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The evaluation of twelve algal species as food for juvenile Sydney rock oysters Saccostrea commercialis (Iredale & Roughley)
Aquaculture, 108 (1992) 277-283 Elsevier Science Publishers B.V., Amsterdam
277
AQUA 50035
The evaluation of twelve algal species as food for juvenile Sydney rock oysters Zzccustreu commevciuh (Iredale & Roughley ) Wayne A. O’Connor, John A. Nell and John A. Diemar N.S. W. Frshmes. Brackish Waler Fish Culture Research Sw:mn. Salamander Bay, N.S. W.. Au.viu/ie (Accepted
24 Apnl I992
1
ABSTRACT O’Connor, W.A.. Nell, J.A. and Diemar. J.A., 1992. The evaluatton oftwelve algal species as footi for juvenile Sydney rock oysters Saccosrreo commercialis (Iredale & Roughley). Aquacuhure, LOB:277283. Juvenile Sydney rock oysters (Saccoslrea commercialis) were fed diets composed of either one of twelve algal species or one of eleven algal species m combination with Skeleronrma cos~Ium. When used as the sole diet for 21 days, the diatoms Skeletonemn cos~~~urn,Chaeroceros calcirrans. Chaeroceros gracills and Thalassrosira pseudonana produced the greztcst live weight increase in spat. When Skelefonrmo co~~al~n~WBI fed in combiwtion a::!~ the remainmg eleven algal species for 19 days, diets including Chae:oceros gracilw. Tetroselms chui and Tewawlmis sacc;ca produced the highest live weight mcreases These findings indicated differences in the food value ofseveral algal species to larvae and spat of the Sydney rock oyster.
1NTRODUCTlOPl
Many studies have been conducted to assess the nutritional value of a variety of algal species as a food source for bivalve spat (Walne, 19701 Enriqht et al., 1986; Laiug and Millican, :9%). 1Yhiie certain algae have been found to pioduce good spat growth with a variety of bivalves, others, such as Dunalida tertiokctu Butcher, have consistently performed poorly (Walne, 1970; Langdon and Waldock, 1981; Enright et al., 1986). A variety of factors %e involved in determining the food value of a particular alga, including cell size, disestibility and lack of toxicity (Webb and Chu, 1983). Of particular importance are the presence of one or both of the long-chair highly unsaturated acids, 205~3 szd 22:6n-3, and the content of dietary carbohydrate (Enrigbt et al., i98J; Whyre et ai., i9Fir). Correspondence to: Dr. Wayne O’Conncr, N.S.W. Fisheries, search Station, Salamander Bay, N.S.W. 2301, Australia.
004%846/92/$05.0@
0 1992 Elsevier Science
Pub1ishersB.V.
Brackish
Water Fish Culture
All rights reserved.
Re-
278
W.A. O’CONNOR ETAL.
Although Sydney rock oyster, Saccostrea commercialis (Iredale & RoughIcy), spat have been reared in hatcheries fur more than 10 years, the nutritional value ofthe varicus algal species fed has not been determined. Predominantly, those species producing the greatest growth in S. commercialis larvae have been fed to spat. These include Pavlova lutheri (Droop) Green, Chaetocet’osculcitrans (Paulsen ) TakdnO and Tahitian Isochrysis aff, galbana (Nel! and O’Connor, i 991). S. commercialis spat are mainiained within the hatch-, ery until they are large enough to be retained upon a 500 pm mesh sievt, during which time their food demand greatly exceeds that of larvae. Since different food sources can be beneficial at different stages of the life cycle (Ukeles, 1975), the assumption that the best larval food will also produce the most rapid growth in spat could prove costly. These experiments were designed to determine which of twelve algal species fed individually or in combination produced the greatest increase in spat live weight gain and rhus determine if the diet used for .S.commercialis larvae is the most appropriate for rapid spat growth. MATERIALS AND METHODS Oyster spat
