The main factor causing the critical point in the larval rearing phase is the determination of the type of feed as initial feed. The purpose of this study was to examine the relationship between the development of mouth opening and the total length of snakehead fish larvae (Channa striata) for the accuracy of natural feeding. Research method Samples were taken from 3 stocked basins, 3 larvae tail were taken from day 3 to 35 day after hatching (HA). Measurement of mouth opening by measuring the maxillae of the larvae mouth with a digital micrometer every day starting on 3-day AH. Measurement of the total length of larvae on AH day 3, 10, 19, 28 and 35. Calculations using the formula Shirota (1970) were analyzed descriptively and calculated the percentage of the size of the mouth opening with the total length of the larvae. The data are presented in tables and graphs, the analysis is analyzed linear regression and descriptively. The results of this study were that the mouth opening of snakehead fish larvae on the 3rd to 5th day AH was less than 1 mm, the size of the larval mouth opening on the 6th day AH reached 1.41 mm and on the 35th day it reached the size of 2.58 mm. The relationship of larval mouth opening to larval length from 6 to 35-day AH was allometric negative, the size of the mouth opening decreased according to the increase in length and age of the larvae. The measured mouth opening makes it easy to feed the natural larvae accordingly.