Defining the allometric relationship between size and individual fatty acid turnover in barramundi Lates calcarifer

An experiment was conducted with barramundi (Asian seabass; Lates calcarifer) to examine the allometric scaling effect of individual fatty acids. Six treatment size classes of fish were deprived of food for 21 days (Treatment A, 10.5 ± 0.13 g; Treatment B, 19.2 ± 0.11 g; Treatment C, 28.3 ± 0.05 g; Treatment D, 122.4 ± 0.10 g; Treatment E, 217.6 ± 0.36 g; Treatment F, 443.7 ± 1.48 g; mean ± SD) with each treatment comprising of fifteen fish, in triplicate. The assessment of somatic losses of whole-body energy and lipid were consistent with previous studies, validating the methodology to be extended to individual fatty acids. Live-weight (LW) exponent values were determined to be 0.817 ± 0.010 for energy and 0.895 ± 0.007 for lipid. There were significant differences among the fatty acids ranging from 0.687 ± 0.005 for 20:5n-3 (eicosapentaenoic acid) and 0.954 ± 0.008 for 18:1n-9 (oleic acid). The LW exponent values were applied to existing fatty acid intake and deposition data of barramundi fed with either 100% fish oil or 100% poultry oil. From this the maintenance requirement for each fatty acid was determined. The metabolic demands for maintenance and growth were then iteratively determined for fish over a range of size classes. Application of these exponent values to varying levels of fatty acid intake demonstrated that the biggest driver in the utilisation of fatty acids in this species is deposition demand and despite their reputed importance, the long-chain polyunsaturated fatty acids had nominal to no maintenance requirement.