Comparative studies of the growth,survival, and reproduction of diploid and triploid Kumamoto oyster,Crassostrea sikamea

Triploid oysters have been used for farming to improve growth but have not been created in the Kumamoto oyster, Crassostrea sikamea, which is one of the crucial aquaculture species on the southern coast of China. In the present study, triploids were created using cytochalasin B to inhibit polar body II release in C. sikamea, with the untreated oysters as controls. Triploidy rates of 87 and 57.67%, on average, were obtained in larvae and adults, respectively. Larval growth and survival of the triploid were significantly lower than that of the controls (p < 0.05). In contrast, the triploid postlarvae and adults had a significant growth advantage over the controls (p < 0.05) during the period of 180 (December) to 450 days (September of the next year). Moreover, the triploids clearly exhibited significant sterility in the reproductive season. The glycogen and triglyceride contents in the gonad, adductor muscle, mantle, and gill were higher in triploids than in controls from 180 to 450 days. As a result, high physiological energy supply was strongly correlated with superior growth and reduced reproduction in triploid C. sikamea. The triploid C. sikamea is an excellent oyster species and can be used to improve growth for C. sikamea farming.     

The effect of mesh covers on the survival and growth of Crassostrea gigas Thunberg grown on the sea bed

Growth and mortality were measured in samples of Crassostrea gigas planted in trays on the beach at 4.5, 7.5 and 20% exposure. The oysters were graded by live weight into < 1, 1 2, 3–4, 5 6 and 8–10-g groups at planting. Three levels of protection were provided: none, 36-mm and 12.5-mm mesh. Five separate trials of 41–108 days covered about a year.Mortality decreased with increasing size of oyster at planting and with increasing degree of cover. On average, oysters of < 1 g and without cover showed 50% survival over 30 days, while oysters of 3–4 g protected with a 12.5-mm mesh showed 97% survival. Neither seasonal variation in survival nor variation related to exposure was detected. Unprotected oysters grew to a smaller size than protected oysters and those at 20% exposure grew less than those at 7.5 or 4.5% exposure. It is probable that the two sizes of mesh provided protection against interference and predation by the shore crab Carcinus maenas.The combined results of the trials indicated that the standing stock at the end of about 6 months, which included the summer, obtained from laying 100, 0.6 g oysters at 4.5% exposure would be 564 g and 99 g with 12.5-mm mesh and no protection, respectively.     

Ultrafiltration for environment safety in shellfish production: Removal of oyster gametes in hatchery effluents

Triploid oysters are favoured by the aquaculture industry because of their sterility, which results in two advantages: a faster growth than natural oysters and a constant quality throughout all the year, which is attractive for consumers. In France, these oysters are mainly produced by mating natural and tetraploid oysters whose production poses a risk for marine environmental biodiversity if biological material is released into the environment. Therefore, effluents from farms which could produce those kinds of oysters must be treated. The objective of this work was to treat shellfish hatchery effluents by ultrafiltration. The retention of gametes by the membrane, was validated for different scenario, 5 log removals were obtained, and their viability was evaluated after treatment highlighting a destruction of these species after air-backwash. The sustainability of the process facing this organic pollution on the duration of each test but also on the period of the study was demonstrated. A protection of the marine environment biodiversity is obtained with ultrafiltration processes.     

