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Purdue University, Department of Forestry and Natural Resources, West Lafayette, IN 47907-1159
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: • yellow perch • phosphatidylcholine • choline • fish nutrition
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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, NRC 1993
).
However, the study of choline nutrition is confounded by other dietary
components, including amino acids, lipids and other vitamins. The most
commonly studied interaction has been with amino acids. Kroening and Pond (1967)
reported that dietary methionine concentrations only
slightly in excess of those required for maximum growth eliminated the
need for dietary choline in pigs and rats. Excess methionine was also
shown to eliminate the need for choline in diets fed to young cats
(Anderson et al. 1979
). However, excess methionine
replaced only a small portion of the dietary choline requirement of
young chicks, and excess dietary choline had only a minimal capacity to
reduce the chick’s requirement for dietary methionine(Baker et al. 1982
). Fewer studies have been conducted with fish. We
recently identified a significant interaction between methionine and
choline in diets fed to tilapia (unpublished data). Rumsey (1991)
reported that a dietary source of betaine spared ~50% of the choline
requirement of rainbow trout (Oncorhynchus mykiss). Excess
methionine was not able to supply the choline requirement in trout. The
other potentially confounding issue in fish has been
phosphatidylcholine
(PC)3
or lecithin.
In contrast to most terrestrial vertebrates (Overland et al. 1993a
, 1993b
and 1994
), dietary
PC improved growth rates and feed efficiency in several species of fish
(Craig and Gatlin 1997
, Hung 1989
,
Hung and Lutes 1988
, Poston 1990
,
Poston 1991a
and 1991b
). However,
lecithin contains choline, fatty acids and a glycerol backbone.
Responses to lecithin could, therefore, be responses to one or more of
the constituent components (Canty and Zeisel 1994
,
Hung and Lutes 1988
) particularly in species for which
few nutritional requirements have been quantified. Further, sources of
PC used in previous studies were typically food grade and contained
numerous other components. At this time, probably only the studies with
rainbow trout and red drum provide meaningful indications of the
benefits of lecithin in diets fed to fish as most of the potentially
confounding nutritional requirements were quantified prior to
evaluation.
Brown et al. (1996)
identified purified diets that could be used in
nutritional research with yellow perch. They reported that a purified
diet containing crystalline amino acids as the primary source of crude
protein supported weight gain that was not significantly different from
that of fish fed the best commercial diet. This dietary formulation has
been used in subsequent research in our laboratory to estimate the
dietary arginine (Twibell and Brown 1997
), lysine
(unpublished data) and total sulfur amino acid requirements
(unpublished data) of yellow perch. The same basic dietary formulation
was used in the present study to estimate the dietary choline
requirement of yellow perch and the ability of PC to meet the choline
requirement.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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All-female yellow perch were obtained from a commercial producer (Coolwater Farms, Cambridge, WI) and transported to the Purdue University Aquaculture Research Facility. All fish were acclimated to laboratory conditions for 6 mo prior to initiation of the experiment. Procedures used during transport, quarantine and experimental period were approved by the Purdue Animal Care and Use Committee (PACUC No. 89–060-98, "Nutritional Studies with Aquatic Animals," Principal Investigator Qualification No. BRO-249).
The closed recirculating system used in this experiment contained 24 individual 38-L aquariums. The experimental system was equipped with two submerged filtration tanks for solid material removal and denitrification of the water. Water was pumped through a sand filter to each aquarium at a rate of ~1 L/min and was maintained at 20 ± 1°C throughout the experiment. The diurnal light/dark cycle of the aquaculture facility remained at 16 h light/8 h dark throughout the study.
Groups of 20 randomly chosen fish were stocked into each aquarium. Fish were acclimated to the experimental system and their respective diets for 3 wk prior to the experiment. During the first 2 wk of the acclimation period, all fish were fed a commercial diet (Bioproducts, Warrenton, OR). During wk 3, all fish were offered their respective experimental diets, which had been randomly assigned to triplicate aquariums. Following the acclimation period, the number of fish in each tank was reduced to 13 so that the total weight of fish in each tank was 208.5 ± 5.0 g. Fish were fed to satiation twice daily during the 11-wk experiment. Water quality was monitored daily and was within acceptable limits throughout the experiment. Dissolved oxygen concentrations were not below 6.0 mg/L, ammonia-nitrogen concentrations were not >0.22 mg/L, and nitrite-nitrogen did not exceed 0.07 mg/L at any point during the study.
Diets.
