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.     

Farming triploid oysters

Although the commercial benefits of triploidy have been evaluated in the Pacific oyster Crassostrea gigas (Thunberg, 1793), eastern oyster C. virginica (Gmelin, 1791), Sydney rock oyster Saccostrea glomerata (Gould, 1850) and European flat oyster Ostrea edulis (Linnaeus, 1750), so far this technique has only been commercialised for Pacific oysters.

Commercial production of triploids on the West Coast of North America began in 1985. Since then production of triploids has greatly increased and the use of tetraploid males to fertilise eggs from diploids to produce batches of 100% triploids has been developed. In 1999/2000, triploid Pacific oysters made up 30% of all Pacific oysters farmed on the West Coast of North America. Some hatcheries now use tetraploid males instead of chemical or physical stress to produce triploids. The rapid uptake of triploid and tetraploidy techniques has been facilitated by the almost total dependence that these oyster industries have on hatcheries for the supply of seed. This industry in the Pacific Northwest of the US and in British Columbia, Canada, would not have developed to its current size without hatchery seed supplies. Triploids are preferred over diploids in summer because diploids are less marketable when in spawning condition.

There was only limited interest in triploidy production in France until 1999, when IFREMER began to make sperm from tetraploids available to commercial hatcheries. In 1999/2000, only 10% to 20% of all the hatchery-supplied Pacific oyster spat were triploids, but with the use of sperm from tetraploid oysters, this could increase sharply.

Elsewhere around the world, the commercial uptake of triploid oysters has been slow to develop. However, in countries where the production of Pacific oysters is based on hatchery supply of seed, it is likely that with the use of tetraploid oysters, the farming of triploid oysters will increase in the near future.     

Parasites, pathological conditions and mortality in QX-resistant and wild-caught Sydney rock oysters, Saccostrea glomerata

Differences in the survival of QX-resistant fifth generation (QXR₅) and wild-caught (Wild-Caught) Sydney rock oysters were assessed over the QX-disease risk period in the Pimpama River, SE Queensland. Cumulative mortality of Wild-Caught oysters (31.7%) was significantly greater than QXR₅ oysters (0.0%) over the 118 days of the experiment. PCR and histological results showed that Wild-Caught oyster did not die from QX disease. Histology revealed oysters were infected with disseminating hemocytic neoplasia, a Steinhausia-like infection, a Rickettsia-like organism infecting epithelial cells of the gill, digenean flukes encysted in the gonadal tissue and a gill response to an unknown toxin. The cause of mortality is attributed to disseminating hemocytic neoplasia.     

Evaluation of cytochalasin B (CB) treatments for triploidy induction in the blacklip abalone, Haliotis rubra (Leach, 1814)

The effectiveness of cytochalasin B (CB) treatments for inducing triploidy was evaluated in the blacklip abalone Haliotis rubra (Leach, 1814) in two orthogonal design experiments. The first experiment employed three dosages (DSs) of 0.25, 0.5 and 1.0 mg CB L^?1, three starting times (STs) of 5, 15 and25 min post fertilization and three treatment durations (TDs) of 10, 20 and 40 min, for a total of 27 treatments. The second experiment comprised of two DSs of 0.25 and 0.5 mg CB L^?1, five STs of 5, 15, 20, 25and 30 min post fertilization, and three TDs of 10, 20 and 40 min, for a total of 30 treatments. Water temperature was held at 17.5–18.5°C. Day 3 larvae were sampled for triploidy using flow cytometry (FCM) and survival. Optimal inductions were treatments starting at 15 or 20 min post fertilization and continuing for 40 min, and those initiated 25 or 30 min post fertilization for 20 or 40 min, using 0.5 mg CB L^?1. These treatments were all targeted at inhibition of the second polar body (PB2) formation and yielded triploidy rates of 84.8–89.5% coupled with (relative) survival rates of 20.1–52.1% in the first experiment, and corresponding rates of 86.5–96.5% and 33.0–74.1%, respectively, in the second experiment. A common and essential feature of these optimal conditions is that treatment must fully span the period of time for most of the eggs to extrude PB2. Treatments that resulted in suppression of the first polar body (PB1) formation induced triploidy levels below 71.5% and 57.6% in experiments 1 and 2 respectively. Treatments that had overlapping effects on both PB1 and PB2 extrusion led to triploidy rates above 80% but very low survival rates of 1.8% and 5.4% in experiments 1 and 2 respectively.     

