Evaluating The Spawning Techniques For Bivalves

Evaluating The Spawning Techniques For BivalvesControl of riposte is a prerequisite in modern bivalves aquculture industries due to un tried and true quantity and quality of natural hassle as well up as market demand on standardized products. Spawning is building blockary critical note in bivalves hatchery, together with fertilization and larval rearing, thus a lot of research has been done to look for prospective methods and understand the process within. Various means in spawning proficiencys be presented herein, i.e. gamete stripping and spawning knowledgeableness by chemical substance or physical stimulants. Where relevant, advantage and disadvantage of each technique are discussed and compared.IntroductionBivalves are aquatic animals belong to the phylum Mollusca which characterized by two calcareous shells covering a soft body, encompassingboth leatherneck and fresh-water species both marine and fresh-water species. Some well-known bivalves, such as clams, adorn, mus sels, and oysters has been successfully cultured since decades or centuries ago (Nash, 2011). Nowadays, bivalves and early(a) members of molluscs accounts for nearly 30% of aquaculture production with volume more than 50 million tonnes in 2006 (FAO, 2008). intense production is needed to meet market demands on edible and full(prenominal) value bivalves (pearl oysters). One valuable key of intensification is suss out over all of the production steps, including management of reproduction which volition lead to higher(prenominal) productivity with lower cost in order to reach best efficiencies and standardized products. Controlled spawning of molluscs is the best focal point to obtain reliable supply of quality seeds and reduce dependencies upon unreliable natural spawning events to collect spat.The development of bivalves hatchery was started in 1879 when William Brooks demonstrated that oyster eggs could be spawned and developed into the larval stage in research laboratory (Ca stagna, 1983). No make report on artificial propagation of bivalve molluscs until 1920s when William Wells successfully reared oyster larvae. These two findings provide important data for further development in molluscan aquaculture.This article will describe a number of common spawning techniques for bivalves, which divided into 2 categories gamete stripping and spawning induction. Henceforward, gamete stripping is considered not induction since the word induction refers to a persuading or stimulating action, whereas another authors may define the other way. reward and disadvantage considerations of each technique are included, particularly in relevance with practical farming aspects.1. Gamete findAs the name indicates, this procedure involves removal of gamete from gonad tissue. Briefly, fully ripe gonad overlies the digestive package was slash repeatedly with scalpel and washed with filtered brine to harvest the gametes. Microscopy examination is needed to determine sex and manner of the ova and sperms. Therefore, solo well-trained operators can carry it out because of high level of difficulties.Due to its issueiveness, gamete stripping has been widely apply to obtain gametes in many Bivalvia species. Pacific oysters (Suquet et al., 2007), pearl oysters Pinctada fucata (Alagarswami et al., 1983a), and European flat oysters genus Crassostrea gigas (Shpigel, 1989) are several(prenominal) of organisms successfully spawned using gamete stripping. Furthermore, this technique obviously the only way to obtain suppurate gametes for species that can not be spawned by any physical or chemical stimulation.In some bivalves, viable eggs does not necessarily obtained immediately later on stripping because naturally a series of activation process takes place in follicle prior to spawning, i. e. removal of germinal vesicles and formation of germinal ear (Loosanof, 1953 Southgate, 2008). Loosanof and Davis (1963) treated eggs of Mercenaria mercenaria with 0.1 N ammonium hydroxide (NH4OH), but the embryos did not develop well and leading to low percentage of normal larvae compared to their naturally spawned counterparts. So far, no reports about detail mechanisms on how NH4OH activates eggs, while comprehensive understanding of the process is absolutely important for optimization or probably backing NH4OH with another potential substance.Stripping itself is a destructive and lethal method, thus it is not a sustainable way to maintain broodstock collections. Sacrificing quality broodstock must be invaluable loss that all hatcheries try to forefend it. Likewise, pearl oysters hatcheries prefer another spawning method that has no detrimental effects, considering the high value of the product and the oysters itself (Southgate, 2008).2. Spawning trigger by Physical and Chemical Means2.1 Chemical stimuli2.1.1 Injections of sex steroidsThe presence of steroids in molluscs has been identified by Hagerman et al. (1957) and its fluctuations h ave a strong correlation with sexual maturation, gamete release, and sex determination in bivalve (Croll and