HUFA Diet Research Articles

Intestinal health in Atlantic salmon post-smolt (Salmo salar) when fed low- and high HUFA diets

It is well established that farmed Atlantic salmon (Salmo salar) need n3-highly unsaturated fatty acids (HUFA) in their diet to thrive and grow. However, the biological functions to the individual HUFAs may differ, implying that future supplementation could require fixed ratios for maximum benefit. The intestinal barrier is essential to fish health, and any disruption of the barrier can have detrimental effects. The current experiment was designed to examine the response of the intestinal hindgut when fed a low HUFA diet with 8.5 g/kg EPA + DHA (4.5% total fatty acid) or two high HUFA diets, with either high DHA (28.7 g/kg and 5.9% total fatty acid) or high EPA (25 g/kg and 14.2% total fatty acid). The diets were fed to Atlantic salmon post-smolt over 10 weeks and thereafter exposed to 3 weeks of chronic stress. After 10 weeks of feeding there were no differences in intestinal permeability and integrity, but intestinal morphology indicated increased intestinal health in the high EPA group. Gene expression also suggest that fish fed the high EPA diet had more regulation of pathways related to protein turnover compared to the high DHA fed fish. There was also indication of lower energy utilization in the low HUFA fed fish than high HUFA. Subjecting fish to 3 weeks of chronic stress led to a reduction in transepithelial resistance, increased ion flux and active l-lysine transport across the intestinal barrier in addition to a decrease in mucosal fold, enterocyte height and supranuclear vacuole density and an increase in thickness of the intestinal muscularis. After stress, the low HUFA group showed signs of inflammation with increased infiltration of MHCII positive cells. Gene expression also showed that low HUFA fed fish had a lower response to chronic stress compared to the high HUFA groups. Comparing fish fed either high DHA or EPA exposed to chronic stress showed few physical effects, but a lower density of supranuclear vacuoles and upregulation in immune-related gene expression indicate inflammation in the high DHA group.

The relationship between membrane fatty acid content and mitochondrial efficiency differs within- and between- omega-3 dietary treatments

An important, but underappreciated, consequence of climate change is the reduction in crucial nutrient production at the base of the marine food chain: the long-chain omega-3 highly unsaturated fatty acids (n-3 HUFA). This can have dramatic consequences on consumers, such as fish as they have limited capacity to synthesise n-3 HUFA de novo. The n-3 HUFA, such as docosahexaenoic acid (DHA, 22:6n-3) and eicosapentaenoic acid (EPA, 20:5n-3), are critical for the structure and function of all biological membranes. There is increasing evidence that fish will be badly affected by reductions in n-3 HUFA dietary availability, however the underlying mechanisms remain obscure. Hypotheses for how mitochondrial function should change with dietary n-3 HUFA availability have generally ignored ATP production, despite its importance to a cell's total energetics capacity, and in turn, whole-animal performance. Here we (i) quantified individual variation in mitochondrial efficiency (ATP/O ratio) of muscle and (ii) examined its relationship with content in EPA and DHA in muscle membrane of a primary consumer fish, the golden grey mullet Chelon auratus, receiving either a high or low n-3 HUFA diet. Mitochondria of fish fed on the low n-3 HUFA diet had higher ATP/O ratio than those of fish maintained on the high n-3 HUFA diet. Yet, mitochondrial efficiency varied up about 2-fold among individuals on the same dietary treatment, resulting in some fish consuming half the oxygen and energy substrate to produce the similar amount of ATP than conspecific on similar diet. This variation in mitochondrial efficiency among individuals from the same diet treatment was related to individual differences in fatty acid composition of the membranes: a high ATP/O ratio was associated with a high content in EPA and DHA in biological membranes. Our results highlight the existence of interindividual differences in mitochondrial efficiency and its potential importance in explaining intraspecific variation in response to food chain changes.

Ocean warming combined with lower omega-3 nutritional availability impairs the cardio-respiratory function of a marine fish.

