Digestion of free‐living nematodes fed to fish

Abstract

Free-living nematodes-Panagrellus sp., Turbatrix aceti, Caenorhabditis elegans and C.hriggsae-were each fed to the fish Danio sp. and the process of their digestion, in the fish alimentary canal, was studied by light and electron microscope.Almost no identifiable nematodes were found in the fish gut when the digestion period was 3 h or more, except for buccal capsules of the four studied species, males' spicules of Panagrellus sp. and Turbatrix aceti and egg-capsules of the Caenorhabditis species. These structures could serve as indicators that the nematodes had been preyed on and digested by the fish.Differences in the mode of digestion were noticed between the various species of nematodes studied, after a period of0.5-I h, in the fish gut. In Panagrellus sp. and T. aceti disintegration of the soft inner tissues occurred mostly at the anterior or posterior ends of the nematode's body, while in Caenorhabditis the majority of digested nematodes were affected at both ends or evenly along the entire body. Digestion seemed to be initiated mostly at the nematodes' body apertures: mouth, anus or cloaca, and vulva which could be due to a more vulnerable cuticle around those areas. Disintegration proceeded from the soft inner parts to the more resistant cuticle that was finally disintegrated. Ofthe three layers of cuticle the most resistant were the external cortex and the basal layers.

Seasonal variation in abundance and diet of the sand goby Pomatoschistus minutus (Pallas) in a northern Baltic archipelago

“…Harpacticoids have an exoskeleton that is slowly digested and remains in the gut for several hours after ingestion, while nematodes are soft-bodied and are digested rapidly (Alheit & Scheibel 1982, Von Hofsten et al 1983). The field data show that P minutus has a somewhat different diet (more emphasis on meiofauna and juvenile macrofauna) than epibenthic predators and larger fish (Mattila & Bonsdorff 1988, 1989, Sandberg & Bonsdorff 1990, Aarnio et al 1991, Mattila 1992.…”

Selection of meiobenthic prey by juvenile spot (Pisces): an experiments, study

“…The validity of gut content analyses has recently been questioned due to possible differences in digestibility of prey types (Hyslop 1980). Von Hofsten et al (1983, for example, have shown that almost no visible nematode remains were found in fish guts after a period of 3 h, and that digestion occurred within 30 min.…”

Development of a low-cost technology for mass production of the free-living nematode Panagrellus redivivus as an alternative live food for first feeding fish larvae

“…Furthermore, the size of even newly hatched A. salina is too large for some larva (Mock et al 1980). It has been shown that the free-living nematode P. redivivus is a suitable food for fish and crustacean larvae (Biedenbach et al 1989;Hofsten et al 1983;Kahan and Appel 1975;Kahan et al 1980;Moheny et al 1990). Its size and shape are suitable for many small-mouthed species (Mock et al 1980).…”