Effects of heat-killed Lactobacillus plantarum (HK L-137) and propionic acid on growth and health of striped catfish (Pangasianodon hypophthalmus)

Heat-killed Lactobacillus plantarum (HK L-137) is known to benefit striped catfish ( Pangasianodon hypophthalmus ) health, but its synergistic potential with short-chain fatty acids remains unexplored. This study investigated the individual and combined effects of HK L-137 and propionic acid (PA) on growth performance, feed utilization, immune responses, and stress response in striped catfish. Striped catfish (n=8,400, mean body mass 4.09 ± 0.08 g) were randomly assigned to six feeding treatments with different levels of HK L-137 and PA (0 [control], 1,000 mg PA/kg feed [PA.1000], 2 mg HK L-137/kg feed [HK.2], 4 mg HK L-137/kg feed [HK.4], 2 mg HK L-137/kg feed + 100 mg PA/kg feed [HK.2+PA.100], and 2 mg HK L-137/kg feed + 1000 mg PA/kg feed [HK.2+PA.1000], for eight weeks (with four replicates for each treatment). Results showed that, compared to the control, HK.2 significantly enhanced growth, improved digestive enzyme activity (amylase, trypsin, and chymotrypsin), and reduced the feed conversion ratio ( P<0.05 ). PA.1000 increased lymphocyte counts, while both HK.2 and HK.4 elevated cortisol and lipid peroxidase levels ( P<0.05 ). Furthermore, catalase activity was significantly increased in HK.4 and HK.2+PA.1000 groups ( P<0.05 ). Notably, both HK.2 and HK.4 groups exhibited a reduced cortisol response following high-density crowding stress (3,000 fish/m 3 ). In conclusion, dietary HK L-1 3 7 effectively improved growth, feed efficiency, and digestive function, while also enhancing stress tolerance in striped catfish; however, the synergistic effects with PA were limited. These findings support the application of HK L-137 as a promising functional feed additive for striped catfish aquaculture.