Predation on naked protozoan microzooplankton by fish larvae

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 exarnined under epifluorescence microscopy after staining with DAPI. Among numerous fragments of copepod nauplii, many flagellate-like cells with a size of 5 pm and ciliate-like cells with a size of 20 to 30 pm 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 rnouth 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 taxonon~ical groups were important predators of protozoa and may be an important link between the microbial loop and the grazing food chain.

Feeding on protists and particulates by the leptocephali of the worm eels <i>Myrophis</i> spp. (Teleostei: Anguilliformes: Ophichthidae), and the potential energy contribution of large aloricate protozoa

“…There is evidence from larval fishes collected in the ocean (Ohman et al, 1991;Fukami et al, 1999;Figueiredo et al, 2005;Pepin and Dower, 2007) and from laboratory experiments (Hunt von Herbing and Gallager, 2000) that oligotrich or choreotrich ciliates might be important food sources for larval fishes. Aloricate ciliates are preferred food of fish larvae in the laboratory (Hunt von Herbing and Gallager, 2000).…”

Trophic flexibility in larvae of two fish species (lesser sandeel, <i>Ammodytes marinus</i> and dab, <i>Limanda limanda</i>)

“…Feeding habits of larval fish are species dependent and several species have been shown to regularly prey on protozoan plankton (Fukami et al, 1999). Larvae of several flatfish species live on prey originating from very low trophic levels (Last, 1978a;Pepin and Dower, 2007).…”

“…The main problem in gut content analysis is the variability in digestion times in relation to the nature of the ingested prey item (Fukami et al, 1999). Prey items containing hard structures like crustaceans can be identified better and at a longer time after ingestion than, for example, protozoan plankton like flagellates or naked ciliates (Fukami et al, 1999). To overcome the discrepancy between what can be found in guts and what consumers actually feed on over longer periods is one of the main reasons for applying stable isotope analysis (Fry, 2006).…”

Seasonal variations and trophic ecology of microzooplankton in the southeastern Arabian Sea

“…Several studies have suggested that even many of the carnivorous zooplankton may also prey up on MZP (Stoecker and Capuzzo, 1990;Fukami et al, 1999). The substantial increase in the abundance and biomass of copepods and many other mesozooplankton during the PSM would be a causative factor for the low abundance of the MZP community during the PSM due to high predation pressure (top down control).…”

“…They are mostly comprised of ciliates, heterotrophic dinoflagellates and crustacean nauplii, capable of exploiting pico and nanoplankton that are inefficiently utilized by other larger zooplankton (Marshall, 1973;Nival and Nival, 1976). MZP also acts as a significant food source for a variety of zooplankton and vertebrate predators (Robertson 1983, Stoecker andCapuzzo 1990;Fukami et al, 1999), thereby acting as a trophic intermediate between pico/nano plankton and mesozooplankton.…”