Defining essential fatty acid deficiency in juvenile barramundi Lates calcarifer

Barramundi (Lates calcarifer), a catadromous teleost of significant and growing commercial importance, are reported to have limited fatty acid bioconversion capability, typical of marine species, and therefore require preformed long-chain polyunsaturated fatty acids (LC-PUFA) as dietary essential fatty acid (EFA). In this study, the response of juvenile barramundi (47.0 g/fish initial weight) fed isolipidic and isoenergetic diets with 8.2% added oil was tested. The experimental test diets were either devoid of any fish oil (FO), and thus with no n-3 LCPUFA (FO FREE diet) or with a low inclusion of FO (FO LOW diet) and were compared against a control diet containing only FO (FO CTRL diet)as the added lipid source, over an eight week study period. Interim samples and measurements were taken every two weeks during the trial in order to define the onset and progression of the aetiology of EFA deficiency. After two weeks of feeding, the fish fed the FO FREE and FO LOW diets had significantly lower live-weights and after eight weeks significant differences were detected for all growth and feed utilisation parameters. The fish fed the FO FREE diet also had a significantly higher incidence of external abnormalities. Sub-clinical signs of deficiency were also noted in the plasma biochemistry with several parameters affected by dietary treatment. The transcription of several genes involved in fatty acid metabolism was affected after only two weeks of feeding with the experimental diets, showing a rapid nutritional regulation. This experiment documents the aetiology of the onset and the progression of EFA deficiency in juvenile barramundi and demonstrates that such deficiencies can be detected within two weeks in juvenile fish.