Hatchery-reared S. commercialis, that had been held in upwellers utilising natural phytoplankton as a food source (Holliday, 1985), were graded with mesh sieves to obtain spat of a uniform size. The average individual spat weight ( !I s.d.) for Experiment 1 was 9.5 f 0.4 mg. Due to difficulties in obtaining hatchery-reared spat, smailer spat were used in Experiment 2 ( 1.9 i 0.3 mg). Experiment 2 was continued until most spat had exceeded the starting weight in Experiment 1 (9.5 mg). Groups of 30 spat were placed in
nylon mesh envelopes and individual envelopes placed in separate 8-I aerated aquaria. The oceanic water (35 %a) used in each aquarium was filtered using 1 pm nominal cartridge filters to reduce the levels of suspended solids. Each aquarium was maintained at 25 + 1“C and the water changed thrice weekly. For bo:h experiments tte daily feed rations were determined according to !he equation &=O.OI W-o.33, where Qa is dry weight (g) of ration/live weight of bivalve (g) and W is the live weight of bivalve (g) (Epifanio, 197oa). The live weight of spat fed each diet was determined weekly and the feed rates adjusted according to Epifanio’s ( 197%) equation. Experimentul design In Experiment 1, spat were fed one of twelve algal species (listed in Table
1) a:3a sole diet. In Experiment 2, the alga producing the greatest live weight incn;ase from Experiment 1 [Ske!etrtnema cosfatum (Greville) Cleve] was fed in combination with each of the remaining algal species on an equal dry weigiit basis (Table 2). Both experiments included an unfed control and used
ALOAE As FOOD FOR SYDNEY ROCK OYSTERS
279
four replicates per treatment. Experiments 1 and 2 were terminated after 2 I and 19 days respectively, and then final mean spat live weights were determined for each aquarium. Algal culture techniques
Algal cultures were grown in aerated ( l-2% CO* enriched) 5-l borosilicate glass flasks. All species were cultured in oceanic water (salinily 34-35 %s) at 21 f 1 ‘C. The nutrient medium, f/2 beta (Guillard, 1983j, was used with NazSiOs-SH,O added to diatom cultures only. Cultures were illuminated with “White, Wattsaver” ft::orescent tubes (Osram, Sydney, Australia) to an intensity of 4000 lux at the container surface using a 16~8b 1ight:dark cycle. All cultures were harvested in growth phase and fed for a maximum of 3 days before replacement with a new culture. A minimum of six individual cultures of each alga was used in each experiment. Dry weight determination of algar cells Samples from six cultures of Thalassiosira p.Feudonana (3H), 5’. costatum and Stichococcus sp. were collected and the ceil densities determined with an
“Improved Neubauer” haemocvtometer (Sunerior Co.. Berlin. Germanv). A known volume (SO-150 ml) was filtered through a 6.7 pm bore sizeglass Bbre filter to collect the algal cells. The filter was washed with LOOml of 0.5 M ammonium formate to remove seasalts (Epifacio, 1979b) and dried at 100°C. The dry weights of suspended solids in the seawater were also determined in this way. Dry weightsof other species used were obtained from previous experimentation (Nell and O’Connor, 1991). Homogeneity of variance was tested using Cochran’s test (Winer, 1971). Data from both experiments were supjetted to single-factor analysis of variance and mean values were compare,?,using Tukey’s honestly significant difference method (Sokal and Rohlf, 143I ). RESULTS
Algal cell mean dry weights for T. pseudonana, S. costatum and Stichococcus sp. were (mean t s.d.) 31 C 4.8 pg, 50 :; 7.3 pg and 3 C 0.8 pg in that order. Levels of suspended solids for Experiments 1and 2 were 0.32 and 0.28 mg I - ’ , respectively. Experiment I
When used as the sole food source, the diatoms S. costatum, C. calcitrans, Chaetoceros gracilis Schiitt and r pseudonuna produced the greatest live weight increase in spat. Tahitian Isochrysis produced significantly less live
W.A.O’CONNOR ETAL.
