Straight-hinge Larvae Research Articles

Internal Anatomy and Biochemical Content of the Cortez Geoduck Panopea globosa during Larval Development

Histological, histochemical, and biochemical changes were assessed in the Cortez geoduck Panopea globosa, during larval development to identify the main energy storage sites and biochemical patterns. Histological sections were stained with polychromic dye, whereas histochemical sections were stained for triglycerides and phospholipids (Sudan black) and for carbohydrates (Alcian blue). Spectrophotometric quantitation of proteins, lipids, and carbohydrates was carried out in 5–35 mg dry weight (DW) samples. Larvae of Panopea globosa showed the typical linear shell growth rate (21 µm d–1) and allometric, power-type relationships between shell length and DW (exponent b = 2.73) or ash-free DW (b = 2.78). Early straight-hinged larvae exhibited a rudimentary digestive system. The crystalline style, intestine, and digestive gland were conspicuous when larvae reached the early umbonate stage, whereas the gills, foot, byssal gland, and adductor muscles were first observed in late umboned larvae. Triglycerides and carbohydrates were mainly stored as droplets in the digestive gland, and their size increased with increasing larval age. Acid mucopolysaccharides were also secreted by the byssal gland. Carbohydrate content was substantially higher than triglycerides in pediveliger larvae. These finding suggests that P. globosa larvae mainly rely on a carbohydrate-based metabolism, both as a biochemical component of the larval–postlarval byssus and as an endogenous energy source during metamorphosis.

Inbreeding depression on growth and survival of full-sib family of Manila clam (Ruditapes philippinarum)

In present study, the inbreeding depression (ID) of growth and survival of Manila clam (Ruditapes philippinarum) was investigated at larval and juvenile stages. Nine inbred families (A2, B2, C2, D2, E2, F2, G2, H2 and I2) were established by mating within nine full-sib families with expected inbreeding coefficient of 0.25. Inbred families showed significant differences in shell length and hatching rate of D-larvae (straight-hinged larvae). The larvae of the nine inbred families grew slower than those of control group (CG), and their ID value ranged from 0.81% ± 6.09% to 16.10% ± 1.49%. The ID value of larval survival rate varied between 27.47% ± 9.36% and 70.50% ± 13.66%. The ID was also detected for juvenile growth in A2, B2, C2, and D2, which ranged from 4.60 ± 2.21 to 17.71 ± 7.73. The A2 family maintained the highest juvenile survival rate, whereas the other inbred families exhibited ID values varying between 62.79% ± 4.54% and 96.14% ± 0.87%. The linear relationship of estimated ID between growth and survival was negatively correlated (R = −0.434, P < 0.05). The results of this study suggested that the ID of growth was common at the larval stage but was less prevalent at juvenile stage. In contrast, the ID of survival increased from larval to juvenile stage. A better understanding of the effect of inbreeding may aid to selective breeding of Manila clam.

Effects of salinity on embryonic development, survival, and growth of Crassostrea hongkongensis

This study examined the effects of salinity on embryonic development, survival, and growth of the Hong Kong oyster Crassostrea hongkongensis. The embryos, larvae, and juveniles of C. hongkongensis were held in artificial seawater at three different salinities (low, 15; medium, 23; and high, 30) to determine the optimum hatchery and nursery conditions for mass production of the seeds. Results showed that the percentage production of straight-hinged larvae from fertilized eggs was significantly lower at the high salinity than at the low-and medium-salinities (P < 0.05). The survival rates of larvae and juveniles differed significantly among the three salinity trials, with the highest survival rate observed at the low salinity (P < 0.05). The shell height of larvae was significantly larger at the low salinity than at the high and medium salinities from days 9 to 15 (P < 0.05), whereas that of juveniles was significantly larger at the low salinity than at the high and medium salinities on day 70 (P < 0.05). These results indicate that the larvae and juveniles of C. hongkongensis are tolerant to a wide range of salinities (15 to 30), but show better growth and survival at relatively low salinities. Thus, it is recommended to use relatively low salinities in hatchery and nursery systems for improved yields of C. hongkongensis.

