Survival and bioconversion of n−3 fatty acids during early development of dolphin ( Coryphaena hippurus) larvae fed oil-enriched rotifers

Abstract

The effects of varying dietary fatty acid profile on survival and bioconversion of linolenic ( n−3) series fatty acids for dolphin ( Coryphaena hippurus) larvae were examined using live feed organisms enriched with oils. First-feeding (3-day-old) larvae were either starved, or fed rotifers ( Brachionus plicatilis) cultured on the algae Nannochloropsis oculata and enriched with emulsified preparations of corn, olive, soybean, and squid oils. A control group was fed rotifers packed with N. oculata alone. Qualitative fatty acid composition of triglyceride (TG) and phospholiqid (PL) fractions from 3-day through 5-day old starved larvae and from 7-day-old fed larvae was determined. In addition, quantitative fatty acid content was measured using tridecanoic acid (C13:0) as an internal marker. The fatty acid composition in PL fractions of 7-day-old larvae paralleled that of the particular enriched rotifer they were fed, except for the levels of C22:6 n−3 which was found in all larvae, although it was only present in rotifers enriched with the emulsified squid oil. However, the absolute level of C22:6 n−3 in larvae fed rotifers deficient in this fatty acid was no higher than it was in 3-day-old, prefeeding larvae. The concentration of all other fatty acids consumed by these larvae, and of C22:6 n−3 in larvae fed squid oil, increased in proportion to the dry matter weight gain of the fish. C22:6 n−3 and C20:4 n−6 were preferentially retained by starved larvae despite a decrease in fatty acid content and type over time. The average survival of all larvae fed oil-enriched rotifers (68%) was 30% greater than that of larvae packed with N. oculata alone (52%). However, survival was not affected by the varying fatty acid profiles of rotifers within the oil-enriched groups. It is concluded that bioconversion of n−3 fatty acid precursors to the higher chain C22:6 n−3 derivative does not occur in dolphin larvae at least during their first week of development. The levels of C22:6 n−3 found in 7-day-old larvae appeared to have originated from endogenous stores which were carried over to this period. Both this endogenous reserve of C22:6 n−3 and dietary lipids, in general, appear important in supporting survival of dolphins through the early larval period.