280 ?ABLE I Comparison of the food value of some algal species fed to alis) spat for 21 days (Experiment I )
Sydney rock oyster (Saccosrreacommerci-
Algal diets
Average live weight after 21 days (me)’
Skelefonema co~larum Chnetoceros calcitrans Chnetoceros grocilis Thalarsiosirapseudonana Tahitian Isorhrysis Tetnw’lmis chui Phaeodactylum sicowrum Pavlova lurheri Terraselmis suecica Srichococcur sp. Dunaliella terrio!ecto Nannochloris atomus
61.1~8.0’ 57.9f3.F 51.5+2.Pbc 49.6+1.5*k 46.8 t 8.9& 42.7 + 6.0c 42.4 ? 6.6’ 39.8?7.7’ 39.0+4.v 20.92 1.qd 16.3+2.od 11.6f0.9d 10.9+0.4d
Unfed
‘Values are means+ s.d. Means with a c~mmrm superscript letter do not differ significanlly (Pz-0.05 Initial average live weight of spat was 9.5 20.4 ma.
).
TABLE 2 Comparison of the food value of some algal species in combination with Skele~onema Sydney rock oyster (Saccosrreacommercialis) spat for 19 days (Experiment 2) Algal diets
co~lalum
to
Average live weigh1ofspat (mg)’
11.5+0.8’ 10.8+ l.Sc 7.2?0.3’
4.9?0.1’ Value; arc meansfs.d. Means witha common superscript le., rdo not differ significantly Initial weight ofspat was 1.9f0.3 mb.
(P>O.OS).
weight increase (P
ALGAE As FOOD FOR SYDNEY RCC’ . OYSTERS
281
Experiment 2
A diet combining S. ;xtatum and C. grucilis produced significantly greater (PcO.05) live weight gains than all other diets tested. Diets incorporating Tetraselmis cl&, T. s:recicn and T. Isochrysis produced significantly greater live weight gains in spat than those fed solely S. cosiatum. Both unfed spat and those fed 5’. cos:nfum/N. atomus produced significantly less (PcO.05) live weight gain thari those fed solely S. costarurn (Table 2). Spat survival in tjoth experiments was greater than 90% and did not differ significantly (P>f.O5) between treatments. DISCUSSION
The signifisant differences (P
282
alent lo that of S. costatum, T. pseudonana, C. calcitrans or C. gracilis. This indicates that other factors are involved in determining the food value of an alga, such as micronutrients, cell size and cell wall digestibility. Both synergistic and nonadditive dietary effects, as described by Epifanio ( 1979b); were observed in the relative food value of the species fed in combination with S. costalum.The addition of C. gracilis, T. suecica. T chui or T. Isochtysis to the diet produced significantlygreater spat growth (PcO.05) than a diet comprising solely S. costatum. The high levels of both 20&z-3 and 22:6n-3 fatty acids and carbohydrate in S. costatum (Emight et al., 1986) may indicate the synergistic effect observed with these combined diets is due to other factors. Bpifanio (1979b) suggested that difficulties associated with the digestion of the theta of Tetraselmis sp. could lead to stomach clogging when fed in large amounts. However, when fed in combination with S. costaturn sufficient time may be available for digestion, possibly explaining the enhanced performance of both T. suecica and T. chui in combination diets. With the axcention ofS. costatum/N. atomus, all other combmed diets tested produced nonadditive dietary effects, that is, they failed to produce signiticantly greater (P> 0.05) growth than predicted by a diet of either of the constituent algae. Whether fed sit& or in combination with S. costatum, N. atomus failed to produce growth significantly greater than unfed controls. There are considerable differences in the food value of algal species to Sydney rock oyster spat and larvae. P. lutheri, found to produce the greatest shell length increase in larvae (Nell and O’Connor, 1991 ), was clearly surpassed in this study by several diatoms. Ukeles (1975) has suggested that diatoms are not usually fed to larvae as most arc too large and difticult to digest. The exception was C. calcitrans, the smallest of the diatoms tested, which produced excellent growth in both spat and larvae (Nell and O’Connor, 1991). The larvae ofthe Sydney ro,.icoyster feed on particles i 10pm in size (Wisely and Reid, 1978) and thus diatoms such as T. pseudonana could be ingested, although the silica frustule surrounding these diatoms may inhibit digestion. In summary, the food value oia variety of commonly cultured algal species to S. commercialis spat varies greatly and differs from that for larvae. To ensure Sydney rock oyster spat reach a size at which they may be removed from the hatchery as rapidly as possible, a mixed diet incorporating species such as the diatoms S. costatum and C. gracilis which are not commonly fed to larvae may be beneficial. ACKNOWLEDGMENTS
We thank the staff ofthe Brackish Water Fish Culture Research Station for their assistance, in particular Lindsay Goard for providing spat. Thanks are also due to Geoff Allan and Dr. Michael Heasman for critically reviewing the manuscript.
