Insect Introductions and Diet Changes in an Endemic Hawaiian Amphidromous Goby, Awaous stamineus (Pisces: Gobiidae)

Abstract

Data are presented from gut content analysis of 94 Awaous stamineus (Edouyx & Souleyet) ('o'opu nakea) collected from the Wainiha River on the north shore of the Hawaiian island of Kaua'i during the period from June 1990 to May 1991. Also presented are results from gut analysis of 11 preserved museum specimens captured in La'iemalo'o stream, O'ahu, in February 1938 and June 1939. The results suggest that introductions of alien insects into the Hawaiian biota are changing the diet of this endemic fish. Comparison with the results of an earlier study indicate that A. stamineus is still dependent primarily on freshwater algae in the genera Cladophora, Rhizoclonium, Oedogonium, and Spirogyra; however, aquatic insect foods in the diet have increased from about 6% to nearly 13% in the current study. The findings suggest a reduced reliance on native aquatic chironomids in the genera Calospectra and Telmatogeton and an increased selection of immature stages of several recent aquatic insect immigrants, most notably two alien caddisfly species, Cheumatopsyche analis (Banks) (Tricoptera: Hydropsychidae) and Hydroptila arctia Ross (Tricoptera: Hydroptilidae), first reported in Hawai'i in 1967 and 1971, respectively.