Calanoid copepod eggs survive passage through fish digestive tracts

An experimental incubation of copepod ( Eurytemora affinis ) eggs found in Baltic herring ( Clupea harengus membras ) faeces resulted in average of 60% hatching to nauplii over a period of 48 h. Eurytemora egg-carrying females were fed to three-spined sticklebacks ( Gasterosteus aculeatus ), nauplii were found hatching from the faeces after 24 h. In experiments with vendace ( Coregonus albula ) from Lake Pyhäjärvi (south-west Finland), calanoid nauplii were found hatching from faeces after 48 h of incubation. This suggests that copepods have evolved an efficient mechanism of preventing population depletion due to predation and that copepod survival relative to the planktivore predation is larger than estimated previously. The fact that successful passage through the fish gut was found in three species of fish and two species of copepods, both in marine and freshwater environments, suggests that the phenomenon may be found in copepod-fish interactions worldwide.