微卫星标记在长牡蛎三倍体鉴定中的应用

为开发一种简单有效的倍性检测方法对长牡蛎三倍体诱导结果进行准确评估,本实验采用细胞松弛素B抑制第二极体释放诱导产生长牡蛎三倍体,选用7个微卫星位点扩增基因组DNA,通过亲子代基因分型进行倍性检测,检测结果采用流式细胞仪加以验证,以评估微卫星标记倍性检测的准确性。另外,本研究探讨了准确鉴定倍性所需的微卫星标记数量与微卫星—着丝粒重组率(y)之间的关系,以期为其他物种采用分子标记进行倍性检测提供理论依据。结果显示,细胞松弛素B诱导产生的115个长牡蛎子代经7个微卫星位点鉴定得到40个三倍体,与流式细胞仪检测结果一致,准确率达到100%,7个微卫星位点的(1-y)的乘积为0.005。随机挑选6个位点,也可鉴定出所有三倍体,(1-y)的乘积为0.005~0.042。研究表明,本研究中开发的微卫星标记可以简单高效地鉴定长牡蛎三倍体,微卫星位点的(1-y)的乘积小于0.005,倍性检测的准确率可达100%,采用微卫星标记进行倍性检测对于加速长牡蛎三倍体育种进程具有十分重要的意义。     

Assessment of homozygosity and fertility in meiotic gynogens of the European sea bass (Dicentrarchus labrax L.)

Analysis of 5–6 microsatellite loci was used to measure the increment of homozygosity in two meiogynogenetic progenies (A and B) of sea bass with respect to their mother. In progeny A and B, 20% and 12% of the meiogynogens retained heterozygosity for all investigated maternal loci, respectively, while complete homozygosity was observed only in 6% of B and in none of A, indicating the occurrence of significant allelic recombination during meiosis. The overall increment of homozygosity for the investigated loci was 27% for A and 47% for B. Although survival at hatching of meiogynogens was about half that of controls, they subsequently grew as controls and displayed the same onset of puberty and reproductive potential at adulthood during three consecutive years when crossed between themselves (11 crosses) or with control fish (13 crosses). In particular, meiogynogenetic females (n=24) underwent vitellogenesis and yielded eggs of good quality upon stimulation with LH–RH analogue similarly to normal fish. Sperm released by meiogynogenetic males (n=23) was equivalent to that of controls in terms of volume, quality and fertilization capability.Second generation meiogynogens were obtained by chromosome set manipulation from meiogynogenetic females and found to be morphologically normal at 3 years of age. Interestingly, under our culture conditions, the percentage of meiogynogenetic males in the second generation was 7% as opposed to 39% in the first generation.     

The mass outdoor culture of macroscopic marine algae

Two species of macroscopic marine algae (Rhodophyceae) were grown and harvested continuously during 1974 in Fort Pierce, Florida. The seaweeds Gracilaria sp. and Hypnea musciformis were grown in both 600-l and 350-l tanks in the third stage of a nutrient removalaquaculture process that included microscopic marine algae and oysters in the first two stages. Mixtures of secondary-treated waste water and sea water constituted the initial nutrient source, with the seaweeds utilizing nutrients not assimilated by the microscopic algae and/or generated by the oysters. Standing crops of up to 7 900 g wet weight of Hypnea and 9 000 g Gracilaria were maintained. The Hypnea cultures could not be maintained in summer when tank temperatures reached 30°C, but Gracilaria grew during the entire year. On the basis of periodic harvesting, yields were consistently between 12 and 17 g dry weight per m² per day for both species. These yields are as high as those achieved by mass cultures of microscopic marine algae, or by fast growing commercial crops such as sugar and rice.     

Effects of the winter Monsoon on the growth,mortality, and metabolism of adult oysters in Kinmen Island,Taiwan

The Pacific oyster, Crassostrea gigas, is cultivated intertidally in Kinmen Island by both a traditional way of growing oysters on the surface of stone blocks, nicknamed “rock oysters”, and a recently introduced and more efficient way of hanging them in clusters on horizontal nylon lines, i.e. “hanging oysters”. We investigated the growth and mortality of both types of oysters from late July to early December 2003, and measured condition index (CI) and rates of oxygen consumption and ammonium excretion for the hanging oyster. Growth of oyster shells stopped in early October for the hanging oysters and early December for the rock oysters. Mortality rates were higher for hanging oysters than rock oysters. Hanging oyster's O/N ratio and CI, determined by a home-made CI meter that measured the volume of oyster's inner shell cavity with high precision, decreased significantly in October. Hanging oysters were apparently in poor physiological condition during the winter Monsoon, which is characterized by cold and persistently strong wind. On Kinmen Island the monsoon season begins in late September and is accompanied by declining seawater temperature and high seston loads in oyster farms. Chlorophyll a concentrations and seston food quality decreased significantly in early October after the winter Monsoon began. The hanging oyster's poor acclimation to the local climate was probably caused by the import of its spat from southwest coast of Taiwan where it is warmer than Kinmen Island in fall and winter. We recommend that oyster growers collect spat locally or from areas of similar climate.     

