Lipid content of stream macroinvertebrates

Total lipid content of freshwater macroinvertebrates from different orders and with different life histories was investigated. Lipids were determined as HIP-extractable lipids (HIP = hexane: isopropanol). Macroinvertebrate ta xa were assigned to different feeding guilds, and life histories for insect taxa: Gammarus pulex (Amphipoda/shredder), Ecdyonurus sp. (Ephemeroptera/h emimetabolous/grazer), Perla sp. (Plecoptera/hemimetabolous/predator), Hydr ophsyche sp. (Trichoptera/holometaboious/ suspension feeder), and Atherix i bis (Diptera/holometabolous/predator). Animals were collected in two stream s in Switzerland bimonthly between October 1994 and October 1995. Lipids, e xpressed as percent dry mass (dm), were estimated using two techniques: (1) as total lipid content, determined by the sulphophosphovanilline method; ( 2) as total fatty acids (= sum of fatty acids), determined by gas chromatog raphy. The annual aver age total lipid contents for G. pulex, Ecdyonurus an d Perla were 6.1 %, 7.0 % and 6.0 % dm, respectively. The two holometabolou s insects, Hyduopsyche (8.0 %) and A. ibis (9.3 %), exhibited the highest t otal lipid content. Total fatty acids as a percentage of total lipids was l owest in G. pulex (62 %), followed by Ecdyonurus (64 %), Perla (73 %), Hydr opsyche (80 %), and A. ibis (85 %). The dry mass of holometabolous insects (Hydropsyche and A. ibis) related positively with lipids, indicating an inc rease in body concentration during larval growth. No or only a weak positiv e relationship with dry mass was found for the hemimetabolous Ecdyonurus an d Perla. Gammarus pulex, in contrast, showed a negative relationship. Male G. pulex attained a larger size and contained less fat than juveniles and a dult females. Seasonal changes in total lipid content were recognisable onl y as weak trends because of high variation among individuals. Gammarus pule x had higher total lipid content in spring, while Perla and Hydropsyche max ima occurred in summer. No seasonal trends in total lipid content could be observed in Ecdyonurus and A. ibis.