Length-weight and length-length relationships were calculated for 48 species of freshwater fishes occurring in Senegal, based on 3352 collection specimens. The values of parameter b of the length-weight regression equations were high, with several species exceeding the threshold value of 3.4, pointing to positive allometry. However, size-dependent preservation effects may be the cause of these high values of parameter b, and only one or a few cases represent true allometry. Differences in parameter b between length-weight estimates based on standard length and total length were related to caudal fin allometry. Form factor calculations for the species studied largely coincided with expected and observed overall body form, except for one species. The results suggest that collection specimens can be used to generate length-weight relationships for species that are otherwise difficult to access, or as a preliminary estimate of length-weight relationships. However, these length-weight relationships should be used with caution due to various and variable effects of preservation, and may not be readily comparable to results based on fresh specimens.