The rate of removal of different microalgal cells in suspension at specific time interval in respect

of six species differing in sizes such as Tetraselmis sp, Cheatoceros sp, Chlorella sp, Dicrataria sp.,

Isochrys sp, Chromulina sp, by  Crassostrea madrasensis has been studied. The study revealed that often exhibit a signifiant degree of selectivity in the rate of filtration of certain algae. Further it is recorded that the filtration rate is not uniform throughout the experimental period of 24 hours. Oysters showed periods of high filtering activity and periods of relative quiescence

Palaniswami, Rani

Rajapandian, M E

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NOTES 159 Anu 1978. Standard mobalr for the examination MAC Anlm~~,  R. H. 1965. Patterns of diversity. d wabr rod waab water. 17th Edn. Am8rican Public Biol. Rev. 40:510-533. Health krodrtion, W~hiItgtOn D.C. MAWXLEP, R. 1967. Ocewgr .  and Mar. Bid. Ann. CRANblUN, R 1985. Mahamgur 18 (1) : 37-48. Rsvinv. 9257-299. DBVASSY, V.P. 1983. Ph.D. Thesis. Univ. of Kenla. RBUW. P. P. 1966. J. 1.01yticd Bid., 13 : 131-144. pp. m. QASIM, S. Z AND T. W. K u w m  1986. Proc. V' P. AND GOBI 1988' Es' Indian Acad Sci., (Anim. ScifPImt Sci,) Suppl. Nov. 1986 ddj SCi, 27: 671685. pp 1-17. a A 1922. E d  3156-162 SANIIIANAM, R, K. KRISHNAMURIW AND V. --, C. p. 1m. J. -. bid. A=. SUNMRNW, 1976. Bull. Dept Mar. Sci., Univ. C&n 14 (2): S68-977. 7 : 769-?77. BLURB, 0. P. 1986. PbytoplaLton ecology: atructme, So- T. 1948. K. danske Vidensk Selsk Skr., f a d o n  rod flw€wtioa. Chpamn and Hall. S (4) : 1-33. JAOAD~~BUN P. 1986. Ph. D. Tbtsia. Armamalri Vmmma,  K 1989. M. Phil. Thesis, Madurai Udv. .p 277. Kamaraj Umv. p. 53. ON TEE MICROALGAL SPECIES AS FEED FOR CONDITIONING ADULT OYSI'ER CRASSOSTREA UADRASENSIS (PRESTON) 'Ihe mle of removal of differcbt microalgal a l b  i n . a w p i o n  at specific time interval in respect of a h  spedts differing in sizes such as TebaseImis sp, Cheafoceros sp, Chlorella sp, Dicratcria tip., Isochy3is sp, ChmnuKna ap, by Cmswsbea nraahseusis has been studied. The study revealed that opten exhibit a signifiant degree of selectivity in the rate of filtration of certain algae. Further it is racotQd that the Ntmtion rate is not uniform throughout the experimental period of 24 hours. Oysters showed perioda of high filbting activity and periods of relative quiescence. l%is study help in developing p p r  feeding p t ~ ~ o 1  f r oyster booth basad on the species of algae, quantification of a l l s  and timings. MICROALGAL feeds am widely used. for conditioning the broodstock of oysters and dams in the hatchery (Dupey er al., 1977; Nayar er at?., 1987; Castagna et af., 1981). Though there have been several studies on filtration and. pumping ,; late of oysters by several authors (Loosanoff and Nomejko, 1946, M a t t i d  and Toner, 1966, Pruder et d., 1976; Galtsoff, 1964) the daily requirement of algal species for adult oysters has received only. little attention (Epifanio and Ewart, 1977; Gerdes, 1983). Mattiessen and Toner (1966) calailated that an oyster could filter 1.1 x lo9 of microalgal cells per day. Pmder et aL, have stated that an oyster weighing 50 g wholeweight cleazd a maximum of 1.05 x 16 cells per g of wholeyeight per day which would support both .growth and conditioning of oysters. Epifanio (1977) and Genies (1983) have ded a few speGes of microalgae known to be good food for adult oysters to study the filtration rate and rate of mnioval in different concentration of algal cells, which differ &rkedly in size. Epifanio and Ewalt (1997) have proposed a discontinuous feeding regime based on the results and formulated an equation for the maximum daily ration of oysters in respect to varic )us sizes, I .. - m me present stuay, me rate or removal of microalgal cells in suspension by the oyster Crassostrea madrasensis at given time intervals in respect of six species of microalgae which are available in the CMFRI Molluscan hatchery at Tuticorin has been investigated. The authors express deep sense of gratitude to Dr. K.S. Rao, Principal scientist for his suggestions and guidance in the preparation of this paper. We also extend our sincere thanks to Dr. C.P. Gopinathan, who provided all necessary help during the course of the experiments. Six species of microalgae namely Tetraselmis qracilis (12 p), Cheatoceros calcizrans (9 p), Chrmulintl fieibergmis (8 p), Isochrysis galbana (7 p), Dicrateria inornata (7 p) and Chlorella salina (3 p) were