Experimental feeding of Sydney rock oysters (Saccostrea commercialis). III. Food concentration and fattening procedures

Sydney rock oysters (Saccostrea commercialis) were fed an artificial diet at 0, 3, 6, 9, 12 and 15 mg dry food/l. At 9 mg/l oyster glycogen content, condition indices and meat weight gains were maximised without increasing mortality rates. In a comparison of fattening procedures, oysters held in a fertilised pond and those fed a second artificial diet fattened in 4 and 6 weeks respectively, whereas those held in an estuary did not fatten at all. The artificial diet produced higher oyster meat glycogen contents than the fertilised pond and estuary treatments.     

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.     

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.     

Sex-specific growth and condition of the Pacific oyster (Crassostrea gigas Thunberg)

In order to study the possibility of gaining commercial benefit from culturing an excess of one sex of the Pacific oyster (Crassostrea gigas), comparative data on the growth rate and condition of male and female oysters are reported. Historically, measurement of sex‐specific growth rate in oysters has been overlooked or confounded by protandric sex. The recent conclusion that the sex ratio of Pacific oysters is predominantly under genetic rather than environmental control introduces the possibility of manipulating sex ratio for commercial gain if they exhibit asynchronous sex‐specific growth rates. Pacific oysters were cultured intertidally in Smoky Bay, south Australia. The observations, made over the 7‐month gametogenic cycle from August to February to ensure no sex reversal, were of growth rates of male and female oysters and ambient chlorophyll a concentrations. Mean shell growth of female oysters was significantly faster than that of males (4.5 ± 3.3 compared with 3.8 ± 3.2 μm day^?1 mm^?1 total length). Sex‐specific asymmetries in length and weight were generally significant and increased in magnitude during the 7‐month study period, suggesting potential commercial benefits from increasing the proportion of cultured female oysters. The fastest increase in the sex‐specific disparity in growth and condition came after the October chlorophyll a peak, suggesting that females utilize blooms more efficiently than males. Our results compare favourably with methods currently used to increase oyster growth (e.g. triploidy can provide growth gains of 13–51%).     

Triploidy induction in Australian greenlip abalone Haliotis laevigata (Donovan) with cytochalasin B

Triploid induction in Australian greenlip abalone, Haliotis laevigata (Donovan), was conducted by blocking the formation of the second polar body using cytochalasin B (CB). Twenty minutes after fertilization, the zygotes of greenlip abalone were treated with four CB concentrations (0, 0.25, 0.5 and 0.75 mg L⁻¹) for 10, 15 and 20 min. The ploidy of resultant larvae was determined using flow cytometry at 72-h post fertilization. Our study showed that fertilization, hatching, survival and induced triploidy of abalone larvae were significantly affected by the CB concentration and treatment duration. The effective range of CB concentration for triploid induction on greenlip abalone was 0.5–0.75 mg L⁻¹ with an induction duration of 10–15 min. The results indicate that the most effective treatment combination for triploid induction in greenlip abalone is 0.5 mg CB L⁻¹ for 15 min starting at 20-min post fertilization.     

Mortality in single‐pair mating families of QX disease‐resistant and wild‐type Sydney rock oysters (Saccostrea glomerata)

QX disease causes mass mortalities among Sydney rock oysters (Saccostrea glomerata). To overcome commercial production losses, Industry & Investment NSW has been developing mass selected QX disease‐resistant breeding lines since 1997. This breeding programme has significantly reduced QX‐associated mortality in the Lime Kiln Bar (LKB) breeding line relative to non‐selected, wild‐type (WT) oysters. The current study assessed mortality in families produced by single‐pair mating between LKB and WT oysters. When these families were grown in a QX disease‐prone area, the progeny of LKB × LKB crosses had significantly lower mortality compared with LKB × WT or WT × WT families. Mortality in the different crosses was associated with infection by sporulating Marteilia sydneyi, the parasite responsible for QX disease. Overall, the study identified a strong association between parentage and mortality resulting from QX disease.     

