Dependence of temperature on loss rates of rotifers, lipids, and ω3 fatty acids in starved Brachionus plicatilis cultures

Abstract

Rotifer cultures of Brachionus plicatilis (SINTEF-strain, length 250 μm) rich in ω3 fatty acids were starved for > 5 days at variable temperature (0–18 °C). The net specific loss rate of rotifer numbers were 0.04 day⁻¹ (range 0–0.08 day⁻¹) at 5–18 °C, but reached values up to 0.25 day⁻¹ at 0–3 °C. The loss rate was independent on culture density (range 40–1000 ind ml⁻¹), but was to some extent 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 °C, where the potcntial growth rate of the rotifer is low (0–0.09 day⁻¹). The loss rate of lipids increased rapidly for higher temperatures where the rotifer can maintain positive growth, and reached 0.19 day⁻¹ at 18 °C. The Q₁₀ for the lipid loss rate versus temperature was higher than the Q₁₀ for respiration found in other strains. This may suggest that other processes than respiration were involved in lipid catabolism. The content of ω3 fatty aeids became reduced somewhat faster than the lipids (i.e. in particular 22:6 ω3), but the fatty aeid per cent distri-bution remained remarkably unaffected by the temperature during starvation.

The results showed that rotifer cultures could be starvcd for up to 4 days at 5–8 °C without essential quantitative losses of lipids, ω3 fatty acids, and rotifers. The rotifers exhausted their endogenous lipids through reproduetion (anabolism) and respiration (including enhanced locomotion) at higher temperaturcs. At lower lemperatures, the mortality rate became very high.