Taxonomy and comparative morphology of giant freshwater stingray himantura chaophraya (Monkolprasit & Roberts 1990) in the Kinabatangan river, Sabah

The Himantura chaophraya, belonging to the Dasyatidae family, is a giant freshwater stingray. It is the first species of freshwater stingray in Sabah found in the Kinabatangan River. However, the data on the taxonomy and biology of this species in the Kinabatangan River are very limited. Therefore, the present study was a follow up effort to add to the existing data on the taxonomy and the biology of this species. Sampling was carried out for five months (March to July 2005) at the Lower Kinabatangan River from Kg. Batu Putih to Kg. Abai, including its tributaries and oxbow lakes. Two main fishing gears were used at selected sites: longlines and gill nets. Four fresh whole specimens were caught during field samplings. Additionally, two tail parts were obtained from local fishermen and one was loaned from the Sabah Museum. Data for morphological study and stomach content were obtained from fresh specimens. Taxonomical study includes morphometric data, meristic counts, squamation, skeletal characteristics and ventral lateral line canals. The squamation was conducted mainly on the tail and the sting. Data on food intake were obtained from a direct observation of the stomach content. The comparative analysis of morphometric measurements showed 77.8% of similarity with previous study. The analysis of the tail and skeletal parts has provided some new insights which were not recorded by previous studies. Specifically, the tail revealed some differences in the arrangements, shapes, and sizes between the dorsal and ventral surfaces at the bases towards the tip region of the tail according to body size. In addition, the skeletal showed a unique projection structure at the base of the interior ridge towards the anteroventral fenestra. Moreover, the biological study of the diet provided firsthand information on the type of food favoured by this particular species and thus, enlightening us on the relationship between food resources and its natural habitat. In conclusion, these taxonomical and biological findings will be useful to conservationists in coming up with the most suitable ways of ensuring the survival of the Himantura chaophray