Comparative Study on the Feeding Metabolism and Carbon Budget of the Triploid and Diploid Pacific Oyster (Crassostrea gigas)

Abstract

Crassostrea gigas, also known as Pacific oysters, are economic shellfish with the widest range of cultivation, the highest yield in the world, and the most important type of mariculture shellfish in China. However, many C. gigas have died during summer in coastal areas worldwide in recent decades. In 2008, the mortality rate of C. gigas cultured in France reached 40%–100%. In 2009, the mortality rate of C. gigas in some area of Sanggou Bay reached 51%. In 2019, the mortality rate of the Rushan area reached 50%–90%, with the death peak occurring in middle and late August. There were many reasons for the large-scale death of C. gigas, such as temperature, dissolved oxygen, salinity, disease, food availability, and reproduction levels, among which high temperature was the most important abiotic stress factor. The high temperature in summer disturbed the enzyme metabolism of C. gigas, resulting in slow or impeded growth. Furthermore, the reproduction and spawning of C. gigas caused a large amount of protein consumption, and physical weakness combined with high-temperature stress induced many deaths. Therefore, considering the problems faced by C. gigas culture during high summer temperatures, the introduction of new varieties will increase the economic benefits to the industry.Due to its high sterility, triploid C. gigas has attributes such as a fast growth rate, resilience excellent economic characteristics, and high energy conversion efficiency. In recent years, a certain farmed scale has formed in China, especially in northern coastal areas. There have been many studies on the biological and physiological differences between triploid and diploid C. gigas worldwide, mainly focusing on the differences in growth characteristics, soft tissue components, gonadal development, disease resistance, and gill structure. However, comparisons between triploid and diploid C. gigas feeding, metabolic physiology, energy budget, and carbon budget have not been reported. Focusing on the specific period of high temperatures in summer, this study investigated the feeding and metabolic physiological characteristics of triploid and diploid C. gigas using the field flow method, and compared and analyzed their energy allocation strategies in response to a high-temperature environment. The study provide data support for revealing the physiological differences caused by the ploidy effect of C. gigas in order to assist with evaluating the culture capacity.Triploid and diploid C. gigas were selected as research objects in August 2022 to analyze the differences in feeding and metabolic physiology and energy/carbon allocation strategies during high temperatures in summer. Physiological parameters related to intake and metabolism, such as water filtration rate, absorption efficiency, oxygen consumption rate, and ammonia discharge rate, were determined based on the field flow method in Sanggou Bay, Rongcheng, Shandong Province, and energy allocation and carbon allocation were estimated based on the principle of the energy budget. The results revealed that the water filtration rate and assimilation efficiency of triploid C. gigas were higher than those of diploid C. gigas, but there were no significant differences (P > 0.05). There were significant differences in the oxygen consumption rate and ammonia discharge rate between triploid and diploid C. gigas (P 0.05). There were significant differences in respiratory energy/carbon, excretion energy/carbon, and growth power between triploid and diploid C. gigas (P < 0.05). Respiratory energy/carbon values of triploid C. gigas were significantly lower than those of diploid C. gigas (P < 0.05), but excretion energy/carbon and growth power values were significantly higher than those of diploid C. gigas (P < 0.05). The oxygen/nitrogen ratio of triploid and diploid C. gigas fluctuated in the range of 7.91–14.11 and 59.81–94.19, respectively. Moreover, the main energy supply substances of triploid C. gigas were proteins, while the main energy supply substances of diploid C. gigas were carbohydrates and fats. These results revealed the differences in energy allocation patterns associated with the ploidy effect of C. gigas during high temperatures in summer.From the perspective of individual physiology and ecology, this study found that, compared with diploid C. gigas, triploid C. gigas showed certain advantages in energy allocation strategies by adjusting feeding and metabolic physiological behaviors during the high-temperature summer. However, the internal molecular mechanism of response strategies adopted by triploid C. gigas to cope with an adverse environment is still unclear. Further interpretation at the molecular level needs to be combined with omics and other systems biology techniques.

Keywords

• crassostrea gigas
• triploid
• diploid
• summer high temperature
• physiological energetics