Exploration of Bioslurry Bacteria Candidate Probiotics for Fish Feed: Identification, Morphological Characteristics and Enzyme Activity

The quality of fish feed is determined by the presence of nutrients that are readily assimilated by fish. The utilization of probiotic bacteria in fish feed constitutes an innovative approach within the context of contemporary fish farming methodologies. The objective of this study was to investigate the potential probiotic properties of bacterial isolates derived from bioslurry. This investigation involved the isolation and identification of the isolates, as well as a comprehensive analysis of their morphological characteristics and enzyme activity. The morphological characteristics were identified using both macroscopic and microscopic examination, followed by Gram staining.  Bacterial types were identified using MALDI-TOF MS, and enzyme activity was assessed based on the enzymatic index. The identification results indicated the presence of ten distinct types of bacteria in the bioslurry. On a macroscopic level, bacteria were predominantly characterized by circular colony shapes, yellow and white colony colors, entire margins, and convex elevations. In accordance with microscopic identification, nine Gram-positive isolates were obtained. The results of the MALDI-TOF MS identification indicated the presence of six bacterial species: NN1 Exiguobacterium aurantiacum, NN4 Bacillus idriensis, NN5 Bacillus cereus group, NN6 Bacillus subtilis, NN9 Paenibacillus lautus, and NN10 Lysinibacillus furiformis. The results demonstrated that the types of isolate bacteria NN1, NN4, and NN5 could be utilized as probiotic candidate bacteria due to their amylase, lipase, and protease enzyme activities. These activities facilitate the breakdown of nutrients in the feed, thereby enhancing the absorption of nutrients by fish.