Genome-Wide Identification of Solute Carrier Family 12 and Functional Characterization of Its Role in Saline–Alkaline Stress Acclimation in the Ridgetail White Shrimp Exopalaemon carinicauda

Solute carrier family 12 (<i>SLC12</i>) encodes electroneutral cation-coupled chloride cotransporters responsible for transmembrane ion transport (Na⁺, K⁺, and Cl^-), which play a critical role in aquatic osmoregulation. However, the <i>SLC12</i> gene of <i>Exopalaemon carinicauda</i> (<i>EcSLC12</i>) has not been systematically identified or functionally characterized. In this study, six <i>EcSLC12</i> genes were identified across the genome and classified into N(K)CC, KCC, CCC9, and CIP subfamilies. Three <i>NKCC1</i> homologous genes (<i>EcSLC12A2.1</i>, <i>EcSLC12A2.2</i>, and <i>EcSLC12A2.3</i>) were reported for the first time in crustaceans. The <i>EcSLC12</i> family exhibited distinct expression patterns in response to low-salinity, high-alkalinity, and saline-alkaline stress. <i>EcSLC12A2.2</i> was highly expressed in the gill, and its expression was closely correlated with saline-alkaline acclimation. Additionally, <i>EcSLC12A2.2</i> knockdown decreased <i>E. carinicauda</i> survival under saline-alkaline stress. Thus, <i>EcSLC12A2.2</i> plays critical roles in osmotic regulation and saline-alkaline acclimation. This study provides crucial insights into <i>E. carinicauda</i>'s saline-alkaline tolerance mechanisms, and the discovery of multiple <i>NKCC1</i> homologs fills a gap in the crustacean <i>SLC12</i> gene family research.