isochrysis galbana, de la Chlorophycée Dunaliella salina et la levure disponible dans le commerce Saccharomyces cerevisiae. F. salina et D. salina ont été échantillonnées, respectivement, à partir d'un bassin d'évaporation et d'un bassin de cristallisation dans la saline de Sfax (Tunisie). Les plus fortes densités de Fabrea sont obtenues avec I. galbana (26 ind ml−1). En revanche, les individus de grande taille (243 μm) sont observés dans le cas où Fabrea est nourri avec D. salina. Les plus faibles valeurs de densité, de taille et de biovolume sont observées avec Fabrea nourri de S. cerevisiae. Le test ANOVA indique que la densité (F=18, d.d.l.=57) et la taille (F=32, d.d.l.=57) de Fabrea nourri avec de la levure diffèrent significativement (p<0.001) de celles de Fabrea nourri avec D. salina et I. galbana. Fabrea de la saline de Sfax pourrait être utilisé pour des applications aquacoles en raison de sa petite taille n'excédant pas 300 μm et de son court temps de génération.

Métadonnées
Reçu le :
Accepté le :
Publié le :
DOI : 10.1016/j.crvi.2007.10.006
Keywords: Fabrea salina, Culture, Dynamic, Length, Biovolume
Mot clés : Fabrea salina, Culture, Dynamique, Longueur, Biovolume

Wassim Guermazi 1 ; Jannet Elloumi 1 ; Habib Ayadi 1 ; Abderrahmen Bouain 1 ; Lotfi Aleya 2

1 Unité de recherche 00/UR/0907 « Écobiologie, planctonologie et microbiologie des écosystèmes marins », département des sciences de la Vie, faculté des sciences de Sfax, université de Sfax, route Soukra Km 3,5, BP 802, CP 3018 Sfax, Tunisie
2 Laboratoire de biologie environnementale, UsC INRA 3184, UMR CNRS 6565, université de Franche-Comté, 1, place Leclerc, 25030 Besançon cedex, France
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     author = {Wassim Guermazi and Jannet Elloumi and Habib Ayadi and Abderrahmen Bouain and Lotfi Aleya},
     title = {Rearing of {\protect\emph{Fabrea} salina} {Henneguy} {(Ciliophora,} {Heterotrichida)} with three unicellular feeds},
     journal = {Comptes Rendus. Biologies},
     pages = {56--63},
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Wassim Guermazi; Jannet Elloumi; Habib Ayadi; Abderrahmen Bouain; Lotfi Aleya. Rearing of Fabrea salina Henneguy (Ciliophora, Heterotrichida) with three unicellular feeds. Comptes Rendus. Biologies, Volume 331 (2008) no. 1, pp. 56-63. doi : 10.1016/j.crvi.2007.10.006. https://comptes-rendus.academie-sciences.fr/biologies/articles/10.1016/j.crvi.2007.10.006/

Version originale du texte intégral

1 Introduction

The heterotrichous ciliate Fabrea salina Henneguy (1889) is the dominant protist in hypersaline environments, as it can withstand high salt environments through mechanisms of osmoadaptation and salt tolerance [1,2]. This protozoan has been shown to produce a mucilaginous substance that inhibits the growth of other halotolerant species such as the microalgae Dunaliella and different life-cycle stages of the Anostracan Artemia [3–5]. These competitive advantages have prompted researchers to investigate the ecophysiology of Fabrea, and experimental evidence is now accumulating on the influence of a variety of environmental factors such as nutrient availability, temperature and irradiance level on Fabrea dynamics [6–9]. Furthermore, because of the decline in the fish resource, a rapid increase in intensive aquaculture is taking place worldwide, requiring high-quality nutritious feeds. In this respect, pelagic Fabrea may be an appropriate candidate to be used by aquafarmers as a feed with minimal cost [10] due to its small length, short generation period, and ability to form resting-cysts. These ciliates have been shown to exhibit remarkable resistance to growth under adverse conditions [11–13] such as those found in multi-ponds salterns. The Sfax solar saltern (Tunisia) has been the focus of a series of hydrobiological studies [14] and we have acquired substantial information on the dynamics of F. salina along saline gradients of several ponds [14]. In the present study, the predation by F. salina of the Prymnesiophyceae, Isochrysis galbana, the Chlorophyceae Dunaliella salina, and the yeast Saccharomyces cerevisiae was estimated during in vitro incubation by monitoring prey abundances and length spectra. While the flagellate Isochrysis is commonly used in aquaculture to enrich zooplankton such as rotifers or Artemia [15], the literature on its use as food item for Fabrea salina is to our knowledge very scarce. The long-term objective of this study is to consider the large-scale culture of Fabrea salina as a food source for the growing aquaculture industry in Tunisia.

