Selective Fatty Acid Metabolism, Not the Sequence of Dietary Fish Oil Intake, Prevails in Fillet Fatty Acid Profile Change in Sunshine Bass

Increasing prices of fish oils (FOs) that are rich in long‐chain (LC) polyunsaturated fatty acids (PUFAs) have led to increased implementation of plant‐derived oils in aquaculture feeds. Use of diets that contain alternative lipids will affect the fillet fatty acid (FA) profile; therefore, the fish may be “finished” to augment fillet LC‐PUFA content before harvest. Understanding tissue FA profile change and selective metabolism of FAs in sunshine bass (female white bass Morone chrysops × male striped bass M. saxatilis) may allow finishing strategies to be optimized for this taxon. We evaluated whether the sequence of dietary LC‐PUFA provision affects tissue composition of sunshine bass and whether profile change is similar after a switch to or from an LC‐PUFA‐rich feed. Sunshine bass were fed practical feeds (∼45% protein, ∼14% lipid) containing FO (rich in LC‐PUFAs) or corn oil (CO; rich in medium‐chain [MC] PUFAs) according to four regimens: FO feed exclusively, CO feed exclusively, or switching from one feed to the other halfway through the trial (from CO to FO or from FO to CO). Administering the FO and CO feeds exclusively or in alternation did not significantly affect production performance. Fillet FA profile changed little for fish that received the exclusive FO and CO regimens and essentially became slightly more FO‐like and CO‐like, respectively. Fillet LC‐PUFA and MC‐PUFA levels were comparable in the alternating FO‐to‐CO and CO‐to‐FO groups at harvest. However, the relative change in profile differed considerably; the increase in fillet LC‐PUFAs for the CO‐to‐FO group was significant, but the corresponding increase in MC‐PUFAs for the FO‐to‐CO group was much greater. This suggested that certain PUFAs were actively included or retained (or both) within the fillet lipid, particularly 18:2(n‐6) (abundant in CO), which can “outcompete” LC‐PUFAs for fillet deposition. Although there appears to be selection for and against the incorporation of certain FAs into fillet tissue, whether these FAs are consumed earlier or later during juvenile growth appears to have little effect on final tissue composition. Received January 16, 2010; accepted April 21, 2010