Effects of diet transition
regimen on survival, growth and lipid composition of intensively reared
Atlantic cod, Gadus morhua, larvae
R.J.
Shields, S. Irwin, P.L. Smith, L.A. McEvoy-2003
Aquaculture
International,11
(1-2): 119-130
Abstract:
Replicated groups of Atlantic cod were reared for up
to 40 days in 100 l tanks stocked at a density of 75 eggs l-1.
Larvae were transferred from rotifers, Brachionus plicatilis, to
either fresh-hatched or enriched Artemia nauplii on each of days 5,
15 and 25 post-hatch (ph). Rotifers were progressively withdrawn over a 5
day period. The type of Artemia offered (fresh-hatched, enriched)
did not affect survival or growth rates at any of the 3 transfer ages.
Larvae transferred to Artemia from day 5 ph suffered a high
incidence of swimbladder over-inflation and high mortality during
metamorphosis (< 1% survival to day 36 ph). Cod in the day 15 and day 25
transfer groups did not differ significantly in weight-specific growth rate
or size on day 40 ph (mean standard length 13.8 mm, dry weight 3.8 mg).
Highest mean survival rates to day 40 ph (18.1%) and lowest mortality
following transfer to nursery tanks were also observed in the day 25
transfer groups. Fish that received Artemia from day 5 ph contained
circa twice as much total lipid per unit body weight and had a 30%
higher triacylglycerol (TAG) content compared to all other groups. Ratios of
the essential fatty acids docosahexaenoic acid (DHA), eicosapentaenoic acid
(EPA) and arachidonic acid (ARA) also differed according to
age-at-transition. DHA:EPA ratio exceeded 1 only in cod transferred to Artemia
on day 25 ph. Based on these findings, it is recommended that intensively
reared Atlantic cod should continue to receive rotifers until completion of
metamorphosis.
(Seafish
Aquaculture, Ardtoe, Acharacle, Argyll PH36 4LD, UK; Present address: The
Oceanic Institute, 41-202 Kalanianaole Highway, Waimanalo, HI 96795, USA,
fax: +1 (808) 259 5971; e-mail: rshields@oceanicinstitute.org)