2 Materials and methods

F. salina and D. salina, were collected using a 5-l Van Dorn bottle below the water surface from multi-pond solar salterns located along the Sfax coast (Tunisia, 34°39′N and 10°42′E) (Fig. 1). F. salina was harvested using a plankton net with a 100-μm mesh size, from the first evaporation pond A16 (salinity close to that of seawater: 78.7±8.8p.s.u.) (Table 1). D. salina was collected from the crystallizer pond TS (saturating salt concentrations: 424.5±35.6p.s.u.), in which the phytoplankton community was entirely composed of this Chlorophyceae (Table 2). The second food item consisted of pure cultures of the Prymnesiophyceae I. galbana (Tinamenor S.A. Marisma de Pesués, Cantabria, Spain). Algae and the ciliate were acclimated over three months to continuous illumination (2000 lux) and to Walne's medium (modified from [16], Table 3), respectively.

Fig. 1

General map of the geographical location of the multi-pond Sfax salterns along the coast to the south of Sfax (Tunisia) showing the ponds from which were harvested Fabrea salina (A16: evaporation pond) and Dunaliella salina (TS: crystallizer pond). Modified from [29].

Table 1

Mean values and standard deviation (S.D.) of several physical, chemical, and biological parameters in the saltern

Ponds A16 TS
Salinity (p.s.u.) 78.7 ± 8.8 424.5 ± 35.6
Temperature (°C) 23.7 ± 7.1 30.6 ± 8.6
pH 7.6 ± 0.7 6.6 ± 0.9
Suspended matter (mg l−1) 222.1 ± 148.6 3578 ± 2067
Water density 1.08 ± 0.05 1.27 ± 0.06
Chemical parameters
Total N (mg l−1) 3.7 ± 2.2 10.1 ± 8.7
Total P (mg l−1) 1.3 ± 2.4 5.2 ± 3.8
N/P ratio 3.7 1.9
Chlorophyll-a (mg M−3) 0.097 ± 0.079 0.036 ± 0.01
Biological parameters
Bacterioplankton (× 106 cells ml−1) 7.7 ± 5.8 25.3 ± 14.7
Phototrophic picoplankton (× 105 cells ml−1) 4.1 ± 2.7 0.0
Nanoplankton (× 105 cells ml−1) 18.6 ± 8.3 0.8 ± 0.4
Phytoplankton (× 106 cells ml−1) 0.4 ± 0.3 1.2 ± 1.4
Ciliates (× 104 cells ml−1) 4.7 ± 3.5 0.0
Zooplankton (× 104 ind m−3) 0.2 ± 0.2 0.0
Table 2

Specific composition of phytoplankton, ciliates and zooplankton sampled in ponds A16 and TS of the Sfax saltern

Ponds A16 TS
Phytoplankton
Diatoms Navicula sp.
Pinnularia sp.
Nitzschia sp.
Surirella sp.
Gyrosigma sp.
Dinoflagellates Oxyrrhis marina
Prorocentrum sp.
Gymnodinum sp.
Protoperidinum sp.
Chlorophyceae Dunaliella salina
Ciliates Urotricha sp.
Fabrea salina
Euplotes sp.
Zooplankton
Copepods Acartia grani
Acartia clausi
Harpacticus littoralis
Bryocamptus sp.
Tisbe longicornis
Mesochra sp.
Micosetella sp.
Copepodits
Nauplii
Rotifers Brachionus urceolaris
Brachionus calyciflorus
Other zooplankton
(Mainly larvae)
Table 3

Chemical composition of the medium used to culture Fabrea salina. MT: Metric tons