REFERENCES Brown, M.R., Jeffrey, SW. and Garland, C.D.. 1989. Nutritional a~pccts of microalgae used in maricuhure: a literature review. CSlRO Mar. Lab. Rep., Hobart, Tas., 44 pp. Enright, C.T., Newkirk, G.F., Craigie, J.S. and Castell, J.D., 1986. Evaluation of phytoplankton as dirts forjuveniie 0sfre.a ddis L. J. Enp. Mar. Bioi. Ecci., 35: t-13. Epifanio, C.E., 1979a. Comparison of yeast and algal diets for bivalve molluscs. Aquaculture, 16: 187-192. Epifanio, C.E., 1979b. Growth in bivalve motluscs: nutritional effects of two or more species of algae in diets fed to the Americrm oyster Crassosrrea wginica (Gmelin) and the hard clam Mercenaria mercenaria (L.). Aquaculture, 18: I-!2. Guillard. R.L., 1983. Culture of phytoplankton ior feeding marine invertebrates. rn: C.J. Bee& Jr. (Editorj, Culture of Marine Invertebrates. Hutchinson Ross Publishing Company, Stroudberg, PA, pp. 108-132. Ho!liday, J.E., 1985. lntemational developments in oyster hatchery technology. Misc. Rep. No. I, Dep. Agric. N.S.W., Brackish Water Fish Culture Research Station, Salamander Bay, N.S.W., 101 pp. Laing, 1.and Millican, P.F., 1986. Relative growth and growth efliciency of Osrrea aft& L. spat fed various algal diets. Aquaculture, 54: 245-262. Lain& I., Childs, A.R. and Janke, A., 1990. Nwitional value of dried algal diets for larvae of Manila clam (T~pesphilippinarum). 1. Mar. Biol. Assoc. U.K., 70: I-12. Langdon, C.J. and Waldock, M.J., 1981. The effect of alp1 and artiticial diets on the growth and fattyacidcompositionofCrassoslreagi8~sspat. J. Mar. Biol. ASSOC. U.K., 61: 431-448. Nell, J.A. and O’Connor, W.A., 1991. The evauation of fresh algae and stored al8al concentrates as a food sxtree for Sydney rack oyster Saccosrrea commerclalis (Iredale .4 Roughley) larvae. Aquaculture, 99: 277-284. Sakal, R.R. and Roblf, F.J., 1981. Biometry. W. H. Freeman and Company, New York, NY, 895 pp. Ukeles, R., 1975. Views on bivalve nutrition. In: KS. Price Jr., W.N. Shaw and KS. Danber& (Editors), Pox. First. Int. Conf. Aquaculture Nutr. Univ. of Delaware, Newark, DE, pp. 127-162. Wait% P.R., 1970. Studies on the food value of nineteen genera of algae to juvenile bivalves of the genera Osfrea, Crus~o:rrt-rr,Mercettarta and &fyri/us. Fishery Invest. Land., Ser. IL 26( 5). 62 PP. Webb, K.L. and Chu. F.L.E.. 1983. Phytoplank:w as a food smtrce for bivalve larvae. In: G.D. Pruder, C. Langdon and D. Conklin (Editors), Proceedings of the Second International Conference on Aquaculture Nutrition: Biochemical and Physiological Appmaches to Shellftsh Nutrition. World Maricult. Sot. Spec. Publ., 2 277-291. Whyte, J.N.C., Boume, N. and Hodgson, C.A., 1990. Nutritionat condition of rock scallop, Crnwr!ctrta gi,e~uren (Grey). !arvae fed mixed algal diets. Aquaculture, 86: 25-40. Wirier, B.J., 197 I. Statistical Principles in Exprrimental Design. McGraw-Hill Kogakusha, Tokyo, pp. 205-210. Wisely, B.. and Reid, B.L.. 1978. Experimental feeding of Sydney rock oysters (.Swccowea corntnrrcialis = Saccostrea cu/cu1/ara). I. Optimum particle stzes and concentrations. Aquaculture, 15: 319-331.
