Prostaglandins (PGs) play extensive regulatory roles in physiological processes such as reproductive development, homeostasis regulation, and tissue regeneration in vertebrates, yet their distribution and functions in invertebrates remain poorly characterized. To address this knowledge gap, this study established a quantitative analytical method targeting prostaglandin E₂ (PGE₂) and prostaglandin D₂ (PGD₂) in multiple tissues of bivalves using liquid chromatography-tandem mass spectrometry (LC-MS/MS) with multiple reaction monitoring (MRM), employing the potential model bivalve dwarf surf clam (Mulinia lateralis) as the experimental organism. Through dual validation of characteristic fragment ions and retention time, we systematically identified the distribution profiles of PGE₂ and PGD₂ in six major tissues of M. lateralis: both PGs were detected in the mantle, gill, gonad, and digestive gland. Quantitative analysis, based on external standard calibration curves, revealed that PGE₂ concentrations were consistently higher than PGD₂ across all examined tissues. Notably, the gill and mantle emerged as the primary accumulation sites for PGs, with their combined PGE₂ and PGD₂ content contributing to 82.14% of the total. Further analysis demonstrated that fast-growing individuals exhibited significantly higher PGE₂ and PGD₂ levels than in slow-growing counterparts (increased by 24.51% and 61.11%, respectively; P < 0.01), suggesting potential involvement of PGs as key regulatory factors in the growth modulation of M. lateralis. This study provides initial insights into the tissue-specific distribution of PGs and their potential association with growth rate in M. lateralis, generating fundamental evidence for investigating growth regulation mechanisms and genetic improvement practices in bivalves.

In terrestrial animals, the somatotropic axis, comprising growth hormone (GH) and insulin-like growth factors (IGFs), is pivotal in regulating growth and development. Marine mollusks play a vital role in the aquaculture industry, and understanding the molecular mechanisms of mollusk growth is of great value to breeding fast-growing and high-yielding varieties. Unlike terrestrial animals, marine mollusks lack a model species for laboratory breeding, leaving many growth-related genes unvalidated. The dwarf surf clam Mulinia lateralis, with its small size, short breeding cycle, and ease of cultivation in laboratory settings, serves as an ideal model for investigating growth regulation. This study is the first systematic identification of genes related to M. lateralis growth, with 195 differentially expressed genes (DEGs) being found between fast- and slow-growing individuals through transcriptome comparison. KEGG analysis revealed significant enrichment of the insulin-like signaling pathway, and the insulin-like peptide (ILP) was the most significantly upregulated. As the insulin signaling pathway is activated by ligand–receptor binding, we further characterized and functionally validated mlILP and its receptor, the insulin receptor-related receptor (mlIRR). RNA interference (RNAi)-mediated knockdown of mlILP or mlIRR resulted in growth retardation, confirming their positive roles in growth regulation. Notably, silencing of these two genes caused significant upregulation of downstream genes, suggesting a compensatory mechanism for maintaining cell homeostasis. Our findings advance the understanding of growth regulation in mollusks and provide candidate genes for scallop breeding aiming at growth improvement.