Non-commercial fish species of shrimp trawls were studied monthly from October 2005 to September 2006 in Mahshahr creeks (Darvish, Doragh, Bihad, Ghazaleh, Ghanam, Zangi and Patil). The trawl nets had a cod-end mesh size of 24mm. Total catch was 6431 individuals weighing 55.5kg, and included 14 species of non-commercial fish species belonging to 14 families. The caught shrimp species were from Penaeidae; comprising only 30% of the total catches (4506 individuals weighting 44kg). Dominant species were Lieognathus hindus (54.8%), Metapenaeus affinis (18.2%) and Parapenaeopsis stylifera (9.8%). Maximum fish abundance was observed in March 2005 (98/3%) and for shrimp in June (66.2%). Bihad creek had the maximum  percentage of fish (91.8%) by-catch and shrimp (42.9%) abundance. We conclude that the by-catch percentage of non-commercial fish is higher than shrimps in the study areas. Warm months witnessed the highest abundance of shrimp while January-March was the time period when by-catch was most abundant.