Abstract: Macrobrachium macrobrachion class structure and sex ratio was studied in Luubara creek of Ogoni land in the Niger Delta area of Nigeria for a period of two years (January, 2006 to December, 2007. Majority of male shrimps were found in the 8 to 16 mm class. In 2006, the size class (8-16 mm) recorded 232 shrimps and constituted 32.08% of the sample population. However, in 2007 most of the male shrimps occurred in the 12-16 mm class, (157 shrimps) and constituted 28.91% of the sample population. In the females, the dominant size class was 8 to 16 mm. In 2006, a total of 324 females were observed in this size and this constituted 49.24% of the sample population. In 2007, a total of 170 female shrimps were obtained in the 8 to 12 mm size class and this constituted 38.20% of the population. There were no female shrimps caught in the 24 to 28 mm class during the study period. Amongst the berried females most of shrimps were found in the size class of 8-20 mm. In 2006 there were 274 berried females in the 8-12 mm group and this constituted 51.40% of the sample population. In 2007 a total of 167 berried females were caught in 8-12 mm group and this constituted 47.87% of the sample population. The sex ratios of shrimps in Luubara creek were variable. There were more females than males. The overall male to female ratio was 1:1.6. It was only in the month of October 2006 that the numbers of male were more than the female with a ratio of 1 male: 0.9 female. The male to female ratio was more than 1:2 in four months namel
