Zoological Studies

Potential Use of Extremely High Biomass and Production of Copepods in an Enclosed Brackish Water Body in Lake Nakaumi, Japan, for the Mass Seed Production of Fishes

Shin-ichi Uye, Shinobu Nakai and Moriyuki Aizaki (2004) We found extremely high abundance, biomass, and production rates of mesozooplankton in an enclosed brackish water body (called the Honjo District) in Lake Nakaumi, Japan, during a 2-yr investigation. To the best of our knowledge, the overall biomass mean of 71.0 mg C m-3 is one of the highest values recorded so far anywhere in the world. Copepods dominated the zooplankton community in terms of abundance (94.4%) and biomass (83.4%). Zooplankton biomass and production rates were twice as high in Honjo District as those in adjacent Lake Nakaumi, although the phytoplankton chlorophyll α concentration was twice as low. Two reasons for the enhanced zooplankton standing stock in Honjo District might be the development of weak benthic deoxygenation and lower numbers of planktivorous fish. We propose to use zooplankton as a food source for the intensive mass seed production of finfish. By our conservative estimate, exploiting 10% of the daily zooplankton production (or around 2.5% of the biomass) of Honjo District would allow the production of 5.6 million red sea bream (Pagrus major) or Japanese flounder (Paralichthys olivaceus) seeds, and 15.4 million ayu (Plecoglossus altivelis) seed fish annually.