Developmental stages and potential mariculture for coastal rehabilitation of endangered Pacific angelwing clam, Pholas orientalis

Sexually mature Pacific angelwing clams, Pholas orientalis, were collected from the wild and spawned and cultured under laboratory conditions to document early developmental stages and to develop culture techniques for coastal rehabilitation of this endangered species. There was a highly significant difference ( P < 0.01) found in induced spawning of P. orientalis using desiccation method compared with those that were not desiccated. Depending upon the size, spawners released between 1 and 2 million eggs. Wild spawners used in this study were functional simultaneous hermaphrodites that self-fertilized their own eggs (43.0 ± 0.8 μm diameter). First cellular division and motile morula occurred after 46 min and 3 h, respectively. Actively swimming early veliger and crawling pediveliger stages emerged after about 15 h and 22 h, respectively. Approximately 99.7% of straight-hinge larvae (58.3 ± 0.3 μm shell length) appeared after about 23 h. Fed with Isochrysis galbana, Chaetoceros calcitrans, and Nannochloropsis sp., the average survival rate at umbo stage (128 μm shell length; 115 μm shell width) after 10 days was 92% at 30.0 ± 1.0‰ salinity, pH 8.04–8.15 and temperature 23.5–29 °C. Survival rate of juveniles (1.046 mm shell length; 0.701 mm shell width) in muddy substrate after 30 days post-spawning was about 16%. This is the first time that P. orientalis has been successfully spawned in captivity and reared through early embryonic, larval, and juvenile stages. Postlarvae of P. orientalis were successfully introduced in the muddy cove of San Dionisio, Panay Island, Philippines (11°13′N, 123°04′E) and have produced successive generations that successfully colonized the area. Coastal rehabilitation and mariculture using hatchery-produced seedstock of this species show very encouraging results.

Survival, growth, settlement and metamorphosis of refrigerated larvae of the mussel Mytilus galloprovincialis Lamarck and their use in settlement and antifouling bioassays

Straight-hinge veliger and pediveliger larvae of the mussel Mytilus galloprovincialis were refrigerated for varying periods for use in bioassays. Straight-hinge veliger larvae grew to the umbo-veliger stage after 2 months in the refrigerator, but no pediveligers were observed during the 3-month refrigeration period. The average survival rate of larvae in the refrigerator was 79% after 1 month, but gradually decreased with the refrigeration period, and was as low as 22% after 3 months. All refrigerated larvae grew to the pediveliger stage in the incubator at 17°C at the same rate as that of the control larvae that were not refrigerated. Settlement and metamorphosis of pediveligers from both refrigerated and control groups were facilitated by microbial film and epinephrine and inhibited by phentolamine. Thus, refrigeration can be used as an effective method of storing larvae of M. galloprovincialis for use in assays to assess candidate settlement inducers and antifouling substances.

Salinity effect on the embryonic development, larval growth and survival at metamorphosis of Placuna placenta Linnaeus (1758)

The effects of salinity on the embryonic development, growth, and survival of D-larvae to plantigrade as well as settling in Placuna placenta were studied. Embryos were developed to D-larvae of shell length (SL) 86±12 μm (SL±S.D.) after 20 h at salinities of 22–34 ppt, but not at lower salinity levels. Percentage production of straight-hinged larvae from fertilized eggs at these salinities ranged from 51% to 63% ( P≥0.05). P. placenta larvae survived and settled in salinities of 16–34 ppt. Settlement occurred first (14 days) in salinities of 22–34 ppt and later (19 days) in 16 ppt when SL≥200 μm. Larval size at metamorphosis was not significantly different among these salinities ( P≥0.05). Percentage survival of plantigrades at 34 ppt (13%) was significantly higher ( P≤0.05) than at 16 ppt (4.5±3%), but not greater than at 22 (6.3±3%) or 28 ppt (7±4%) salinity. The best salinity levels for embryonic development and larval survival at metamorphosis ranged from 22 to 34 ppt and larval growth from 16 to 34 ppt. The tolerance of P. placenta to lower and higher salinities progressively increased as larvae develop from embryo to the plantigrade stage.