selected for study. Initiril concentration of the algal cells 10 1 of glass trough and made up to 7 1 with filtered sea water. Two oysters of same size group (100-110 mm) weighing nearly 150 gms were placed in each glass trough. \The .oysters were starved for 24 hours before the start of the experiment. h e  troughs were covered by a black cotton cloth to prevent passage of light and arrest multiplication of algae. Aeration was provided and temperature maintained at 25 * lo C. The pH was maintained at 8.2 and salinity at 31 t ppt. At hourly inte~vals aliquot samples were drawn from each trough and microalgal counts made. - I Dl0 CHCl TET CWI  CHL Cbk ).3 D E  C M  CHE .TET F I ~ .  1. A-B. Percentage of hourly filtration of cells., C. Filtration rate of different microalgal speciw in.suspeosion and, D. Total number of cells reinoved/hr/oyster in respect to different algal species. in suspension ranged from 0.06 to 1.8 million The filtration rate F, expressed in cells per ml. The cell count was made by mvhrloyster was calculated using the formula hameocytometer. The cultures were poured into F=R/C where R is the mean number of cells NOTES 161 removed from suspension per hour per oyster and C is the number of cells per ml in suspension (Epifanio and Ewart, 1977). The total number of cells removed per hour per oyster was calculated using the formula : Where in is the initial concentration in the suspension and T is the time and V is the volume of the sea water in the ,container (Gerdes, 1983). The results on the percentage of cells in suspension at hourly intervals in respect of the six algal species tested are given in Fig. 1 A-B. The total time for the partial or complete removal of cells was found to exceed 12 hours in the experiments with Tetrasehis sp., Chcatoceros sp., and Chbrella and the complete removal of cells ocCurred within 4 to 6 hours in the experiment with Dicrateria, Isochrysis and Chromulina. Only 44.7% of Chlorella and 60.5% of Cheatoceros were removed at the end of 6 hr. At the end of 12 holis they were found in decomposed state at the bottom of the tank. During the first hour of experiment the rate of removal was high for Dicrateria, Isochtysir and Chrmulina showing 74.5%, 60.1% and 58% of removal respectively. Subsequently 'fhe- removal of cells was continuous- but there were periods of high filtration and periods of relative quiescence. The filtration rate of oysters (Fig. 1C) wexe 3019, 2601, 2314, 1384, 1068 and 754 ml/hr/oyster respectively with Isochry~is~. Dicrateria, C h m l i n a ,  Tetraselmis, Cheatoceros and Chlorella. The volume of the water filtered by oysters in these experiments also varied with the algal species. Isochrysis gave better result than Dicrateria and Chromulinu which are almost similar in size. The total number' of cells temoved per hour per oyster from suspension were 5,64,666 x ld 597,500 x ld, 1,43,500 x ld, 1,45800 x id, 2,64000 x id and 73,228 x id in the case of Chlorella, Isochrysis, Dicrateria, Chromulina, Cheatoceros and Tetraselmis respectively (Fig. ID) Larger the size of cells, lesser their numbers were removed. For example Tetraselmis and Chlorella having 3 p size showed the highest removal of cells per hour per oyster. Among Isochrqsis, Dicrateria and Chromulina, the first one showed comparitivdy better result than the other two. The results obtained in the hourly removal of cells are comparable to those obtained by Epifanio and Ewart (1977) in Crassostrea virginica. It is observed that there was appreciably a higher rate of removal of cells in the first hour and in the subsequent hours both high and low filtering activity have been noted during the experimental period of 24 hours. This is explained by Epifanio and Ewart (1977) that the period of low filteration coincides with period of maximum digestibility. Once the digestive process is completed the filtering activity increases. These authors further stated that the periods of high filtering activity and periods of relative quiescence depend on the quantities of the algal material present in suspension and also vary with different species of algae. They observed this rhythm in the filtration of cells in certain concentration of different algal species. In higher concentrations of Cromonas and Carteria and at intermediate concentration of Isochrysis a well defined rhythm has been observed by Epifanio and Ewart (1977). They stated that this feature was absent in higher concentrations of Isochrysis and lower concentration