Elements Concentrations (g MT−1)
Chlorides 16560
Sodium 9210
Sulphates 2324
Calcium 350
Potassium 343
Bicarbonates 127
Brominates 19
Strontium 7
Boron 5
Fluorine 1.2
Manganese 1.359
Molybdenum 0.690
Lithium 0.170
Rubidium 0.110
Iodine 0.070
Aluminium 0.062
Zinc 0.035
Copper 0.0036

The commercially available dry yeast, Saccharomyces cerevisiae, was also used as a third food item for Fabrea. Cultures for experimental purposes were maintained in exponential-growth phase by regular transplants to a fresh medium. The cultures were synchronised, 24 h prior to the beginning of the grazing experiments. This was carried out for 6 days in 200-ml pre-sterilised flasks. Two sets of control (algae without Fabrea) and experimental flasks (two replicates each) were used during the experiment in a batch system with a salinity of 50 p.s.u. and maintained at 24 °C in temperature-controlled chambers, and under an illumination of 2000 lux. Ciliates were counted three times in each replicate flask.

The initial concentration of Fabrea was 4 cells ml−1 and the three food items were inoculated separately from each other, in the morning, during the six days of incubation at a density of 4×106cellsml−1, estimated using a Burcker haemocytometer. The food density was maintained during the experiments by a daily cell enumeration. To stop the experiment, a glutaraldehyde solution (Sigma grade I, final concentration 1%) was added to inhibit protozoan motion [17]. A Sedgwick-Rafter counting cell (Graticules LTD, Tonbridge, Kent, UK), mounted on a Type Leica DM LS2 microscope (20X magnification), was used to estimate the average daily changes in Fabrea numbers; Fabrea length and width were estimated using a micrometer and the biovolume of Fabrea was measured according to [18].

The specific growth rate was calculated using the following formula:

μ(day−1)=1/t×ln(AtA0)
with t being the incubation time (days), A0 and At the culture density, respectively at the beginning and at the end of the experiment.

2.1 Statistics

Mean and standard deviation (SD), as well as boxplots are reported when appropriate. Simple linear regression was used when analyzing how each food item could explain the relation between the length and biovolume of Fabrea. One-way ANOVA followed by a post-hoc comparison using Tukey's test [19] was applied to identify significant differences between food treatments for (i) density, (ii) length, and (iii) biovolume of Fabrea.

3 Results

3.1 Fabrea density and growth rate

The density of Fabrea fed with D. salina did not exhibit significant changes from the start until the third day of the experiment. The growth rate was low (μ=0.12day−1) and cell numbers did not exceed 2.5 (±1.41) cells ml−1 (Fig. 2a). However, from day 4 until the end of incubation, Fabrea cell numbers increased rapidly (μ=0.94day−1), reaching 17 ± 2.12 cells ml−1 on the 6th day (Fig. 2a). When cultured with I. galbana, the density of Fabrea increased until day 3 (μ=0.50day−1, 18.25±1.77indml−1) and then collapsed (0.5±0.71cellsml−1). From the 4th day until the end of the experiment, Fabrea grew strongly (μ=1.31day−1) up to 25.75±6.01cellsml−1 (Fig. 2b). A similar pattern in the distribution of Fabrea was recorded when the protozoan was fed with the yeast S. cerevisia. However, no latency time on the fourth day was observed (Fig. 2c). Indeed, Fabrea grew (μ=0.18day−1) until the second day (7±0.71cellsml−1), then its density decreased until the fourth day (1.75±1.77cellsml−1). From day 4 onwards, the ciliate growth rate increased again (μ=0.31day−1), yielding a cell density of 4.5±2.83cellsml−1. From the first day until the end of each grazing experiment, the specific growth rates (μ) of Fabrea fed with Isochrysis, Dunaliella and Saccharomyces were 0.3, 0.24 and 0.02, respectively (Fig. 3).

Fig. 2

Daily evolution of the density of Fabrea salina reared in the presence of Dunaliella salina (a), Isochrysis galbana (b) and Saccharomyces cerevisiae (c). The vertical bars represent the standard deviation.

Fig. 3

Specific growth rates (μ) of Fabrea fed with different preys from the start to the end of grazing experiments.

3.2 Length and biovolume of Fabrea

When fed with D. salina, the length of Fabrea varied from 200±9μm, recorded in the latency phase to 281.5±15μm, recorded on the second day, corresponding to a biovolume of 15.8×105μm (Table 4). The average length of Fabrea was 243.2±31.71μm, corresponding to a biovolume of 18.6±10.15×105μ m3. During the exponential growth phase, the length of Fabrea was high (260.7±46μm), with a biovolume of 14.7±9.91×105μ m3 (Table 4).

