Rapid identification and quantification of preserved zooplankton samples using a bench-top VPR (B-VPR)

Abstract

The Fisheries Research Agency of Japan has been conducting spawning surveys of pelagic fish in the Kuroshio area since 1947 and a huge amount of formalin-preserved zooplankton samples from an extensive area has been stocked. While the total biomass (wet-weight) of every sample has been analyzed, the taxonomic composition has been analyzed only for limited samples, because it requires taxonomic skill, much effort and time. Since the size composition of zooplankton is very important information for analyses on the quality of food for larval fish, we designed the bench-top Video Plankton Recorder (B-VPR) to analyze the abundances and size compositions of copepods in formalin-preserved samples more rapidly and conveniently. Using B-VPR, one plankton net sample (ca. 10000 particles) can be imaged and analyzed within 90 min. We have already analyzed over 4000 samples of zooplankton collected in the Kuroshio area since the 1960s. From the results of the B-VPR analyses, long-term variations in the size composition of copepods was observed. Long-term monitoring is necessary to analyze the mechanisms attacting the dynamics of fish stocks. B-VPR will be a useful instrument for analyses of large numbers of samples for long-term monitoring.