Wang, 2007). A serotonin, 5 hydroxytryptamine (5-HT), works synergistically with steroid for those functions because steroids regulate 5-HT receptor on the membrane of gametes (Kadam et al., 1991). Combinations of 5-HT and steroid intragonadal injections are the close to widely used in aquaculture farming practice.Efficacy of steroid treatment must be assessed on species basis because a particular steroid may give different results in different species. Similarly, one species could give various responses to some steroids, even if they have similar chemical structure. Published reports by Wang Croll (2003 2004 2006) relieve clearly about gonadal maturation as well as spawning responses in sea scallop Placopecten magellanicus towards a number of steroid injections, both in vitro and in vivo.In vitro study by Wang and Croll (2003) shows 10-5-10-8 M progesterone and 17-estradi ol potentiated gamete release in 5-HT-induce gonads tissue of P. magellanicus, both fe masculine and/or male. On the other side, testosterone (10-5-10-7 M) was only effective in male and no significant effects on dehydroepiandrosterone (DHEA) and 4-androsterone injections. operation of steroid inhibitors and control group (5-HT-incubated gonads) in the experiment strongly suggest steroids and steroid receptors involve in molluscan reproduction.Those results are confirmed with in vivo study by Wang and Croll (2006), although slightly different. Progesterone, which is able to initiate gamete release in male and female gonads tissue in vitro, demonstrated inhibitory effect in 5-HT-induced female P. magellanicus. another(prenominal) interesting fact is the number of gametes released (spawning intensity) are sharply increased up to 300% and the response measure after(prenominal) injection (spawning latency) reduced about 30%.Despite of its advantages, administration of sex steroid in bivalves farming apparently impose additional cost since serotonin must be used in parallel to obtain optimal result. In-depth economic calculations might be necessary to reach a correspondence between cost and benefits.2.1.2 Hydrogen peroxide (H2O2)H2O2 application to induce bivalves spawning was first reported by international Morse code et al. (1977). He and his colleagues found that addition of 5mM of H2O2 to alkaline seawater successfully induced spawning, in both male and female gravid abalone Haliotis rufescens, within about 3 hours after the first addition. This effect results from activation of prostaglandin endoperoxidase by peroxides, which eventually triggers the spawning response.Their paper convincingly pointed that H2O2, neither another contaminants nor substances, initiates the spawning (Table 1). Destruction of H2O2 by catalase and mercaptoethanol (reducing agent) in effect blocks spawning. Aspirin, an inhibitor of cyclooxygenase and prostaglandin peroxidase synthe sis, shows endoperoxidase synthesis is required for induction of spawning by H2O2.Table 1. Induction of spawning in gravid H. rufescens discourseTotal Number of AnimalstestedSpawnedControls77 (47F, 30M)3 (2F, 1M)H2O18 (13 F, 5 M)0H2O231 (17 F, 14 M)30 (16 F, 14 M)Aspirin, then H2O226 (12 F, 14 M)2 MCatalase, then H2O25 M0Mercaptoethanol, then H2O25 M0Note F = female, M = male. germ Morse et al. (1977)Nevertheless, less success was achieved in Indian pearl oysters P. fucata with H2O2 treatment as with abalone did (Alagarswami et al., 1983b). balmy spawning only occurred with 6mM H2O2 for 5 hours immersion. Supplementation of seawater with Tris buffer at pH 9.1, which usually effective for abalone, does not works well for P. fucata. These conversely results indicate H2O2 concentration must be optimized for any cultured species, sometimes in combination with other treatments.Since peroxide method is a simple and rapid technique, an assay for spawning bivalves which previously known d ifficult to spawn can be developed quite easily. Morse (1984) has been able to secern optimal conditions for gametogenesis and spawning of green (H. fulgens), pink (H. corrugata), and black abalone (H. cracherodii) using peroxide method. Spawning of these animals can be induced by H2O2 in a slightly high temperature (20-25C).2.1.3 Injections of neurotransmittersserotonin, 5-HT, is the most widely used and probably the most potent neurotransmitter for artificial spawning purpose. In vitro study shows ovarian tissue of Patinopecten yessoensis released high number of eggs after been immersed in 10-6M serotonin (Matsutani and Nomura, 1987). The study also demonstrated interaction between serotonin and its receptors in ovary, as well as on how prostaglandins regulate serotonin performance in scallop.The efficacy of serotonin in vitro was confirmed in many in vivo studies. Gibbons and Castagna (1984) injected six species of bivalves with 2mM serotonin, nearly similar to the concentration used by Matsutani and Nomura (1987), and all of them spawned as expected with spawning latency 15-30 minutes (Table 2). For an unknown reason, there is a tendency serotonin more likely affected males than females.Table 2. Number of bivalves