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Revista de Biología Tropical

On-line version ISSN 0034-7744Print version ISSN 0034-7744

Rev. biol. trop vol.49 n.1 San José Mar. 2001

 

 Effect of three food types on the population growth of Brachionus calyciflorus and Brachionus patulus (Rotifera:  Brachionidae)
 
 
S.S.S. Sarma1,*, Paula Susana Larios Jurado1 & S. Nandini2
 
 
Received  6-XII-1999.    Corrected   18-VII-2000.    Accepted     31-VII-2000
 
Abstract
 
We compared the population growth of B. calyciflorus and B. patulus using the green alga Chlorella vulgaris, baker’s yeast Saccharomyces cerevisiae or their mixture in equal proportions as food. Food was offered once every 24 h in two concentrations (low:  1x106 and high:  3x106 ind. ml-1) separately for each species. The experiments were terminated after 15 days. In general, at any food type or concentration, B. patulus reached a higher population density. A diet of Chlorella alone supported a higher population growth of both rotifer species than yeast alone. B. calyciflorus and B. patulus achieved highest population densities (103±8 ind. ml-1 and 296±20 ind. ml-1, respectively) on a diet of Chlorella at 3x106 ind. ml-1. When cultured using the mixture of Chlorella and yeast, the maximal population densities of B. calyciflorus were lower than those grown on Chlorella. Under similar conditions, the maximal abundance values of B. patulus were comparable in both food types. Regardless of food type and density the rate of population increase per day (r) for B. calyciflorus varied from 0.13±0.03 to 0.63±0.04. These values for B. patulus ranged from 0.19±0.01 to 0.37±0.01. The results indicated that even though Chlorella was a superior foof for the tested rotifers, yeast can be effectively used at low concentrations to supplement algal requirements in rotifer culture systems.
 
Key words:  Population growth, alga, yeast, Rotifera.
 
 
Laboratory cultivation of brachionid rotifers has been successfully done using green algae. In order to supplement the algal quantity, Hirata and Mori (1967) introduced the use of bakers' yeast as food for the saline water species Brachionus plicatilis. Since then a number of investigators have used bakers' yeast as food for this species; rotifers grown in this way have also been nutritionally enriched (Fernandez-Reiriz and Labarta 1996, Lie et al.  1997). A vast majority of researchers used yeast only for B. plicatilis and Brachionus rotundiformis. In aquaculture, in addition to these two species, several other rotifer taxa such as B. calyciflorus, B. rubens and B. patulus are used as starter food (Rottmann et al.  1991, Mookerji and Rao 1994).

Several algal species have been used while testing the use of freshwater rotifer species. Since algal cultivation under controlled conditions is laborious, time consuming and expensive, alternative food types such as yeast, wastewater from food industry and livestock have been used for mass rotifer cultures (Klekot and Klimowicz 1981). However, controlled laboratory experiments using these food types for rotifers are necessary to compare the population growth with conventional algal diets. It is also not known whether different Brachionus species show different population growth rates when grown on yeast. At the same time, a comparative information about the growth of different rotifers grown on alga, yeast and their mixture separately has rarely been published (Guevara et al.  1996).

The aim of this study was to test the effect of different concentrations of green alga and yeast and their mixture on the population growth of two brachionid rotifer species commonly found in freshwater systems.
 
Materials and methods
 
We used clonal populations of each of the two rotifer species Brachionus calyciflorus and Brachionus patulus maintained at least for 3 months prior to testing. Both the rotifer species were mass-cultured (40 l glass aquaria) using the green algae Chlorella vulgaris as the exclusive food. Two weeks prior to experimentation, the test rotifer species were also offered baker's yeast Saccharomyces cerevisiae in addition to the algal diet. For maintaining mass rotifer cultures we used reconstituted hardwater (EPA) as medium (Anonymous 1985). This was also used as medium for rotifer growth experiments.

Chlorella was cultured using Bold-basal medium. Log phase algae were harvested, centrifuged and resuspended in EPA medium. Commercially available baker's yeast was freshly procured, resuspended in EPA medium and filtered using a 20 m mesh to remove clumps. Algal and yeast cell density was estimated using haemocytometer. For each rotifer species we offered food in the following ways: 1. only alga, 2. only yeast, and 3. alga+yeast in equal density.

Each food type was offered in two densities viz. low (1x106) and high (3x106 ind. ml-1). For each food type and density, we maintained four replicates. Thus for population growth of B. calyciflorus, we maintained a total of 24 plastic jars (3 food types x 2 food concentrations x 4 replicates), each containing 20 ml of EPA medium with appropriate food density. The initial density of rotifers in each test jar was 5 ind. ml-1. For the population growth of B. patulus also the above design was used. Experiments were conducted at 23±2°C.