Triploid Induction of Green Tiger Shrimp,Penaeus semisulcatus (De Haan, 1844) Using Temperature and Chemical Shock

Triploidy in fertilized eggs of Penaeus semisulcatus was induced by temperature and chemical shocks. The eggs, which were obtained from the shrimp broodstock maintained at 29 C, were exposed to cold temperature (8, 10, 12, and 14 C) and 6‐dimetiloaminopurine (6‐DMAP) concentrations (100, 150, 200, and 250 μM) for different durations (4, 6, and 8 min) 9 min after spawning was detected. While the highest triploidy rate of 49.7 ± 4.5% was obtained with a 200 μM 6‐DMAP concentration for a duration of 8 min, the best mean triploidy rate of 45.5 ± 2.8% for cold shock was obtained at a temperature of 10 C for a duration of 8 min. Temperature and 6‐DMAP concentration did not have significant effect on triploidy rate (P > 0.05) but shock duration had significant effect on triploidy rate for individual cold temperature shock or 6‐DMAP chemical shock (P < 0.05). Although longer durations of shock agent increased the rates of triploid induction, they generally had an adverse effect on hatching rates in the study.     

Resistance of Dermo in eastern oysters, Crassostrea virginica (Gmelin), of North Carolina but not Chesapeake Bay Heritage

Growth, intensity of Perkinsus marinus (Levine) infection, and survival of synchronously spawned North Carolina (NC) and Chesapeake Bay‐heritage (CB) oysters, Crassostrea virginica (Gmelin) were evaluated under standard tray culture conditions at several sites in both regions (Wye River, Maryland; Mobjack Bay, Virginia; Pamlico River, NC and Bogue Banks, NC). Infection prevalence reached 100% in oysters held at all high‐ and moderate‐salinity sites, at which time the CB strain ceased to grow. Shortly after growth ceased, CB oysters exhibited mortality that rapidly progressed to 100%. Unlike the CB strain, growth continued in the NC strain despite high P. marinus prevalence. When mortality did occur in the NC strain, at a reduced rate of 37–40%, it was associated with higher intensity of P. marinus than the infection intensity correlated with death of CB oysters. At the low‐salinity site in NC, P. marinus infection persisted at low weighted prevalence throughout the latter portion of the culture period but was not associated with mortality of either strain. These trends in growth and disease resistance for the two strains demonstrate that aquaculture performance is related to the level of disease resistance in oyster strains, salinity of water in growing areas and virulence of P. marinus.     

The effects of dietary supplements of polyunsaturated fatty acid on pearl oyster,Pinctada margaritifera L., gonad composition and reproductive output

Black‐lip pearl oyster, Pinctada margaritifera broodstock was collected from the wild. Egg production, hatching rate and larval development were compared between oysters induced to spawn within 2 days after collection in the wild (T1), oysters fed a pure microalgae diet during 24 days before spawning (T2) and oysters fed the same microalgal diet in which 10% of the algae were replaced with 2 μm polyunsaturated fatty acid (PUFA)‐rich microspheres (T3). Administration of lipid microspheres resulted in larger sized eggs, a higher percentage of D‐larvae and larger sized 48‐h‐old larvae (P<0.05). The total and neutral lipid contents of the gonad increased after oysters were fed with microalgae only or with supplementary diet. The major neutral and polar fractions of saturated fatty acid (SFA) were 16C and 18C fatty acids, and not influenced by the diet (P>0.05). The gonads of oysters fed supplementary PUFA contained more docosahexaenoic acid (DHA) and less monounsaturated fatty acids. Higher level of DHA in gonads of T3 was associated with oogenesis and embryogenesis success. The n‐3/n‐6 ratio in the neutral lipid fraction provides a good indication of the spawning condition and predicting egg size and hatching rate.     

Artificial spawning of carp (Cyprinus carpio L.); differences between the effects of reproduction in females of Hungarian, Polish and French origin treated with carp pituitary homogenate or [D-Tle6, ProNHEt9] GnRH (Lecirelin)

The investigation concerned the reproduction effects in carp females of the Hungarian strain 8, Polish strain 2 and French strain F of ovulation stimulation with carp pituitary homogenate (0.3 mg kg^?1 and after 12 h 2.7 mg kg^?1) or [D‐Tle⁶, ProNHEt⁹]GnRH (Lecirelin) with metoclopramide (15 μg kg^?1 and 10 mg kg^?1 respectively). The ovulation stimulators did not affect the weight of eggs (expressed in g and as the percentage of female body weight). However, in the group treated with pituitary homogenate (I) the least‐square means estimated for these parameters were higher than in the group treated with Lecirelin (II). A statistically significant (P≤0.05) difference in the mean percentage of living embryos after 48‐h incubation was observed between groups I and II, with the eggs obtained from females of group I being of better quality. The origin of females significantly (P≤0.05) affected the weight of eggs. The weight of eggs from females of Hungarian strain 8 was higher (P≤0.05) than the weight of eggs of the other two lines. With respect to parameters for egg quality (percentage of fertilized eggs and percentage of living embryos after 24‐, 36‐ and 48‐h incubation), no effect of the origin of females was observed. The interaction between the spawning agent and the origin of the females was not statistically significant with respect to the two parameters for the weight of the eggs. The least‐square means test for the investigated interaction showed that after the application of pituitary homogenate, the weight of eggs obtained from strains 8 and F was similar (respectively 711.2 g and 665.0 g). However, after the application of Lecirelin the females of strain 8 yielded eggs of a high weight (934.3 g) and those of strain F of a very low weight (373.2 g). A statistically significant (P≤0.05) interaction between ovulation stimulator and origin of females was recorded for the percentage of living embryos after 24‐ and 36‐h incubation. A dependence was found between the latency time and the reproduction effects.     