Tetraploid induction by meiosis inhibition in the dwarf surfclam Mulinia lateralis (Say 1822): effects of cytochalasin B duration

Different durations of a cytochalasin B (CB) treatment were tested for tetraploid induction by meiosis inhibition in the dwarf surfclam Mulinia lateralis Say. Cytochalasin B, 0.67 mg L^?1, was applied to newly fertilized eggs at 8–10‐min post fertilization and removed when in the untreated eggs: (1) Polar body 1 (PB1) was released in 90% of the eggs and polar body 2 (PB2) began to form (T1); (2) Polar body 2 was released in about 25–30% of the eggs (T2); (3) Polar body 2 was released in about 70–75% of the eggs (T3); or (4) eggs began to enter mitosis I or the polar lobe began to form (T4). Three replicates were produced using different sets of parents. The ploidy of resultant larvae and juveniles was determined by flow cytometry. Blocking PB1 alone in T1 groups produced mostly tetraploids, and longer CB treatments in T2 and T3 resulted in increasing numbers of pentaploids. In T4 groups where both PB1 and PB2 were inhibited, larvae were predominantly pentaploids. Pentaploid larvae were arrested at the trochophore stage. The majority of tetraploid larvae died as trochophores, although a small fraction reached D‐stage. Among 478 juvenile clams sampled from a T1 group, three (0.6%) were confirmed as tetraploids. This study shows that tetraploid embryos can be produced at high efficiencies (40–90%) by blocking meiosis I. Tetraploids produced by meiosis inhibition in normal eggs are viable in M. lateralis, but their survival beyond metamorphosis is extremely low.     

Growth and mortality of sibling triploid and diploid Sydney rock oysters, Saccostrea glomerata (Gould), in the Camden Haven River

Growth and mortality of sibling triploid and diploid Sydney rock oysters, grown at two tidal heights, three stocking densities and three different sites on the Camden Haven River estuary, were compared. Triploids grew faster than diploids. The majority of the growth rate difference occurred after the oysters reached 2 years of age. By 3.2 years, triploids were 49% heavier than diploids. Oysters grown intertidally were larger than those grown subtidally. Oysters stocked at the lightest density of 2 L per basket grew to a significantly larger size than baskets stocked at 3 or 4 L. Growth rates were significantly different at the three sites. Growth was reduced the further the oysters were from the mouth of the estuary. There was no significant difference in mortality between ploidy level, but there were differences between tidal heights, stocking densities and sites. Intertidal oysters suffered higher mortality than subtidal. Oysters stocked at the highest density had a significantly higher mortality than the lowest density; neither of these was significantly different from the medium density. The site closest to the mouth of the estuary had significantly lower mortality than the middle and upper estuary sites.     