277
AQUA 50035
The evaluation of twelve algal species as food for juvenile Sydney rock oysters Zzccustreu commevciuh (Iredale & Roughley ) Wayne A. O’Connor, John A. Nell and John A. Diemar N.S. W. Frshmes. Brackish Waler Fish Culture Research Sw:mn. Salamander Bay, N.S. W.. Au.viu/ie (Accepted
24 Apnl I992
1
ABSTRACT O’Connor, W.A.. Nell, J.A. and Diemar. J.A., 1992. The evaluatton oftwelve algal species as footi for juvenile Sydney rock oysters Saccosrreo commercialis (Iredale & Roughley). Aquacuhure, LOB:277283. Juvenile Sydney rock oysters (Saccoslrea commercialis) were fed diets composed of either one of twelve algal species or one of eleven algal species m combination with Skeleronrma cos~Ium. When used as the sole diet for 21 days, the diatoms Skeletonemn cos~~~urn,Chaeroceros calcirrans. Chaeroceros gracills and Thalassrosira pseudonana produced the greztcst live weight increase in spat. When Skelefonrmo co~~al~n~WBI fed in combiwtion a::!~ the remainmg eleven algal species for 19 days, diets including Chae:oceros gracilw. Tetroselms chui and Tewawlmis sacc;ca produced the highest live weight mcreases These findings indicated differences in the food value ofseveral algal species to larvae and spat of the Sydney rock oyster.
1NTRODUCTlOPl
Many studies have been conducted to assess the nutritional value of a variety of algal species as a food source for bivalve spat (Walne, 19701 Enriqht et al., 1986; Laiug and Millican, :9%). 1Yhiie certain algae have been found to pioduce good spat growth with a variety of bivalves, others, such as Dunalida tertiokctu Butcher, have consistently performed poorly (Walne, 1970; Langdon and Waldock, 1981; Enright et al., 1986). A variety of factors %e involved in determining the food value of a particular alga, including cell size, disestibility and lack of toxicity (Webb and Chu, 1983). Of particular importance are the presence of one or both of the long-chair highly unsaturated acids, 205~3 szd 22:6n-3, and the content of dietary carbohydrate (Enrigbt et al., i98J; Whyre et ai., i9Fir). Correspondence to: Dr. Wayne O’Conncr, N.S.W. Fisheries, search Station, Salamander Bay, N.S.W. 2301, Australia.
004%846/92/$05.0@
0 1992 Elsevier Science
Pub1ishersB.V.
Brackish
Water Fish Culture
All rights reserved.
Re-
278
W.A. O’CONNOR ETAL.
Although Sydney rock oyster, Saccostrea commercialis (Iredale & RoughIcy), spat have been reared in hatcheries fur more than 10 years, the nutritional value ofthe varicus algal species fed has not been determined. Predominantly, those species producing the greatest growth in S. commercialis larvae have been fed to spat. These include Pavlova lutheri (Droop) Green, Chaetocet’osculcitrans (Paulsen ) TakdnO and Tahitian Isochrysis aff, galbana (Nel! and O’Connor, i 991). S. commercialis spat are mainiained within the hatch-, ery until they are large enough to be retained upon a 500 pm mesh sievt, during which time their food demand greatly exceeds that of larvae. Since different food sources can be beneficial at different stages of the life cycle (Ukeles, 1975), the assumption that the best larval food will also produce the most rapid growth in spat could prove costly. These experiments were designed to determine which of twelve algal species fed individually or in combination produced the greatest increase in spat live weight gain and rhus determine if the diet used for .S.commercialis larvae is the most appropriate for rapid spat growth. MATERIALS AND METHODS Oyster spat
Hatchery-reared S. commercialis, that had been held in upwellers utilising natural phytoplankton as a food source (Holliday, 1985), were graded with mesh sieves to obtain spat of a uniform size. The average individual spat weight ( !I s.d.) for Experiment 1 was 9.5 f 0.4 mg. Due to difficulties in obtaining hatchery-reared spat, smailer spat were used in Experiment 2 ( 1.9 i 0.3 mg). Experiment 2 was continued until most spat had exceeded the starting weight in Experiment 1 (9.5 mg). Groups of 30 spat were placed in
