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

Authors: EVERSON, JEREMY - West Virginia University; Weber, Gregory - Greg; MANOR, MEGHAN - West Virginia University; TOU, JANET - West Virginia University; KENNEY, P. BRETT - West Virginia University

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2020
Publication Date: 8/25/2020
Citation: Everson, J.L., Weber, G.M., Manor, M.L., Tou, J.C., Kenney, P. 2020. Polyploidy affects growth, fillet composition, and fatty acid profile in two- year old, female rainbow trout, Oncorhynchus mykiss. Aquaculture. 531:735873. https://doi.org/10.1016/j.aquaculture.2020.735873.
DOI: https://doi.org/10.1016/j.aquaculture.2020.735873

Interpretive Summary: Gonadal development in fish slows growth and alters fat metabolism, thereby affecting fillet quality. The rainbow trout industry mitigates the negative impacts of gonadal development by producing triploid fish that have three sets of chromosomes, which makes them sterile and prevents the ovaries from developing. Triploid rainbow trout are traditionally generated by pressure-induced shock of zygotes (3NP). Alternatively, sterile triploids (3NC) can also be produced by crossing diploid (2N) and tetraploid fish. We have previously demonstrated that 3NC fish have faster growth rates than 3NP fish. In the present study we compared fillet yield, fillet texture, and fillet fatty acid composition among 2N, 3NP, and 3NC female rainbow trout as they approached the age of sexual maturity. The 3NC fish exhibited superior growth, fillet yield, and had higher concentrations of crude fat compared to 3NP and 2N fish and had no measurable differences in fillet texture or fatty acid profile of most intramuscular lipids. This study demonstrates advantages of 3NC fish for producers that use triploidy to avoid negative impacts of gonadal development on food fish production.

Technical Abstract: Gonadal development in fish is a dominant physiological process that alters growth and fat metabolism, thereby affecting fillet quality. Sterile, triploid (3N) female rainbow trout, generated by pressure-induced shock of zygotes (3NP), are used to eliminate reduced growth and product quality associated with gonadogenesis. However, triploid rainbow trout can also be produced by crossing a diploid (2N; fertile) female and a tetraploid (4N; fertile) male to produce triploid offspring 100% of the time (3NC; sterile). We have previously shown female intercross-triploids (3NC) have faster growth rates than pressure-induced-triploids (3NP). Using the same animals, we examined fillet yield, texture attributes, fillet fatty acid composition and fatty acid composition of triglycerides and phospholipids. Variables were measured immediately prior to ovulation of (2N; 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 much higher yields than 2N (38.3%) individuals. Composition of body weight gain differed with 3NC fillets containing more (P<0.05) intramuscular crude fat than 3NP and 2N fillets (13.4%, 11.2%, 8.17%, respectively). Also, based on relative peak area, 2N 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 mobilized stored SFA for egg development. Although 2N fillets contained a greater ratio of (P<0.05) total polyunsaturated fatty acids (PUFA, 28.7%) compared to 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 and C14:0 compared to 2N. Fatty acids C16:0 and 16:1 were highest (P<0.05) in 3NC and 2N 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 2N followed by 3NP and 3NC muscle (P<0.05). Thin Layer Chromatography plates were used to separate lipid classes and examine preferential mobilization. Ploidy did not affect (P>0.05) fatty acids present in triglyceride and phospholipids. However, triglycerides had higher levels of C16:1, C18:1n9c, C18:2n6c, C18:3n3 and C22:1n9 compared to the phospholipids while; 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, fillet yields, and higher concentrations of crude fat compared to 3NP and 2N females, without measurable differences in texture or ploidy production affecting fatty acid profile of intramuscular lipids with the exceptions of C18:2n6c, C16:0, and C16:1.