Effects of salinity and temperature on the timing of germinal vesicle breakdown and polar body release in diploid and triploid Hong Kong oysters, Crassostrea hongkongensis , in relation to tetraploid induction

Abstract

Tetraploids are crucial important for commercial production of all-triploid Crassostrea hongkongensis. Successful production of tetraploid C. hongkongensis requires precise control of fertilization and applying treatment. The germinal vesicle breakdown (GVBD) ratio of stripped eggs before fertilization influences the efficiency of tetraploid inductions. According to our research, in both diploids and triploids, the time to 50% polar body 1 (PB1) release was significantly reduced if a GVBD ratio of 100% was reached before fertilization (p < 0.05). We consider the time at which there is 100% GVBD of stripped oocytes to be the optimum time point to start fertilization. 50% PB1 release is an important time point to apply the treatment for inducing tetraploids. Since lowering salinity (from 25 to 15 ppt) and increasing temperature (from 25 to 31°C) both accelerate the GVBD and the PB1 release rate of eggs, 31°C and 15 ppt are the most appropriate temperature and salinity level in which to perform tetraploid induction of C. hongkongensis. In these conditions, we found that there was significantly more variation in timing of 100% GVBD and 50% PB1 release among eggs from different triploids compared to different diploids (p < 0.05), creating difficulties in controlling fertilization and duration of treatment in tetraploid induction using triploid eggs. For reducing the variation, we recommend that treatments for tetraploid induction of C. hongkongensis should use eggs from individual triploid females. K E Y W O R D SCrassostrea hongkongensis, germinal vesicle breakdown ratio, polar body, salinity, temperature, tetraploid

Comparison of the Biochemical Composition and Nutritional Quality Between Diploid and Triploid Hong Kong Oysters, Crassostrea hongkongensis

“…The glycogen storage levels of Mytilus edulis and C. gigas were lowest during the reproductive phase, while phytoplanktonic food was potentially abundant, suggesting that diploids were unable to store reserves at this time due to gametogenesis. Based on Zhang et al ( 2017 ) and Qin et al ( 2018 ), the gonad development and spawning stage of diploid Hong Kong oysters lasts from May to August. In our study, the diploids went through the maturation stage until July, and needed to consume large amounts of glycogen to support gonad development.…”

“…Precisely the opposite from C. gigas, C. hongkongensis live in a high temperature and low salt sea area. As C. hongkongensis grow slowly, it usually takes 3 years to reach the specified commercial size (Qin et al, 2018 ). Dyerberg noted that an increase in the ratio of n-3/n-6 PUFAs increases the availability of n-3 PUFAs, which are beneficial for human health (Dyerberg, 1986 ).…”

“…According to the protocols developed by Downing and Allen ( 1987 ) and Qin et al ( 2018 ), the ploidy status of each individual oyster was determinated using flow cytometry using a CyFlow Ploidy Analyser (Sysmex). Then, subsamples of gill, mantle, adductor muscle, labial palps, and gonad tissue were stored at −80°C for glycogen and protein content analysis, and all tissues were lyophilized before use.…”

The Sperm Proteome of the Oyster Crassostrea hongkongensis

“…Sperm of each apparently healthy oyster were removed from the mature gonad, suspended in beakers containing filtered seawater and rinsed through a 25 µm screen. [ 20 ] Three biological replicates were collected and each sample contained sperm from three male individuals. Concentrated sperm samples were dissolved in 8 m urea, transported to Hong Kong Baptist University on dry ice and stored at −80 °C until use.…”

Meiotic Spindle Formation Following Inhibition of First Polar Body Formation in the Zhikong Scallop (Chlamys farreri Jones et Preston)

“…Chromosome manipulation of marine bivalves has received considerable research interest. Following inhibition of polar body 1 (PB1) formation, tetraploids have been reported in Manila clam Ruditapes philippenarum (Li et al, 2017), Pacific abalone Haliotis discus hannai (Arai et al, 1986), American oyster Crassostrea virginica (Stanly et al, 1981), Pacific oyster Crassostrea gigas (Stephens and Dowing, 1988;McCombie et al, 2005), Hong Kong oyster Crassostrea hongkongensis (Qin et al, 2018), pearl oyster Pinctada martensii (He et al, 2000), and other mollusk species (Yamamoto and Sugawara, 1988;Guo and Allen, 1994;Yang et al, 2000a;Tan et al, 2017). When PB1 formation was blocked in C. gigas zygotes, observations of chromosome segregation revealed possible mechanisms of different ploidy formation (Guo et al, 1992).…”