INFLUENCE OF DIETARY BLENDS OF MENHADEN OIL AND CANOLA OIL ON GROWTH,MUSCLE LIPID-COMPOSITION, AND THYROIDAL STATUS OF ATLANTIC SALMON (SALMO-SALAR) IN SEA-WATER
Bs. Dosanjh et al., INFLUENCE OF DIETARY BLENDS OF MENHADEN OIL AND CANOLA OIL ON GROWTH,MUSCLE LIPID-COMPOSITION, AND THYROIDAL STATUS OF ATLANTIC SALMON (SALMO-SALAR) IN SEA-WATER, Fish physiology and biochemistry, 19(2), 1998, pp. 123-134
The effects of various dietary blends of menhaden oil (MO) with canola
oil (CO) on the growth performance, whole body proximate composition,
flesh quality (muscle proximate and lipid composition) and thyroidal
status of immature Atlantic salmon in sea water were studied. Atlantic
salmon (initial weight, 145.2-181.3 g), held on a natural photoperiod
and in 1100 L fibreglass tanks that were supplied with running, aerat
ed (D.O., 9-10.5 p.p.m.), ambient temperature (8-10.5 degrees C) sea w
ater (salinity, 28-30 parts per thousand), were fed twice daily to sat
iation one of four isonitrogenous (similar to 36% digestible protein)
and isoenergetic (similar to 18.8 MJ of digestible energy kg-l) extrud
ed high-energy diets for 112 days. All diets contained omega -3 (n-3)
fatty acids in excess of requirements and differed only with respect t
o the source of the supplemental lipid which was either, 25% MO; 20.75
% MO and 4.25% CO; 16.5% MO and 8.5% CO; or 12.25% MO and 12.75% CO. T
hus, CO comprised, respectively, 0, 15.5, 31.2, or 47.0% of the total
dietary lipid content (similar to 28% on an air-dry basis). Dissimilar
percentages of saturated fatty acids in the dietary lipids were not f
ound to be consistently related to the apparent gross energy digestibi
lity coefficients of the diets. Atlantic salmon growth, dry feed intak
e, feed and protein utilization, percent survival, thyroidal status, a
nd whole body and muscle proximate compositions were generally not inf
luenced by the different sources of supplemental lipid. Therefore, our
results suggest that canola oil may comprise as much as 47% of the li
pid in high-energy grower diets for Atlantic salmon without compromisi
ng performance. The muscle lipid compositions generally mirrored those
of the dietary lipids which, in turn, were influenced strongly by the
concentrations and compositions of the CO and MO in the diet. Hence,
as the dietary CO level was increased there were attendant increases i
n percentages of oleic acid (18:1(n-9)), linoleic acid (18:2(n-6)), to
tal omega-6 (n-6) fatty acid content, and ratios of (n-6) to (n-3) and
decreases of eicosapentaenoic acid (EPA; 20:5(n-3)), docosahexaenoic
acid (DHA; 22:6(n-3)) and n-3 HUFAs (EPA & DHA) in the flesh lipids. T
he ranges for percentages of saturated and unsaturated fatty acids in
the flesh lipids were, however, much less than those noted respectivel
y in the dietary lipids probably because of selective metabolism of ma
ny of the former acids and some of the 18 carbon unsaturates for energ
y purposes.