The present paper deals with the characterisation and distribution of the mucosubstances elaborated by the gill in fresh water mussel by employing recent well-established histochemical techniques. The results showed that the gill secretes the mucosubstances consisting of neutral mucins, sulfomucins, sialomucins and atypical high pH azurophilic mucosubstances having alcianophilia at pH = 5.6. Hyaluronic acid could not be detected. The importance of these mucins is discussed with reference to feeding.