The basal diet was formulated to provide 33.3 g of crude
protein/100 g diet (Table 1
). Casein and gelatin served as intact protein sources and provided a
total of 10.1 g of crude protein/100 g diet. An
L-amino acid mixture (Table 2
) supplied the remaining 23.2 g of crude protein/100 g diet. The
L-amino acid mixture was formulated so the basal diet
contained 1.41 g of arginine/100 g diet (Twibell and Brown 1997
) and 1.10 g of lysine/100 g diet (unpublished data
from our laboratory), thus meeting the dietary requirement of yellow
perch for these amino acids. The L-amino acid mixture was
also formulated to provide 1.0 g of TSAA/100 g diet as a
ratio of 49:51 met/cys, which was determined to be near the requirement
for this species (unpublished data). The remaining dietary essential
amino acid concentrations met or exceeded the highest known
requirements for fish (NRC 1993
). The basal diet
contained 6.0 g of lipid (menhaden oil)/100 g diet and 33.5 g
of carbohydrate (dextrin)/100 g diet (Cartwright 1998
).
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). Two additional diets were
supplemented with 31 g of lecithin/kg diet. One of those diets was
supplemented with 4.00 g of choline/kg diet; the other was not
supplemented with choline. A level of 31 g of lecithin/kg diet
provided the equivalent of 4.00 g of choline/kg diet from the
choline moieties of PC and lysophosphatidylcholine, based on the
guaranteed analysis provided by the supplier. The analyzed choline
concentration of the diet containing 31 g of lecithin/kg diet and
no choline chloride was 4.65 g of choline/kg diet. The analyzed
choline concentration of the diet containing 31 g of lecithin/kg
diet and 4.00 g of choline/kg diet was 10.12 g of choline/kg diet.
Choline chloride was added to the basal diet at the expense of
cellulose. Lecithin was added at the expense of menhaden oil.
Dry ingredients were thoroughly mixed in a twin-shell V-mixer
(Patterson-Kelly, East Stroudsburg, PA). Diets were then transferred to
a Hobart mixer (Hobart Corporation, Troy, OH) where choline chloride
was added to the diet in a water carrier. Lipid and additional water
were then added to the dry ingredients and mixed. For the diets
containing lecithin, the material was heated to a liquid and added to
the dry ingredients prior to mixing. Diets were adjusted to pH 7.0
± 0.2 with saturated sodium hydroxide (Wilson et al. 1977
) and pelleted. The diets were air-dried for 48 h
then stored under air-tight conditions at -20°C until needed.
Sample collection and analysis.
All fish were anesthetized(tri-caine methanesulfonate; Argent
Chemical, Redmond, WA) and weighed 24 h after the final feeding.
Three randomly chosen fish were collected from each dietary replicate
and frozen at -20°C for subsequent proximate analysis.
Whole-body moisture was determined by drying fish for 24 h in
a forced-air oven at 100°C. Crude protein was estimated from
whole-body nitrogen values, which were determined in an elemental
nitrogen analyzer (LECO Corporation, St. Joseph, MI). Ash content was
determined by incinerating samples at 600°C for 24 h in a muffle
furnace. Whole-body lipid concentration was determined as described
by Folch et al. (1957)
.
Livers from three randomly chosen fish in each dietary replicate were
removed and weighed for calculation of relative liver weight (liver
weight x 100/body weight). The livers were then frozen at
-20°C for subsequent determination of total lipids using the method
of Folch et al. (1957)
. Visceral fat was removed from an additional
group of three randomly chosen fish in each dietary replicate for
calculation of intraperitoneal fat (IPF) ratio (IPF x 100/body
weight).
Statistical analyses.
Data were analyzed as a completely randomized design using each
aquarium as an experimental unit and dietary treatment as the
independent variable. The data were analyzed as two distinct sets: one
to establish the quantitative dietary choline requirement and one to
compare the dietary treatments containing lecithin to those containing
choline. In the first statistical analysis, only data from fish fed
graded levels of choline were included in the data set and
broken-line analyses of weight gain and feed intake data were used
to estimate the dietary choline requirement (Robbins et al. 1979
). In the second analysis, all data were included and
Student-Neuman-Keuls test separated mean values when significant
differences were detected by ANOVA. Both data sets were analyzed with
the Statistical Analysis System (SAS 1990
). Accepted
level of significance was 0.05.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). Broken-line analysis of weight gain data indicated the dietary
choline requirement of yellow perch was 0.598 g/kg diet.
Broken-line analysis of feed intake data indicated that the dietary
choline requirement was 0.634 g/kg diet.
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. Weight gain of fish fed either diet
containing lecithin was not significantly different from fish fed
0.34 g of choline/kg diet or higher concentrations. Feed intake of
fish fed diets with lecithin was significantly higher than that of fish
fed 0.34 g of choline/kg diet and lower concentrations, but not
significantly different from fish fed 0.75 g of choline/kg and
higher concentrations. There were no significant differences in feed
efficiency among fish fed any level of choline or PC.