Tetraploid induction in tropical oysters,Crassostrea belcheri (Sowerby) and Crassostrea iredalei (Faustino)

Tetraploid induction has been conducted on temperate oysters but not on tropical oysters. In this study, different heat shocks (32, 35 and 38°C) and cold shocks (1, 4 and 7°C) were used to induce tetraploidy in two tropical oyster species, Crassostrea belcheri and Crassostrea iredalei, through meiosis I inhibition. Temperature shocks were applied on the newly fertilized eggs at 8–10 min post fertilization and terminated when second polar bodies began to form in the control eggs. The ploidy of the larvae and spat was determined via direct chromosome count. The percentage of larval survival until Day 20 was low (between 0.4% and 42.9%) for both temperature shocks and oyster species. No surviving larva was recorded for induction at 1, 4 and 38°C. Tetraploid spat was only recorded in C. iredalei but the percentage is low through heat shock induction of 32 and 35°C. This study shows that the tetraploid induction success rate was slightly higher in C. iredalei compared to C. belcheri. No surviving tetraploid spat were recorded for both oyster species through the cold shock method. This study shows that heat shock can be used to inhibit meiosis for the production of tetraploids but more experiments need to be conducted to determine the optimum temperature when dealing with tropical oysters.     

Assignment of parentage in triploid species using microsatellite markers with null alleles,an example from Pacific oysters (Crassostrea gigas)

Triploid production in aquaculture is increasing because of their more profitable growth and reproduction traits. Triploids are mostly produced through mass spawning techniques, meaning that exact pedigree is unknown. The ability to trace the pedigree of high performing triploids would allow selection of broodstock to perpetuate triploids of greater economic value. This study aimed to develop a method of determining parental assignment in triploids and test its accuracy on triploid oysters. Using a likelihood approach and accounting for null allele frequencies, a method was developed which proved to be efficient at determining the pedigree of triploid oysters. This method was able to provide accurate pedigree on simulated data and two commercial cohorts of triploid oysters. The analysis of the triploid cohorts showed that mass spawning to produce triploid oysters, like that for diploid and tetraploids, results in a strong bias in parental contributions, with the effective population size being 34‐49% lower than the census population. This highlights the need for pedigree control in breeding programs and indicates that the ability to determine parentage of triploids will be a valuable tool for breeding programs.     

Maximum ration of four algal diets for the oyster Crassostrea virginica Gmelin

The rate of removal of four species of alga from suspension by the oyster Crassostrea virginica was determined. The number of cells removed per hour depended upon the size of algal cells, but the total dry weight of algal material removed over 24 h was independent of size. Filtration rate was dependent upon the density of the algal suspension, and large quantities of pseudofeces were produced by oysters filtering algae from suspensions denser than 10 μg/ml.Oysters showed periods of high filtering activity and periods of relative quiescence during experimental trials of 24 h duration. Based on the periodic filtering activity of the oysters, a discontinuous feeding regime is proposed along with an equation predicting the maximum daily ration of oysters of various sizes.     

The effect of different grading equipment on stress levels assessed by catecholamine measurements in Pacific oysters,Crassostrea gigas (Thunberg)

In this study the effects of exposure to two air temperatures (15 and 27.5 °C) and three graders commonly used in South Australia (Rotary, Flat Bed and Inside/Out) on Pacific oysters were investigated using post-exposure or post-grading catecholamine levels as a stress indicator. During the 48 h experimental period the circulating dopamine and noradrenaline levels of oysters exposed to 15 °C air temperature did not differ significantly from controls sampled directly from the 15 °C water tank. Conversely, in oysters exposed to 27.5 °C air temperature, dopamine and noradrenaline became significantly different from controls after 8 and 12 h air exposure, respectively, and then returned to the control levels at 24 h.Significant increases (P < 0.05) in circulating noradrenaline and dopamine levels were observed in oysters graded by the Flat Bed and the Inside/Out graders. The circulating noradrenaline concentrations in oysters subjected to the Flat Bed grader were significantly higher (P < 0.05) than those observed in the Rotary graded oysters and close to being significantly higher (P = 0.052) than those levels measured in the Inside/Out graded oysters. The circulating noradrenaline levels in oysters subjected to the Inside/Out grader were, in turn, significantly higher than those recorded in the Rotary graded oysters. These results suggest that in relation to the three graders used in South Australia, the Flat Bed induces the highest stress levels in oysters and the Rotary grader the lowest.     

