DEPENDENCE OF TEMPERATURE ON LOSS RATES OF ROTIFERS, LIPIDS, AND OMEGA-3-FATTY-ACIDS IN STARVED BRACHIONUS-PLICATILIS CULTURES

Rotifer cultures of Brachionus plicatilis (SINTEF-strain, length 250 m um) rich in omega3 fatty acids were starved for > 5 days at variable t emperature (0-18-degrees-C). The net specific loss rate of rotifer num bers were 0.04 day- 1 (range 0-0.08 day-1) at 5-18-degrees-C, but reac hed values up to 0.25 day-1 at 0-3-degrees-C. The loss rate was indepe ndent on culture density (range 40-1 000 ind ml-1), but was to some ex tent dependent on the initial physiological state of the rotifers (i.e ., egg ratio). The loss rate of lipids was 0.02-0.05 day-1 below 10-de grees-C, where the potential growth rate of the rotifer is low (0-0.09 day-1). The loss rate of lipids increased rapidly for higher temperat ures where the rotifer can maintain positive growth, and reached 0.19 day-1 at 18-degrees-C. The Q10 for the lipid loss rate versus temperat ure was higher than the Q10 for respiration found in other strains. Th is may suggest that other processes than respiration were involved in lipid catabolism. The content of omega3 fatty acids became reduced som ewhat faster than the lipids (i.e. in particular 22:6 omega3), but the fatty acid per cent distribution remained remarkably unaffected by th e temperature during starvation. The results showed that rotifer cultu res could be starved for up to 4 days at 5-8-degrees-C without essenti al quantitative losses of lipids, omega3 fatty acids, and rotifers. Th e rotifers exhausted their endogenous lipids through reproduction (ana bolism) and respiration (including enhanced locomotion) at higher temp eratures. At lower temperatures, the mortality rate became very high.