of Cromonas. This rhythm was observed invariably in all the six species used in the pment study, though it is less pronounced in the case of Isochrysis and Chlorella. Epifanio and Ewart (1977) opined that there may be a threshold in the number of cells in suspension for each species of algae .and below this level will . ot be ideal for the oysters to utilise a maximum ration. They also proposed a discontinuous feeding regime, based on the periodic filtering activity of the oysters. The results of our experiments also support 162 NOTES this type of discontinuous feeding pattern and the minimum and maximum algal concentrations in the suspension for effective filteration. Since Cheatoceros and Chlorella were not completely removed by the oyster in the given time, feeding them. in higher concentrations is not advisable. Dicrateria and Chlorella which were completely removed at 4 and 5 hours respectively showed more than 60% of cell removal in the first hour. This is significantly higher than that of the other species of microalgae. Estimates of the rate of water transport by an adult oyster vafy from several litres to 34 litrdhr. (Lawanoff and Nomejke, 1946). Galtsoff (1%4) has stated that the rate of water transport depends on the size of the oyster, its physiological state and the environmental condition. From the present study it is clear that Crassostrea madrasensis exhibits specificity of algae with regard to the filtration rate. Isochrysis which gives good results (3019' mUhr/oyster) is widely accepted as the best food for adult oysters and larvae (Walne, 1981; Epifanio and Ewart, 1977; Nayar ef. al., 1987). Gerdes (1983) found that the filtration rate and the quantity of algae filtered out increase from 47.6 to 2383.3 mVhr1oyster with increase in the body weight of oyster. This result cannot be compared with our data since we have not used oysters of different body weights. The filtration rate of Chlorella is the lowest (754 mvhrloyster) and 44.7% of the cells were left in the medium being unfiltered. This may be due to the poor digestibility by the oystem since Chlorella has a double cell wall made up of an inner chitinous and an outer cellulose material. Epifanio and Ewart (1977) have observed that the total number of ql ls  removed from suspension was clearly less for bigger cells and vice versa. An adult oyster removed around 5,64,666 x ld cells of Chlorella whereas it was only 73,288 x ld in the case of TetraseImis which is almost 4 times bigger in size than Chlorella. It is inferred that it is desirable to provide algal cells in the medium at alternate periods which coincide with the active filtration phase, rather than maintaining the same cell concentration throughout. It is also clear that feeding Chlorella and ~heatixeros to adult oysten in higher concentration is not advantageous. The present study also indicates that the optimum filteration rate of the oyster depends on several factors such as starvation level of the oyster and digestibility, size and density of the algal cell concentration. To prepare the mixed algal diet for conditioning adult oysters, Ispchrysis, Dicrateria and Chromulina were &commended in view of their suitability for high filtration and faster utilisation of the cells. Central Marine Fisheries Research Instinrte, R. C. aticorin. CASTMNA M. AND KRAWlIJR N. JOHN. 1981. Spl. Rep. Appl Mari. Sci. Ocean Eng. No. 249, Virginia. Inst Mar. Sci. Gloucestor Point Virginia. D m ,  J. J., N. T. WINDSORAND C.E. SUTIIIN. 1977. Spl. Rep. 142 Appl Mar. Sci.Ocean Eng. Virginia Inat Mar. Sci.Gloucestor Point. Virginia. ErrPANIO, E. AND C. J. E~ART. 1977. Aquaculbtre, 11 : 13-29. GAL~OII? P. S. 1964. Fish Bull. Fish and Wildlife Sew. 64. GBR~BS. D. 1983. Aqua&lhtre, '31 : 195-219. LOOSANOPP, V..L., AND C. A. NOMBIM). 1946. Biol. Bull. 90 : 244-264. MATI~ESSBNXND TONBR, R. C. 1966. Marim Rurearch Foundation, Edgastown, Mass., 137 pp. NAYAR, K NAM,. M. E. RAJAPANDIAN, C. P. GOPINATHAN D A. D. GANDHI, 1987. Bull. Cent. Mar. Fish Res.  ins^, 38. F'RUDLIR, G. D., BOTION E. T., GRBBUHAUOH E. E.AND BAGGALBY R. E. 1976. Proc. 71% Annu. Workshop. Workl, Mariculhtre Soc. WALNE, P. R. 1981. Fishing News (Books) Ud., pp. 1-173. 

Microalgal species as feed for conditioning adult oyster Crassostrea madrasensis (Preston)

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Microalgal species as feed for conditioning adult oyster Crassostrea madrasensis (Preston)

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