Abstract
As nutrition-related expenses constitute the majority of the costs for aquaculture farms, it is essential for them to use feeds that provide an ideal combination of nutrients for the species of choice. In this study, the relative effect of consuming three different pelleted feeds (B, C and D) in comparison to frozen baitfish (A; control) were compared on juvenile Asian seabass (77.3 ± 22.4g) that were selected for increased growth rate over two generations. Our objectives were: 1) to evaluate the effects of different pelleted feeds based on overall physiological changes and nutritional quality of fillets; 2) improve our understanding of the underlying mechanisms with transcriptomic analysis; 3) if possible, identify the feed type that supports the growth of these fishes without substantially reducing the nutritional quality of fillet. The growth performance, fatty acid composition of fillet, hepatic histology and transcriptome of the fishes (Groups A-D) were analyzed. The majority of fatty acids of the fillets, except γ-linolenic acid (GLA, C18:3n6), correlated significantly with the respective diets. Asian seabass fed Feed C showed highest specific growth rate (SGR) and feed conversion efficiency (FCE) with closest histology and transcriptomic profile to control, but their fillet contained the highest n6/n3 ratio. When the liver-based transcriptomes were analyzed, a complex set of differentially expressed genes were detected between groups fed pelleted feeds and controls as well as among the pellet-fed groups themselves. Significant enrichment of genes with growth-related function tallied with the morphological data measured. When compared with control (Group A), ‘Biosynthesis of unsaturated fatty acids’ and ‘Steroid biosynthesis’ pathways were significantly enriched in pellet-fed groups. Reduced goblet cell numbers were observed in the gut of pellet-fed fish compared to controls and fads6 was found to be a suitable candidate gene to separate wild-caught Asian seabass, from pellet-fed ones. These results provide insights for researchers on the various effects of feeds on the biochemistry and global gene expression of the fish and potentially for seabass farms to make more informed feed choices.
Highlights
The global aquaculture production of food fish has increased tremendously over the last decade, reaching 62.7 million metric tonnes in 2011 or about 40.1% of world total fish production [1]
Biochemical analysis of the feeds (Table 1) re-confirmed most of the wide-ranging differences observed among the composition of the feeds that were expected from the nutrition labels provided on the packaging (S1 Table)
No statistical significant differences could be observed for daily body weight gain, feed conversion efficiency (FCE) and condition factor between Groups B and D
Summary
The global aquaculture production of food fish has increased tremendously over the last decade, reaching 62.7 million metric tonnes in 2011 or about 40.1% of world total fish production [1]. In collaboration with the Marine Aquaculture Centre of Agri-Food and Veterinary Authority (MAC, AVA, Singapore), we have been performing a selection program to develop elite lines of Asian seabass since 2004 through the utilisation of molecular genetics and genomic tools, such as genotyping, linkage mapping and transcriptomics [4,5,6]. The ability to convert eicosapentaenoic (EPA, C20:5n3) to docosahexaenoic acids (DHA, C22:6n3) might be possible but the conversion rate is usually too low to meet the high demand for DHA in rapidly growing and developing fry and fingerlings [11]. It would require feeds that contain much higher levels of fish oil as it does not possess or has only limited ability to convert C18 polyunsaturated fatty acids (PUFA) into long-chain PUFA (lcPUFA) [12,13]. It is well established that fish oil- and fish meal-based feeds are essential for Asian seabass, as their absence would result in growth retardation and reduction in all major n3-lcPUFAs, including EPA and DHA [8,9]
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