Fish assemblages threatened by invasive species and aquarium trade harvest - a longitudinal survey of the Koyoan River, Indonesia

Abstract

The riverine ichthyofauna of Sulawesi, the largest island in the Wallacea biodiversity hotspot, remains understudied with few longitudinal surveys. This study explored the ichthyofauna of the Koyoan River on the east coast of Banggai Regency, Central Sulawesi, Indonesia. Samples were collected at five stations from estuarine to upland reaches. Of the 39 morphotypes (putative taxa) from 14 families and 26 genera, nearly half were not identified to species level. The majority (64%) were amphidromous gobies. The results indicate longitudinal zonation (lower, mid and upper reaches) and habitat (substrate, flow type) preferences within the Koyoan River ichthyofaunal community. Threats identified included two invasive alien species and the ornamental fish trade. Presence of the widely cultured Nile tilapia Oreochromis niloticus in the estuarine reaches may indicate feral saline tilapia, while the green swordtail Xiphophorus hellerii is a predatory ornamental fish from Central America. This study highlights the need for further exploration to fill gaps in the scientific record as well as the urgency of measures to conserve the rich but threatened riverine ichthyofauna of Sulawesi, in particular to control the poorly recorded and unregulated ornamental fishery and invasive species.

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