Seasonal variations in the immunological and physiological parameters of the Pacific oyster Crassostrea gigas cultured in Bahía de Macapule (Sinaloa,Mexico)

Triploid Crassostrea gigas were cultured during 13 months in Nestier‐type oyster trays. The impact of environmental parameters on the physiological and immunological parameters was evaluated. Temperature, salinity and seston were recorded monthly. Seventeen oysters were sampled monthly for immunological and condition index (CI) analyses. Samples were obtained as a haemolymph lysate supernatant (HLS). Protein content was determined using the Bradford method. The activity of hydrolytic enzymes was determined using the API ZYM kit and the lysoplate assay. Seston showed different patterns throughout the cycle. Condition index showed a positive correlation with the protein content of HLS. Protein showed a negative correlation with temperature. Eleven hydrolytic enzymes were detected in samples and higher enzymatic activity corresponded to leucine arylamidase and esterase. Leucine arylamidase and lysozyme activity showed a positive correlation with temperature. Oyster mortality was 28% in our modules and 70% in the oyster farm. Oysters showed low values of CI and haemolymph protein content in summer–autumn when mortalities were observed in the culture system. This finding suggests that these stressed oysters may have insufficient energy to invest in their immune system. It appears that oyster mortality in the culture system resulted from a combination of animal overcrowding, high temperature and low salinity.     

Accumulation of copper and nickel from anti-fouling compounds during cultivation of scallops (Pecten maximus L.) and Pacific oysters (Crassostrea gigas Thun.)

Scallops [Pecten maximus (L.)] and Pacific oysters [Crassostrea gigas (Thunberg)] have been grown for 31 weeks in nets treated with a copper oxide-based anti-fouling paint, and on trays constructed from copper-nickel (90:10) alloy mesh. Copper was accumulated by both species in the net enclosure during the initial 6 weeks of cultivation, and over the subsequent 25 weeks copper was gradually lost from the scallops, but retained by the oysters. Both species accumulated high concentrations of copper from the alloy trays (up to 280 mg/kg in scallop digestive gland, and 790 mg/kg in whole oysters). Transfer of the shellfish to untreated enclosures at week 31 resulted in a further loss of copper from scallops, but the oysters maintained their copper levels for the following 10 weeks. No significant accumulation of nickel occurred in either species.     

Studies on triploid oysters in Australia: effect of initial size on growth of diploid and triploid Sydney rock oysters, Saccostrea commercialis (Iredale & Roughley)

In a 2-year grow-out trial, triploid Sydney rock oysters, Saccostrea commercialis (Iredale & Roughley), from two initial size grades grew faster (in terms of both mean whole weight and shell height) than the equivalent initial size grades of sibling diploids (P < 0.05). Small size grade triploids caught up with and had significantly heavier (P < 0.05) final whole weights than large size grade diploids after a 2-years grow-out period. The initial size grade had a significant effect on final mean whole weight and shell height for both ploidy types. After the 2-years grow-out trial, the final mean whole weights (but not shell heights) of small and large diploids (35.8 ± 0.6 g and 39.4 ± 0.5 g, respectively) were significantly different (P < 0.05). Small and large triploids grew at a similar rate for the first 18 months despite the significantly (P < 0.05) heavier final mean weight of large grade triploids (48.4 ± 0.8 g and 61.2 ± 0.7 g, respectively). The effect of the initial size grade on subsequent growth of both diploid and triploid oysters which was demonstrated in the present study is of significant commercial value to hatchery and nursery operators as well as growers of single seed oysters. In addition, small-grade triploids appeared to be more valuable in terms of potential growth rate than all diploid grades. There was no significant difference in the final percentage triploidy between small and large grade triploids. A large proportion of diploid/triploid mosaicism was detected in adult oysters.     