Highly unsaturated fatty acids of the omega-3 series (HUFA) are major constituents of cell membranes, yet are poorly synthesised de novo by consumers. Their production, mainly supported by aquatic microalgae, has been decreasing with global change. The consequences of such reductions may be profound for ectotherm consumers, as temperature tightly regulates the HUFA content in cell membranes, maintaining their functionality. Integrating individual, tissue and molecular approaches, we examined the consequences of the combined effects of temperature and HUFA depletion on the key cardio-respiratory functions of the golden grey mullet, an ectotherm grazer of high ecological importance. For 4months, fish were exposed to two contrasting HUFA diets [4.8% eicosapentaenoic acid (EPA)+docosahexaenoic acid (DHA) on dry matter (DM) versus 0.2% EPA+DHA on DM] at 12 and 20°C. Ventricular force development coupled with gene expression profiles measured on cardiac muscle suggest that combining HUFA depletion with warmer temperatures leads to: (1) a proliferation of sarcolemmal and sarcoplasmic reticulum Ca2+ channels and (2) a higher force-generating ability by increasing extracellular Ca2+ influx via sarcolemmal channels when the heart has to sustain excessive effort due to stress and/or exercise. At the individual scale, these responses were associated with a greater aerobic scope, maximum metabolic rate and net cost of locomotion, suggesting the higher energy cost of this strategy. This impaired cardiac performance could have wider consequences for other physiological performance such as growth, reproduction or migration, all of which greatly depend on heart function.

A simple and low-cost recirculating aquaculture system for the production of arapaima juveniles

A simple and low-cost recirculating system (RAS) for production of arapaima ( Arapaima gigas ) juveniles is described. Twenty arapaima fry (mean 13.0 cm, 12.0 g) were housed in three production tanks and fed a high HUFA diet resulting in 90% of fry successfully progressing to juveniles (mean 17.4 cm long; 40.2 g). The fish were then reared for a further 72 days fed on commercial extruded pellet feed achieving a mean length of 42.6 cm and 656.6 g. The simple and low-cost RAS holds good potential for production of arapaima juveniles.

Reduced n-3 highly unsaturated fatty acids dietary content expected with global change reduces the metabolic capacity of the golden grey mullet

In this study, we hypothesised that a reduction in n-3 HUFA availability for higher consumers, as expected with global change, would negatively impact the physiological performances of fish. The aim was to experimentally evaluate the effect of n-3 HUFA dietary content on cardio-respiratory performances of the golden grey mullet (Liza aurata), a microalgae grazer of high ecological importance in European coastal areas. These performances were evaluated in terms of critical swimming speed U crit, associated oxygen consumption MO2, post-exercise oxygen consumption and calcium fluxes in cardiomyocytes. Two replicated groups of fish were fed on a rich (standard diet, SD diet: 1.2 % n-3 HUFA on dry matter basis, DMB) or a poor n-3 HUFA (low n-3 HUFA diet, LD diet: 0.2 % n-3 HUFA on DMB) diet during 5 months and were called SD and LD groups, respectively. The results showed that the LD diet reduced growth rate as well as the aerobic capacity of L. aurata at 20 °C, suggesting that fish may have to save energy by modifying the proportion of energy allocated to energy-demanding activities, such as digestion or feeding. In addition, this LD diet induced higher levels of haematocrit and plasma osmolality, indicating a stress response at the second and third levels in that group. However, the LD diet caused a massive increase in swimming efficiency. This should improve the capacity of L. aurata to migrate and to forage over a wide area. In turn, these could then compensate for the reduction in growth rate and aerobic metabolism.

