Abstract The full-length cDNA of X-box binding protein 1 ( PmXbp1 ) in the giant tiger shrimp, Penaeus monodon was identified. It was 1762 bp in length containing an ORF of 855 bp corresponding to 284 amino acids. The expression level of PmXbp1 in different ovarian stages of wild intact broodstock was comparable but greater than that of cultured juveniles ( P PmXbp1 in stages III (late vitellogenic) and IV (mature) ovaries of wild P. monodon broodstock ( P PmXbp1 in ovaries of domesticated 18-month-old broodstock at 24 hpi ( P PmXbp1 (185 bp) were examined in domesticated 3-month-old juveniles (average body weight and total length = 12.32 ± 5.13 g and 11.30 ± 1.58 cm, N = 162) by single-strand conformational polymorphism (SSCP) analysis. Association between SSCP patterns of PmXbp1 and growth-related parameters was found where the average body weight (15.07 ± 5.04, N = 44) of juveniles carrying pattern A (corresponding to a T/T 349 SNP) was significantly greater than that (11.37 ± 4.80, N = 116) of juveniles carrying pattern B (corresponding to a T/C 349 SNP). The relative expression levels of PmXbp1 in the hepatopancreas of juveniles carrying different SSCP/SNP genotypes were significantly different (A P PmXbp1 in shrimp exhibiting a greater growth performance (22.08 ± 2.97 g and 13.60 ± 0.56 cm; N = 11) was significantly lower than that with a lesser growth performance (5.00 ± 0.89 g and 8.60 ± 0.98 cm; N = 8) ( P PmXbp1 seems to play an important role in reproduction and growth of P. monodon . Statement of relevance In aquaculture, the primary goal of genetic selection is the growth improvement of economically important species. Molecular markers that allow for selection of juveniles and broodstock with a high breeding value for reproductive maturation and/or growth rates are useful for the shrimp industry. Information on correlation between genotypic and phenotypic variations in penaeid shrimp is rather limited. Identification of molecular markers linked with growth/reproduction or those regulating the growth/reproduction mechanisms can be applied to improve artificial selection processes of P. monodon . To assess the possible biological roles of X-box binding protein 1 in reproduction and growth of P. monodon , the PmXbp1 cDNA sequence was characterized. Expression patterns of PmXbp1 during ovarian development in wild P. monodon broodstock were examined. Effects of eyestalk ablation (wild broodstock) and serotonin induction (domesticated broodstock) on expression levels of ovarian PmXbp1 were examined. In addition, analysis of relationships between SNP detected by SSCP and DNA sequencing and expression levels of PmXbp1 , and growth traits in juvenile shrimp was examined.