Table 4

Mean and standard deviation (SD) of length (μm) and biovolume (× 105 μm3) of Fabrea salina reared separately from each other with different preys

Feeds Dunaliella salina Isochrysis galbana Saccharomyces cerevisiae
Parameters Length Biovolume Length Biovolume Length Biovolume
Days Media Min Max Media Min Max Media Min Max Media Min Max Media Min Max Media Min Max
2 281.5 140.5 290.2 15.8 7.9 16.3 165.0 148.1 207.4 4.2 2.7 6.0 140.0 110.6 160.6 4.5 2.9 7.2
3 251.9 180.0 270.1 14.2 6.4 15.2 191.0 163.0 222.2 7.5 5.1 11.7 152.0 118.5 177.8 4.7 2.8 7.4
4 200.0 163.0 266.7 19.2 6.7 30.0 251.9 180.1 265.0 2.6 6.4 14.6 148.1 100.5 180.3 4.3 3.1 7.9
5 260.7 190.0 278.3 14.7 8.7 15.7 219.0 89.0 104.0 10.7 7.4 13.3 177.8 120.4 210.0 7.4 4.7 8.9
6 234.6 192.6 266.0 20.0 7.9 39.0 180.0 133.0 222.0 11.8 5.5 28.8 165.0 148.0 207.0 5.6 4.3 8.6

When I. galbana was used as diet, the length of Fabrea varied from 165±20.95μm on the second day (4.23±3.07×105μ m3) to 251.9±10μm recorded on the fourth day (2.6±1.02×105μ m3). Mean Fabrea biovolume recorded over the 6 days of experiments (mean±SD=8.15±5.14×105μ m3), corresponded to a mean length of 189.01±30.83μm. However, at the end of the experiment, the length of Fabrea decreased, to reach 180±40.15μm.

When fed with dry yeast, the length of Fabrea ranged between 140±20μm and 177.8±5μm (mean±SD=160.49±22.63μm), corresponding to a mean biovolume of 5.33±1.81×105μ m3. Conversely to the temporal distribution of the prey-predator couples FabreaIsochrysis and FabreaDunaliella, the average length of Fabrea cultured with yeast increased throughout the experiment (Figs. 4 and 5).

Fig. 4

Daily evolution of the length of Fabrea salina in the presence of Dunaliella salina, Isochrysis galbana and Saccharomyces cerevisiae. Vertical bars represent the standard deviation.

Fig. 5

Boxplot showing the distributions of the variables: density, length, and biovolume of Fabrea for the three treatments with Dunaliella, Isochrysis and Saccharomyces. (The thick line in the middle of the box indicates the median value.)

