Investigating the effects of commercially available aquafeeds on Asian seabass Lates calcarifer

To reduce the burden on marine resources, fish meal and fish oil have been gradually replaced by suitable alternatives in aquafeed productions resulting in a wide range of commercial aquafeeds available in today’s market. As part of good aquaculture practice, it is essential to use aquafeeds that fulfill the nutritional requirements for the species of choice; however, very few studies have evaluated the effects of different commercial aquafeeds onto farmed fish, and none of those studies have used genomic approaches for assessment. In this Thesis, the relative effects of consuming eight aquafeeds have been evaluated at three different stages of Asian seabass culture (larvae: 2- 28 dph, juvenile: 107-168 dph and grow-out: ~270-300 dph). Fatty acid analyses detected a large amount of plant-based oils in three aquafeeds and interestingly, no detrimental impacts have been observed in the liver histological and growth profile of the fishes having plant oil based diets. On the other hand, the fillet nutritional quality of those fishes was found to be suboptimal, with 20% higher n6 polyunsaturated fatty acid (PUFA) than n3 PUFA. Several biological processes linked to metabolism were observed to be significantly enriched among the various groups of fishes via microarray-based transcriptomic analyses. In addition, enrichment of growth related transcripts was observed in those juvenile fishes that grew the largest. During larval weaning from live feed to aquafeeds, adaption stress overwhelmed the possible changes in the gut and tank water microbiota due to different nutritional factors. After seven days post-weaned, unique microbial signatures were detected in the gut microflora due to different dietary effects and positive enrichment in mucin-type O-glycan biosynthesis pathways were observed through intestinal RNA analyses comparison. These results provided a snapshot on how different aquafeeds were able to modulate the gut microflora and cause changes to the morphological, physiological and nutritional aspects of the fish. Taken together with the sensory results indicating that taste differences caused by diets could be masked by preparation methods; proper feed selection and further improvement of Asian seabass-specific diets are necessary to ensure the well-being of cultured fishes and maximizing their nutritional value.Master of Scienc