Mortality of yellowtail
flounder, Limanda ferruginea (Storer), eggs: effects of temperature
and hormone-induced ovulation
T.S. Avery, D. Boyce, J.A. Brown-2004
Aquaculture, 230(1-4): 297-311
Abstract:
Yellowtail flounder, Limanda ferruginea
(Storer, 1839), is a highly marketable fish species that used to be a
significant groundfish in the northwest Atlantic region. The potential of
yellowtail flounder for mass rearing has recently been investigated, but
studies into aspects of mortality during early ontogeny are lacking. We
investigated the impact of spawning inducement on mortality of eggs from
fertilisation until hatch, and the effects of rearing temperature on
mortality and hatching time in this multiple batch spawning flounder. An
ash-free dry mass (AFDM) technique for determining mortality was employed.
This technique reduced rearing tank disturbances and provided quantitative
mortality estimates. We found (1) that spontaneously ovulated (SO) mean egg
mass (AFDM 24.84±0.73 µg) was significantly higher than mean egg mass from
induced ovulation (IO) (AFDM 20.09±0.54 µg); (2) that mortality of SO eggs
was lower than IO eggs (p=0.028), (3) that SO eggs reached a
relatively constant (maximum) mortality by about day 3 and IO eggs by about
day 5; (4) that there was no significant difference in mortality between
eggs incubated at 10 °C and those incubated at 4 °C (p=0.320); and
(5) that time to 100% hatch took significantly longer for eggs incubated at
4 °C (256.0±73.5 h) than those incubated at 10 °C (77.9±11.6 h) (p=0.003).
There was considerable variation in egg mortality among batches and females;
nevertheless, general trends indicate that GnRHa-induction of ovulation
tends to decrease egg quality. In addition, the AFDM technique was an easily
employed and accurate method of determining mortality. We recommend that
unless coordination of spawning is important to a particular rearing
protocol, induced ovulation should not be employed.