Blood antioxidant defenses and hematological adjustments in crowded/uncrowded rainbow trout ( Oncorhynchus mykiss) fed on diets with different levels of antioxidant vitamins and HUFA

Rainbow trout maintained at crowding or noncrowding conditions were fed on five experimental diets that were formulated considering two levels of vitamin E (25.6 and 275.6 mg/kg diet), vitamin C (0 and 1000 mg/kg diet) and HUFA (12.5 and 30.5 g/kg diet): −E−HUFA, −E+HUFA, +E−HUFA, +E+HUFA, −C+E+HUFA. Hematological parameters, the activity of some antioxidant enzymes and lipid peroxidation from RBC were evaluated. The SOD isoenzyme pattern was analyzed by nondenaturing PAGE. Hematological response to crowding stress was manifested by increased hemoglobin and RBC count in most of the crowded groups. Antioxidant enzyme activity was clearly affected by dietary HUFA levels, with uncrowded fish fed on +HUFA diets showing a higher SOD activity compared to those fed on −HUFA diets. In uncrowded groups, only one CuZn-SOD isozyme was detected, whereas in the crowded fish a great variability was revealed with up to five isozymes. G6PDH activity was increased in uncrowded −E+HUFA fish compared to the remaining groups. Lipid peroxidation was significantly increased in −E+HUFA fish regardless of fish density. Data supported the negative correlation of lipid peroxidation and hematocrit or hemoglobin explained by decreased erythrocyte stability. Dietary imbalances in vitamin E and HUFA supplementation may promote oxidative stress which triggers hematological deterioration, which in turn would affect the whole hematological status and ultimately fish welfare.

Is it possible to influence European sea bass ( Dicentrarchus labrax) juvenile metabolism by a nutritional conditioning during larval stage?

The purpose of this study was to check if it is possible to influence sea bass juvenile metabolism by a conditioning of larvae from day 6 post hatching to day 45 to a low or a high HUFA compound diet (LH, 0.8% EPA + DHA and HH, 2.2% EPA + DHA) when reared at 16 or 22 °C. Following a 3-month intermediate period (at 19 °C using a commercial diet), the adaptability of the 4 initial larval groups to a HUFA experimental deprived diet (0.5% EPA + DHA) were tested at 19 °C in a 60 day-experiment (d-151–211). The four experimental duplicated conditions were ex-LH16 and ex-HH16 for the 2 groups previously reared at 16 °C (initial weight, 7.3 ± 0.5 g) and ex-LH22 and ex-HH22 for the 2 groups previously reared at 22 °C (initial weight, 11.1 ± 0.5 g). Survival was maximal and there was a 1.6–2 fold increase in mass during the experiment. Growth was similar in the 4 experimental groups: NS difference in growth curve slopes ( P = 0.7). At the end of the experiment (d-211), whole body fat levels were in the same range in all groups (13–15% WW). The fatty acid (FA) composition in polar lipids (PL) and total lipids (TL) were significantly affected by initial weight related to larvae conditioning, which can be mainly attributed to a dilution effect (impact of initial FA content on final FA content versus relative mass increase during the course of the experiment). Conversely to this trend, DHA content in PL was higher in the ex-LH groups than in the ex-HH groups whatever thermal conditioning of larvae was. This indicated that ex-LH groups had a better capacity to adapt to a deficient HUFA diet than ex-HH fish. The relative expression of the delta-6 desaturase (Δ6D) was significantly higher in ex-LH than in ex-HH groups ( P < 0.001) between d-151 and d-181, which suggested that Δ6D transcription in ex-LH groups was positively modulated by the HUFA-deprived diet. This stimulation of the first step of the desaturation/elongation pathway could allow synthesizing FA needed to compensate low dietary HUFA supply. This study shows for the first time that it seems possible to influence juvenile fish metabolism by a nutritional conditioning during the larval stage.

Impact of essential fatty acid deficiency and temperature on tissues' fatty acid composition of European sea bass ( Dicentrarchus labrax)

