The alewife (Alosa ~S B U~O~W I T B~~L~~S )is an obligate planktivore which rases a variety of methods for capturing zooplankton. Alewife eat Mysis rekictca, especially larger individuals, at night during a vertical migration by bath predator and prey. We proposed and tested the hypothesis that alewife use the lateral line to sense prey and feed particulately (single prey at a time) in the dark. We used Daphnia BnQgnwl and Artemia sakima adults as prey. Prey densities were such that they did not elicit filter feeding. Observations using infrared video showed that alewife captured individual prey and bit at a vibrating inert bead. We concluded that under appropriate conditions, alewife were size selective and that streptomycin (which blocks the lateral line sensory cells) eliminated this feeding behavior. RCsnmC : Ee gaspareau (Alosa pseudokarengus) est un planctivore obligC qui utilise des rnkthodes diverses pour capturer le zooplancton. t e gaspareau consomme des Mysis relicfa, particulikrernent les individus de grande taille, en se nourrissant la nuit au cours d' uame migration verticale effectuCe ii la fois par le prCdateur et par sa proie. Nous avons proposC et test6 l'hypothese selon laquelle le gaspareau se servirait de sa ligne latkrale pour percevoir la prCsence des proies et se amourrirait sklectivement (une proie h la fois) dans le noir. Nous avons utilisC comme proies des adultes de Daphnia rnagna et d7Artemia snlinca. Les densitCs des proies Ctaient telles qu'elles ne favorisaient pas un mode d'alimentation par filtration. Les observations rCalisCes ii l'aide de la vidCo dans 19infrarouge ont rnontrC que le gaspareau capture une proie 8 la fois et s'attaque B une perle de rnatikre inerte qui vibre. Nous concHuons que, dans des conditions apgropriCes, le gaspareau sklectionne ses proies en fonction de leur taille. Nous avons Cgalement observC que la streptomycine (qui bloque les cellules sensorielles de la ligne IatCrale) Climine ce comportement d'alimentation. [Traduit par la RCdaction]The tactics of interactions between fish and zooplankton, predator and prey, are diverse (lazzaro 1889). Where sizeselective feeding is indicated by field dietary studies, it is presumed (generally) that planktivsres operate by visually detecting prey. Vertical migration of zooplankton is inferred to minimize predation risk when the upper part of the water column is well lighted. Young and Watt (1983) argued that during the day, zooplankters ought to be deep enough to be visually undetectable and ascend into the phytoplankton-rich zone when it is too dark to be seen. This situation appears to be true for interaction of Mysis relicla with the alewife (Alma pseudohareragus). Janssen and Brandt (1988) found that during the day, at a 50-rn bottom depth, Wgysis were on the bottom and unavailable to the alewife because alewife have difficulty feeding on the bottom (Janssen 1998a). At night, W s i s migrated into the water column and larger individuals were eaten by alewife, although the mechanism by which Mysis were detecte...

During reproduction male Cottus bairdi defend cavities beneath stones and perform defense and reproductive displays. Using a geophone to detect substrate vibrations under dark conditions (infrared viewing), we recorded three types of sounds. 'Knocks' are produced during head nods and an acoustically similar sound is produced when the fish slaps the head to the substrate. A third sound, the 'drum roll' appears to be a fast repetition of several knocks followed by a head slap. We argue that these signals traveling through the substrate are of greater importance than sounds traveling through the water because (1) the substrate vibration attenuates at a much lesser rate than the water vibration and, (2) even near riffles, which generate much water vibration, the background noise in the substrate is low enough for the fish to detect such sounds.