nylon mesh envelopes and individual envelopes placed in separate 8-I aerated aquaria. The oceanic water (35 %a) used in each aquarium was filtered using 1 pm nominal cartridge filters to reduce the levels of suspended solids. Each aquarium was maintained at 25 + 1“C and the water changed thrice weekly. For bo:h experiments tte daily feed rations were determined according to !he equation &=O.OI W-o.33, where Qa is dry weight (g) of ration/live weight of bivalve (g) and W is the live weight of bivalve (g) (Epifanio, 197oa). The live weight of spat fed each diet was determined weekly and the feed rates adjusted according to Epifanio’s ( 197%) equation. Experimentul design In Experiment 1, spat were fed one of twelve algal species (listed in Table
1) a:3a sole diet. In Experiment 2, the alga producing the greatest live weight incn;ase from Experiment 1 [Ske!etrtnema cosfatum (Greville) Cleve] was fed in combination with each of the remaining algal species on an equal dry weigiit basis (Table 2). Both experiments included an unfed control and used
ALOAE As FOOD FOR SYDNEY ROCK OYSTERS
279
four replicates per treatment. Experiments 1 and 2 were terminated after 2 I and 19 days respectively, and then final mean spat live weights were determined for each aquarium. Algal culture techniques
Algal cultures were grown in aerated ( l-2% CO* enriched) 5-l borosilicate glass flasks. All species were cultured in oceanic water (salinily 34-35 %s) at 21 f 1 ‘C. The nutrient medium, f/2 beta (Guillard, 1983j, was used with NazSiOs-SH,O added to diatom cultures only. Cultures were illuminated with “White, Wattsaver” ft::orescent tubes (Osram, Sydney, Australia) to an intensity of 4000 lux at the container surface using a 16~8b 1ight:dark cycle. All cultures were harvested in growth phase and fed for a maximum of 3 days before replacement with a new culture. A minimum of six individual cultures of each alga was used in each experiment. Dry weight determination of algar cells Samples from six cultures of Thalassiosira p.Feudonana (3H), 5’. costatum and Stichococcus sp. were collected and the ceil densities determined with an
“Improved Neubauer” haemocvtometer (Sunerior Co.. Berlin. Germanv). A known volume (SO-150 ml) was filtered through a 6.7 pm bore sizeglass Bbre filter to collect the algal cells. The filter was washed with LOOml of 0.5 M ammonium formate to remove seasalts (Epifacio, 1979b) and dried at 100°C. The dry weights of suspended solids in the seawater were also determined in this way. Dry weightsof other species used were obtained from previous experimentation (Nell and O’Connor, 1991). Homogeneity of variance was tested using Cochran’s test (Winer, 1971). Data from both experiments were supjetted to single-factor analysis of variance and mean values were compare,?,using Tukey’s honestly significant difference method (Sokal and Rohlf, 143I ). RESULTS
Algal cell mean dry weights for T. pseudonana, S. costatum and Stichococcus sp. were (mean t s.d.) 31 C 4.8 pg, 50 :; 7.3 pg and 3 C 0.8 pg in that order. Levels of suspended solids for Experiments 1and 2 were 0.32 and 0.28 mg I - ’ , respectively. Experiment I
When used as the sole food source, the diatoms S. costatum, C. calcitrans, Chaetoceros gracilis Schiitt and r pseudonuna produced the greatest live weight increase in spat. Tahitian Isochrysis produced significantly less live
W.A.O’CONNOR ETAL.
280 ?ABLE I Comparison of the food value of some algal species fed to alis) spat for 21 days (Experiment I )
Sydney rock oyster (Saccosrreacommerci-
Algal diets
Average live weight after 21 days (me)’
Skelefonema co~larum Chnetoceros calcitrans Chnetoceros grocilis Thalarsiosirapseudonana Tahitian Isorhrysis Tetnw’lmis chui Phaeodactylum sicowrum Pavlova lurheri Terraselmis suecica Srichococcur sp. Dunaliella terrio!ecto Nannochloris atomus
61.1~8.0’ 57.9f3.F 51.5+2.Pbc 49.6+1.5*k 46.8 t 8.9& 42.7 + 6.0c 42.4 ? 6.6’ 39.8?7.7’ 39.0+4.v 20.92 1.qd 16.3+2.od 11.6f0.9d 10.9+0.4d
Unfed
‘Values are means+ s.d. Means with a c~mmrm superscript letter do not differ significanlly (Pz-0.05 Initial average live weight of spat was 9.5 20.4 ma.
