Physiological, Transcriptomic, and Metabolomic Insights into Ammonia-Nitrogen Stress in the Hepatopancreas of Litopenaeus vannamei Acclimated to Low Salinity

Elevated ammonia nitrogen significantly reduces the survival rate of Litopenaeus vannamei under low-salinity conditions. Low-salinity culture is widely adopted in shrimp farming but susceptible to ammonia accumulation; however, relevant studies mainly focus on juvenile shrimp under single stress or normal salinity. With the aim of exploring how L. vannamei responds physiologically and molecularly to elevated ammonia nitrogen after low-salinity adaptation, shrimp were gradually acclimated to 5‰ salinity. They were reared at 5‰ for one week before being exposed to high levels of ammonia nitrogen for 96 h. Under these conditions, the shrimp’s hepatopancreas showed antioxidant imbalance and oxidative damage. Elevated blood ammonia, urea nitrogen and uric acid reflected activated synthesis pathways that clear excess ammonia. Transcriptomic and metabolomic profiling at 12, 48, and 96 h revealed 112 DEGs and pronounced alterations in lipids and amino acid derivatives. Integrated gene-metabolite correlation analysis uncovered three core pathways, along with 11 key DEGs and 17 associated metabolites. In the secretion pathway, solute carrier family 4 (anion exchanger),member 2 (slc4a3) was strongly correlated with saquinavir and carnitine. In the metabolism pathway, nicotinamide/nicotinate riboside kinase (nmrk1), chitinase (chia), Gamma-glutamyltranspeptidase (ggt1), UDP-glucose 4-epimerase (gale), and spermine oxidase (smox) were linked to L-pyroglutamic acid, betaine, etc. In the immune pathway, mitogen-activated protein kinase 8/9/10 (bsk) and integrin beta 1 (cd29) were associated with leukotriene E4 and niacin. This study reveals that ammonia stress after low-salinity acclimation induces oxidative stress damage, elevated physiological changes in L. vannamei, and further elucidates the regulatory pathways underlying its response to ammonia nitrogen stress.