This study aimed to investigate the combined effects of two most potent probiotic bacteria Lactobacillus acidophilus and Lactobacillus plantarum on overall health and immune status of freshwater crayfish, marron under laboratory conditions. A total of 36 marron were distributed into six different tanks and two different feeding groups, control and probiotic-fed group. After acclimation, control group was fed with basal diet while probiotic group was fed 10 9 cfU/mL per kg of bacterial supplemented feed for 60 days. The results showed no significant differences in weight gain, however, probiotic feed significantly enhanced some hemolymph parameters and biochemical composition of tail muscle. Histology data revealed better hepatopancreas health and higher microvilli counts in the marron gut fed probiotic diet. The probiotic bacteria triggered significant shift of microbial communities at different taxa level, mostly those reported as beneficial for crayfish. The probiotic diet also enriched the metabolic functions and genes associated with innate immune response of crayfish. Further correlation analysis revealed significant association of some taxa with increased activity for hemolymph and immune genes. therefore, dietary Lactobacillus supplementation can modulate the overall health and immunity as well as gut microbial composition and interaction network between gut microbiota and immune system in crayfish. Aquaculture has become an important food sector for meeting the overall protein demand for growing population. The global consumption of crustaceans has increased greatly and especially those with live transport abilities are increasingly becoming popular 1-3. Marron (Cherax cainni) is one of the largest freshwater crayfish farmed in Western Australia (WA) that has high nutritive value and widespread consumer preferences 4,5. In addition, long distance live transportation ability of marron further increases its international demand, and thus has become an ideal crayfish species for commercial farming 6,7. However, the production of marron in WA has remained stagnant for a long time 7. Selection of proper diets and maintaining the optimum water quality are the two most crucial factors required for marron farming 5,7. Although no disease outbreaks have yet been reported, the interest and intend of intensification in marron farming can expose marron to possible crayfish pathogens including Vibrio, Aeromonas and Rhodobacter 5,6. In the past, several laboratory based trials have been conducted 3,6-9 , however, finding a suitable diet and identifying the beneficial bacteria that potentially can influence the growth and immune performance of marron has still remained unknown. Towards sustainable development of aquaculture, the use of feed additives including probiotics, prebiotics, synbiotics, parabiotics and phytogenics in crustacean's diet to boost biological indices has gained extensive attention from the researchers and farmers. Probiotics are microorganisms associated with health and immune benefits for the host ...