Hailing from various environments such as land, freshwater, estuaries, mangroves, and marine habitats, true crabs (Brachyura) are a remarkably successful group of crustaceans. Their triumph is closely tied to their life cycle, particularly their reproductive strategies. These strategies are crucial for the species’ survival and have played a significant part in the evolutionary development of crabs. Grasping these reproductive systems and strategies is key to understanding crab phylogeny and biology.
The complex reproductive process of the mud crab (Scylla paramamosain), essential for advancing artificial breeding on a large scale, has been thoroughly detailed by a collaborative team from Shantou University. Led by Professor Hongyu Ma, and joined by Dahe Wang, Yang Yu, Weifeng Gao, Zifei Xiang, Zilin Zhao, Hanafiah Fazhan, Khor Waiho, and Professor Mhd Ikhwanuddin, the team has combined their expertise to investigate the dynamic transformation of sperm from its formation to its final dispersion. Their findings, featured in Aquaculture Reports, provide crucial insights for enhancing crab breeding methods.
In this groundbreaking research, a total of 60 crabs—comprising 30 mature males and 30 near pubertal molting females on the brink of adulthood—were carefully chosen. These crabs, sourced from Guangdong province in China, were individually raised at Shantou University, where they were paired for mating in a controlled environment. This setup was critical for obtaining precise data while adhering to ethical animal treatment standards.
The research team used a series of detailed and gentle examination methods to study crab tissues. These tissues were treated with a special solution, preserved, and then prepared for microscopic examination. This process allowed the researchers to closely examine the cellular structures within the crabs’ reproductive organs.
Additionally, the team used advanced digital scanning technology to capture highly detailed images of the crab’s reproductive organs at various stages of development. This state-of-the-art scanning allowed for an in-depth view at varying levels of magnification.
To delve deeper into the structural aspects, tiny tissue samples were meticulously prepared for electron microscopy, a technique that allows for the observation of minute details. These samples were treated, dehydrated, and embedded in a resin medium, then finely sliced for detailed examination. This approach provided profound insights into the structure and changes of the sperm and reproductive organs. Moreover, preparations were made to observe the surface of the spermatozoa using a scanning electron microscope, enabling the researchers to view the sperm in incredible detail.
The collected data were methodically analyzed using various software tools to ensure statistical accuracy and reliability. The research team employed statistical analysis methods to compare the data, ensuring the results were significant and reliable.
Professor Hongyu Ma, a lead investigator in the study, shares key discoveries: “Following mating, the spermatophores and sperm mass exhibit noticeable changes in shape and location within the seminal receptacle. This includes the rupture of spermatophore walls, formation of a substantial sperm mass, and dispersion of sperm during multiple ovulation events”. He further elaborates, “Our research unveiled dynamic transformations of spermatozoa throughout the reproductive cycle of the mud crab, including the stages of spermatophore creation, transit, and dispersion. Additionally, we observed critical changes in the sperm during its preparation for fertilization, such as widening of the protective cap, accumulation of specific substances, and reduction in the chromatin density in the nucleus. These insights contribute significantly to our understanding of the reproductive processes in mud crabs”.
This research represents a significant stride in aquaculture, particularly for species like the mud crab that are economically and ecologically important. The insights from the Shantou University team do not just enhance our scientific understanding of crab reproductive biology; they also pave the way for advancements in breeding practices, vital for maintaining and enhancing mud crab populations in aquaculture.
JOURNAL REFERENCE
Dahe Wang, Yang Yu, Weifeng Gao, Zifei Xiang, Zilin Zhao, Hanafiah Fazhan, Khor Waiho, Mhd Ikhwanuddin, Hongyu Ma. “Dynamic changes characteristics of the spermatozoon during the reproductive process of mud crab (Scylla paramamosain): From spermatophore formation, transportation to dispersion”. Aquaculture Reports, 2023. DOI: https://doi.org/10.1016/j.aqrep.2023.101866.
ABOUT THE AUTHORS
Dr. & Prof. Hongyu Ma serves as the Director of International Joint Research Center for the Development and Utilization of Important Mariculture Varieties Surrounding the South China Sea Region, and as the Director of STU-UMT Joint Shellfish Research Laboratory. He is the Vice Chairman of Technological Innovation Platform of Chinese Mud Crab Industry, the Council Member of Chinese Association of Young Scientists and Technologists, and the Director of Agricultural Science and Technology Professional Committee of Guangdong Young Scientists Association. He is also a Visiting Professor at Universiti Malaysia Terengganu and a Visiting Associate at California Institute of Technology. Prof. Ma devotes his energies to address key scientific and technological issues in marine biotechnology, breeding and aquaculture. In the past decade, he led a team to (1) draw a high-quality whole genome map at chromosome-level of mud crab and reveal the structural characteristics. He identified sex-specific SNP loci and mapped them at high-density genetic maps, and further uncovered the ZZ/ZW sex determination mechanism of mud crab. He also elucidated the mechanism of sex determination and differentiation through phenotypic and ncRNA/gene perspectives. (2) He first developed genome selection technology based on liquid SNP chip and GWAS, and obtained a new crab strain with fast growth rate and gentle-aggressive behavior. He also first constructed inter-specific hybridization technology for crabs and cultivated two hybrid combinations with fast growth rate and strong disease resistance. Moreover, he created indoor and outdoor artificial hatchery production and nursery technology, and integrated multi-trophic aquaculture technology in ponds and land-based terrestrial three-dimensional recirculating aquaculture technology. The above achievements have strongly promoted the development of genetics and aquaculture industry of marine crustaceans.