The effects of essential fatty acid deficiency and temperature on the fatty acid profiles of polar lipids (PL) and neutral lipids (NL) from various tissues (muscle, liver, gills, eyes and brain) of European sea bass juveniles were compared in a two factorial design. Fish (60 g) were held for 84 days at 22 or 29 °C (upper limit for growth) and fed either at a lower or a higher level than n − 3 HUFA minimal requirement for growth (0.4% and 2.2% n − 3 HUFA dry matter for diets LD and HD, respectively). Essential fatty acid deficiency had a major influence on fatty acids in NL fraction of all tissues, a more moderate influence on PL of muscle, liver and gills, while a low and very low diet influence was observed on eyes and brain PL fatty acid content, respectively. DHA and EPA content in brain PL as well as DHA in eyes PL were not affected by diet. DHA contents were similar in gill PL of 22-HD, 29-HD and 22-LD but was reduced in 29-LD fish. Most of brain PL fatty acids displayed a significant effect of temperature (at 29 °C; 18 : 0, 18 : 1 n − 9 contents were higher, and 20 : 5 n − 3, 22 : 6 n − 3, 20 : 4 n − 6 contents were lower than at 22 °C). Temperature had more influence on PL than on NL fatty acid content, except in liver. A lipogenic activity seemed to occur, both 16 : 0 and 18 : 0 were high particularly in liver NL and dependent on temperature (higher at 29 than at 22 °C). An enhanced 18 : 3 n − 6 content in fish fed on the deficient HUFA diet indicated a desaturation activity, mainly in liver NL and gill PL, with higher arachidonic acid content in PL of gills than other tissues. Muscle fatty acid profiles in NL and PL were more similar to those of whole body than other tissues, however total lipid content then PL : NL ratio differed. This study shown that beside known characteristics of each tissue in term of PL fatty acid content, each tissue have also characteristics in term of response to temperature and dietary deficiency influence. Among then, neural tissue displayed the highest capacity to regulate DHA content in PL, preserving functionality despite HUFA deficiency.

Effects of n-3 HUFA content in broodstock diet on spawning performance and fatty acid composition of eggs and larvae in Plectorhynchus cinctus

The effects of n-3 highly unsaturated fatty acid ( n-3 HUFA) content in broodstock diets on the quality and fatty acid composition of eggs and larvae were investigated in Plectorhynchus cinctus. Broodstocks were fed a natural diet (trash fish) and four formulated diets with similar proximate compositions but different levels of n-3 HUFA (1.12, 2.40, 3.70 or 5.85%) through their reproductive cycle. Compared with the natural diet-fed group, the egg production per kg of females, percentage of buoyant eggs, survival and length of larvae at 3 days post hatching were similar in fish fed 2.40% and 3.70% n-3 HUFA diets, but markedly decreased in the groups fed 1.12 and 5.85% n-3 HUFA diets. The content of most fatty acids and fatty acid class in eggs and larvae was directly influenced by dietary n-3 HUFA levels and exhibited parallel change pattern with the respective dietary levels. The results showed that either deficient or excess level of dietary n-3 HUFA had a negative effect on egg and larval quality, good spawning performance was obtained when the dietary n-3 HUFA content was 2.40 and 3.70%, or the n-3 HUFA level took 12.17 and 18.63% of the total fatty acids. Dietary n-3 HUFA content may affect egg and larval quality by influencing their fatty acid composition.

Consumption vs. deposition of essential fatty acids in gilthead sea bream ( Sparus aurata) larvae fed semi-purified diets

