Feeding Selectivity and Diet Shift of Protosalanx chinensis during Spring in Lake Dalong, Northeastern China

Ontogenetic niche shifts have played an important role in the life history and ecological functions of fish. The clearhead icefish (Protosalanx chinensis, Basilewsky, 1855) is a small, pelagic, and commercially important fish that mainly feeds on zooplankton and will transition to feeding on fish when prey fish are available, though its life span is only about one year. In fact, we know little about the food selectivity and diet shifting of P. chinensis before its transition to feeding on fish. To reveal the food selectivity of P. chinensis before its transition to feeding on fish, the gut contents and environmental zooplankton community were investigated simultaneously in Lake Dalong of Northeastern China from April to June 2021. The results showed that P. chinensis experienced a diet shift from copepoda to cladocera during spring in Lake Dalong. From April to early June, both the size of cladocera and copepoda in guts increased as the size of P. chinensis increased. However, the favorite category changed to the smaller cladocera in late June, when the density of the smaller cladocera was rather high relatively. Considering June was the critical period for P. chinensis to prepare for transitioning to feeding on fish, the food resources availability must be seriously considered for sustainable aquaculture of P. chinensis. It was hypothesized that there was a trade-off of feeding selectivity between the size and density of the prey.