The scope of this paper, the first part of a general ecological study of fishes living in the coral reef of Tulear, is restricted to the fishes of the inner reef flats. A residual sheet of water, individualised at very low tide between the boulder tract and the sandy deposit, enables the development of an original reef fish population. 231 species belonging to 52 families were identified.

Two primary ichthyological stocks are distinguished: a permanent stock and a temporary stock. The inner flat is divided into three geomorphologically distinct zones; their ichthyological peculiarities are described and each of them is characterised by some species of the permanent population; the species of this population are distributed into seven ecological categories, according to their habitat and feeding behaviour. The permanent stock composition is the same during the day or at night, but active populations vary greatly. On the contrary, the species composition of the temporary stock is quite different.