The effect of micro algal diet and rearing condition on gonad maturity, fecundity and embryonic development of the window-pane shell, Placunaplacenta Linnaeus

Immature Placuna placenta (Linnaeus) broodstock were given the micro algae Isochrysis galbana (T-ISO) Parke and Tetraselmis tetrahele (G.S. West) at different combinations and density levels and reared in tanks with or without mud substrate. The animals were also reared in the estuary and fed on available natural food. Monthly examination of gonad histology showed a significantly higher gonad index in broodstock reared in tanks with mud substrate than without ( P<0.05). In addition, those given a high-density algal diet (200,000 cells ml −1, 3:1 mixture of I. galbana and T. tetrahele) had a significantly faster gonad development than the low-density diet (100,000 cells ml −1, 1:1 mixture) fed broodstock reaching sexual maturity and gonad index of 330±14 after 1 month ( P<0.0001). P. placenta given the low-density algal diet attained gonad maturity after 3 months and estuary-reared animals after 2 months. Seawater irradiated by ultraviolet light (925–1395 mW h/l) induced spawning of all mature P. placenta. Estuary-reared animals had a higher fecundity and larger eggs and a higher percentage of fertilized eggs developed to straight-hinged larvae than those reared under other condition. Animals given a low-density algal diet released low number of small eggs which did not fertilize. Natural spawning also occurred in the estuary 2 months after stocking.

Larval rearing and spat production of Marcia opima (Gmelin)

The ‘baby clam’ Marcia opima (Gmelin) was spawned on seven occasions in the shellfish hatchery at the Tuticorin Research Centre, India. The fertilized eggs measured 47.8 μm in diameter and the straight hinged larvae attained at 20 h were 87 μm in length and 71 μm in height. Settlement occurred on day 9 at 273 μm. The percentage of settlement varied from 13.9% to 56.2%. The growth of post-set clam spat has been described by the equation of L=0.0086 x 1.4672, where L is the length in mm and x is the number of days. The clam seed reached a size of 11.5 mm at 4 months. The significance of this study is to standardize the techniques for hatchery production of the seeds of M. opima.

Transfection of eastern oyster ( Crassotrea virginica) embryos.

There is a need for research in disease resistance and microbial elimination in the eastern oyster Crassosostrea virginica. Gene transfer may lead to advances in this area, and a means of selecting transfected larvae would be useful. We transfected 3-hour-postfertilization embryos with the bacterial gene aminoglycoside phosphotransferase II (neo(r)), which confers resistance to neomycin and related antibiotics such as G418. The antibiotic G418 was examined as a potential selective agent. A neutral red assay was used to determine survival after 48 hours of exposure to various concentrations of G418 (0-4 mg/ml). We examined the effects of electroporation and chemically mediated transfection of 3-hour-postfertilization embryos on survival to straight-hinge larvae. DNA alone was found to have no effect on survival (P >.05). For electroporation we found that increased voltage and pulse duration decreased survival (P <.05). Chemically mediated transfection did not significantly affect survival (P =.5172). Transgenic larvae were identified after electroporation and chemically mediated transfection. These larvae were reared for 24 hours and exposed to G418 at 0.3 mg/ml for 48 hours. Significant differences in survival between transfected and nontransfected larvae were detected for electroporation (P =.0147) and chemically mediated transfection (P =.037). Gene transfer was also confirmed with polymerase chain reaction and observation of expression of green fluorescent protein. This study documents the first successful insertion and expression of foreign DNA in eastern oyster larvae.

Embryo-larval tolerance of Mytilus galloprovincialis, exposed to elevated seawater metal concentrations—II. Stage-specific fluctuations in sensitivity toward Zn and Cd and their bioaccumulation into veliger larvae

Acute intoxication of selected embryo-larval stages of M. galloprovincialis within successive 8-hr exposure intervals by elevated zinc and cadmium seawater concentrations, indicated stage- and metal-specific variations appearing in different proportions in normally developed straight-hinge veliger larvae. Zinc was found to be markedly more toxic than cadmium, particularly within the period of early cleavage and blastula stages. Embryos undergoing tissue differentiation and formation of the trochophora stage were substantially more sensitive regarding both metals tested in comparison with later veliger stages. Combined cadmium-zinc toxicity within each exposure interval tested appears to be less than additive, possibly associated with a markedly higher level of induced MT. The ability of developing embryos to concentrate seawater zinc (CF65Zn = 399) was approximately 2.5 times higher than for cadmium (CF109Cd = 160), which may also contribute to the observed difference in their tolerance levels

Carbon contribution through bacterivory in larvae of the Pacific oyster Crassostrea gigas