Semi-purified diets were used to feed gilthead sea bream larvae as first food from mouth opening until day 17. Four diets were formulated on the basis of a previous one used as control (D1). Three experimental diets differed only by the lipids added. One diet contained n-3 highly unsaturated fatty acids (n-3 HUFA) plus arachidonic acid (D2), one diet n-3 HUFA without arachidonic acid (D3) and one diet without n-3 and n-6 HUFA (D4). The three experimental diets contained 18:3n-6 in order to follow the influence of dietary HUFAs on elongation-desaturation capacities. Larval growth and survival were similar with diet D1 and D2. Lowest growth and survival were observed for larvae fed the HUFA free diet D4. Larval survival but not growth was significantly decreased by lack of arachidonic acid in diet D3 compared to D2. Utilization of fatty acids by larvae was studied by comparing the fatty acid quantities per larva in initial (before feeding) and final samples. In larvae fed the HUFA-free diet D4, a significant increase of 20:3n-6 showed that some elongation from 18:3n-6 occurred, while quantities of arachidonic acid and n-3 fatty acids (except 18:3n-3) decreased compared to initial larvae. A consumption of endogenous HUFAs was evidenced despite effective incorporation of dietary fatty acids such as 18:2n-6, 18:1n-9 and 18:3n-3. Fatty acid profile of these larvae changed, according to dietary fatty acid influence, by turnover rather than by a raw incorporation of fatty acids. Larvae fed the n-3 HUFA diet depleted in arachidonic acid (D3) had a total fatty acid content lower than those fed with arachidonic acid (D2); compared to those fed D4, the elongation of 18:3n-6 to 20:3n-6 seemed to be repressed by dietary n-3 HUFA. Consumption of long-chain unsaturated fatty acid is a main conclusion of this study; a rate of loss around 1.1, 0.5 and 0.05 mg day −1 g −1 mean dry body weight of larvae for docosahexaenoic, eicosapentaenoic and arachidonic acid, respectively, may be estimated in larvae fed the HUFA free diet D4. No desaturation capacities of gilthead sea bream larvae were evidenced; however, some low capacities might be masked by the consumption of HUFAs.

Consumption vs. deposition of essential fatty acids in gilthead sea bream (Sparus aurata) larvae fed semi-purified diets

Semi-purified diets were used to feed gilthead sea bream larvae as first food from mouth opening until day 17. Four diets were formulated on the basis of a previous one used as control (D1). Three experimental diets differed only by the lipids added. One diet contained n-3 highly unsaturated fatty acids (n-3 HUFA) plus arachidonic acid (D2), one diet n-3 HUFA without arachidonic acid (D3) and one diet without n-3 and n-6 HUFA (D4). The three experimental diets contained 18:3n-6 in order to follow the influence of dietary HUFAs on elongation-desaturation capacities. Larval growth and survival were similar with diet D1 and D2. Lowest growth and survival were observed for larvae fed the HUFA free diet D4. Larval survival but not growth was significantly decreased by lack of arachidonic acid in diet D3 compared to D2. Utilization of fatty acids by larvae was studied by comparing the fatty acid quantities per larva in initial (before feeding) and final samples. In larvae fed the HUFA-free diet D4, a significant increase of 20:3n-6 showed that some elongation from 18:3n-6 occurred, while quantities of arachidonic acid and n-3 fatty acids (except 18:3n-3) decreased compared to initial larvae. A consumption of endogenous HUFAs was evidenced despite effective incorporation of dietary fatty acids such as 18:2n-6, 18:1n-9 and 18:3n-3. Fatty acid profile of these larvae changed, according to dietary fatty acid influence, by turnover rather than by a raw incorporation of fatty acids. Larvae fed the n-3 HUFA diet depleted in arachidonic acid (D3) had a total fatty acid content lower than those fed with arachidonic acid (D2); compared to those fed D4, the elongation of 18:3n-6 to 20:3n-6 seemed to be repressed by dietary n-3 HUFA. Consumption of long-chain unsaturated fatty acid is a main conclusion of this study; a rate of loss around 1.1, 0.5 and 0.05 mg day −1 g −1 mean dry body weight of larvae for docosahexaenoic, eicosapentaenoic and arachidonic acid, respectively, may be estimated in larvae fed the HUFA free diet D4. No desaturation capacities of gilthead sea bream larvae were evidenced; however, some low capacities might be masked by the consumption of HUFAs.

