Lambir halfbeak project (proposal)

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Alex Kim and Sachi Oshima



The streams of the Lambir Hills are sluggish to swift-flowing, turbid to clear, and vary both in depth and substrate, providing a broad range of habitats for freshwater organisms. Freshwater fish are integral components of most tropical streams, occupying a number of trophic categories and exhibiting considerable variability in body form. Many of the fish species present in the Lambir Hills belong to exclusively freshwater families; however, there are also groups like the Hemiramphidae, or halfbeaks, which have both marine and freshwater representatives.

Halfbeak Background

Halfbeaks are so named for the prominence of their lower jaws. The species present in the streams of the Lambir Hills appears to be Dermogenys pusillus, which we observed swimming at the surface, either alone or in small schools.


We hypothesize that there will be a difference in the morphology of the fish at different sites due to various physical and chemical differences between different sections along the stream. These differences could reflect adaptations to the subtle environmental conditions along the stream.

Specifically, we predict that halfbeaks from the four sites will fall into four "monophyletic" groupings in the dendrograms: fish from any given site will be more similar to each other than to any fish from another site. In the PCA analysis, beak length will be the most heavily weighted trait.


How does morphometric variation in Dermogenys pusillus relate to the physical and chemical qualities of the streams they inhabit?


Capture 10 halfbeaks from each of four sites (defined as a 10m stretch) along the length of the stream that flows from Latak Waterfall. Record the following environmental parameters at each site: temperature, total dissolved solids, conductivity, salinity, average stream depth, average stream width, and flow rate. Using electronic calipers, measure total length, beak length, head width (at beak base), and body depth (at operculum) of each fish, to the nearest 0.01 mm.


After size-correcting the other three fish measurements through division by total length, construct dendrograms in R to reveal relationships amongst individuals. Observe whether any general patterns of association between fish from certain sites become apparent. Do the same for the environmental measurements to determine the similarity of the four sites themselves. For a non-hierarchical method of data visualization, construct principal components analysis (PCA) plots for these two datasets as well.