spawned by 5-HT injectionSpeciesTreatmentNumber ofTestedSpawning MalesSpawning FemalesArctica islandicaControl7000serotonin70154Argopecten irradiansControl3521Serotonin35291Crassostrea virginicaControl3000Serotonin30210Geukensia demissaControl2010Serotonin2081Mercenaria mercenariaControl7000Serotonin32911621Spisula solidissimaControl4501Serotonin45189 microbe Gibbons and Castagna (1984).Positive result was also obtained in giant clams, only Hippopus hippopus was less sensitive to serotonin (Braley, 1985). some other tested species (Tridacna gigas, T. derasa, T. maxima, T. crocea, T. squamosa) did very well in terms of spawning latency and spawning duration, even with a low acid of serotonin. Therefore, injection of serotonin provides reliable way to induce spawning in giant clams, besides gametes-overlay method.Velez et al. (1989) carried out a more comprehensive research to see effect some neurotransmitters upon spawning induction in scallop Pecten ziczac. inclined the number of neurotransmitters (dopamine, epinephrine, norepinephrine), only serotonine could induce spawning process. Moreover, they noticed that females give less response to serotonine than males do similar to what Gibbons Castagna (1984) found.2.1.4 supplement of gametesTridacnid clams, such as T. maxima and T. squamosa, can be induced to spawn in captivity by introducing gonad extract from the opposite-sex into the mantel cavity (Gwyther and Munro, 1981 Munro et al., 1982). Three different gonad extracts were performed gonad biopsy, freshly unify gonad, and freeze-dried blended gonad. Unfortunately, the author did not compare the treatments and describe the relevant results more detail.This induction technique is fairly simple in principles and impl ementation. Spawning occurs simply because synchronized release of gametes, on which gamete act as chemical cues or pheromones (Soong et al., 2005), a natural adaptation to increase external fertilization probability for broadcasting-gametes organisms.2.1.5 Ultraviolet (UV)-irradiated seawaterSeawater irradiated by light was a very powerful spawning inducer. Window-pane shell Placuna placenta responded quickly after been immersed in UV-irradiated seawater (Madrones-Ladja, 1997). The average number of eggs released per female using this treatment is as high as in serotonin treatment furthermore the stimulus did not affect the viability of gametes.Besides of its reliable efficiency, this technique is very cost-effective and simpler than serotonin injection. It is also applicable for either individual or big money spawning, and does really works for both sexes of bivalves.2.2 Physical stimuli2.2.1 Temperature manipulationManipulating water temperature is the most popular methods of sp awning induction in bivalve hatcheries mainly because of its ease of application and reliable effectiveness. This technique has been studying intensively and implemented in pearl oyster P. maxima (Southgate and Beer, 1997) and various edible bivalves, such as American oyster Ostrea virginica (Soria et al., 2010) and briny water bivalve Corbicula japonica (Baba et al., 1999).Reproductive physiology of O. virginica has been discovered more than decades ago, thus artificial reproductive control method has been set up very well (Galtsoff, 1938a 1938b 1940). Sudden change in water temperature from 20 to 32-35C was found effectively stimulate spawning than long exposure to lower temperatures.In C. japonica, rising the temperature must be accompanied by salinity. Baba et al. (1999) demonstrated temperature 26C with salinity 2.3-4.5 practical salinity unit (psu) give optimum yield. Moreover, addition of gamete suspension into the water is able to increase its fecundity. These three differen t factors may bring some complexity in terms of hatchery practice because optimization of those components is more likely indispensable.2.2.2 organisation of microalgal foodImmersing razor clams Siliqua patula in high density of phytoplankton is the only method so far that scientifically effective to induced spawning process. Breese and Robinson (1981) found 2-2.5 million cells ml-1 microalgae Pseudoisochrysis paradoxa stimulates razor clams to spawn. No published report that explains this phenomenon, so the exact mechanism does not understood well. It is maybe only a raw material instinct of reproduction in nature when food present abundantly in environment.This method could be a good alternative instead of gamete stripping. The number of eggs released per clam as well as hatching rate was much higher compared to those obtain by stripping. In terms of aquaculture practicality, this technique is considerably easy and fairly inexpensive.3. ConclusionsThere are numerous techniques t o stimulate spawning process in bivalves. Basically, they are only mimicking natural process involved in natural reproduction cycle. No one of those techniques is more superior to another, therefore choosing the appropriate technique should be based on species cultured. Any cost associated, for instance chemicals and equipments, must be also taken into consideration.