Size and feeding behaviour
in Artic Charr (Salvelinus aplinus) embryos during the first feeding
period
Aquaflow Technical Leaflet 2002-77
European Network for the Dissemination of Aquaculture
RTD Information (Q5CA-2000-30105) and previously FAIR-3837, URL: http://www.aquaflow.org/
First feeding in farmed fish is an important life
history event, affecting survival and performance at later stages. The
primary objectives of this study were to test the hypothesis that the onset
of first feeding in Arctic charr is size dependent; and to compare the
feeding behaviour of small and large embryos during the period when they
learn to feed.
All experimental embryos originated from one female
and one male. Immediately after fertilisation (day zero) all the eggs were
size classified by eye into large and small (average sized eggs were
discarded). This classification was verified at day 145 by weighing sampled
embryos and comparing each group. The day after (day 146), 20 embryos from
each size class were individually placed in separate transparent incubators.
They were fed daily with dry start-food pellets and observed for: (i)
behavioural reaction to the food and (ii) obvious visual signs of food in
their digestive tract. The experiment was stopped when all of the embryos
had started to feed - that is embryos had been observed eating and/or food
particles observed in their gut/stomach. Embryos were kept in formalin for
at least ten days before they were blotted and total weight and length
measured. After that they were dissected, stomach contents evaluated and
remaining yolk-sac removed and weighed.
The embryos started to eat during the 161-166 day
period (after fertilisation). On average larger embryos started to feed 1.5
days earlier than the small embryos. Large embryos were also found to be
more active than small embryos, showing clear movements towards the food
items during observations, while the small ones remained motionless on the
bottom during feeding and observational period. However, food was observed
in their stomach/gut later on in the day. That is, small embryos did not
start eating immediately after food distribution, but later in the day.
Thus, despite the fact that larger embryos move more when food is delivered
they do not start feeding earlier during ontogeny than small embryos, which
are less mobile during the actual delivery of food.
Earlier work on the timing of first feeding in groups
of arctic charr indicated that larger embryos started to feed earlier than
small embryos. Comparing this finding with the present results suggests that
in a social environment, larger charr may start feeding earlier than smaller
embryos because they are more mobile and may thus gain easier access and
possibly dominate the food resource to some extent, thus causing smaller
embryos to start later to feed actively. Thus the importance of size
variation for variability in early behaviour with potential consequences for
later growth and performance is minimised when individuals are isolated but
are amplified in a social environment. These findings have implications for
the ecology as well as the culture of arctic charr.
For more information:
REYR HANSEN Broddi
Hólar College
551
Sauđárkrókur
Iceland
Phone : +354 453 6300
Fax : +354 453 6301
e-mail: broddi@holar.is