Mass mortality during metamorphosis to megalops in the seed
production of mud crab Scylla serrata (Crustacea, Decapoda,
Portunidae)
K. Hamasaki, M. Suprayudi, T. Takeuchi-2002
Fisheries
Science, 68(6): 1226-1232
Abstract:
The
phenomenon of mass mortality of larval mud crab Scylla serrata is
described during the metamorphosis to megalops due to abnormal molting by
morphologically advanced last stage zoeas (fifth stage) in the seed
production. Seven seed production trials were carried out using 100 kL
concrete tanks. The larvae were reared on rotifers and after the third or
fourth zoeal stage with Artemia nauplii. Minced mysid was also given
from the megalopal stage. The seven trials were based on the addition of
different concentrations of the marine phytoplankton Nannochloropsis
or of the freshwater Chlorella to the larval rearing water. The
survival rate, morphological features of the fifth stage zoeas, and
frequency of abnormal molting during the metamorphosis to megalops were
examined. The mass mortality occurred during the metamorphosis to megalops
in tanks containing high concentrations of Nannochloropsis. The fifth
stage zoeas in these tanks were equipped with some advanced morphological
features similar to those of megalops, such as, long endopods of the second
antennae, large chelipeds and pleopods with plumose setae. The frequency of
abnormal molting tended to increase depending on the degree of megalopal
features in the fifth zoeal stage. We propose that zoeal morphogenesis is
accelerated by the nutritional conditions of zoeas due to the supplementary
effect of Nannochloropsis, which contains eicosapentaenoic acid; an
essential fatty acid for larval mud crab.
(Yaeyama Station, Japan Sea-Farming Association,
Ishigaki, Okinawa 907-0451, Japan, e-mail: katsuyuki-hamasaki@jasfa.or.jp)