Nonspecific immune response of rainbow trout ( Oncorhynchus mykiss Walbaum) in relation to different status of vitamin E and highly unsaturated fatty acids

This study was designed to examine the effects of dietary vitamin E (VE) on modulation of immune responses when supplied with two levels of n-3 highly unsaturated fatty acids (n-3 HUFA) in rainbow trout, Oncorhynchus mykiss. Six semipurified diets were prepared containing three levels of dietary VE (0, 100 or 1000 mg α-tocopheryl acetate kg −1diet) and n-3 HUFA either at 20 or 48% of dietary lipid provided from fish oil or docosahexaenoic acid (DHA) concentrated fish oil respectively. The diets were fed to rainbow trout (100 g initial mean weight) for 15 weeks. The VE, vitamin C (VC) content in plasma and tissues and the nonspecific immune responses, both humoral (alternative complement activity, total immunoglobulin) and cellular (phagocytosis, nonspecific cytotoxicity) were examined. VE contents in the kidney reflected the dietary input but were lower in fish fed 48% n-3 HUFA diets, and could have impaired some of immune responses compared to fish fed 20% n-3 HUFA. VC contents in kidney followed the same pattern as VE. Both humoral and cellular immune functions deteriorated in fish fed VE deficient diets whereas improvement in most of the parameters corresponded to its supplementation. However, the higher dose of dietary VE did not substantially enhance the responses assayed compared to the 100 mg dose. Besides clearly indicating the role of VE in maintaining the immune functions in fish in relation to dietary n-3 HUFA, this study has revealed that optimum health benefits could be achieved when VE is maintained slightly above the levels generally recommended for normal growth.

Requirement of dietary n-3 highly unsaturated fatty acids for juvenile flounder ( Paralichthys olivaceus)

The effect of dietary n-3 highly unsaturated fatty acids (n-3 HUFA) level on growth and body composition was investigated to determine the n-3 HUFA requirement for juvenile flounder. Eight diets of different n-3 HUFA levels ranging from 0.0% to 2.4% were fed to juvenile flounder for 8 weeks. For varying n-3 HUFA level, mixtures of mainly EPA (0.0–1.1%) and DHA (0.0–0.9%) were used except one diet containing only 1.2% EPA. Weight gain, feed efficiency and protein efficiency ratio increased significantly with increasing dietary n-3 HUFA level up to 0.8%; however, those values gradually decreased after n-3 HUFA level became higher than 1.6%. The result of second-order polynomial regression showed that the maximum weight gain could be attained at 1.0% n-3 HUFA level. The weight gain was significantly lower for the diet containing 1.2% EPA than for the 1.2% n-3 HUFA diet containing both EPA and DHA. The contents of DHA and n-3 HUFA in whole body polar lipid increased with dietary n-3 HUFA level. Monoenoic fatty acids content and 18:1n/n-3 HUFA ratio decreased with increasing dietary n-3 HUFA level. The results suggest that the requirement of dietary n-3 HUFA for juvenile flounder is about 0.8–1.0%; however, excessive n-3 HUFA supplement may impair the growth of juvenile flounder.

The Serum LDL/HDL Cholesterol Ratio Is Influenced More Favorably by Exchanging Saturated with Unsaturated Fat Than by Reducing Saturated Fat in the Diet of Women

We compared the effects of a high fat diet [38.4% of energy (E%) from fat; HSAFA diet, polyunsaturated/saturated fatty acid (P/S) ratio = 0.14], a low fat diet (19.7 E% from fat; LSAFA diet, P/S = 0.17), both based on coconut oil, and a diet with a high content of mono- and polyunsaturated fatty acids (PUFA; 38.2 E% from fat; HUFA diet, P/S = 1.9) on serum lipoproteins. The 25 women studied consumed each diet for 3-wk periods in a crossover design. The two high fat diets were identical except for the quality of the test fat. The LSAFA diet was identical to the HSAFA diet except that half the fat was replaced by carbohydrates. Serum total cholesterol, LDL cholesterol and apoB concentrations did not differ between the HSAFA and the LSAFA diet periods. Total cholesterol, LDL cholesterol and apoB were lower when women consumed the HUFA diet than when they consumed the other two diets. HDL cholesterol and apoA-I were 15 and 11%, respectively, higher when women consumed the HSAFA diet than when they consumed the LSAFA diet; HDL cholesterol and apoA-I were lower when women consumed the HUFA diet than when they consumed the HSAFA diet, but not the LSAFA diet. The LDL cholesterol/HDL cholesterol and apoB/apoA-I ratios were higher when women consumed the LSAFA diet than when they consumed the HSAFA diet. The LDL/HDL cholesterol ratio was higher when women consumed either the LSAFA or the HSAFA diet than when they consumed the HUFA diet, whereas apoB/apoA-I was higher when women consumed the LSAFA diet than when they consumed the HUFA diet. Triacylglycerol and VLDL cholesterol were higher when women consumed the LSAFA diet than when they consumed either the HSAFA or the HUFA diet. We conclude that, to influence the LDL/HDL cholesterol ratio, changing the proportions of dietary fatty acids may be more important than restricting the percentage of total or saturated fat energy, at least when derived mainly from lauric and myristic acids, both of which increase HDL cholesterol.

