The otolith micro-increment technique was applied to assess the growth trajectory of early stages of the neotropical catfish Megalechis thoracata in Kaw Swamp, a coastal swamp in French Guiana, and two contrasting habitats in Suriname: the coastal Lelydorp Swamp with standing water and a rain-forest creek with running water, the Maykaboeka Creek. Daily deposition of increments on the lapilli was validated for the first 35 d after hatching and the innermost increments were deposited from hatching onwards. The natural habitats of M. thoracata in French Guiana and Suriname showed considerable variation in physico-chemical characteristics of the water, density of food organisms and fish fauna. Instantaneous growth rates and size-at-age differed significantly among two vegetation types in Kaw Swamp (3.5% d-1 and 4.1% d-1), Lelydorp Swamp (3.0% d-1) and Maykaboeka Creek (2.5% d-1). Spearman's rank correlation coefficient between instantaneous growth rates and environmental parameters differed significantly from 0 only for water temperature. Hatch date analysis revealed an extended spawning season from January to June in the rain-forest creek.