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Sea Fish Aquaculture, Ardtoe, Argyll PH36 4LD, Scotland, U.K. and * Institute of Aquaculture, University of Stirling, Stirling FK9 4LA, Scotland, U.K.
2To whom correspondence should be addressed.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: • halibut • fish larvae • polyunsaturated fatty acids • retina • pigmentation
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). In the case of marine fish, these PUFA are the highly
unsaturated fatty acids (HUFA) of the (n-3) series, eicosapentaenoic
acid [20:5(n-3); EPA] and docosahexaenoic acid [22:6(n-3); DHA]
(Sargent et al. 1995a
). The (n-3) HUFA requirement of
juvenile marine fish is ~0.5–1.0% of the dry weight of their diet,
but the requirement in the early developmental stages of larvae is
likely to be greater because of their rapid growth and the critical
early development of specialized cells and tissues. Several
investigators have studied the (n-3) HUFA requirements of a number of
marine fish species (Estevez and Kanazawa, 1996
,
Izquierdo et al. 1989
, Reitan et al. 1994
, Rodriguez et al. 1994
, Takeuchi et al. 1994
), and all suggest that DHA is more efficacious than
EPA in promoting larval health and survival.
DHA and EPA are essential fatty acids (EFA) for marine fish species
because they do not have or have only a very low 
5-desaturase
activity, which is necessary for the conversion of C-18 PUFA to
long-chain HUFA (Sargent et al. 1993
). In addition,
although these fish may be capable of converting EPA to DHA, the rate
at which they do so may be too low to satisfy the high DHA requirement
during early larval growth (Sargent et al. 1995a
). DHA,
which is abundant in all fish tissues (Sargent et al. 1989
), tends to accumulate in terrestrial vertebrates in neural
and reproductive tissues, suggesting a specific functional role for DHA
in particular cell membranes of these tissues (Sastry 1985
, Tinoco 1982
). However, neural membranes of
fish are also especially rich in DHA (Bell and Dick 1991
, Tocher and Harvie1988
), suggesting that
the same specialized function(s) exists for DHA in fish as in
terrestrial vertebrates. Studies with larval sea bass
(Dicentrarchus labrax) and herring (Clupea
harengus L.) fed DHA-deficient diets established a deficit of
didocosahexaenoyl phospholipids in the eyes of the fish, which was
correlated with impaired visual performance in the latter species
(Bell et al. 1995 and 1996
). In addition, normal dorsal
pigmentation in flatfish larvae post-metamorphosis is influenced by
dietary HUFA, and it has been suggested that albinism may be linked
with impaired larval neural function (Estevez and Kanazawa 1996
, Reitan et al. 1994
).
The small size and poorly developed digestive function of marine fish
larvae (Segner et al. 1994
) means that, for most
species, pelleted or microencapsulated diets are unsuitable for first
feeding. The only viable alternative involves live-prey species
such as rotifers (Brachionus plicatilis) and brine shrimp
nauplii (Artemia spp.). However, these organisms are
deficient in long-chain HUFA, especially DHA (Navarro et al. 1993
) and must be enriched with these fatty acids to improve
their nutritional quality before being fed to marine fish larvae.
Several enrichment techniques have been developed, including
microalgae, oil-based emulsions and microencapsulated preparations
(Barclay and Zeller 1996
, Leger et al. 1986
, McEvoy et al. 1996
, Southgate and Lou 1995
). However, most commercially available enrichment
preparations are unable to provide a DHA/EPA ratio >1 in the enriched
Artemia (McEvoy et al. 1996
, Navarro et al. 1995
); thus, the efficacy of this live prey to deliver
sufficient DHA to the developing larvae remains a matter of concern.
Marine zooplankton offer an obvious alternative to Artemia
nauplii as live-prey organisms for first feeding marine fish
larvae, although problems exist in obtaining adequate numbers of
zooplanktonic organisms to coincide seasonally with marine larval
production. Marine zooplankton are the natural food organism for marine
fish larvae in the wild and are naturally enriched in long-chain
HUFA, generally having DHA/EPA ratios substantially >1 during their
naupliar and early copepodite stages (Gronkjaer et al. 1995
, Naess et al. 1995
, Sargent and Henderson 1986
).