Following inoculation of B. calyciflorus or B. patulus, at every 24 h interval, we counted the number of female rotifers alive under a stereomicroscope. For this we either counted the whole volume of the test vessel or two aliquot samples each of 1-5 ml depending the density of rotifers per container. After estimating the density, the individuals were transferred to fresh EPA medium containing appropriate food type. The transfer of rotifers to fresh medium was done either individually, when the densities were low, or using a 50 m mesh during later stages of the study. Experiments were terminated after 15 days when most populations began to decline. Thoughout this study males were not encountered.

The rotifer population growth was obtained from a mean of 4-5 values during the exponential phase using the equation r = (ln Nt - ln No)/t, where, No = initial population density, Nt = density of population after time t (days) (Krebs, 1985).

Results
 
The population growth curves of B. calyciflorus and B. patulus reared under three food types and two densities are shown in Figs. 1 and 2. The maximal population density of B. patulus influenced significantly (p<0.01) by food type, its concentration as well as their interaction but not for B. calyciflorus (p>0.05, ANOVA). In general, at any food type or concentration, B. patulus reached higher population density when compared to B. calyciflorus. In 1x106 ind. ml-1, B. calyciflorus reached 77±12 ind. ml-1; at the same food level B. patulus attained 109±26 ind. ml-1. At 3x106 ind. ml-1 density, B. calyciflorus reached a peak density of 103±8 ind. ml-1. Under comparable conditions, B. patulus reached much higher peak abundance 296±20 ind. ml-1. When yeast was used as exclusive food, the maximal abundance values reached by B. calyciflorus were 62±19 and 57±25 ind. ml-1 under low (1x106 ind. ml-1) low and high (3x106 ind. ml-1) food concentrations, respectively. On the other hand, B. patulus showed peak population abundances of 97±17 and 50±6 ind. ml-1 in low and high concentrations of yeast. B. calyciflorus reached a peak abundance of 54±9 and 86±3 ind. ml-1 for low and high food densities when both these food types offered in equal concentrations. Comparable values of B. patulus were 251±12 and 259±32 ind. ml-1.

The day of maximal population density was not significantly different for the food concentrations used for both B. calyciflorus and B. patulus (p>0.05). However, food type had a significant effect on this variable (p<0.01) for both the species. The highest rate of population growth (r) recorded for B. calyciflorus was 0.63±0.04 and the lowest r value (0.13±0.03) was observed for the same species when grown in high concentration of yeast. Regardless of food type and density the r values of B. patulus ranged from 0.19±0.01 to 0.37±0.01 (Fig. 3). The r values for B. patulus were significantly affected by food type, density and their interaction (p<0.001). For B. calyciflorus only the food type had a significant effect (p<0.01). An inverse relation occurred for both B. calyciflorus and B. patulus when the daily rate of population increase was plotted againt the population density of the same day (Figs. 4 and 5).
 

Table 1.
Rate of population increase (r) per day of selected rotifer species, family Brachionidae.
 
Species Experiment Food type Food level r value Reference
Anuraeopsis fissa Population growth Scenedesmus obliquus 0.5 - 8 x 106 cells ml-1 0.45 - 0.86 Dumont et al. , 1995
  Population growth Scenedesmus acutus 0.5 - 40.5 x 106 cells ml-1 0.44 - 0.88 Sarma et al. , 1996
  Life table - - 0.10 Ooms-Wilms, 1997
Brachionus angularis Population growth Stichococcus bacillaris - 0.58 Walz, 1993
B. calyciflorus Life table - - 2.20 Wang and Li, 1997
  Population growth Scenedesmus acutus 0.5 - 40.5 x 106 cells ml-1 0.79 -1.49 Sarma et al. , 1996.
  Population growth Various types of algae  - 0.80 Rothhaupt, 1990
B. patulus Life table Chlorella 1-4 x 106 cells ml-1 0.14-0.61 Sarma and Rao, 1991
  Population growth Chlorella 1-3 x 106 cells ml-1 0.12-0.24 Sarma and Rao, 1990
B. plicatilis Population growth Tetrathelmis tetrathele 0.05 x 106 cells ml-1 0.24 - 0.49 Okauchi and Fukusho, 1984
  Population growth Chlorella 1.5 x 106 cells ml-1 0.16-0.47 Okauchi and Fukusho, 1984
B. rubens Population growth Various types of algae - 0.80 Rothhaupt, 1990
  Population growth Chlorella 3 x 106 cells ml-1 0.79 Iyer and Rao, 1993
B. urceolaris Life table - - 1.32 Wang and Li, 1997
Keratella cochlearis Population growth Cryptomonas erosa 0.005-0.01 x 106 cells ml-1 0.28-0.40 Smith and Gilbert, 1995
  Population growth - - 0.13 Ooms-Wilms, 1997
K. crassa Population growth Cryptomonas erosa 0.005-0.01 x 106 cells ml-1 0.32 Smith and Gilbert, 1995
K. testudo Life table  - - 0.15 -0.39 Stemberger, 1988
 The method of calculation of r also depends on the source of data and culture conditions. The negative r values as a result of stress (e.g. toxicant) are not included.
 
