The theory of system identification was used to determine the time constant T of a 1 litre flow through differential calorimeter (Setaram GF 108) at a flow rate of 50 ml min- ‘_ By numerical differentiation the impulse response function g(t). the time derivative of the step
response,f(r), was calculated. With the aid of the Prony method, the time constant a2 of the time-discrete system of the decimated dataset was calculated, giving a mean value of 0.7402 k 0.0044(n = 4).This value was converted to  the time constant T of continuous system, giving a value of 33.25 k 0.65 min (n = 4).The description of the system agreed with a model for a first order process. For control of the time constant value, the step response ,f(r) and the impulse response g(t) signal were simulated from the original block diagram u(t) which gave a suitable fit. Via the technique of deconvolution, the
datasets of a biological case study with goldfish (Carassius auratus L.) were desmeared to describe the dynamic responses of the biological processes in the calorimetric vessel with a much reduced time constant T. Finally, the timescale on which the process of metabolic depression takes place in this species during anaerobiosis was estimated to be several minutes.