Host associated probiotics improve growth performance, biochemical composition, tissue histomorphology, and enhance protection against pathogenic bacteria in Malaysian mahseer, Tor tambroides juveniles

The origin of the probiotics, the age and size of the fish, the length, dosage, and technique of application, as well as the culture environment, affect the efficacy of probiotics. Juveniles of Tor tambroides (initial weight 2.53 ± 0.02 g) were used in the feeding experiment to compare the effects of host associated probiotics (HAPs) and commercially prepared probiotics (CP) on growth performances, biochemical composition, tissue histomorphology, and protection against infection. A total 360 fish were fed for 70 days where control fish received basal feed only, two HAPs (T1: Aeromonas sp. KT27; T2: Enterococcus sp. strain KM07) and a commercial probiotic (T3: CP, Bacillus sp.) received experimental diets (1×10 8 CFUg − 1 ). Fish from all treatments were exposed to the pathogen Vibrio parahaemolyticus at the completion of the feeding trial by intraperitoneal injection of the lethal dose (LD50: 1×10 8 CFUml − 1 ). The results revealed that fish fed diets supplemented with HAPs exceeded control fish in all growth metrics and had higher post-challenge test survival (%). The proximate composition of the whole body did not change within treatments. However, both HAPs (T1 and T2) treatments improved the levels of total n-6, C18:3n-3, and C18:2n-6 in T. tambroides' whole body. Based on histological analysis, both HAPs had a good impact on gut shape reflected by increased villus height, width, and area as well as better hypertrophic muscle growth. The dietary application of HAPs, notably Enterococcus sp. strain KM07, showed overall better performances in T. tambroides juveniles and may be used as a potential probiotic in T. tambroides aquaculture.