Changes in lipid and fatty acid composition of pre- and post- spawning Onchidium struma

Onchidium struma is a very important mollusk with high nutritional and pharmic value, which natural habitat is localized on the mudflats of the intertidal zone especially in Jiangsu, Shanghai and Zhejiang. Nowdays, O.struma become a very popular invigorant in east China, so there is an increasing demand for this species production. However, the culture technology of all life stage of O.struma (broodstock, larvae and juveniles) have not been established in China, the seed of O.struma are collected from wild area of their natural habitat. Although there are many research reports on morphological characteristics, reproductive behavior, ecological habits, embryonic development and gonadal development of Onchidium spp, only two available studies have been conducted to investigate the proximate compositions of O.struma. The experiments were conducted to investigate the changes on tissue indices, moisture content in the different tissues, lipid class and fatty acid composition of pre- and post spawning O.struma by gas chromatography (GC) and IAROSCAN TLC-FID. The results indicated that: (1) Hepatosomatic Index (HSI), Digenetic Gonadosomatic Index (DGSI) and Egg Albumen Gland Index (EAGI) of O.struma decreased significantly after spawning (P0.05). Meanwhile, the moisture content in those tissues increased significantly while the lipid content droped sharply. The decreased range of EAGI was 41.41% from pre-spawning to post-spawning, while the lipid content in hepatopancreas dropped from 23.51% to 15.07% tissue dry weight. (2) The lipid class of adult O.struma in different tissues mainly included phospholipids (PL), cholesterol (Cho),triacyglycerol (TG) and free fatty acids (FFA), while monoacylglycerol (MG) could be detected only in hepatopancreas. There were significant declines on FFA content in hepatopancreas and PL content in digenetic gonad of Ostruma after spawning. Then, no siginificant difference could be found on lipid class on other tissues. (3) After spawning, the C16:1n7, C20:5n3 (EPA) and C22:6n3 (DHA) contents in hepatopancreas decreased significantly, while the ∑SFA increased sharply. At the same time, the AA and EPA contents in mucous gland and male prostate dropped significantly, while there was a important rise on the contents of C16:0 and C18:1n9. As for digenetic gonad, there was significantly drop on the contents of C20:2n6, C22:2n6 and C22:5n3 (DPA), while C20:4n6 (AA) content raised sharply. Based on the proportion of ∑PUFA in these tissues, it could be ranked with the turn of digenetic gonad (33.83%-37.72%, mean 35.78%) muscle (30.53%-30.58%, mean 30.56%) mucous gland (26.26%-31.92%, mean 29.09%) egg albumen gland (29.02%-29.09%, mean 29.06%) male prostate (25.19%-31.48%, mean 28.34%) hepatopancreas (15.90%-20.16%, mean 18.03%). In conclusion, these results suggest that PL and PUFA are very vital to the gonad development of O.struma, and the higher content of FFA in hepatopancreas may be relevant to the lipid metabolism during the reproductive period. During the gonad development of O.struma, the HUFA (i.e. EPA and DHA) in hepatopancreas maybe transported to gonad.