Morphology, reproductive biology and ecology of the little file snake, Acrochordus granulatus at Phangnga Bay, Thailand

Abstract

A total of 119 little file snakes (Acrochordus granulatus), collected at Phangnga Bay from January-December 2002, were studied. The variation in body shape and coloration are low in this species. Their skull elements show the neomorphic form of advanced snakes. The size at maturation in both sexes is 580 mm SVL or more. The snakes were divided into four groups according to their sex and reproductive stage; juvenile males, adult males, juvenile females and adult females. The t-test was used to analyze the data on sexual size dimorphism. Significant differences (t-test, p [is less than or equal to] 0.05) in 11 of 14 morphological characters were found between the sexes of adult snakes. In juvenile snakes, only two morphological characters were significantly different between the sexes. Results from discriminant function analysis gave the equation for predicting the sexes of adult little file snakes with the original grouped case correctly classified at98.3%. Reproductive data indicates that the breeding season begins in July. From July to December, the testicular volume increased, surpassing that observed from January to June. Following an increase in size of follicles to vitellogenesis, ovulaton was observed in November. The embryos were first observed in January and full term embryos were observed in May. The young snakes of about 360-400 mm SVL were first caught in June. Maternal size had a positive influence on clutch size. A granulatus is distributed widely in the coastal areas of Thailand. They are usually found in the estuary or nearby the river mouth where mudflats and mangrove forests are present. The relative abundance of snakes at the three locations in Phnangnga bay were compared. Their bodies are adapted for living in shallow sea water. Their main diet is fish and females tend to feed on bigger prey than do males.