We designed and tested a wooden box splitter for use in subsampling estuarine Ichthyofauna in the field. Results showed that the splitter operator had a significant effect on the estimation of the original sample volume whereas the splitter being used did not. Estimates of the original sample volumes of water or original fish abundances were biased. Coefficients of variation ranged from 1.90% to 4.10% for the volumetric subsamples and from 0.00% to 29.02% for fish abundance subsamples. The precision of estimates of abundance or of species composition decreased with increased splitting. However, the species composition and length-frequency distribution of the original samples were preserved in the subsamples for 75% or more of the first-level splits. This subsampling device is practical in the field and statistically adequate for use in a fisheries program.