Alterations of the biochemical composition and survival of the rotifer Brachionus plicatilis have been investigated. During starvation the proportion of total protein increased from 45-3 to 62-7% while that of total lipid, carbohydrate and glycogen decreased from 20-1 to 6-9%, from 21-2 to 14-1 % and from 17-3 to 4-9% dry weight, respectively. The proportion of polar lipids and free sterols in total lipids increased, from 8-3 to 32-0% and from 29-2 to 58-3% whereas triacylglycerol decreased from 54-7 to 4-2% dry weight. The most abrupt alteration in these fractions took place in the interval from 24 to 48 h. The proportion of monoacylglycerols, diacylglycerols, free fatty acids and esters of waxes and sterols increased from 1-2 to 3-0% (72 h), from 0-2 to 1-8 (48 h), from 0-7 to 2-4 (72 h) and from 5-7 to 12-1% (48 h) and then decreased to the level of 1-1, 0-9,1-2 and 1-3%, respectively.The protein amino acid composition, on the whole, was rather stable but some alterations took place in valine, methionine and tyrosine whose proportions decreased, while those of leucine, serine, proline and isoleucine increased.The total content of free amino acids decreased from 29-5 to 6-84 mg per g dry weight (with the most significant decrease occurring in the interval from the beginning of starvation to 20 h). In this case the percentages by weight of lysine, arginine, glutamic acid, ethanolamine and isomethylhistidine increased and those of valine, alanine, tyrosine and hydroxylysine decreased.Fatty acid composition of neutral and polar lipids were rather constant and the percentages of only a few acids changed markedly during starvation: in the neutral fraction 16:1 w7 decreased from 22-1 to 18-1% and 20:5w3 decreased from 13-5 to 8-8%; in the polar fraction 16:0 decreased from 20-1 to 14-8%, 16:lw7 decreased from 13-3 to 9-4%, 20:5w3 decreased from 16-9 to 9-1% and 22:5w3 increased from 5-3 to 8-2%.A decrease in the proportion of total poly-unsaturated acids in neutral lipids in contrast to an increase in polar lipids was another distinguishing feature of these fractions.

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