The lipoprotein and lipid composition of the serum in postabsorptive haddock was characterized. A low level of very low density lipoproteins (VLDL; <50 mg dL1) was observed in serum. High density lipoprotein (HDL) was the predominant lipoprotein class followed by low density lipoproteins (LDL). Of the lipoprotein classes, the highest proportions of triacylglycerol (28%) and phospholipid (64%) were observed in the lipid of VLDL and HDL, respectively. Serum lipid (48%), phospholipid (50%) cholesterol ester (65%) and HDL (51%) contained a high level of polyunsaturated FA, particularly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Serum triacylglycerol (38%) and VLDL (36%) contained a lower proportion of polyunsaturated fatty acid. The phospholipid, triacylglycerol, cholesterol ester and cholesterol contents of the whole serum were 739, 214, 201 and 141 mg dL1 respectively. On the basis of total acyl carbon number, the 38C (36%) and 36C (24%) molecules were the predominant phospholipids. The 50C (11%), 52C (17%), 54C (21%), 56C (21%) and 58C (15%) molecules were the major triacylglycerols. High molecular weight apo B-like proteins were observed in the VLDL, LDL and intermediate density lipoprotein (IDL) fractions. An apo AI-like protein was predominant in the HDL fraction. The prevalence of enlarged fatty livers in cultured gadoid fish (i.e. haddock and cod) is a major constraint to their commercialization and has been associated with the level of dietary lipid. Information on lipid (triacylglycerol) transport out of the liver through the serum as lipoproteins (VLDL) has implications for our understanding of fatty liver development in cultured gadoid fish. The low level of VLDL triacylglycerol (<12 mg dL1) circulating in the serum of postabsorptive haddock suggests either a low level of lipid transport out of the liver as triacylglycerol or relatively rapid turn over of VLDL.