Date of Graduation

2009

Document Type

Thesis

Degree Type

MS

Committee Chair

P. Brett Kenney

Abstract

Egg development (vitellogenesis) is a dominant physiological process that alters growth efficiency and compromises muscle quality in some species. Lipid mobilization from fat stores supplies energy required for this process. To study the effect of vitellogenesis on lipid mobilization, triploid (3N; sterile) and diploid (2N; fertile) rainbow trout females were derived from two families (70 and 71). Fish growth, egg development, proximate composition, and fatty acid composition of muscle, liver, visceral fat, and gonads were determined from July 2008 to March 2009. There were no differences in growth measurements (whole body weight, length, condition factor, eviscerated body weight, and empty body weight) between ploidies. Gonadosomatic index (GSI) of diploid females was higher than triploid GSI for all months except July when diploids were in the early stages of vitellogenesis (p< 0.05). Percent viscera (excluding gonads) of 3N females was higher than 2N females beginning in November (20 months) indicating that 3N females had more visceral fat than diploids (p< 0.05). Crude fat content of triploid fillets increased while the fat content of diploid fillets remained unchanged from July (16 months) to March (24 months). This observation shows that diploids were using additional fat while triploids were depositing fat in the muscle (p< 0.05). This observation and the declining visceral weights imply that diploids were depleting visceral fat stores and not mobilizing lipid from muscle, suggesting that muscle fat was a secondary source of energy during gonadogenesis under a high nutritional plane. Fatty acid profile of all tissues changed to some extent throughout maturation. Saturated fatty acids decreased while linoleic acid (C18:2n-6) and docosahexanenoic acid (C22:6n-3) increased from July to March in 2N fillets (p< 0.05). Palmitic acid (C16:0) and oleic acid (C18:1n-9) decreased while highly unsaturated fatty acids (C20:5n-3 and C22:6n-3) increased from July to March in 3N fillets (p< 0.05). Palmitic acid (C16:0) and eicosapentaenoic acid (C20:5n-3) increased while eicosanoic acid decreased from July to March in 2N liver (p< 0.05). Palmitoleic acid (C16:1), stearic acid (C18:0), and oleic acid (C18:1n-9) increased while the highly unsaturated fatty acids (C20:5n-3 and C22:6n-3) decreased from July to November in 3N liver. Saturated fatty acids (C16:0 and C18:0), Į-linolenic acid (C18:3n-3), and eicospentaenoic acid (C20:5n-3) decreased while linoleic acid (C18:2n-6) increased in 2N visceral fat. Linoleic acid (C18:2n-6), calendic acid (C18:3n-6), Į-linolenic acid (C18:3n-3), and eicospentaenoic acid (C20:5n-3) decreased from July to March in 3N visceral fat. Palmitoleic acid (C16:1) and oleic acid (C18:1n-9) decreased while stearic acid (C18:0) and docosahexanenoic acid (C22:6n-3) increased from July to September in 2N gonads Highly unsaturated, long chain fatty acids appear to play an important role in gonadogenesis, either as a source of energy or deposited in eggs for the survival of offspring. Myristic acid (C14:0) appears to play a minor role in lipid metabolism during vitellogenesis. However, when fish are on a high nutritional plane, differences in growth and preferential mobilization of fatty acids, as a result of ploidy, may be affected. This information provides a glimpse into specific changes in composition and fatty acid content that occur as fish dramatically alter their lipid metabolism during egg growth and development. Gaining a better understanding of these changes will allow for development of better management strategies to yield a higher quality product in animals of both ploidies.

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