A comparison of the lipoprotein profiles in male trout (Salmo gairdneri) before maturity and during spermiation.

1. The distribution and concentration of blood lipoproteins were determined in three groups of male rainbow trout (Salmo gairdneri) each, fed the same diet and reared at a temperature of 17-18 degrees C. 2. The three groups (A, B and C) differed as to age (A and B were 1 yr old, while C was 3 yr old) and to degree of sexual maturity (A was sexually immature, while B and C were in spermiation). 3. Total serum lipoprotein levels reached high values in A, B and C (1900, 2400 and 1500 mg/100 ml. respectively) but their distribution depended largely on the degree of sexual maturity of the fish. 4. Very low density lipoproteins (VLDL) and low density lipoproteins (LDL) were predominant in juvenile trout, whereas high density lipoproteins (HDL) accounted for more than 50% of the total lipoproteins in spermiating trout. 5. In the latter class of lipoproteins, the phospholipid comprised 70% of the total lipid. 6. Essential 22:6 (n-3) was the main polyunsaturated fatty acid in all the lipid fractions of each of the lipoprotein classes; it was found in higher percentages in structural lipid, phospholipid and cholesterol ester, comprising between 35 and 40% of the total fatty acids. 7. These findings support the hypothesis that the production and utilization of lipoproteins in trout are related to the annual formation of gonadal tissue. The lipoproteins might be vehicles for cholesterol and essential fatty acid 22:6 (n-3), incorporated into gonadal tissue during gametogenesis.