MEPS 185:285-291 (1999)  -  doi:10.3354/meps185285

Predation on naked protozoan microzooplankton by fish larvae

Kimio Fukami1,*, Aki Watanabe1, Shinji Fujita2, Kosaku Yamaoka3, Toshitaka Nishijima1

1Laboratory of Aquatic Environmental Science (LAQUES), Kochi University, Nankoku, Kochi 783-8502, Japan
2Nishinihon Institute of Technology, Wakamatsu-cho, Kochi 780-0812, Japan
3Usa Marine Biological Institute, Kochi University, Tosa, Kochi 781-1164, Japan

ABSTRACT: To evaluate the role of fish larvae as a link between the microbial loop and higher trophic levels, predation of protozoan zooplankton by young larvae was investigated. More than 400 individual fish larvae with total lengths of less than ca 10 mm in 52 different taxonomic groups were collected at different sampling times from several coastal regions, and the gut contents of larvae were examined under epifluorescence microscopy after staining with DAPI. Among numerous fragments of copepod nauplii, many flagellate-like cells with a size of 5 µm and ciliate-like cells with a size of 20 to 30 µm were frequently recognized. The number of protozoan cells varied significantly from one larva to another. Some individuals had more than 60 protozoa, while others contained none at all. The amount of protists contained in the gut of larvae depended on the fish species and did not show any trend with the body or mouth sizes of larvae, nor the sampling site or season. Fish taxa were divided into 3 groups depending on the amount of protists in the gut: 'abundant', 'moderate', and 'none'. The Acanthopterygii group contained the highest concentration of protozoa. Results of the present study suggested that fish larvae of some taxonomical groups were important predators of protozoa and may be an important link between the microbial loop and the grazing food chain.

KEY WORDS: Protozoa · Predation · Diet of fish larvae · Microbial loop · Grazing food chain · Gut content

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