A bacterium (Strain CA2) that enhanced survival and growth of oyster Crassostrea gigas (Thunberg) larvae was used to determine the potential contribution of bacterial carbon towards the total carbon requirements of bivalve larvae. Expermental methods that reduced label recycling in 14C feeding trials permitted determination of larval retention efficiencies for bacterial and algal (Isochrysis galbana) carbon when these foods were provided to larvae at equivalent carbon concentrations. Straight-hinged oyster larvae (ca 100 pm mean shell length) fed CA2 bacteria at 1.5 X 10' cells ml-l could meet 147 % of their total metabolic carbon requirements with bacterial carbon retained in 'pulsechase' I4C feeding experiments. In addition, this bacterial carbon represented 48.5 % of the carbon retained by straight-hinged larvae fed on a similar biomass of algal carbon (I, galbana at 54 000 cells ml-l). The potential contribution of bacterial carbon towards the metabolic carbon requirements of oyster larvae decreased as larvae grew in size. Only 4 1 % of the total metabolic carbon requirements of a 283 pm larva could be met by the bacterial carbon retained after feeding on CA2 bacteria at 1.5 X 107 cells rnl-l.

Swimming rate and responses of larvae of three mactrid bivalves to salinity discontinuities

Straight-hinge, umbo and pediveliger larvae of the mactrid bivalves Spisula solidissima, Mulinia lateralis and Rangia cuneata were exposed to intense salinity discontinuities of 0, 5, 10 and 15 O/w in vertically oriented swimming chambers. Larvae concentrated in the region of highest gradient, i. e. at the salinity discontinuity, regardless of species, stage of development or larval brood. S. solidisima larvae, initially swimming at 30 O/w salinity, crossed discontinuities of both 5 and 10 %O but not of 15 %o. M. lateralis larvae, initially swimming at 25 %O salinity, also crossed a discontinuity of 5 %O but not of 10 or 15 %o. R. cuneata larvae, initially swimming at 10 %O salinity, generally preferred to remain at that salinity. Swimming and passive sinking velocities, defined as vertical distance traversed per unit time, were measured in different salinities under constant temperature and light. For all species, swimming rate changed with larval stage, highest velocity occurring at the umbo stage. Upward swimming rate of S. solidissima larvae ranged from 0.18 to 0.49 mm S-' and increased with increasing salinity. Upward swimming rate of M. lateralislarvae ranged from 0.25 to 0.50 mm S' , but was not consistently related to salinity. Upward swimming rate of R. cuneata larvae ranged from 0.18 to 0.53 mm S-'; swimming rate of pediveliger larvae increased consistently as salinity decreased. Downward swimming rates were similar to upward rates. No significant differences in downward swimming rate were detected in relation to salinity. Passive sinking was more frequent than active downward swimming in umbo and pediveliger larvae. Sinking rate increased with larval size of S. solidissima and M. lateralis larvae; however, R. cuneata straight-hinge larvae sank faster than umbo and pediveliger larvae. Species-specific differences in larval sinking and swimming are related to the different habitats occupied by adults. Larvae of S. solidissima, a marine stenohaline species, remained in high salinity water. Larvae of M. lateralis, a euryhaline species, use their preference for discontinuities or higher salinity water to assist retention in partially mixed estuaries. High sinking rate and short larval period of R, cuneata may offset the behavioural characteristic and aid in the retention of R. cuneata larvae in the low salinity zone of most partially mixed estuaries.

Effect of zinc on the growth and development of larvae of bay scallopArgopecten Irradians

The 48-h straight-hinge larvae ofArgopecten irradians were exposed for 9 days to various concentrations of zinc in seawater. The growth rate of larvae in the 50 ppb Zn mediums was 77% that of the controls, and nearly zero in the 200 ppb Zn mediums. A progressive decrease in growth and increase in larval deformity and mortality was observed with increasing zinc concentrations from 50 to 200 ppb. 50 and 100 ppb Zn resulted in delayed development of eye spot and metamorphosis and reduced numbers of larvae at both stages. All larvae subjected to higher zinc concentrations died before attaining the eye-spot stage. The zinc concentrations which caused 50% reduction in growth (G C50) and 50% mortality (LC50) were 109 and 120 ppb respectively. Growing in the medium with 100 ppb Zn, the larvae fed withIsochrysis galbana cultured in a medium with 100 ppb Zn showed more suppressed growth and development than those fed with normal food. It is suggested that zinc contaminated food has strong influence on the bay scallop larvae.

