The occurrence and reproductive status of Yucatan molly Poecilia velifera (Regan, 1914) (Poeciliidae; Cyprinodontiformes): an alien fish invading the Songkhla Lake Basin, Thailand

Abstract

A non-native fish, the Yucatan molly Poecilia velifera (Regan, 1914), has recently become established in the Songkhla Lake Basin, south Thailand. Based on our field surveys in December 2007, we conclude that this species is present only in the Haadkaew Lagoon and the southernmost part of the Songkhla Lagoon, the Thale Sap Songkhla. We sampled P. velifera monthly for 13 months (January 2007-January 2008), using beach seine and cast net, to obtain information on its population structure, morphology and reproduction. It was found that male and female P. velifera became sexually mature at 16.8 and 17.1 mm standard length, respectively. The overall sex ratio of males to females was 1.0:1.8. However, the proportion of males was less within specimens belonging to larger size classes. P. velifera reproduced continuously throughout the year but with two peaks, one in March-May and another in August-December.