Effects of high levels of n−3 HUFA in broodstock diet on egg quality and egg fatty acid composition of Japanese flounder, Paralichthys olivaceus

We investigated the effect of high levels of n−3 highly unsaturated fatty acids ( n−3 HUFA) in broodstock diet on egg quality and chemical composition of eggs of Japanese flounder. The broodstock were fed diets containing three levels of n−3 HUFA (2.1%, 4.8% or 6.2%) 2 months before and during the spawning period. No significant difference was found for weight gain of broodstock among the treatments. Egg production was highest in fish fed the highest level of n−3 HUFA. However, egg quality parameters, such as percentage of buoyant eggs, hatching rate and percentage of normal larvae, were significantly higher in the group fed the lowest n−3 HUFA diet. The fatty acid composition of eggs was influenced more markedly in the neutral lipid fraction than in the polar lipid fraction by dietary n−3 HUFA levels. Arachidonic acid (AA; 20:4 n−6) and egg quality parameters both decreased with increasing dietary n−3 HUFA levels. The results suggest that a high level of n−3 HUFA in broodstock diet negatively affects egg quality of Japanese flounder.

Effect of different levels of n−3 highly unsaturated fatty acids on growth and fatty acid composition of juvenile gilthead seabream (Sparus aurata)

The requirements of juvenile gilthead seabream for n−3 highly unsaturated fatty acids (n−3 HUFA) were studied by feeding fish with diets containing 4 different levels of n−3 HUFA ranging from 0.76 to 2.94% of the diet. Juvenile fish weighing 42.5 ± 0.21 g were randomly divided into 12 groups of 15 fish and pair fed the 4 experimental diets for 8 weeks. No mortality was observed during the feeding trial, but significant differences were found in growth rate and biochemical composition of the fish. Fish fed low dietary n−3 HUFA (0.76% of the diet) showed poor growth rates and low feed efficiency ratios, but these parameters improved by the elevation of the n−3 HUFA levels in the diet up to 1.9%. Fish fed the lowest n−3 HUFA diet showed the highest levels of crude lipid in the liver and gills. Muscle and gill phospholipids were generally less influenced by the type of diet than the liver. Results of this experiment suggest that with dietary lipid contents of 8–10%, the requirements for essential fatty acids of juvenile gilthead seabream is about 1.9% n−3 HUFA of the dry diet.

The importance of n-3 highly unsaturated fatty acids for growth in larval Sparus aurata and their effect on survival, lipid composition and size distribution