Artificial spawning of female Lithuanian strain B carp (Cyprinus carpio L.) after treatment with carp pituitary homogenate, Ovopel or [d-Tle6, ProNHEt9] GnRH-a (Lecirelin)

The results of reproduction of females from Lithuanian strain B carp after ovulation stimulation with carp pituitary homogenate (CPH; 0.3+2.7 mg kg^?1; group I), Ovopel (1/5+1 pellet kg^?1; group II) or [d ‐Tle⁶, ProNHEt⁹] GnRH‐a (Lecirelin) with metoclopramide (15 μg kg^?1+10 mg kg^?1 respectively; group III) were investigated. The lowest percentage of spawning females (71%) was recorded in the group treated with CPH. In case of Ovopel or Lecirelin induced ovulation, 86% of females spawned. No statistically significant effect of the ovulation stimulator (group) on the weight of eggs was found; however, the highest mean weight of eggs (expressed both in grams and in the percentage of female body weight) was recorded for the group treated with Ovopel (1400 g and 13%). After the treatment with CPH or Lecirelin, the weight of eggs was 1140 g (11%) and 1100 g (10%) respectively. The ovulation stimulator significantly affected the percentage of live embryos after 36 and 48 h incubation of eggs (P≤0.05; P≤0.01). After treatment with [d ‐Tle⁶, ProNHEt⁹] GnRH‐a, eggs of the best quality were obtained and after 36 and 48 h incubation the mean percentages of live embryos were significantly higher than the means calculated for the remaining two groups. No statistically significant differences were found between the percentage of living embryos after 36 and 48 h incubation of groups I and II.     

Evaluation of resistance to Dermo in eastern oyster strains tested in Chesapeake Bay

We investigated growth, Dermo disease, and survival for nine groups of oysters, Crassostrea virginica (Gmelin) cultivated in Chesapeake Bay (CB). Five regional strains (upper CB, North Carolina (NC), South Carolina (SC), Louisiana (LA) and LA triploids) and four additional hybrid strains (CB oysters mated with NC, SC, LA and Texas (TX) oysters) were held in floating rafts at three locations representative of lower CB: ‘low’ salinity (3–14 g L^?1), ‘moderate’ salinity (5–20 g L^?1) and ‘high’ salinity (14–24 g L^?1). At each site, patterns of growth and incidence of infection with Perkinsus marinus (Levine), the causative agent of Dermo disease, were similar. However, mortality trends were markedly different at each site; the CB strain being notable for accelerated mortality following infection with P. marinus. In addition, hybrids between CB and all four of the regional strains exhibited similar accelerated mortality in response to infection. Mortality was strongly correlated with infection only at the high salinity site implicating interaction of differences in both oyster strain and virulence of Dermo between moderate and high salinity areas as factors in differential mortality across sites.     

Blocking polar body with cytochalasin B in the fertilized eggs of the small abalone, Haliotis diversicolor supertexta (Lischke), and the development and ploidy of the resultant embryos

The effects of blocking polar body I (PB1) or polar body II (PB2) with four different dosages of cytochalasin B (CB) on the development and ploidy of resultant embryos were studied in the small abalone, Halitis diversicolor supertexta (Lischke). To block the release of PBI, the fertilized eggs were treated with 0.25, 0.5, 1.0 or 2.0 mgL^?1 of CB for 10min beginning at 3 min post-fertilization at 24°C. To block the release of PB2, the fertilized eggs were treated under the same conditions as PB1, except that the treatment was begun 10min post-fertilization. In the control group, only 41.8% of the cells had a diploid number of 32 chromosomes, although spontaneous haploids (9.0%). tripolids (7.5%) and aneuploids (41.7%) were also observed. In CB treatment of PB1 and PB2 groups. 5.0-28.6% of the cells remained as diploid. triploids (10.0-18.9%) and aneuploids (41-1-61.0%). With regard to the development of the resultant embryos, the proportion of normal embryos in the control group was 87%, while in the treatment groups, the proportions of normal embryos in the FBI and PB2 groups were 57-58% and 53-56% in the 0.25 mg L^?1 and 0.5mg L^?1 CB treatments, respectively. From this data on induced triploids and the resultant development of normal embryos, the proportions suggest that 0.25-0.5 mg L^?1 of CB for 10min was sufficient for blocking the release of FB1 or PB2 to produce triploids in the small abalone.     

