Planktivorous Feeding Ecology of Arctic Grayling (Thymallus arcticus)

A component analysis approach was applied to studies of the zooplankton feeding of Arctic grayling (Thymallus arcticus) of 3–20 cm standard length using all arctic zooplankton species common in the area. Unlike other fish species, larger grayling have greater reactive distance. As expected, the ability of grayling to locate prey was found to increase with size of prey and with light intensity. Grayling vision was found to increase dramatically at light intensities higher than 100 lx. Generally, grayling located and attacked any species within the visual field, locating all by core body size. One exception was the copepod Diaptomus pribilofensis, which was of appropriate size and pigmented a bright red, but was never attacked and eaten by any grayling. The large copepod Heterocope septentrionalis was able to evade grayling feeding attack, but Heterocope evasion was dependent on grayling size and water temperature. Analysis of inter-gill-raker spacing showed that spacing increases linearly with fish length up to 13 cm, at which length no further increase was observed. Such change in inter-gill-raker spacing suggests the feeding niche of grayling may be broader than that of similar sized, temperate centrarchid planktivores.Key words: Arctic grayling, Thymallus arcticus; planktivorous fish, predator–prey interaction, prey evasion, zooplankton