The aim of this study was to determine whether enriched brine shrimp nauplii satisfy the HUFA requirements of larval Atlantic halibut to the same extent as natural marine copepods.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The halibut feeding experiment was carried out at Seafish
Aquaculture's Marine Farming Unit, Ardtoe, Scotland. All developmental
stages were reared using sea water maintained at a salinity of 33–35
g/L, filtered to 5 µm and UV-sterilized. Eggs and
yolk sac larvae were reared following the method described by
Gara et al. (1998)
. At 220 degree days post-hatch,
700 larvae were removed from the yolk sac rearing tank and stocked into
each of two circular feeding tanks (150 cm diameter, 90 cm depth)
containing 1300 L seawater to which marine microalgae
(Nannochloris atomus) had been added to provide
"green water" conditions. The practice of adding microalgae to
the rearing water is widespread in the culture of a wide range of
marine fish species. Although the mechanism of their beneficial effects
is unclear, microalgae may provide a nutritional influence as well as
altering the light distribution within the rearing tanks (Naas et al. 1992
, Reitan et al. 1997
). The water
temperature was 10°C and light intensity was set at 50 lx at the
water surface.
The calanoid copepods were collected from a static outdoor tank (150 m3 volume) at Ardtoe, by means of an airlift directed into a semisubmerged sieve. Copepods collected in this way were size graded by rinsing through sieves with different mesh sizes. The halibut larvae were initially fed copepods in the 125- to 250-µm size fraction before being switched to the 250- to 400-µm fraction on d 19 post-first feeding (PFF).
Enrichment grade (EG) cysts (INVE Aquaculture NV, Baasrode, Belgium) were used for the Artemia-fed halibut larvae. All sea water for incubating and rinsing the Artemia was filtered to 5 µm and UV-sterilized. Enrichments were carried out in 10-L polyethylene containers, at a density of 150,000 individuals/L, using vigorous aeration. Decapsulated cysts were incubated in sea water (34 g/L, 28°C) for 18 h, after which the nauplii were harvested and rinsed. The spray dried chromist Schizochytrium (Algamac 2000, Aquafauna Biomarine, Hawthorne, CA) was used for enrichment at a concentration of 0.6 g/L. The material was suspended and prehydrated by blending the appropriate quantity in 400 mL sea water for 1 min. Artemia nauplii were enriched at 27°C in this suspension for 18 h. SuperSelco (INVE Aquaculture NV) was also mixed by blending in sea water and then applied to the enrichment container in two aliquots (0.3g/L per aliquot) over 18 h at 27°C. Samples of enriched Artemia and copepods were obtained for lipid analysis by collecting 25,000 Artemia per replicate on a nylon sieve of 64-µm mesh size. The Artemia were rinsed using distilled water, blotted on absorbent tissue, transferred to a cryovial, weighed and stored in liquid nitrogen. Four size fractions of copepods (64–125 µm, 125–250 µm, 250–400 µm and >400 µm) were collected similarly and stored.
Each tank received a single daily ration of 50,000 newly hatched EG grade Artemia nauplii from d 1 to 9 PFF. The water temperature was raised from 10 to 12°C over the first 2 d, and water exchange was started on d 5 PFF at an inflow rate of 0.24 L/min. On d 10 PFF, one tank was switched to a diet of calanoid copepods, Eurytemora velox. This tank was supplied with a single ration of 20,000 copepods per day, selected from the 125- to 250-µm size fraction. The second tank was switched from Artemia nauplii to enriched Artemia nauplii on d 10 PFF. This switch in live feed was based on the requirement for increased prey size in rapidly growing halibut larvae. Fifty thousand instar II Artemia nauplii separately enriched using SuperSelco and Algamac 2000 were provided to this tank in a single daily ration at a ratio of 1:1; the former was provided in the morning and the latter in the evening.
On d 16 PFF, 44 halibut larvae were counted from each of the two 1300-L
tanks and stocked into cylindrical polyethylene tanks (diameter 50 cm,
depth 70 cm) containing 120 L sea water, "greened" using
Nannochloris atomus. Four tank replicates were set up
for the copepod diet treatment and three replicates for the
Artemia treatment. The lack of a fourth replicate tank
in the Artemia treatment was due to an insufficient
number of larvae from the Artemia-fed population. A
diagrammatic illustration of the experimental design is shown in
Figure 1
. Comparison of the copepod and Artemia diets was
continued in this replicated rearing system for 55 d until d 71
PFF. Each tank was illuminated from above by a single PAR 38 tungsten
floodlight (Osram Concentra, 80 W, Specialist Lamp Distributors,
Glasgow, Scotland) fitted with a dimmer switch. Initial
illumination was set at 50 lx at the water surface and was increased to
1500 lx over the next 7 d. All tanks received a partial daily
water exchange (20% of tank volume) via a surface inflow (300 mL/min
for 2 h) and were supplemented daily with Nannochloris
atomus. Water temperature ranged from 12.9 to 13.5°C over the
experimental period.
