Abstract
The rivers of São Tomé Island are colonized by Sicydium bustamantei (Greeff 1882), an amphidromous fish that spawns in those areas. After hatching, larvae drift to the ocean with the river flow. In the marine realm, the planktonic larvae develop and migrate to freshwater as post-larvae. The migrations of post-larvae support important local fisheries at the mouth of rivers in tropical volcanic islands. Amphidromous post-larvae rely on plankton as their main source of organic matter. However, the biology and ecology of S. bustamantei in the West African islands are understudied, despite its importance for local fisheries. Thus, this study aimed to start bridging this gap by studying its feeding ecology. Our objectives were to identify the main prey of S. bustamantei post-larvae, combining gut content with stable isotope analyses. The gut contents included zooplankton (Chaetognatha, Ostracoda, and unidentified crustaceans), debris from plant and/or macroalgae-derived material, and microplastics (including microfibers). The stable isotopes analysis indicated that zooplankton and macroalgae detritus were the main sources of organic matter assimilated by this species. We also demonstrated that S. bustamantei post-larvae are omnivorous and secondary consumers. These data provide pioneering information that can be used in management plans that still need to be developed.
Highlights
Amphidromy is a type of diadromy that requires freshwater-marine connectivity in the early stages of a species life cycle [1,2]
Sicydium bustamantei post-larvae were acquired in the city of São Tomé fish market and caught in the Mangrove of Malanza River
30 Oceans mm (26.7 the wet season and between 18 and 28 mm (24.8 ± 2.2 mm) in the dry season 6 (Figure 3). These values are within the range described for the total length of post-larvae of other species of Sicydiinae during their return migrations [3,7]
Summary
Amphidromy is a type of diadromy that requires freshwater-marine connectivity in the early stages of a species life cycle [1,2]. Amphidromous species such as gastropods, decapods, and fish are adapted to tropical and subtropical insular environments [2,3,4,5]. The Sicydiinae subfamily (Gobiidae) is typically associated with small oceanic islands with geologically recent volcanic origin [6,7,8] They inhabit swift, high-gradient rainforest streams and rivers with large waterfalls and elevation changes [3] which are generally oligotrophic and exposed to extreme hydrological and climatic seasonal variability [3,8].
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