Lipid as an index of growth and viability in three species of bivalve larvae

The larvae of three species of bivalve molluscs, Crassostrea virginica (Gmelin), Ostrea edulis (L.) and Mercenaria mercenaria (L.) were cultured under a variety of temperature and food species regimes in the laboratory. Data were collected on growth, survival, total lipid content and lipid class composition of both healthy and starved larvae. Subsamples were stained specifically for lipid content with the lipid-specific stain Oil Red O. Newly formed straight hinge larvae of all three species exhibited small lipid droplets dispersed throughout the tissues. These were resorbed within 4 days of the initiation of feeding while the digestive gland filled with exogenously supplied lipid. Embryogenesis took place at the expense of 69 and 71% of parentally derived total lipid, 92.8 and 68.3% of which was composed of triacylglycerols ( M. mercenaria and C. virginica, respectively). After 8 days of feeding on Isochrysis aff. galbana (clone T-ISO), total lipid had increased 2.7-fold in larvae of C. virginica grown at 25°C, 37.6-fold in larvae of M. mercenaria grown at 22°C, and 1.7-fold in larvae of O. edulis grown at 25°C. Shell growth in larvae of C. virginica grown at 30°C was initially higher than that at 25°C, but lipid was accumulated 2.5 times slower and survival of pediveliger larvae through metamorphosis was considerably reduced at this elevated temperature. The lipid class composition of healthy larvae of C. virginica and M. mercenaria was dominated by triacylglycerols and phospholipids in approximately equal proportions; however, triacylglycerols were preferentially catabolized during starvation and were responsible for greater than 80% of the total lipid loss. Color photographs of larvae stained with Oil Red O are presented that illustrate lipid levels in developing larvae in both healthy and poor condition. From these, a visual index of lipid content was developed to allow comparisons between larval survival and lipid levels. In general, high survival was always accompanied by a high lipid index but a high lipid index did not guarantee good survival. We suggest that the lipid index may be used to document visually the lipid content in individual bivalve larvae as an indicator of physiological condition and potential for successful metamorphosis.

Physiological and biochemical energetics of larvae of Teredo navalis L. and Bankia gouldi (Bartsch) (Bivalvia : Teredinidae)

The biochemical composition of larvae of Teredo navalis L. and Bankia gouldi (Bartsch) (Bivalvia: Teredinidae) was examined throughout larval development at 23°C and 30–32%. salinity in the presence of the phytoplankton food Isochrysis aff. galbana (clone T-ISO), during a delay of metamorphosis in the presence of food but absence of a wood substratum and during periods of enforced starvation. Newly released Teredo navalis larvae had a mean length ( L) and height ( H) of 89.3 and 76.1 μm respectively. The first appearance of pediveliger larvae at 212.1 μm L and 230.0 μm H occurred 27 days after release. Larval dry weight increased from 0.29 μg to 1.96 μg during this period. Newly formed straight hinge larvae of Bankia gouldi had dimensions of 62.8 μm L and 49.8 μm H. Metamorphically competent B. gouldi larvae had dimensions of 230.0 μm L and 282.9 μm H and were first observed 20 days after fertilization. Larval dry weight increased from 0.06 μg to 2.20 μg during this period. During enforced delay of metamorphosis the ash-free dry weight of Teredo navalis larvae decreased whereas the ash free dry weight of Bankia gouldi larvae increased. During the early period of shelled larval development both species showed similar decreases in lipid, protein and carbohydrate levels (μg·mg dry weight −1); however, this was reflected in a decrease in biochemical content (μg·larva −1) only in Teredo navalis. During enforced starvation the major proportion of both the weight and caloric losses were due to protein. Lipid also contributes significantly to these losses whereas the contribution of carbohydrate was small. Larval oxygen consumption rates were determined directly by manometry and indirectly by estimates of decrease in caloric content during periods of enforced starvation. Direct and indirect determinations for T. navalis are described by the relationships R = 1.16 W 1.05 and R = 0.98 W 1.24 respectively where R is the respiration rate in nl O 2 · larva −1 · h −1 and W is dry weight inclusive of shell in μg. Direct and indirect determinations for Bankia gouldi are described by the relationships R = 1.37 W 1.25 and R = 1.81 W 1.25 respectively. When data for both assay procedures are combined for each species the relationships R = 1.10 W 1.07 and R = 1.44 W 1.18 are obtained for Teredo navalis and Bankia gouldi respectively.

