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Journal of Fish Biology 82(6)

Home Forums Ichthyology Journal of Fish Biology 82(6)

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    Matt
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    Species compositions and ecology of the riverine ichthyofaunas in two Sulawesian islands in the biodiversity hotspot of Wallacea

    Abstract

    This account of the riverine ichthyofaunas from the islands of Buton and Kabaena, off south-eastern mainland Sulawesi, represents the first detailed quantitative checklist and ecological study of the riverine fish faunas in the biological hotspot of Wallacea. The results are based on analysis of samples collected by electrofishing at a wide range of sites from July to September in both 2001 and 2002. While the fauna was diverse, with the 2179 fishes caught comprising 64 species representing 43 genera and 22 families, the catches were dominated by the Gobiidae (26 species and 25% by numbers), Eleotridae (seven species and 27% by numbers), Zenarchopteridae (three species and 22% by numbers) and Anguillidae (two species and 12% by numbers). The most abundant species were the eleotridsEleotris aff. fusca-melanosoma and Ophieleotris aff. aporos, the anguillid Anguilla celebesensis, the zenarchopterids Nomorhamphus sp. and Nomorhamphus ebrardtii and the gobiids Sicyopterus sp. and Glossogobius aff. celebius-kokius. The introduced catfish Clarias batrachus was moderately abundant at a few sites. Cluster analysis, allied with the similarity profiles routine SIMPROF, identified seven discrete groups, which represented samples from sites entirely or predominantly in either Buton (five clusters) or Kabaena (two clusters). Species composition was related to geographical location, distance from river mouth, per cent contribution of sand and silt, altitude and water temperature. The samples from the two islands contained only one species definitively endemic to Sulawesi, i.e. N. ebrardtii and another presumably so, i.e. Nomorhamphus sp., contrasting starkly with the 57 species that are endemic to Sulawesi and, most notably, its large central and deep lake systems on the mainland. This accounts for the ichthyofaunas of these two islands, as well as those of rivers in northern mainland Sulawesi and Flores, being more similar to each other than to those of the central mainland lake systems. This implies that the major adaptive radiation of freshwater fishes in Sulawesi occurred in those lacustrine environments rather than in rivers.

    Metabolic divergence between sibling species of cichlids Pundamilia nyererei and Pundamilia pundamilia

    Abstract

    This study compared Pundamilia nyererei and Pundamilia pundamilia males in routine metabolic rate (RR) and in the metabolic costs males pay during territorial interactions (active metabolic rate, RA). Pundamilia nyererei and P. pundamilia males housed in social isolation did not differ in RR. In contrast to expectation, however, P. nyererei males used less oxygen than P. pundamilia males, for a given mass and level of agonistic activity. This increased metabolic efficiency may be an adaptation to limit the metabolic cost that P. nyerereimales pay for their higher rate of aggressiveness compared to P. pundamilia males. Thus, the divergence between the species in agonistic behaviour is correlated with metabolic differentiation. Such concerted divergence in physiology and behaviour might be widespread in the dramatically diverse cichlid radiations in East African lakes and may be an important factor in the remarkably rapid speciation of these fishes. The results did not support the hypothesis that higher metabolic rates caused a physiological cost to P. nyererei males that would offset their dominance advantage.

    Species-specific ontogenetic diet shifts among Neotropical Crenicichla: using stable isotopes and tissue stoichiometry

     

    Ontogenetic diet shifts were compared among five sympatric pike cichlids Crenicichla in a subtropical South American stream using stable C and N isotopes and tissue stoichiometry (C:N). Within species, stable N isotopes were positively related to body size while C:N showed negative relationships. Stable C isotopes, however, were not related to body size in any species. By modelling the switch to piscivory using gut content-isotope-body size relationships, diet shifts were shown to be species-specific with regard to both rate and degree of piscivory. Compared to other piscivorous lineages, Crenicichla appear to be unusually small-bodied (based on maximum body size). Because of their diversity, abundance and dynamic size-structured functional roles, Crenicichla may exert broad and complex predation pressures on the aquatic community.

     

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