Introduction to trophology of walleye pollock

Abstract

Various aspects of walleye pollock feeding at different stages of its ontogenesis are reviewed and discussed. Structure and functional features of its mouth organs are considered with meristic and quantitative description of the filter one. Lists of pollock prey are presented with attention to changes of food composition and dominant species in the process of its growth from larvae to adult fish. Daily rhythm of feeding is not usual for pollock, but it appears locally and temporary under regional or seasonal conditions of its prey (i.e. plankton). An important feature of the pollock trophology is cannibalism on its own larvae and underyearlings that allows to the population to extend the food spectrum toward small-sized zooplankton. Activity of the pollock feeding can change in several times during the year in dependence on food resources and physiological state of the fish. Year-to-year variability of mass groups of prey (copepods, euphausiids, hyperiids) abundance sometimes coincides with the pollock stock changes in the northern Okhotsk Sea, but variations of arroworms abundance (not important for pollock) never coincide with the stock changes. Daily food ration of pollock (relative to body weight) decreases with its age, but its absolute individual consumption increases that could be a reason of food conversion underestimation. However, large fish are few and feed mostly on fish and benthic invertebrates (similar to cod), so their consumption of zooplankton could be ignored.