Thermal tolerance by embryos and larvae of the surf clam Spisula solidissima

Thermal tolerance was tested in three developmental stages of the surf clam Spisula solidissima: cleavage stages, trochophore, and straight hinge larvae. Experiments were designed to simulate larval entrainment in the cooling system of a power plant. Eleven different temperatures were investigated from 20.2 to 43°C. Exposure times varied from 1 min to 6 hr and following each of the (88) different exposures, larvae were returned to the incubation temperature for a further period of development which facilitated differentiation of dead and live animals. Pooled mortality data from triplicate experiments (for each larval state) were subjected to a stepwise regression analysis (percentage mortality on temperature and time). Equations were derived from the regression program comprising first-, second-, and third-order terms for temperature and time, and these were used to generate response surfaces relating mortality to temperature-time exposure. As with earlier work on Mulinia, the term (temperature) 3 provides the best single predictor of larval mortality. Spisula is the only fully marine bivalve species so far subjected to this type of thermal tolerance test and is clearly the most temperature sensitive of all species investigated to date.

Oyster egg development as related to larval production in a commercial hatchery

The effect of the percentage of egg development on production is analyzed in relation to the corresponding larval growth and setting in the operation of a commercial oyster hatchery. During the production period, the percentage of eggs developing into straight-hinge larvae decreased each month. However, the larvae showed no negative effects in time of growth or setting. Larvae from eggs with only 20% straight-hinge development did as well as larvae from eggs with 100% development. The percentage of egg development to straight hinge is not an indication of the success of the larval population during growth or setting.

Thermal tolerance in embryos and larvae of the bay scallop Argopecten irradians under simulated power plant entrapment conditions

Thermal tolerance was tested in cleavage stages, trochophores and straight hinge larvae of the bay scallop Argopecten irradians. Experiments were des~gned to simulate larval entrainment in power plant coollng systems. An 11 (temperature) X 8 (time) matrix was used with temperatures ranging from 20.6 to 43.0 C and exposure times from 1 min to 6 h. Pooled mortality data from triplicate experiments for each larval stage were subjected to stepwise regression analysis (darcsine 90 mortality on temperature and time). Equations derived from these analyses, comprising first, second and third order terms for temperature and time, were used to generate response surfaces relating mortality to temperature and exposure time. In general, higher mortalities were associated with higher temperatures and with longer time exposure at any one temperature. However, there was some evidence of cold shock in trochophore and straight hinge larvae, with elevated mortalities occurring at temperatures lower than the spawning temperature. There was a trend towards increased thermal tolerance in older larvae, although in general A. irradians showed the greatest sensitivity to thermal shock of the estuarine bivalves so far tested in our laboratory.

Dwarf Males in the Teredinidae (Bivalvia, Pholadacea)

Extreme sexual dimorphism in the Bivalvia is rare. The occurrence of dwarf males in Zachsia appears to be the first case in the Teredinidae and the first outside the Leptonacea. Female Zachsia release straight-hinge larvae that develop in the plankton and settle on living rhizomes of Phyllospadix. Larvae entering mantle pouches of females become males. Evolution of this life history pattern is tied to problems of living in a fragile, patchy habitat-that is, the rhizomes of Phyllospadix.

A comparison of ozone and chlorine toxicity to three life stages of the American oyster Crassostrea virginica

The effects of ozone-produced oxidants (OPO) on three developmental stages of the American oyster, Crassostrea virginica, were evaluated. Both straight-hinge (48-h post fertilisation) and setting pediveliger larvae were exposed to a series of OPO concentrations ranging from 0·05 to 0·30 mg/litre OPO (as total residual chlorine) at 25°C for 96 h. Mortality was used as the response parameter and results were quantitatively compared with the effects of chlorine-produced oxidants (CPO) obtained from the literature on these same developmental stages. Adult oysters (2- to 4-year class) were exposed to OPO concentrations ranging from 0·01 to 0·50 mg/litre at 15°C for 5 days and to the same concentration range at 25°C for two consecutive 6-day periods. Shell deposition and faecal matter accumulation were used as the response parameters for this stage. Straight-hinge larvae were significantly more sensitive to OPO than setting pediveliger larvae. Both larval stages were significantly more sensitive to CPO than to OPO. Shell deposition was significantly inhibited at all OPO concentrations for both 15°C and 25°C acclimated adult oysters. No significant differences were found between the shell deposition response of oysters at the two acclimation temperatures. Faecal matter accumulation was significantly reduced at OPO concentrations ≥ 0·05 mg/ litre at both 15°C and 25°C. It was significantly (p < 0·05) greater for 25°C acclimated oysters than for 15°C acclimated oysters at OPO concentrations < 0·10 mg/ litre but not at higher concentrations.