Life history and fatty acid composition of the marine rotifer Synchaeta cecilia valentina fed different algae

Abstract

A strain of the marine rotifer Synchaeta cecilia valentina, isolated from 'El Hondo de Elche', a Spanish Mediterranean coastal lagoon, was cultured in the laboratory in 20 ml test tubes, at 20°C and 25 ppt salinity and fed with the algae Tetraselmis sp., T. chuii, Cryptomonas sp., Rhodomonas salina and R. baltica. The effects of these 5 algal diets and 3 food levels (2.1, 3.2 and 4.2 µg ml-1 dry wt) on life history traits of this rotifer were studied in life tables performed with replicated individual cultures of 1 ml, at the temperature and salinity mentioned above. Algal diet had a significant effect on both average lifespan (LS) and net reproductive rate (R0), but food concentration only had an effect on R0. Tetraselmis sp. provided the best results: LS ranging from 4.4 to 6 d, R0 from 10.9 to 12.8 offsping female-1, and intrinsic growth rate (r) from 0.84 to 1.12 d-1. S. cecilia valentina also grew with the remainder of the algae, except with R. baltica. With this alga the rotifer grew only in 500 ml cultures performed at a higher food concentration (5.55 µg ml-1 dry wt). The effect of the algal diet on the fatty acid composition of the rotifers was analysed to infer its nutritional value according to the changes induced by diet. Saturated fatty acids made up 34 to 40% of total fatty acids, whereas monoenes accounted for 15 to 23%, and polyunsaturated fatty acids constituted 20 to 29%. Main fatty acids were: 16:0 (which ranged from 17 to 22%), 18:0 (10 to 12%), and 18:1 (8.5 to 12%). In certain algal treatments (both Tetraselmis species), the linolenic acid 18:3n-3 was moderately abundant (5 to 9%). Eicosapentaenoic acid, 20:5n-3, was markedly lower in rotifers fed with R. baltica (less than 3%), whereas docosahexaenoic acid, 22:6n-3, was found in a higher proportion in Cryptomonas sp. (4.9%) and R. salina (3.4%) treatments. The nutritional value deduced from the lipid composition was similar to that reported in the literature for other rotifers such as Brachionus plicatilis.