The effects of prebiotics on the growth performance and gastrointestinal microflora modulation in oreochromis mossambicus in Hardap region, Namibia
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Date
2022
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Publisher
University of Namibia
Abstract
Aquaculture across the world is growing exponentially, and has certainly gained popularity among small scale farmers in Namibia. Aquaculture aims to take on the increasing demand of fish as a food source in light of depleting fish stocks in natural water systems. Therefore, studies aiming to improve aquaculture production in eco-friendly and sustainable ways, such as, adopting measures that improve fish performance and health are necessary, for example, the use of feed additives such as prebiotics, probiotics and synbiotics. This study aimed to investigate the prebiotic effect of dietary inulin and Termitomyces schimperi mushroom powder incorporated in fish feed on the growth performance and modulation of gastrointestinal microflora in Oreochromis mossambicus. Three experimental diets; inulin, inulin+ mushroom and control were made at 1% dry weight of feed inclusion level. Furthermore, initial and final body mass and daily feed consumption records were used to determine growth performance and feed utilization parameters; while fish tissue samples were used to determine proximate composition analyses. 16S metagenomics sequencing of the bacterial communities available in the intestinal samples were carried out on Illumina Miseq with primers targeting the V3-V4 region of ribosomal ribonucleic acid (rRNA). The results of this study showed that the weight gain rate (WGR) and specific growth rate (SGR) of fish fed the control diet (152.59 ± 9.61 & 2.15 ± 0.09 respectively) were significantly higher (P value ≤ 0.05) than those fed the inulin diet (117.25 ± 6.20 & 1.80 ± 0.07 respectively). However, the results indicated that there were no significant differences (P values ≥ 0.05) among the experimental diets in terms of feed conversion ratio (FCR), survival rate (SR), fat, moisture, ash and protein contents. The colony-forming units (CFU) in the inulin group ii (3.54 ± 0.05 log 10 CFU/g) were significantly lower (P value ≤ 0.05) than the control group (3.54 ± 0.05 log 10 CFU/g). On the other hand, it was discovered that I group showed higher alpha and beta diversity indexes in comparison to the control and inulin + mushroom groups. Typical examples of phyla identified include Firmicutes, Actinobacteria, Proteobacteria and Bacteroidetes. At the genus level, relative abundance showed higher variation in the most abundant genera between samples. This study established that the inclusion of inulin and T. schimperi powder had no significant effect on the growth performance and proximate composition of O. mossambicus. On the other hand, the inclusion of inulin powder resulted in the reduction of viable gut microbiota counts in culture dependent methods, as well as higher alpha & beta diversity indices in culture independent methods in comparison to mushroom powder and the control. To the best of our knowledge, this is the first study to document the inclusion of T. schimperi powder as a prebiotic in fish feed. This study recommends the incorporation of prebiotics in fish feed before extrusion to ensure homogeneity of prebiotics and feed mixture. In addition, future studies should consider doing stress challenges to the fish to test the health benefit (resistance to stress) of fish fed with prebiotics. Moreover, further sequence analyses are recommended to identify the amplicon sequence variants (ASVs) without taxonomic classification in this study.
Description
A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Science (Microbiology)
Keywords
Prebiotics, Growth performance, Hardap region, Farmers