4 Discussion

The results indicate that under controlled experimental conditions, F. salina was able to grow when its diet consisted of D. salina, I. galbana and S. cerevisiae. Indeed, continuous light, a temperature of 24 °C, a salinity of 50 p.s.u. and a small water volume (200 ml) were sufficient to yield optimal growth of Fabrea. This is consistent with the findings of several authors, who showed that Fabrea can develop with various nutritional items [13]. Moreover, Rattan et al. [20] indicated that Fabrea can even grow with fermented wheat and rice grains. However, Repak [6] indicated that this ciliate does not grow in the presence of the Cyanobacteria Synechococcus spp. Many other protists have been successfully cultured, such as Favella sp., Uronema sp., Gymnodinium sp. [21,22]. A high growth rate (r=0.60day−1) was also recorded when the Tintinnid Favella sp. was fed with the Prymnesiophyceae Prymnesium parvum [22]. One should also bear in mind that it is of fundamental importance to keep growth and ingestion constant to evaluate growth yield in ciliates feeding different preys [23–25]. Although yield is constant, absolute biomass production may be higher in one prey than in another. Both high density and growth rates of F. salina were recorded when the diet consisted of I. galbana (26 cells ml−1, r=1.31day−1). Indeed, the peak density recorded on the third day indicated a short-generation period of Fabrea, which may suggest that I. galbana had a high nutritional value, as already reported by Brown [26]. To our knowledge, the culture of Fabrea with Isochrysis has never been reported, so we were unable to compare our findings with those of others. The only available data concerned the genera Strobilidium and Strombidium, which exhibit a maximum growth rate of 2.2 day−1 when fed with Isochrysis [27]. Although the effects of this flagellate on Fabrea development were remarkable, both the length and biovolume of the ciliate were smaller than those recorded when the Fabrea diet consisted of D. salina. This discrepancy may suggest that Fabrea underwent reproduction, as evidenced by the existence of two peaks of Fabrea density recorded on the third and sixth days (Fig. 2b), coinciding with a decrease in cell dimensions on the sixth day (Fig. 4). In support of this, we also found the weakest correlations between the length and biovolume of Fabrea fed with I. galbana (r=0.45, d.f.=27, p<0.01), versus D. salina (r=0.77, d.f.=17, p<0.01) and the yeast (r=0.95, d.f.=10, p<0.01). The highest densities of Fabrea were found when the latter was fed with D. salina and I. galbana. Pandey and Yeragi [13], who worked under similar experimental conditions, reported similar results with D. salina, but they did not consider I. galbana as a food item. They recorded cell densities of 44 and 64 Fabrea ml−1 when grown in 1 and 5-l containers, respectively. Concerning the yeast S. cerevisiae, our results indicate that it was not a good food item for Fabrea, because the ciliate induced the lowest growth rate, cell length, and biovolume. The ANOVA analysis shows that both the density (F=18, d.f.=57), length (F=33, d.f.=57) and biovolume (F=19, d.f.=57) of Fabrea fed yeast differed significantly (p<0.001) from those of Fabrea fed both with D. salina and I. galbana (Tables 5 and 6). This difference may be explained by the deterioration of the medium throughout the experiment induced by yeast, as already suggested by [20]. Indeed, the high Fabrea density recorded on the second day implies a very rapid growth generation period which was strongly stimulated by S. cerevisiae at the beginning of the experiments. Yeast is widely used as a dietary supplement to support the growth of several species such as rotiferans and the anostracan Artemia. Pandey and Yeragi [13] found a density of 20 Fabrea ml−1 when fed with yeast at concentrations of 5 mg l−1. Overall, our results are slightly lower than those reported by Repak [6,7] and Pandey and Yeragi [13]. The maximal length of Fabrea recorded in this study (207 μm) is similar to that recorded by Dolapsakis et al. [28], who cultured F. salina obtained from a Greek saltern in which the salinity varied from 60 to 144 p.s.u. Furthermore, both the length and biovolume of Fabrea recorded in this study were higher than those found in the Sfax saltern. The values reported by [14] from this ecosystem did not exceed 111 μm and 180.1×103μ m3, for salinities ranging between 70 and 170 p.s.u., respectively.

Table 5

Results of ANOVA analysis to assess the effect of different food combinations on the density, length and biovolume of Fabrea

Parameters F value d.f. P value
Density 18 57 6.38×10−7***
Length 33 57 3.48×10−10***
Biovolume 19 57 5.61×10−7***
Table 6

Post-hoc comparison using Turkey's test to identify significant differences among treatments

Feeds Density Length Biovolume
Isochrysis–Dunaliella 0.12 0.00 0.00
Saccharomyces–Dunaliella 0.00 0.00 0.00
Saccharomyces–Isochrysis 0.00 0.02 0.45

p values below 0.05 indicate significant differences between the two treatments.

In conclusion, our study indicates that the ciliate Fabrea salina was able to grow with different feeds, and may be a good candidate species as food source for the Tunisian aquaculture industry. To improve our overall understanding of the various preys–Fabrea relationships, we are currently investigating the ecophysiological responses of Fabrea to changes in light, temperature, salinity, together with its fatty acid composition.

Acknowledgements

We gratefully acknowledge support from the staff of the Sfax Saltern Campany. We would like to thank especially Dr. Roberto Marangoni for helpful advices and comments on the manuscript. The pure culture of Isochrysis galbana was kindly provided by Dr H. Chavanne (Lazzaro Spallanzani Institute, Milan, Italy). This work was conducted as part of a collaborative project between the University of Sfax (Tunisia) and the University of Franche-Comté (Besançon, France). We thank the Tunisian Ministry of Research and Technology for financial support.


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