C.B.L. Srivastava and M. Seal,     Department of Zoology, University of Allahabad, Allahabad, India

SUMMARY

Four Indian freshwater catfishes, viz. Clarias batrachus, Heteropneustes fossilis, Rita rita and Mystus vittatus, have been investigated for detailed structure of their ampullary organs. The ontogenetical development of these organs was followed in one of these catfishes, namely H. fossilis, using light microscopy. It was found that the organs of these catfishes essentially resemble those of freshwater catfishes of other tropical parts of the world and of tropical freshwater weakly electric teleosts of S. America and S. Africa. The ecological conditions of the water and nocturnal habit of the fishes in the case of the Indian species parallels those of fishes of other countries. All these facts suggest an electroreception function for the ampullary organs of Indian species as well. Developmental studies show that in H. fossilis, fully formed ampullary organs are present in the larval stage, indicating that these may be functional at this stage of life as well as assisting in the location of food and the detection of enemies.In the ontogeny of the ampullary organ, histogenesis shows a primordial stage very similar to that found in the development of ordinary lateral line organs. This feature, which we report here for the first time, is the first developmental evidence in favour of homology between these two categories of organs. It has also been brought to light that the canal of the ampullary organ has a developmental origin independent of neuromastic origin of the sensory epithelium of the ampulla. A constant accompaniment of the ampullary organs of freshwater catfishes seems to be a compact collagen layer in the dermis.

INTRODUCTION

In India a number of catfishes inhabit tropical waters (muddy bottoms of ponds and rivers, swamps and paddy fields) in which visibility is poor owing to increased turbidity. Still other catfishes live in clear water of rivers, but the nocturnal habit of these catfishes renders eyes useless. These fishes, eyes notwithstanding, may, thus, be thought to depend on a sense other than vision for normal perception of the surroundings. The electroreception mechanism, known to occur in a number of tropical freshwater teleosts including some catfishes inhabiting conditions of poor visibility (Lissmann and Machin, 1958), is also a likely candidate for Indian catfishes. Histological demonstration of ampullary organs (small pit organs) in these fishes would be the first requirement for such a suggestion. Preliminary reports have indicated the occurrence of such electroreceptor organs in Indian catfishes (Mittal, 1968; Lahiri and Kapoor, 1975; Srivastava et al., 1978; Seal and Srivastava, 1978). The present paper aims at a detailed investigation of the structure of the ampullary organs in four Indian catfishes: Clarias batrachus, Heteropneustes fossilis, Rita rita and Mystus vittatus, and of the development of the ampullary organs in one of these, namely H. fossilis. It may be pointed out that development of ampullary organs is not known, except for a brief report on Parasilurus (Sato, 1956), owing to the difficulty in procuring the developmental stages of electric and nonelectric electroreceptive teleosts.

MATERIALS AND METHODS

The catfishes were procured from local markets or collected from fishing sites on rivers. Pieces of skin from head and trunk, especially from the dorsal surface, were excised and fixed in Bouin’s fluid by immersion. Material was then processed for paraffin microtomy and 6 to 8 μm thick sections were cut. Staining was done with Haematoxylene-eosin. Developmental stages of H. fossilis consisted of spawn from induced breeding*, which was raised in the laboratory. Entire larvae were processed as above and serially sectioned. Ampullary organs were first located in an advanced stage and then these were traced back through intermediate developmental stages to their earliest recognisable stage.

OBSERVATIONS