|
. Ration levels in the Artemia treatment were
adjusted daily according to consumption with the aim of minimizing the
levels of residual prey. Calculated individual feed rates increased
from 250 Artemia per fish per day on d 16 PFF to 1500/d
on d 44 PFF. By contrast, daily ration levels in the E.
velox diet treatment were constrained by the numbers of
copepods available from the outdoor collection tank. The ration levels
were at all times lower than those supplied in the
Artemia treatment and averaged 180 copepods per day
throughout the experiment. The experiment was conducted in accordance
with the British Home Office guidelines regarding research on
experimental animals.
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A sample of 10 larvae was collected from each of the two 1300-L tanks on d 16 PFF for calculations of mean wet and dry weight. The larvae were killed by anesthesia in 3-aminobenzoic acid ethyl ester methane sulfonate (MS222, Sigma Chemical, Poole, U.K.), then immersed in distilled water and blotted on absorbent tissue for 30 s before measuring wet weight. The larvae were then frozen (-20°C) before being freeze-dried for 24 h and reweighed to obtain dry weight.
At the end of the experiment (d 71 PFF), all surviving fry were counted
to calculate survival rates and each fish was examined. The fish were
killed by anesthetization and wet weight was recorded. Eye migration
was classified for each individual using a 4-point scale (Gara et al. 1998
). The distribution of pigment on the "ocular"
(top) and "blind" (bottom) surfaces of the body was classified
according to the method of Gara et al. (1998)
. The
frequency of each pigment category was converted to a percentage of the
whole population for individual replicates.
Livers, eyes and brains were dissected from an additional six fish per treatment on d 65 PFF. The organs were pooled into three 1-mL polypropylene vials (nalgene cryovial, Nalge UK) providing three replicates from two fish for each dietary treatment. The pooled samples were weighed and stored in liquid nitrogen in preparation for lipid analysis.
Lipid extraction and analysis.
Total lipids were extracted from frozen samples of
Artemia, copepods and larval tissue samples by
homogenizing in 10 volumes of chloroform/methanol (2:1, v/v) using a
glass/teflon homogenizer. Total lipid was prepared and measured
gravimetrically according to the method of Folch et al. (1957).
Fatty acid methyl esters were prepared by
acid-catalyzed transesterification of total lipids according to
Christie (1982)
. Extraction and purification of fatty
acid methyl esters was performed as described by Ghioni et al. (1996)
. Fatty acid methyl esters were separated and quantified
by gas-liquid chromatography (Carlo Erba Vega 6000, Thermo Quest,
Manchester, England) using a 30 m x 0.32 mm capillary column (CP
Wax 52 CB, Chrompak, London, U.K.). Hydrogen was used as carrier gas
and temperature programming was from 50 to 150°C at 40°C/min and
then to 230°C at 2.0°C/min. Individual methyl esters were
identified by comparison with known standards and by reference to
published data (Ackman 1980
).
Histology.
Two larvae per tank were fixed for histology (saline buffered formalin,
or Bouin Picro formol) on d 32, 46 and 65 PFF. The samples were
dehydrated and embedded in paraffin wax for sectioning. Sagittal
sections of 3–5 µm were stained with
hematoxylin-eosin, periodic acid Schiff or Masson's trichrome
stain. The rod/cone ratio was measured in histological sections of the
retina. In the ventrotemporal region of the retina, the numbers of
nuclei in the outer nuclear layer were counted in a zone corresponding
to thirty cones. The numbers of nuclei exceeding the number of cones
were used as an estimate of rods (O'Connell 1963
).
Counts were performed on six larvae per treatment, and each value was
the mean of three counts from the ventrotemporal region of the retina
from one larva.
Statistical analysis.
Statistics were applied to the data collected over the period d 16–71
PFF. Diet-related differences in rearing parameters, pigmentation
characteristics and lipid compositions were analyzed using one-way
ANOVA. Differences between means were compared using Tukey's test.
Percentage data were arc-sin transformed before analysis.
Chi-squared analysis was applied to the nominal eye migration data
(Zar 1984
). All statistical analyses were carried out
using the Minitab (State College, PA) statistical package. A
significance level of 95% (P < 0.05) was used
throughout.
