Polyploidy affects fillet yield, composition, and fatty acid profile in two-year old, female rainbow trout, Oncorhynchus mykiss

Abstract

Gonadal development in fish is a dominant physiological process that alters growth and fat metabolism, thereby affecting fillet quality. Sterile, triploid (3 N) female rainbow trout are generated by pressure-induced shock of zygotes (3NP), and by crossing a diploid (2 N; fertile) female and a tetraploid (4 N; fertile) male to produce triploid offspring 100% of the time (3NC; sterile). We have shown female intercross-triploids (3NC) have faster growth rates than pressure-induced triploids (3NP). Using a subset of these animals, we examined fillet yield, texture and fatty acid composition; additionally, fatty acid composition of triglycerides and phospholipids was determined. Variables were measured immediately prior to ovulation of (2 N; fertile) animals. Separable muscle as a percent of whole body weight was higher (P ≤ 0.05) in 3NC (46.5%) compared with 3NP (43.6%) fish, and both had higher yields than 2 N (38.3%) individuals. Fillets from 3NC fillets contained more (P ≤ 0.05) intramuscular crude fat than 3NP and 2 N fillets (13.4%, 11.2%, 8.17%, respectively). Also, 2 N fillets contained (P ≤ 0.05) fewer total saturated fatty acids (29.2%) compared to 3NP (33.4%) fillets which in turn, had fewer than 3NC (34.9%) fillets; suggesting diploids that stored SFA were used for egg development. Although 2 N fillets contained more (P ≤ 0.05) total polyunsaturated fatty acids relative to all fatty acids (PUFA, 28.7%) than 3NC and 3NP fillets (23.6% and 24.8%, respectively), the 3NC had the highest concentration per gram of fillet. 3NC and 3NP muscle had higher (P ≤ 0.05) levels of C12:0, C14:0, compared to 2 N. Fatty acids, C16:0 and 16:1, were highest (P ≤ 0.05) in 3NC, and 2 N muscle contained more (P ≤ 0.05) C22:6n3, C20:3n6 and C18:1n9c compared to 3NC and 3NP. Linoleic acid (18:2n6c) was highest in 2 N followed by 3NP and 3NC muscle (P ≤ 0.05). Thin Layer Chromatography plates were used to separate lipid classes and to evaluate the fatty acid composition of each lipid class. Ploidy did not affect (P > 0.05) fatty acids present in triglyceride and phospholipids. Albeit, triglycerides had higher (P ≤ 0.10) levels of C16:1, C18:1n9c, C18:2n6c, C18:3n3 and C22:1n9 compared to the phospholipids; whereas phospholipids contained higher levels of C16:0, C20:4n6, C20:5n3, and C22:6n3. Notably, phospholipids contained 3 times more C22:6n3 docosahexaenoic acid (DHA) compared to triglycerides. Overall, intercross-triploids (3NC) exhibited superior growth and fillet yields and higher concentrations of intramuscular crude fat compared to 3NP and 2 N females, fillet texture and fatty acid profile were not different, with the exceptions of C18:2n6c, C16:0, and C16:1.