Prevention of surface death
of marine fish larvae by the addition of egg white into rearing water
T.
Kaji, M. Kodama, H. Arai, M. Tanaka, M. Tagawa-2003
Aquaculture, 224(1-4): 313-322
Abstract:
In the seed production of several marine teleosts,
large numbers of dead larvae are frequently observed on the water surface
around the time of first feeding. We tried to prevent such "surface
death" by the addition of chicken egg white (EW) into the rearing
water. In the first experiment, larvae of striped bonito, Sarda
orientalis, at the first feeding stage (2 and 3 days after hatching)
were transferred to plastic beakers using a 5-ml pipette at a density of 10
larvae/l, in the absence or presence of EW (80 µl/l). No diet was supplied,
the water was not renewed throughout the experiment, and dead larvae were
removed daily. Numbers of surviving larvae of the EW-treated group were
significantly higher than those of the control group. In particular,
survival at the first observation (next day after transfer) was less than
30% in the control, while 100% in the EW-treated group. In a second
experiment, mortality at 2 h after transfer was compared with special
attention to the location of the dead larvae. Significantly (P<0.01)
higher mortality was found in the control group, and more than 70% of the
dead larvae were located on the water surface. Upward swimming toward the
water surface was observed in both groups, but larvae "trapped" at
the surface were only observed in the control group. In a third experiment,
an oil film that was artificially created on the water surface prevented
larval death after the transfer as well as the dissolved EW. Since the oil
film is known to prevent "surface trap" of larvae and decrease
"surface death" in a grouper, the addition of EW was considered to
have a similar effect in reducing mortality. In a fourth experiment using
30-l tanks, survival of larval pez cochero, Dules auriga, was also
higher in the presence of EW, especially during a period when dead larvae
were frequently found on the water surface in the control. Thus, the
addition of EW to the rearing water is suggested to prevent surface death in
a variety of marine fish larvae, and the possibility of applying the method
in practical rearing is discussed.