Materials.
TLC and high performance TLC (HPTLC) plates, coated with silica gel 60, were obtained from Merck, Darmstadt, Germany. All solvents were of HPLC grade and were obtained from Fisher Scientific (Loughborough, U.K.).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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. The Algamac 2000–enriched
Artemia contained similar amounts of DHA and EPA, resulting
in a DHA/EPA ratio of 1; in addition, it contained 2.5% of 22:5(n-6).
The SuperSelco enrichment produced Artemia containing
slightly more DHA compared with the Algamac enrichment but appreciably
more EPA, resulting in a DHA/EPA ratio of 0.4. The smaller size range
of E. velox copepods, which comprised largely nauplii and
copepodites, contained high levels of DHA and EPA and had a DHA/EPA
ratio of 2.0. The larger size class of copepods, which comprised
largely immature and mature adults, contained much lower levels of DHA
and EPA and had a DHA/EPA ratio of 0.9. The percentage decrease in
(n-3) HUFA in the larger size copepods was due to increased
accumulation of saturated and particularly monounsaturated fatty acids.
The survival and growth parameters of the two groups of halibut over
the period d 16–71 PFF are summarized in Table 2. No significant differences between replicate tanks, fed the same
experimental diets, were observed. Halibut larvae fed copepods
exhibited a significantly greater mean survival rate (66.4 ± 2.3%) compared with those fed enriched Artemia (44.7
± 9.5%). The halibut larvae fed Artemia attained
significantly higher final weights than those fed copepods. However,
differences in mean specific growth rates were not significant because
of the different start weights. The indices of eye migration on d 71
PFF were not significantly different between dietary treatments with
mean values >2 in both cases (Table 2)
. The eye data are summarized in
the frequency distributions in Figure 2
and establish that ~55% of the halibut fry in both diet
treatments exhibited complete eye migration (index of 3).
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. Almost
40% of halibut larvae fed copepods exhibited perfect metamorphosis
attributes, whereas only 3.5% of the fish fed Artemia fell
into this category. The large difference in metamorphosis attributes is
accounted for by differences in pigment distribution between the two
groups of halibut fry. By reference to frequency distributions of the
pigment categories (Fig. 3
), it can be seen that ~45% of the halibut fed
Artemia were "albino" (pigment category I/I), whereas
this category was not recorded at all in fish fed copepods. Conversely,
only 13% of the halibut fed Artemia exhibited correct
pigmentation of the ocular and blind surfaces (category V/I) compared
with 55% of the larvae fed copepods. Fish receiving both diet
treatments displayed an abnormal trait on the blind body surface of
partial pigmentation of the skin (Fig. 3
, pigment categories I/II and
V/II).
|
. The rod/cone ratio was significantly higher in the
copepod-fed group. Light microscope sections of liver were analyzed
at d 46 and 65 PFF. At d 46 PFF, lipid-containing vacuoles filled
most of the hepatocytes in the copepod-fed larvae, whereas these
vacuoles were much smaller in the Artemia-fed larvae
(Fig. 4
). However, at d 65 PFF, lipid-containing vacuoles were equally
abundant in the livers of both groups of larvae (data not shown).
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. The eyes from fish fed copepods contained significantly greater
amounts of 16:0, 16:1(n-7), 24:1 and 22:6(n-3) and significantly lower
amounts of 18:1(n-9), 18:1(n-7), 18:2(n-6), 20:4(n-6), total (n-6)
PUFA, 18:3(n-3), 20:3(n-3), 20:5(n-3) and 22:5(n-3), compared with
those fed enriched Artemia. The larvae fed copepods had a
significantly higher DHA/EPA ratio compared with larvae fed enriched
Artemia, but the EPA/arachidonic acid (AA) ratio was not
different. The long-chain HUFA [22:6(n-3), 20:5(n-3) and
20:4(n-6)] compositions of brains and livers from halibut larvae fed
either enriched Artemia or copepods are shown in
Figures 5
and
6. The percentages of these three essential HUFA in brain and liver
were affected similarly by dietary treatment to the changes described
for halibut eyes. In brain, DHA was significantly greater, whereas EPA
and AA were significantly lower, in fish fed the copepods compared with
those fed enriched Artemia. The EPA/AA ratios were
significantly higher in brains of Artemia-fed fish compared
with those fed copepods (3.4 ± 0.1 and 3.1 ± 0.1,
respectively). In liver, DHA was significantly greater and EPA
significantly lower in the copepod-fed halibut compared with those
fed enriched Artemia. In both tissues, the DHA/EPA ratio was
increased in fish fed copepods compared with those fed enriched
Artemia. The EPA/AA ratios in liver were significantly
higher in fish fed the enriched Artemia compared with those
fed copepods (3.6 ± 0.4 and 2.9 ± 0.1, respectively).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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similarly reported better pigmentation
characteristics for zooplankton-fed halibut larvae compared with
those fed SuperSelco–enriched Artemia.
