Using a liposome diet to deliver D5-18:3n-3 to four
species of marine planktonic zooplankton, we found
that the amounts of PUFA produced from this precursor
over periods up to 96 h were negligible. Extremely
low levels of D5-20:5n-3 and D5-22:6n-3 were detected
in female C. finmarchicus, D. forcipatus and Euphausia
superba calyptopus larvae, whereas no products of desaturase
activity were present in Calanoides acutus after 96 h
incubations. The elongation product D5-20:3n-3 was
the major anabolite in all four species. Elongation is an
easier enzymic step than desaturation and desaturases
are frequently rate liming in PUFA synthesis. It was
however not possible to distinguish if the small amounts
of PUFAs that were produced were synthesized by the
copepods themselves, or bacteria inhabiting their guts.
It has previously been established that there is a high
prevalence of PUFA-producing bacteria in high latitude
environments (Nichols et al., 1993) including some
strains that were isolated from the guts of marine zooplankton
(Jøstensen and Landfald, 1997).