Induced spawning of Asian catfish, Clarias batrachus (Linn.): effect of various latency periods and SGnRHa and domperidone doses on spawning performance and egg quality

An experiment was conducted to induce ovulation in Asian catfish, Clarias batrachus, by a single injection of SGnRHa (d ‐Arg⁶, Trp⁷, Leu⁸, Pro⁹, Net) in combination with domperidone. The effects of latency periods, 11, 14, 17, 20 and 23 h, and doses of inducing agent, 10 μg SGnRHa+5 mg domperidone, 20 μg SGnRHa+10 mg domperidone, 30 μg SGnRHa+15 mg domperidone and 40 μg SGnRHa+20 mg domperidone kg^?1 body weight, were studied on the total egg output, stripping response, fertilization, hatching and normal larval production. The highest (P<0.05) number of eggs were stripped at 23 h of post injection of 20 μg SGnRHa+10 mg domperidone kg^?1 female body weight. The highest (P<0.05) stripping response was observed when the females were stripped at 20 and 23 h latency, at all dose levels of the inducing agent. The eggs stripped at 11 h latency did not fertilize, and hence did not hatch irrespective of administration of any dose levels of the inducing agent. The fertilization and hatching per cent of eggs had significantly increased (P<0.05) with increase in latency period to 14–23 h at a dose of 20 μg SGnRHa+10 mg domperidone. The latency period of 14–17 h, and dose of 20 μg SGnRHa+10 mg domperidone and 30 μg SGnRHa+15 mg domperidone kg^?1 of female, was found to be suitable to obtain best spawning performance, and good‐quality egg and larval production in C. batrachus.     

The use of a biodeposition collector for estimation of assmilation efficiency in oysters

A device is described that automatically separates and collects the feces and pseudofeces of oysters. This quantitative method allows accurate estimation of assimilation efficiency. Oysters were fed the diatom Thalassiosira pseudonana at either of two algal concentrations, 1 × 10⁶ and 4 × 10⁶ μm³/ml of algae. Ingestion, and fecal and pseudofecal production were greater at the higher concentration but assimilation efficiencies were not significantly different (α = 0.05).     

Insights on the association between somatic aneuploidy and ostreid herpesvirus 1 detection in the oysters Crassostrea gigas,C. angulata and their F1 hybrids

Cytogenetic abnormalities associated with viral infections, including from viruses of the Herpesvirales order, have been reported in vertebrate species. Ostreid herpesvirus 1 (OsHV‐1) has been detected worldwide during mortality outbreaks of the Pacific oyster Crassostrea gigas. On the other hand, a high proportion of aneuploid cells in somatic tissues have been observed in C. gigas. In this study, we analysed the putative association between aneuploidy levels and the detection of OsHV‐1 in gills of C. gigas, the Portuguese oyster C. angulata and their F1 hybrids cultured in Ria Formosa (Portugal). OsHV‐1 was detected by PCR in 5.4% of the total of oysters analysed (n = 111) namely in 11.1%, 8.0% and 1.7% of C. gigas, C. angulata and F1 hybrid respectively. Sequencing analysis of a viral fragment amplified with the C2/C6 primer pair revealed a high similarity with the OsHV‐1 reference type. Moreover, in situ hybridization confirmed the presence of OsHV‐1 in gill tissue. Oysters where OsHV‐1 was detected had a significantly higher mean percentage of aneuploid cells (25%) than the ones where the virus was not detected (18%). However, the overall low percentage of positive samples contrasted with the high mean percentage of aneuploidy observed, with 50% of the oysters analysed showing a percentage of aneuploid cells between 20% and 30%. We hypothesize that somatic aneuploidy may adversely affect oysters making them more prone to OsHV‐1 infection, but the virus is unlikely to be the cause of somatic aneuploidy.