In experiments with larval turbot (Scophthalmus maximus),
increased pigmentation success was positively correlated with an
increased dietary and tissue ratio of DHA/EPA (Reitan et al. 1994
). In this study, the ratio of DHA/EPA in copepod nauplii
and copepodites was significantly greater than in enriched
Artemia; consequently, the DHA/EPA ratio in eyes, brains and
livers of halibut larvae fed copepods was always greater than in those
fed Artemia. We conclude, therefore, that the superior
performance of copepods compared with Artemia nauplii
reflects, at least in part, a relative deficiency of DHA in the
supplemented Artemia. Moreover, because there was little or
no difference in the EPA/AA ratio in larvae fed copepods and those fed
supplemented Artemia, there is no reason to believe that the
levels of EPA or AA are in any way unsuitable in the supplemented
Artemia, most notably in relation to possible influences on
eicosanoid metabolism in the larvae.
In addition to the benefits of maintaining a high DHA/EPA ratio in
live-prey and larval tissues, there exists the potential importance
of dietary phospholipid and vitamin A in preventing pigmentation
abnormalities in larval flatfish (Kanazawa 1991 and 1993
). The naupliar and copepodite stages of the E.
velox copepods used in this study contained an excess of
phospholipids over triacylglycerols, whereas the opposite composition
was always evident in enriched Artemia (results not shown).
Evidence suggests that phospholipids are more easily digested by larval
fish compared with triacylglycerols, and their presence may enhance
digestion of other lipids in the rudimentary digestive tract of larval
fish (Kanazawa et al. 1983
, Koven et al. 1993
). Further studies have identified the superior growth and
development in a number of larval fish species, including red sea
bream, ayu, striped jack, carp, sea bass and turbot, when diets
contained lecithin (phosphatidylcholine) supplements, suggesting an
absolute requirement for lecithin in developing larvae (Geurden et al. 1995 and 1997
, Kanazawa 1985
,
Takeuchi et al. 1992
). The benefits of dietary lecithin
cannot be explained by their HUFA composition alone because both soy
and tuna lecithin were equally effective in promoting growth and
development in some of these studies. It is possible, however, as
suggested by Geurden et al. (1995 and 1997)
that fish
larvae have only a limited ability to biosynthesize phospholipids de
novo such that intact phospholipids in the diet are essential for
maximal growth. It may be that Artemia nauplii are limiting
in this respect, particularly given the high level of triacylglycerols
in their total lipid.
Histological examination (data not shown) of the developing larval gut
has indicated that in the period following first feeding (up to d 46
PFF), lipid absorption was occurring largely in the hind gut; only
later, when the stomach was more fully developed, did absorption of
lipid occur in the fore gut (Luizi et al. 1998
). During
early development, lipid droplets were visible in the mucosal
epithelium of the hind gut of copepod-fed larvae, but largely
absent in the hind gut of larvae fed Artemia. In addition,
during the early part of the experiment, Artemia appeared to
pass through the gut largely undigested, whereas copepods were more
completely assimilated. The observations of Luizi et al.
(1998)
support the histological analysis of the liver in larvae
at d 46 PFF (Fig. 3)
, which showed a high degree of lipid vacuolation
in larvae fed copepods; this is consistent with an active assimilation
of dietary lipid and was not present in the livers of larvae fed
Artemia. However, sections of liver analyzed at d 65 PFF, at
which point gut development would more easily allow assimilation of
ingested Artemia, showed lipid vacuoles present in larvae
fed both copepods and enriched Artemia.
Studies performed by Japanese researchers have suggested that, in
addition to the provision of essential (n-3) HUFA, supplementation with
adequate vitamin A is vital for successful skin pigmentation
(Kanazawa 1993
, Miki et al. 1990
).
