Fishes of inland waters of the Phu Quoc Island, Gulf of Thailand, Vietnam: ichthyofauna structure and some remarks on the major evolutionary trends in its genesis

Abstract

Background. The ichthyofauna of the Phu Quoc Island (Vietnam), situated in the Gulf of Thailand in the proximity of the coastline of Cambodia, has not been sufficiently studied. The isolation of the island combined with the knowledge on its geological history could yield conclusions on the evolutionary trends and speculations on how individual faunistic groups were formed. The aims of this study were to investigate the recent ichthyofauna of the Phu Quoc Island and to analyze the major evolutionary trends in its history by a comparison with recent faunas of the neighbouring mainland. Materials and methods. A total of about 4000 fishes representing 97 different teleostean species were collected at 46 sampled sites in the Phu Quoc Island from 6 December 2011 to 12 January 2012 by using different kinds of sampling equipment and collection methods as well as through exploring different habitats. Verification of field species identification and further morphological studies were based on 1290 specimens. Results. The list of fishes collected in inland waters of the Phu Quoc Island includes 97 species representing 13 orders and 39 families of teleostean species. The majority of these species correspond to the main diagnostic characters of known valid taxa. Two species (Kryptopterus bicirrhis and Brachygobius doriae) demonstrate some differences from their previously recorded diagnostic features, and two cypriniform species significantly differ from their valid congeners and should be described as new taxa. Conclusion. The major trends in the history of the ichthyofauna of Phu Quoc Island were the elimination of true freshwater stenobiontic species and the progressive development of euryhaline and eurytropic species which replaced former species in seasonally variable biotopes of relatively small tropic island. These eurytropic species are characterized by rather wide morphometric variability and do not demonstrate significant differences in their diagnostic characters comparing the island- and the mainland populations. Two species evolved into separate new taxa during the about 10 000 year time interval of the fauna’ isolation are characterized by the only common feature—belonging to small short-lived species. As such they were more prone to faster evolutionary changes and the pace of the speciation process. The evolutionary process in fish of the Phu Quoc Island was characterized by weak founder effect and weakly pronounced disruptive selection—producing a low number of evolved species.

Keywords

• ichthyofauna
• genesis
• Phu Quoc Island
• speciation