First feeding of cod larvae
with “large” and “small” rotifers
Aquaflow Technical Leaflet 2002-63
European Network for the Dissemination of Aquaculture
RTD Information (Q5CA-2000-30105) and previously FAIR-3837, URL: http://www.aquaflow.org/
The quality rotifers, Brachionus plicatilis,
fed to larvae during the initial period of first feeding is very important
in the intensive production of Atlantic cod Gadus morhua. The food value of
rotifers as prey for marine fish larvae generally depends on their
biochemical composition, but also on their size and density in the fish
larval tanks.
Rotifer strains of two different sizes were tested in
first feeding of larval cod. “Large” rotifers are about 270 µm long and
have a volume of 15-17 µm3, while “small” rotifers measure 180 µm in
length and have a volume of 5-7 µm3. Cod larvae were either fed the same
density of “large” and “small” rotifers (5000 ind. per litre) or
they received 12000 “small” rotifers per litre. 12000 “small”
rotifers correspond approximately to the biomass of 5000 “large”
rotifers. “Large” and “small” rotifers were cultivated, fed and
enriched in the same way. Cod larvae were fed rotifers from day 4 until day
20 after hatching, when the prey density was adjusted several times per day.
In all treatments larvae were fed equal amounts of rotifers and of the brine
shrimp Artemia franciscana in the period from day 17 to day 43.
Weaning to dry food was started on day 31, and the experiment ended at day
45, when the fish were transferred to bigger tanks.
Fish larvae fed “large” rotifers showed best
survival and growth. Survival was about 37% in tanks fed “large”
rotifers, while the fish larvae fed 5000 and 12000 “small” rotifers per
litre had an average survival of 33% and 34%, respectively. Larvae fed the
“large” rotifers reached a considerably higher average dry weight of 239
µg at the end of the rotifer period (day 17) compared to the larvae fed the
“small” rotifers. The latter larvae had an average dry weight of 157 µg
(5000 ind litre-1) and 211 µg (12000 ind litre-1). The daily growth rate
during the initial five days of first feeding was highest for larvae fed the
larger strain of rotifers. These larvae had an average growth rate of 8.9%
per day between day 5-10, while larvae fed the same amount of “small”
rotifers (5000 per litre) showed no growth, and some larvae even seemed to
starve. Larva fed “small” rotifers in equal biomass (12000 rotifers per
litre) showed an average growth of 3.3% per day in the same period. The
differences in dry weight were still evident at day 43 after hatching, even
tough all treatments received the same amount of prey during the later Artemia
phase. There was hardly any mortality after the transfer to bigger tanks on
day 45, when the juveniles reached a weight of about 6-7 gram.
The results show that it is advantageous to feed cod
larvae a large strain of rotifers. Catching of prey is an energy consuming
process for the larvae. To gain the same amount of energy, larvae have to
catch fewer individuals when feeding on bigger prey. For a high net gain of
energy, it is crucial that the energy value of the prey exceeds the effort
(loss) of catching it.
The work was part of the project “Intensified
production of rotifers as feed to cod fry”, supported by the Norwegian
“Landsdelsutvalget” (Regional committee of Northern Norway).
For more information:
ŘIE Gunvor
SINTEF Fiskeri og Havbruk ASAvd. Bioressurser
N-7465 Trondheim
Norway
Phone : 73 59 05 81
Fax : 73 59 63 63
e-mail: Gunvor.Oie@chembio.ntnu.no