Efcient coding has been proposed as a rst principle explaining neuronal response properties in the central nervous system. The shape of optimal codes, however, strongly depends on the natural limitations of the particular physical system. Here we investigate how optimal neuronal encoding strategies are inuenced by the nite number of neurons N (place constraint), the limited decoding time window length T (time constraint), the maximum neuronal ring rate f max (power constraint), and the maximal average rate h f i max (energy constraint). While Fisher information provides a general lower bound for the mean squared error of unbiased signal reconstruction, its use to characterize the coding precision is limited. Analyzing simple examples, we illustrate some typical pitfalls and thereby show that Fisher information provides a valid measure for the precision of a code only if the dynamic range ( f min T, f max T) is sufciently large. In particular, we demonstrate that the optimal width of gaussian tuning curves depends on the available decoding time T. Within the broader class of unimodal tuning functions, it turns out that the shape of a Fisher-optimal coding scheme is not unique. We solve this ambiguity by taking the minimum mean square error into account, which leads to at tuning curves. The tuning width, however, remains to be determined by energy constraints rather than by the principle of efcient coding.