Effect of stocking density
and addition of proteins on larval survival in Japanese flounder, Paralichthys
olivaceus
M. Tagawa, T. Kaji, M. Kinoshita, M. Tanaka-2004
Aquaculture, 230(1-4): 517-525
Abstract:
The effects of larval density, rearing media, and
protein additions on fish larval survival were tested by rearing larvae in
small containers. Yolk-sac larvae of Japanese flounder, Paralichthys
olivaceus, were transferred 1 day after hatching to plastic dishes and
cell-culture microplates by Pasture pipette at densities ranging from 0.3 to
30 individuals/ml and incubated at 16 °C without food. Dead larvae were
removed and counted every 12 h. Three peaks of larval mortality were
observed: the first peak appeared just after the transfer, the second
corresponded to the completion of yolk absorption, and the third occurred
10–12 days after the transfer. Since about 50% of larvae survived until
the third peak, it was clear that mortality at the second peak (completion
of yolk absorption; equivalent to the first feeding) was not due to
starvation. At the first mortality peak, better survival was unexpectedly
recorded at higher larval densities (30 individuals/ml), suggesting that
some material beneficial for survival is derived from the larvae. This idea
was further supported by the improved survival in media previously used to
rear larvae at high densities. The addition of bovine serum albumin (BSA) at
10 µg/ml effectively reduced mortality in microplates and in 30-l tanks. To
reduce the larval mortality just after handling, addition of egg white at a
dilution rate of 1/30,000 (vol/vol) or less is recommended as a practical
alternative to BSA. Since the addition of polyethylene glycol 6000 (1 µg/ml)
also effectively reduced mortality, reduction in mortality could not be
attributed to a specific mechanism. The precise determination of the
magnitude and timing of larval mortality was attained through the use of
small containers, and a method to prevent mortality due to handling was
identified in this study. These types of tests may allow the logical
evaluation and establishment of better rearing procedures for seed
production in aquaculture.
(Division
of Applied Biosciences, Graduate School of Agriculture, Kyoto University,
Sakyo, Kyoto 606-8502, Japan, e-mail: tagawa@kais.kyoto-u.ac.jp)