 
Discussion
 
Studies concerning the population growth of B. patulus using baker's yeast have not been published so far. It is evident from the present study that yeast can be used for culturing B. patulus together with alga. The range of algal food densities chosen here were earlier used for growth studies of B. calyciflorus and B. patulus. As shown in many other studies (Halbach and Halbach-Keup 1974), an increase in Chlorella level from 1x106 ind. ml-1 to 3x106 ind. ml-1 resulted in an increase in the maximum population abundance of both B. calyciflorus and B. patulus (Figs. 1 and 2). However, when different food types were combined, the maximum peak density of B. calyciflorus was not statistically significant due to similar growth curves of rotifers fed yeast in low and high food densities. Sarma et al.  (1996) have grown B. calyciflorus in a wide range of Scenedesmus (0.5x106 to 40.5x106 ind. ml-1) and found no inhibitory effect of the algae, although the mean peak population abundances did not exactly correspond to the food levels offered. The present peak abundance values of B. calciflorus are comparable to those of Sarma et al.  (1996) under similar food densties. Sarma and Rao (1987) used 1x106 - 4x106 ind. ml-1 of Chlorella for growing B. patulus and reported peak abundance values of  110 - 325  ind. ml-1. In the present study, we found peak abundance values ranged from 109±26 to 296±20 depending on the algal food level.

The rates of population increase (r) observed here for both B. calyciflorus and B. patulus are within the range recorded earlier for Brachionidae (Table 1). In general, B. calyciflorus has a higher population growth rate compared to B. patulus. This is also evident from Fig. 3. It is however, important to note that species with higher r values need not always be competitively superior to those with lower growth rates (Sarma et al.  1999).
 
The inverse relation between population density and per capita rate of increase as recorded for B. calyciflurus and B. patulus was earlier observed for other zooplankton (DaphniaKerfoot et al.  1985, AnuraeopsisDumont et al.  1995).
 
This study showed that Chlorella vulgaris is a superior food as compared to Saccharomyces cerevisiae for these rotifer species. However, when offered a mixture of alga and yeast at low food density, B. calyciflorus and B. patulus reached higher peak population abundances comparable to or higher than on a diet of alga alone. It was found that the freshwater rotifers Brachionus calyciflorus and B. patulus were able to grow well on a mixed diet of Chlorella vulgaris and baker's yeast at 1x106 ind. ml-1 density. Only yeast was not suited for both rotifer species under 1x106 and 3x106 ind. ml-1 density. Thus, although a diet of yeast alone was not comparable to that of Chlorella, it can be effectively used at low concentrations to supplement algal requirements in rotifer culture systems.

Acknowledgements

SSSS and SN thank the National System of Investigators, Mexico (SNI-18723 and 20520, respectively) for support. Jose Luis G. Flores helped with the Spanish summary.
 
Resumen
 
Se comparó el crecimiento poblacional de dos especies planctónicas (B. calyciflorus y B. patulus) desarrolladas con el alga verde Chlorella vulgaris, la levadura de cerveza Saccharomyces cerevisiae y la mezcla de ambas dietas en proporciones iguales. B. patulus alcanzó las mayores densidades con cualquier tipo de alimento utilizado en comparación con B. calyciflorus. La dieta a base de Chlorella vulgaris sola promovió el mayor crecimiento poblacional en relación con la dieta de levadura sola. B. calyciflorus y B. patulus alcanzaron las mayores densidades de 103±8 ind. ml-1 y 296±20 ind. ml-1, respectivamente, con la dieta de Chlorella en 3x106 células ml-1. En condiciones similares, los valores máximos de abundancia de B. patulus fueron semejantes para ambos tipos de alimento. La tasa de incremento poblacional por día (r) para B. calyciflorus vario de 0.13±0.03 a 0.63±0.04, sin importar el tipo y densidad de alimento. Los resultados indican que la dieta a base de Chlorella fue mejor para los rotíferos considerados, y que la levadura puede usarse de manera efectiva a concentraciones bajas para complementar los requerimientos algales del sistema de cultivo de rotíferos.
 
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1 Carrera de Biología, UNAM Campus Iztacala, AP 314, CP 54090, Los Reyes, Tlalnepantla, Edo. de México, México. Fax:  +52 5 623 1155, e-mail:  sarma@servidor.unam.mx

2 CyMA Project.

*Corresponding author
 

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