).
TABLE 2 Comparison of the food value of some algal species in combination with Skele~onema Sydney rock oyster (Saccosrreacommercialis) spat for 19 days (Experiment 2) Algal diets
co~lalum
to
Average live weigh1ofspat (mg)’
11.5+0.8’ 10.8+ l.Sc 7.2?0.3’
4.9?0.1’ Value; arc meansfs.d. Means witha common superscript le., rdo not differ significantly Initial weight ofspat was 1.9f0.3 mb.
(P>O.OS).
weight increase (P
ALGAE As FOOD FOR SYDNEY RCC’ . OYSTERS
281
Experiment 2
A diet combining S. ;xtatum and C. grucilis produced significantly greater (PcO.05) live weight gains than all other diets tested. Diets incorporating Tetraselmis cl&, T. s:recicn and T. Isochrysis produced significantly greater live weight gains in spat than those fed solely S. cosiatum. Both unfed spat and those fed 5’. cos:nfum/N. atomus produced significantly less (PcO.05) live weight gain thari those fed solely S. costarurn (Table 2). Spat survival in tjoth experiments was greater than 90% and did not differ significantly (P>f.O5) between treatments. DISCUSSION
The signifisant differences (P
282
alent lo that of S. costatum, T. pseudonana, C. calcitrans or C. gracilis. This indicates that other factors are involved in determining the food value of an alga, such as micronutrients, cell size and cell wall digestibility. Both synergistic and nonadditive dietary effects, as described by Epifanio ( 1979b); were observed in the relative food value of the species fed in combination with S. costalum.The addition of C. gracilis, T. suecica. T chui or T. Isochtysis to the diet produced significantlygreater spat growth (PcO.05) than a diet comprising solely S. costatum. The high levels of both 20&z-3 and 22:6n-3 fatty acids and carbohydrate in S. costatum (Emight et al., 1986) may indicate the synergistic effect observed with these combined diets is due to other factors. Bpifanio (1979b) suggested that difficulties associated with the digestion of the theta of Tetraselmis sp. could lead to stomach clogging when fed in large amounts. However, when fed in combination with S. costaturn sufficient time may be available for digestion, possibly explaining the enhanced performance of both T. suecica and T. chui in combination diets. With the axcention ofS. costatum/N. atomus, all other combmed diets tested produced nonadditive dietary effects, that is, they failed to produce signiticantly greater (P> 0.05) growth than predicted by a diet of either of the constituent algae. Whether fed sit& or in combination with S. costatum, N. atomus failed to produce growth significantly greater than unfed controls. There are considerable differences in the food value of algal species to Sydney rock oyster spat and larvae. P. lutheri, found to produce the greatest shell length increase in larvae (Nell and O’Connor, 1991 ), was clearly surpassed in this study by several diatoms. Ukeles (1975) has suggested that diatoms are not usually fed to larvae as most arc too large and difticult to digest. The exception was C. calcitrans, the smallest of the diatoms tested, which produced excellent growth in both spat and larvae (Nell and O’Connor, 1991). The larvae ofthe Sydney ro,.icoyster feed on particles i 10pm in size (Wisely and Reid, 1978) and thus diatoms such as T. pseudonana could be ingested, although the silica frustule surrounding these diatoms may inhibit digestion. In summary, the food value oia variety of commonly cultured algal species to S. commercialis spat varies greatly and differs from that for larvae. To ensure Sydney rock oyster spat reach a size at which they may be removed from the hatchery as rapidly as possible, a mixed diet incorporating species such as the diatoms S. costatum and C. gracilis which are not commonly fed to larvae may be beneficial. ACKNOWLEDGMENTS
We thank the staff ofthe Brackish Water Fish Culture Research Station for their assistance, in particular Lindsay Goard for providing spat. Thanks are also due to Geoff Allan and Dr. Michael Heasman for critically reviewing the manuscript.
