In this paper the author defines some statistical terms used, describes the sampling techniques adopted in the study of some fish, and quotes some problems concerning the determination of the composition of the stocks. The commercial fleet was utilized to sample the stocks of fish, in the assumption that the catch as landed on the fish market reflects the composition of the stocks in the sea. The paper is restricted to the evaluation of the length distribution of Sardine landed and for that purpose the Author examined 143 samples taken at random from August 1958 to December 1959. The analysis of those samples are shown in Table II and were plotted in Figure 3. The reliable sample size limit for Sardine was established as 300, with the acceptance of an error of 0.1 cm, considering the catch per boat as a population.