Choline or PC did not significantly affect relative liver weight, and
values ranged from 1.2 to 4.4 (data not shown). There were no
significant differences in total liver lipid concentrations among fish
fed any level of dietary choline (Table 3)
. However, fish fed the diet
with lecithin and deficient in choline exhibited significantly higher
liver lipid concentrations compared to fish fed any of the other diets,
including those fed lecithin with 4.00 g of choline/kg diet.
Dietary choline and PC significantly affected carcass composition of
yellow perch (Table 4
). While ANOVA indicated significant differences in IPF,
Student-Neuman Keuls test did not differentiate among means.
Choline or PC did not significantly affect moisture or protein content
of the fish. Whole-body fat concentrations were significantly
different and generally increased in fish fed increasing concentrations
of choline. Fish fed diets containing lecithin, as well as fish fed the
diet containing 1.22 g of choline/kg diet, had significantly
higher whole-body fat concentrations compared to fish fed the basal
diet. Whole-body ash levels were significantly different among
dietary treatments and decreased as dietary choline concentration
increased. Fish fed the diets containing lecithin and 4.00 g of
choline/kg had significantly lower whole-body ash concentrations
compared to fish fed the basal diet.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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, Poston 1991c
,
Rumsey 1991
). Dietary choline requirements of other fish
are 1.00 g/kg for 5.0 g lake trout (Salvelinus
namaycush) (Ketola 1976
), 1.70–3.20 g/kg for
34.1 g white sturgeon (Hung 1989
), 0.59 g/kg for
5.5 g red drum (Craig and Gatlin 1996
), 0.50 g/kg
for 10.5 g hybrid striped bass (Morone saxatilis x
M. chrysops) (Griffin et al. 1994
) and 0.40
g/kg for 5.6 g channel catfish (Ictalurus punctatus)
(Wilson and Poe 1988
). Although comparisons of dietary
choline requirements among species are difficult due to differences in
initial weight of fish, dietary composition and experimental
conditions, apparently, the estimates obtained in the present study are
within the range of dietary choline requirements for fish, which are
0.05 to 4.00 g/kg diet.
Weight gain of yellow perch fed the diets containing lecithin, with or
without choline, was not different from that of fish fed at least
0.34 g of choline/kg diet. This indicates that yellow perch can
use lecithin as a source of choline for growth. Further, perch likely
have some form of phospholipase. Apparently, there are no reports of
phospholipase activity in the gastrointestinal tract of fish, but there
are reports of cellular forms in muscle (Jonas and Bilinski 1967
), liver (Neas and Hazel 1984
) and whole
larval fish (Evans et al. 1998
). However, since there
was no difference in weight gain between fish fed the diets containing
lecithin, it appears that lecithin provides no additional benefit when
diets contain choline at approximately six times the dietary
requirement. Furthermore, liver lipid concentration was significantly
higher in fish fed lecithin and deficient in choline. Further studies
should be conducted to evaluate potential interactions of dietary
choline and PC.
Liver lipid concentration has been used as an indicator of choline
status in a variety of animals. It is thought that accumulation of
liver lipids in choline-deficient animals is a result of impaired
hepatic lipoprotein secretion and subsequent accumulation of
triglycerides (Chan 1991
). However, liver lipid
concentration has not been a consistent indicator of choline status in
fish. Dietary choline supplied at or above the requirement resulted in
significantly lower liver lipid concentrations in channel catfish
(Wilson and Poe 1988
), lake trout (Ketola 1976
) and hybrid striped bass (Griffin et al. 1994
), but higher liver lipid levels in red drum (Craig and Gatlin 1996
). Liver lipid levels were not responsive to
dietary choline in rainbow trout (Rumsey 1991
) or yellow
perch in the present study. However, carcass composition of yellow
perch was responsive to increasing dietary choline. A reduction in
protein and increase in fat in fish fed increasing concentrations of
choline were observed. Similar results were reported for Atlantic
salmon (Poston 1990
) and rainbow trout (Poston 1991c
).
When sulfur amino acid concentrations are provided at the requirement, choline is clearly an essential vitamin in diets fed to juvenile yellow perch with an initial weight of 16 g. This is similar to studies with other species of fish and terrestrial vertebrates, yet a complete understanding of choline nutrition in fishes has not been developed. Specifically, there have not been studies designed to understand ontogenetic differences in choline nutrition in fishes, nor is there a complete understanding of the numerous interactions that can occur in the sulfur amino acid catabolic pathway.
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FOOTNOTES |
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3 Abbreviations used: PC, phosphatidylcholine;
Manuscript received April 2, 1999. Initial review completed May 28, 1999. Revision accepted October 7, 1999.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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