Pigmentation may require signal transmission via the visual system to
the brain, which allows increased melanocyte-stimulating hormone
production and consequent synthesis of melanin (Estevez and Kanazawa, 1996
, Kanazawa 1993
). A deficiency in
dietary vitamin A, which is a precursor of rhodopsin, will disrupt
transmission between the eye and the brain. Marine copepods are rich in
carotenoid pigments (8.2–43.6 µmol astaxanthin/g lipid
for the four E. velox size ranges, highest value in 125- to
250-µm size fraction), including mono- and diesters of
astaxanthin as well as unesterified astaxanthin, whereas
Artemia contain lower quantities of the related carotenoid
canthaxanthin (4.5–5.9 µmol canthaxanthin/g lipid for the
enriched Artemia used in this study), which is present only
in the unesterified form (Krinsky 1965
, J. McEvoy,
Institute of Aquaculture, University of Stirling). Although both
canthaxanthin and astaxanthin can be converted to vitamin A in fish
(Olson 1989
), the higher quantity of total carotenoid in
E. velox, coupled with the apparent increased digestibility
of copepods in early developing larvae, may allow more efficient uptake
and metabolism of these vitamin A precursors in halibut fed copepods
compared with those fed Artemia.
Marine fish are naturally enriched with 22:6(n-3) and their neural
tissues are especially rich in this HUFA (Bell and Dick 1991
, Tocher and Harvie 1988
). Membranes that
are highly enriched in DHA such as those of the rod outer segment
membrane are highly "stressed" due to the packing properties of
di-22:6(n-3)–containing phospholipids; this can facilitate rapid
conformational changes of the membrane structure as seen during the
cis to trans transition that occurs on light
activation of rhodopsin (Brown 1994
). Thus, DHA may have
a quite specific role in visual cell membranes. In addition,
DHA-rich membranes are cycled between the retinal epithelium
membrane and the photoreceptor membrane, and dietary DHA deficiency can
interfere with this process (Bazan et al. 1992
). In
young developing mammals, dietary (n-3) PUFA deficiency is known to
impair visual acuity (Hrboticky et al. 1991
,
Neuringer et al. 1984
). A similar loss in visual
function has been observed in larval herring (Clupea
harengus L.); DHA deprivation caused impaired visual performance,
particularly at low light intensities when rod cells are active
(Bell et al. 1995
). A linear relationship has been shown
between the recruitment of rods in the herring retina and its content
of di-DHA molecular species of phospholipids (Bell and Dick 1993
). On the basis of these findings, it can be inferred that
the significantly lower number of rod cells present in the retinas of
Artemia-fed larvae may reflect a relative lack of dietary
DHA and, consequently, retinal membrane DHA, in comparison to
copepod-fed larvae.
Although problems in obtaining a sufficient supply of copepods to
satisfy demand are likely to prevent their exclusive or even extensive
use in marine fish culture, copepods clearly represent a more
nutritionally optimized live prey organism than rotifers or
Artemia. Naess et al. (1995)
demonstrated
that halibut pigmentation characteristics benefit even from partial
supplementation of an Artemia-based diet with copepods, and
this combined feeding strategy may offer a practical means of
overcoming the developmental abnormalities associated with the use of
enriched Artemia. Whether the superior qualities of marine
copepods can be assigned to their high (n-3) HUFA content alone or to a
combination of factors including carotenoid and phospholipid content
remains the subject of continuing research.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
|---|
3 Current address: European Aquaculture Society
Secretariat, Slijkensesteenweg. 4, B-8400, Oostende, Belgium.
4 Current address: Mannin Seafarms, Castletown,
Derbyhaven, Isle of Man IM9 1TU.
5 Abbreviations used: AA, arachidonic acid; DHA,
docosahexaenoic acid; EFA, essential fatty acid; EG, enrichment grade;
EPA, eicosapentaenoic acid; HPTLC, high performance thin layer
chromatography; HUFA, highly unsaturated fatty acids; PFF,
post-first feeding; PUFA, polyunsaturated fatty acids.
Manuscript received September 18, 1998. Initial review completed December 23, 1998. Revision accepted February 17, 1999.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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3. Bazan N. G., Gordon W. C., Rodrigurez de Turco E. B. Docosahexaenoic acid uptake and metabolism in photoreceptors: retinal conservation by an efficient retinal pigment epithelial cell-mediated recycling process. Adv. Exp. Med. Biol. 1992;318:295-306[Medline]
4. Bell M. V., Batty R. S., Dick J. R., Fretwell K., Navarro J. C., Sargent J. R. Dietary deficiency of docosahexaenoic acid impairs vision at low light intensities in juvenile herring (Clupea harengus L.). Lipids 1995;30:443-449[Medline]
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