The giant freshwater prawn (GFP), Macrobrachium rosenbergii, is one of the largest palaemonids in the world, found in tropical marine, estuarine, and freshwaters, and is among the most commercially cultured crustaceans. According to research, mature males usually develop differences in cheliped morphology, growth characteristics, and agonistic behavior. The identification of such morphotypes is critical for effectively managing and handling prawns. The present study aimed to describe the GFP male population structure in culture ponds (the Yangtze River delta, China). Sixteen morphometric traits and four weight data were measured for each four male morphotype. Principal component and clustering analyses were conducted to investigate the morphological variation among the four morphotypes. The study of relative growth was also employed to estimate the growth patterns of body structures (dependent variables) in relation to the carapace length (independent variable). A detailed description of the cheliped’s macroscopic characteristics that differed among morphotypes was provided, which corroborated with previous studies of the species. The four morphotypes were statistically different regarding the cheliped morphology, size, and morphometric relationships and equations, indicating a considerable variation in growth among the four male morphotypes. The present results contribute to a clear understanding of the population biology of GFP and support future management and broodstock selection activities.

Macrobrachium rosenbergii, commonly known as giant freshwater prawns (GFPs), is an economically and nutritionally important decapod crustacean species in China. Understanding the genetic diversity of selective breeding populations is crucial in breeding plans for selecting genetically diverse broodstocks and maintaining genetic diversity. The genetic structure of six breeding populations (Hefu (HF), Nantaihu No.2 (NTH), Jiaxin (JX), Shufeng (SF), Taiwan (TW), and Guangxi (GX)) of GFP in China was examined using 16 newly developed microsatellite loci and the mitochondrial control region (D-loop). The microsatellite data revealed that all 16 loci have high diversity, with all values of polymorphism information content (PIC) more than 0.5. The average expected heterozygosity (He, 0.89) and the number of alleles (Na, 18.25) of SF were the highest, followed by He (0.89) and Na (14.75) of the JX, and GX has the lowest He (0.83) and Na (11.31). The average PIC value for the six stocks ranged from 0.80 to 0.87. Pairwise comparisons revealed that Fst ranged from 0.03541 to 0.09637 and was significant (p < 0.05) between most populations, indicating from low to moderate genetic differentiation among the six populations. The D-loop analysis identified 114 variable sites and 29 haplotypes, with an average haplotype diversity (Hd) and nucleotide diversity (π) of 0.640 and 0.01247, respectively. Genetic differentiation among the six populations based on the D-loop was from moderate to high, with Fst values of 0.05603–0.80788, and all p < 0.05. This study demonstrates that selective breeding stocks of M. rosenbergii in China show moderate to high genetic diversity and have the potential for further selective breeding, providing a theoretical basis for conserving and utilizing M. rosenbergii genetic resources.

Vibrio parahaemolyticus is an important foodborne and aquaculture-associated pathogen, and its increasing antimicrobial resistance threatens shrimp production, seafood safety, and public health. Although bacteriophages have emerged as a potential solution to the growing challenge of antimicrobial resistance, whether antibiotic resistance is associated with phage tolerance remains unclear. This study characterized antimicrobial resistance profiles and resistance genes in Vibrio parahaemolyticus isolates from Zhanjiang shrimp aquaculture farms and evaluated their association with bacteriophage susceptibility. A total of 132 isolates were tested against 18 antibiotics, while molecular and phage-related analyses were performed on 132 isolates. High resistance was observed against kanamycin (95.5%), sulfamethoxazole (94.7%), cefazolin (78.8%), imipenem (78.8%), amoxicillin (70.5%), and ampicillin (65.2%). Multidrug resistance was detected in 131/132 isolates (99.24%), indicating an extensive resistance burden. PCR analysis showed high detection rates of aphA (100.00%), sul1 (99.24%), blaTEM (98.48%), blaOXA (73.48%), blaCTX-M (53.03%), qnrA (45.45%), tetA (37.88%), and tetB (21.21%). Phage response analysis showed that 70.45% and 68.18% of isolates were phage-resistant at 4 h and 5 h, respectively. Genes potentially associated with phage–host interactions were also detected, with luxS showing the highest frequency (85.61%). Association analysis revealed significant links between tetA, tetB, blaOXA, and bacteriophage responses. These findings suggest that antimicrobial resistance and reduced phage susceptibility can co-occur among V. parahaemolyticus isolates recovered from shrimp farms in Zhanjiang, highlighting the need for regional resistance surveillance and careful phage selection.