REFERENCES Brown, M.R., Jeffrey, SW. and Garland, C.D.. 1989. Nutritional a~pccts of microalgae used in maricuhure: a literature review. CSlRO Mar. Lab. Rep., Hobart, Tas., 44 pp. Enright, C.T., Newkirk, G.F., Craigie, J.S. and Castell, J.D., 1986. Evaluation of phytoplankton as dirts forjuveniie 0sfre.a ddis L. J. Enp. Mar. Bioi. Ecci., 35: t-13. Epifanio, C.E., 1979a. Comparison of yeast and algal diets for bivalve molluscs. Aquaculture, 16: 187-192. Epifanio, C.E., 1979b. Growth in bivalve motluscs: nutritional effects of two or more species of algae in diets fed to the Americrm oyster Crassosrrea wginica (Gmelin) and the hard clam Mercenaria mercenaria (L.). Aquaculture, 18: I-!2. Guillard. R.L., 1983. Culture of phytoplankton ior feeding marine invertebrates. rn: C.J. Bee& Jr. (Editorj, Culture of Marine Invertebrates. Hutchinson Ross Publishing Company, Stroudberg, PA, pp. 108-132. Ho!liday, J.E., 1985. lntemational developments in oyster hatchery technology. Misc. Rep. No. I, Dep. Agric. N.S.W., Brackish Water Fish Culture Research Station, Salamander Bay, N.S.W., 101 pp. Laing, 1.and Millican, P.F., 1986. Relative growth and growth efliciency of Osrrea aft& L. spat fed various algal diets. Aquaculture, 54: 245-262. Lain& I., Childs, A.R. and Janke, A., 1990. Nwitional value of dried algal diets for larvae of Manila clam (T~pesphilippinarum). 1. Mar. Biol. Assoc. U.K., 70: I-12. Langdon, C.J. and Waldock, M.J., 1981. The effect of alp1 and artiticial diets on the growth and fattyacidcompositionofCrassoslreagi8~sspat. J. Mar. Biol. ASSOC. U.K., 61: 431-448. Nell, J.A. and O’Connor, W.A., 1991. The evauation of fresh algae and stored al8al concentrates as a food sxtree for Sydney rack oyster Saccosrrea commerclalis (Iredale .4 Roughley) larvae. Aquaculture, 99: 277-284. Sakal, R.R. and Roblf, F.J., 1981. Biometry. W. H. Freeman and Company, New York, NY, 895 pp. Ukeles, R., 1975. Views on bivalve nutrition. In: KS. Price Jr., W.N. Shaw and KS. Danber& (Editors), Pox. First. Int. Conf. Aquaculture Nutr. Univ. of Delaware, Newark, DE, pp. 127-162. Wait% P.R., 1970. Studies on the food value of nineteen genera of algae to juvenile bivalves of the genera Osfrea, Crus~o:rrt-rr,Mercettarta and &fyri/us. Fishery Invest. Land., Ser. IL 26( 5). 62 PP. Webb, K.L. and Chu. F.L.E.. 1983. Phytoplank:w as a food smtrce for bivalve larvae. In: G.D. Pruder, C. Langdon and D. Conklin (Editors), Proceedings of the Second International Conference on Aquaculture Nutrition: Biochemical and Physiological Appmaches to Shellftsh Nutrition. World Maricult. Sot. Spec. Publ., 2 277-291. Whyte, J.N.C., Boume, N. and Hodgson, C.A., 1990. Nutritionat condition of rock scallop, Crnwr!ctrta gi,e~uren (Grey). !arvae fed mixed algal diets. Aquaculture, 86: 25-40. Wirier, B.J., 197 I. Statistical Principles in Exprrimental Design. McGraw-Hill Kogakusha, Tokyo, pp. 205-210. Wisely, B.. and Reid, B.L.. 1978. Experimental feeding of Sydney rock oysters (.Swccowea corntnrrcialis = Saccostrea cu/cu1/ara). I. Optimum particle stzes and concentrations. Aquaculture, 15: 319-331.