The effect of feeding Artemia nauplii containing different levels of n-3 HUFA on growth, survival and size distribution was tested in 22–36-day Sparus aurata larvae. Five treatments were prepared by feeding 24-h-old nauplii various percent ratios (0:100, 10:90, 25:75, 50:50, 75:25) of a commercial emulsion (high in n-3 HUFA) and a soybean oil-egg yolk emulsion (3:1 preparation, deficient in n-3 HUFA). Each treatment had five replicates and provided the following n-3 HUFA levels in Artemia: 2.6, 7.4, 12.3, 18.8, 29.8 mg/g DBW nauplii. Dietary n-3 HUFA showed a linear correlation ( P < 0.01) with larval relative growih rate (RGR), length and final tank biomass. Fish fed the highest level of n-3 HUFA demonstrated an RGR (86.4%) and final tank biomass (30.9 g wet wt) that was more than double the values exhibited by fish fed the lowest n-3 HUFA diet (39.9%, 14.0 g wet wt, respectively). Survival, in contrast, was not linearly correlated with dietary n-3 HUFA although there was a significant survival ( P < 0.05) effect between the n-3 HUFA poorest diet and the majority of remaining treatments. The lesser n-3 HUFA diets (2.6, 7.4 and 12.3 mg/g DBW) nauplii produced larval populations consisting mainly of small fish (6.9 mg ± 1.9) while n-3 HUFA rich diets (18.8 and 29.8 mg n-3 HUFA/g DBW nauplii) increased the fraction of larger larvae (23.0 ± 6 mg). The level of n-3 HUFA (mg/g DBW) in larval phospholipid was highly influenced by the content of these fatty acids in the diet. However, the phospholipid n-3 HUFA levels (mg/g DBW) in larvae fed the same diet were similar regardless of fish size. Finally, by examining different size larvae in groups under the various n-3 HUFA treatments, this study found that the inverse relationship between larval lipid and moisture was a function of growth rate and not dietary n-3 HUFA.

Essential fatty acid nutrition of larval striped bass ( Morone saxatilis) and palmetto bass ( M. saxatilis × M. chrysops)

Essential fatty acid (EFA) requirements of striped bass and palmetto bass (striped bass × white bass) larvae were investigated using three Artemia nauplii diets: (1) a control diet (Great Salt Lake strain), and same strain enriched with (2) corn oil, and (3) highly unsaturated n − 3 fatty acids (HUFA = 20:3 < n − 3 fatty acids). The n−6/ n−3 ratio increased (6 fold) while the HUFA content of fish decreased (10 to 30 fold) in all treatments by age. At 28-d posthatch, palmetto bass showed no size differences among treatments, although striped bass fed the HUFA diet were significantly larger than those fed the other two diets. At metamorphosis from larvae to juveniles (26–28 d posthatch), both genetic groups fed the control and corn oil diets displayed EFA deficiency syndrome and mass mortality (85–99%), while larvae fed the HUFA diet had excellent survival (80%). Palmetto bass were more sensitive to EFA deficiencies than striped bass in the control and corn oil diets, as mortality was greater. Regression analyses revealed that the HUFA content, and not the other fatty acid families of diet and larvae, was responsible for the variation in growth and survival; the higher the HUFA content, the better the survival and growth. Both genetic groups emulated marine species with respect to their EFA requirements, and dietary HUFA was required at levels of 5.7 mg g −1 dry-wt Artemia nauplii.

Requirement of juvenile striped jack Longirostris delicatissimus for n-3 highly unsaturated fatty acids.

The requirement of juvenile striped jack for n-3 highly unsaturated fatty acids (n-3 HUFA) was determined by feeding fish meal diets containing different levels on n-3 HUFA ranging from 0.7 to 3.5% in the diet. Juvenile fish weighing 0.26g and 1.78g were fed the experimental diets for 60 days in Expt. I and 56 days in Expt. II, respectively.In Expt. I after 9 days of feeding, a high mortality and poor appetite were observed in fish receiving the diet lowest in the n-3 HUFA content (0.7%). Fish fed a diet containing 1.2% n-3 HUFA also began to show a high mortality around the 55th day of feeding. On the other hand, no mortality was observed in the fish receiving the 3.5% n-3 HUFA diet in Expt. I and all the diets in Expt. II. In both experiments, growth of fish and feed efficiency were proportional to n-3 HUFA levels in the diets and reached a plateau at a level of 1.7% in the diet.Feeding diets low in the n-3 HUFA level resulted in an increase of 18:1, but not 20:3 (n-9) in the polar lipids of both whole body and liver. Elevation of dietary n-3 HUFA levels effectively reduced the 18:1 level and increased n-3 HUFA levels. From these results, the requirement of juvenile striped jack for n-3 HUFA is estimated to be around 1.7% in diet.