Experimental deepwater culture of the Sydney rock oyster (Crassostrea commercialis): III. Raft cultivation of trayed oysters

Sydney rock oysters, normally intertidal, were submerged below rafts in vertical stacks of 15 oyster trays extending 2 m deep. Growth rates and mortality were not good or economically encouraging. The best growth was from small culled spat (43 whole oysters/kg) to large seconds (28/kg), an increase of 59% in 9 months. The minimum mortality was 52%. Fouling growths of barnacles, tunicates, sponges and hydroids were restricted by placing experimental trays on top of the raft for several days to dry out. Compared with controls, this resulted in increased oyster growth in experimental trays during the next 6 months. Oyster mortality and incidence of mudworm blisters (resulting from the polychaete Polydora websteri) were similar in both control and experimental trays during this period. For improved growth of trayed submerged oysters the optimum vertical distance between trays and the optimum density of oysters on trays need to be determined.     

The growth and survival of experimental batches of hatchery-reared spat of Ostrea edulis L. and Crassostrea gigas thunberg,using different methods of tray cultivation

The seasonal growth and survival of experimental batches of hatchery-reared spat of the European oyster (Ostrea edulis) and the Pacific oyster (Crassostrea gigas) was followed in North Wales during the period 1972 to 1975. Three methods of tray cultivation were compared. These were: (a) trays suspended from a raft in the Menai Straits, (b) trays supported on trestles on the foreshore of the Menai Straits, and (c) trays in a laboratory nursery system which were supplied with sea water from Conwy estuary via a pumped storage system.Growth of oysters in the nursery system was consistently inferior to that of oysters kept at either site in the sea. Although in several years there were significant differences between the growth of oysters on the raft and in trays supported by trestles, on average neither site consistently produced larger oysters.Survival was significantly better in the nursery system for both species of oyster, but no consistent differences in survival were observed between either site in the sea.Seasonal growth of both species of oyster as well as the mortality of O. edulis were positively related to temperature. It was concluded on the basis of cost that (i) cultivation in systems employing pumped sea water would not be viable in the long term, and (ii) raft cultivation would only be suitable for post-hatchery sized oysters up to about 5 g live weight.     

Effects of copper- and tin-based anti-fouling compounds on the growth of scallops (Pecten maximus) and oysters (Crassostrea gigas)

Fouling is an important problem in shellfish cultivation. This paper gives the results of growth trials of adult and juvenile scallops, and adult Pacific oysters in enclosures treated with various anti-fouling compounds: copper(I) oxide-based paint, bis-(tri-n-butyltin) oxide (TBT)-based paint, and copper-nickel alloy mesh trays.With the copper oxide treatment there was some increase in the growth of scallop spat, but no effect was observed on the growth of adult scallops or Pacific oysters. The copper-nickel trays, however, caused high mortalities and inhibited growth in adult scallops, but had no effect on oysters. The TBT paint was detrimental to the growth and survival of juvenile scallops, and caused high mortalities, poor growth and thickened shells in oysters. It had no effect on adult scallops.     

Studies on triploid oysters in Australia: farming potential of all-triploid Pacific oysters, Crassostrea gigas (Thunberg), in Port Stephens, New South Wales, Australia

Triploid Pacific oysters Crassostrea gigas farmed in Port Stephens, NSW had an exceptionally fast growth rate and reached a whole weight of 55 g in 13 months versus 20 months for diploids. Mortality of the triploids (24.5±2.94%) was significantly lower (P<0.05) than that of the diploids (40.0±2.26%) over the duration of the experiment (July 2002–February 2004). Unfortunately, this advantage was offset by discoloration of the meats of the triploids when they were in better condition than the diploids over summer (October 2003–March 2004). However, discoloration of meat of triploids had cleared up by April 2004 and neither did they suffer this problem from April–September 2003. The triploids also had a lower peak condition than the diploids. Oysters in peak meat condition, i.e. spawning condition, are preferred for the half shell trade in Australia and in this study, there was at least a six‐month period prior to discoloration, when the triploids were large enough and had sufficient meat condition for marketing on the half shell.