Marron (Cherax cainii), a native iconic species in Western Australia is the largest farmed fresh water crayfish. Commercial culture of marron has a lot of positive aquaculture attributes including high consumer preference, high market value, and disease resistance. However, the production of marron has remained stagnant over the last few decades. Probiotics including Lactobacillus species has long been used in commercial aquaculture as a growth promoter and immune enhancer. In marron aquaculture, however, effects of Lactobacillus spp. as feed supplements has yet to be fully investigated.
A 60-days feeding trial was conducted with four different test diets, fishmeal based control (CT), L. acidophilus (LA), L. plantarum (LP) and L. casei (LC) supplemented with CT. The ingredients of CT were purchased from Glenn Forest, Perth, Australia, and probiotic feed was formulated by supplementing 109 CFU/mL of probiotic species per kg of feed according to standard methods. A total of 80 were transported to Curtin Aquatic Research Laboratories under live conditions and distributed randomly into 16 different tanks. After acclimation for a week, marron were fed with the respective test diets at 1.5% of the total body weight per day.
The results showed no significant differences in growth with any of the test diets, however, P-value of 0.059 for L. plantarum fed marron suggest that LP could be a diet of interest to marron. All probiotic supplemented diets positively influenced the total haemocyte counts in the haemolymph while tail muscle protein and gross energy were improved only by L. plantarum supplementation. Further microbiome analysis revealed significant (P<0.05) enrichment of gut microbial communities in terms of alpha-beta diversity in the probiotic fed diets wherein L. plantarum augmented higher (P<0.05) lactic acid bacteria in the hindgut of marron (Table 1). Finally, increased (P<0.05) marron survival was observed in the probiotic fed marron after 14 days of challenge with Vibrio mimicus (Figure 1A). The probiotic diets also significantly upregulate the expression of prophenoloxidase (proPO) and cathepsin L (PcCTSL) at 48 h post- injection with V. mimicus, the genes linked to innate immune response of crayfish (Figure 1B).