successful
early weaning of atlantic halibut (HIPPOGLOSSUS HIPPOGLOSSUS L.) in small
shallow raceway systems
T. Naess, K. Hamre, J.C. Holm-2001
Aquaculture Research, 32(3): 163-168
Abstract:
Small raceways were used in a weaning experiment with
Atlantic halibut (Hippoglossus hippoglossus L.) larvae. The size of the
tanks was 1.0 x 0.4 m with a 1- to 2-cm water level. Duplicate larval group
were transferred to the raceways from circular first feeding tanks at 0.07,
0.10 and 0.16 g wet weight, while recommended weaning size of this species
is 0.2-0.3 g. During the first 7 days of weaning, Artemia was used as a food
supplement in combination with the formulated dry feed. Thereafter only dry
feed was used. The dry feed used in this experiment was produced by a
special heat technique. The 0.07, 0.10 and 0.16 g larval groups were
evaluated after 31, 25 and 17 days respectively (same date). The
corresponding average survival was 81.4%, 78.0% and 96.6% and the specific
daily growth rate was 3.18%, 3.17% and 2.38% respectively. In the Artemia
control group, a survival rate of 96.0% and a growth rate of 5.28% was
achieved. To evaluate the weaning success, the groups were followed in a
22-day post-weaning period on a commercial dry diet. Higher growth rates,
5.8-6.9%, were then obtained in all experimental groups, but showed some
differences between replicates. One hundred per cent survival was achieved
during weaning in the former Artemia group. From the start of weaning to the
end of the post-weaning period, the survival rates averaged 64% for the 0.07
and 0.10 g groups, approximately 80% for the 0.16 g group and 96% in the
Artemia control group. Higher variance (CV) through the experiment and
highest growth of the 75% quartiles of the fish groups compared with the 50%
and 25%, indicated suppressed growth of the smaller fish. The successful
weaning at these small sizes considerably reduced the live food period.
Based on the present knowledge of the energetic demands of this species, it
is calculated that weaning at 0.07 g compared with 0.25g will reduce the
amount of Artemia needed by at least 60%. No differences in pigmentation or
degree of completed eye migration were detected between groups, indicating
that this is determined at earlier developmental stages.
(Institute of Marine Research, Austevoll Aquaculture
Research Station, N-5392 Storebø, Norway)