Species Diversity, Abundance and Environmental Associations of Loaches (Nemacheilidae and Balitoridae) in the Central region of Thailand

Abstract

Environmental associations favorable for benthic loaches within the families Nemacheilidae and Balitoridae were the objective of this study that was conducted at 160 sites within five river systems: Southeastern, Mekong, Chao Phraya, Maeklong and Peninsula, in the central region of Thailand. Loaches in this study represented seven genera and 19 species; one each of Tuberoschistura and Homalopteroides, two Acanthocobitis, Homaloptera and Pseudohomaloptera, four Nemacheilus and seven Schistura. Fewest species (n = 3) were found in the Southeastern system with four species from each of the Mekong, Chao Phraya and Peninsula systems and 13 species in the Maeklong system. Species diversity within all systems was greatest for Schistura. Species and relative abundance of all fishes and of loaches varied directly and inversely, respectively, with river order for the two rivers in which this was examined. Abundances varied widely among species and sites with the most abundant species being Schistura aurantiaca, Schistura cf. sexcauda, Homalopteroides smithi and Acanthocobitis zonalternans. Species’ distributions across all five river systems examined by canonical correlation analysis (CCA) varied significantly with six environmental variables. Of greatest significance were elevation and water temparature followed by water velocity, ambient oxygen, pH and Silica. Several adaptations for co-existence in fast flowing water are identified and discussed.