John D. Castell

Effects of purified diets containing different combinations of arachidonic and docosahexaenoic acid on survival, growth and fatty acid composition of juvenile turbot (Scophthalmus maximus)

The objective of this study was to determine the relative essential fatty acid (EFA) growth-promoting activities of pure arachidonic (AA, 20:4n−6) and docosahexaenoic (DHA, 22:6n−3) acids and various concentrations of these two acids in the diet of juvenile turbot (Scophthalmus maximus). Casein-based, semi-purified diets containing 15% fish oil or 14% hydrogenated coconut oil/oleic acid (1:1) supplemented with 1% 20:4n−6, 1% 22:6n−3 or 1% of various combinations of these two acids were fed to duplicate groups of 26 juvenile turbot for 11 weeks. In this trial, feeding the diet containing 20:4n−6 as the only highly unsaturated fatty acid (HUFA) resulted in higher growth and survival than any of the mixtures of the two fatty acids or 22:6n−3 alone. The diet containing 22:6n−3 as the sole HUFA resulted in the lowest growth and survival of all dietary treatments. The control diet with 15% fish oil resulted in a greater growth rate than any of the pure HUFA-supplemented diets. There was a significant effect of dietary lipid on the somatic index of the brain but not heart, kidney or liver. The percentage of lipid in the liver, but not of heart, brain, eyes, gills or kidney, was influenced by dietary lipid, with the highest percentage in fish supplemented with DHA alone. After 11 weeks, the 20:4n−6 and 22:6n−3 levels in whole-body total lipids were strongly influenced by the content of these fatty acids in the diets. The relative effect of dietary levels of these two fatty acids on their content in fish lipids varied considerably among the various organs and tissues of the fish that were analyzed. Brain and eye lipids were generally highest in 22:6n−3 while gill and kidney lipids were consistently higher in 20:4n−6 than the other organs analyzed. The effect of dietary 20:4n−6 on the content of that HUFA in organ lipid was greatest in gill and liver. The greatest impact of dietary 22:6n−3 level on content of that acid in organ lipid was seen in gill and kidney. There were also significant effects of dietary HUFA content on organ lipid levels of saturated, mono-unsaturated fatty acids and other members of the n−3 and n−6 PUFA, and HUFA series. The present study suggests that the EFA growth-promoting activity of arachidonic acid provides strong support for the contention that dietary 20:4n−6 is essential for juvenile turbot.

Effects of different dietary arachidonic acid : docosahexaenoic acid ratios on phospholipid fatty acid compositions and prostaglandin production in juvenile turbot (Scophthalmus maximus).

Five purified diets containing AA (20:4n-6) at 0.02–0.78% dry weight and DHA (22:6n-3) at 0.93–0.17% dry weight were fed to duplicate groups of juvenile turbot (Scophthalmus maximus) of initial weight 0.87 g for a period of 11 weeks. The dietary DHA:AA ratio ranged from 62 to 0.2. Incorporation of AA into liver phospholipids increased with increasing dietary AA input. Phospholipids from fish fed diets containing 0.02, 0.06 and 0.11% of dry weight as AA generally contained less AA compared to fish fed fish oil while those fed diets containing 0.35 and 0.78% of dry weight as AA had higher AA levels in their phospholipids. The highest levels of AA were found in PI but the greatest percentage increase in AA incorporation was in PE and PC. Brain phospholipid fatty acid compositions were less altered by dietary treatment than those of liver but DHA content of PC and PE in brain was substantially lower in fish fed 0.93% pure DHA compared to those fed fish oil. This suggests that dietary DHA must exceed 1% of dry weight to satisfy the requirements of the developing neural system in juvenile turbot. In both tissues, (20:5n-3) concentration was inversely related to both dietary and tissue PI AA concentration. Similar dietary induced changes in AA, EPA and DHA concentrations occurred in the phospholipids of heart, gill and kidney. PGE2 and 6-ketoPGF1α were measured in homogenates of heart, brain, gill and kidney. In general, fish fed the lowest dietary AA levels had reduced levels of prostaglandins in their tissue homogenates while those fed the highest level of AA had increased prostaglandin levels, compared to fish fed fish oil. In brains, the PGE2 concentration was only significantly increased in fish fed the highest dietary AA.

Influence of dietary lipid sources on fecundity, egg hatchability and fatty acid composition of Chinese prawn (Penaeus chinensis) broodstock

The effect of feeding four semi-purified diets containing different lipid sources (anchovy oil, linseed oil, corn oil and pork lard) on fecundity, egg hatchability and egg and spent gonadal tissue fatty acid composition of Chinese prawn (Penaeus chinensis) broodstock was compared with a fresh clam diet in a 60-day feeding trial. Broodstock prawn fed the diet containing pork lard showed poor fecundity and low egg hatchability. Broodstock fed the diets containing linseed or corn oil showed improved egg production (P<0.05); however, no significant improvement in hatchability was observed. When broodstock were fed the diet containing anchovy oil, both fecundity and egg hatchability were significantly improved (P<0.01). Eggs from broodstock fed anchovy oil as sole dietary lipid had a higher n−3 highly unsaturated fatty acid (HUFA) content (27.6%) compared with those of prawn fed diets containing linseed oil (19.5%), corn oil (14.0%) or pork lard (12.8%). Good correlations between the 20:5n−3 content of the egg lipid and fecundity and between 22:6n−3 content and hatchability were observed. The results suggest that each of these n−3 HUFAs may play different and specific roles in crustacean reproduction and that either or both must be included in the broodstock diet.

The effects of dietary fatty acids on the fatty acid composition of the harpacticoid copepod, Tisbe sp, for use as a live food for marine fish larvae

Abstract The marine harpacticoid copepod Tisbe sp. was isolated from plankton collected near Halifax, Nova Scotia and raised in the laboratory for over 20 generations. The effects of feeding various algal (Chaetocerus calcitrans, Dunaliella tertiolecta, and Isochrysis galbana) and bakers yeast diets on the nutritional value, or essential fatty acid (EFA) composition, of the copepod for use as an alternative live food for cold-water marine finfish larvae was evaluated in this study. The copepod was able to synthesize a significant amount of the EFAs, 20:5n−3 (EPA) and 22:6n−3 (DHA) from shorter chain n−3 polyunsaturated fatty acids, when fed the algae D. tertiolecta (6.2% EPA, 12.4% DHA) or bakers yeast (12.4% EPA, 28.4% DHA) which are deficient in these EFAs. The copepod also maintained a consistently high DHA:EPA ratio (>2) when fed each of the dietary treatments.

Essential fatty acid requirement of the Chinese prawn, Penaeus chinensis

The aim of this study was to determine the essential fatty acid (EFA) requirement of one of the most important commercially cultured crustacean species in the world, Penaeus chinensis. Groups of 16 individually housed juvenile Chinese prawn were fed for 60 days with 12 semi-purified experimental diets. These diets were based on the crab-protein-concentrate Standard Reference Diet and contained either 5% of a mixture of tripalmitin (16:0) and triolein (18:1n−9) (EFA deficient control diet), or 4% of this mixture and a 1% supplement of various purified polyunsaturated fatty acids (PUFA) or highly unsaturated fatty acids (HUFA). Prawns fed the EFA-deficient control diet suffered 100% mortality. The prawns fed a diet containing 1% trilinolenin (18:3n−3) had higher growth and longer survival than that of animals fed the diet containing 1% trilinolein (18:2n−6). Feeding a diet containing a mixture 0.5% of each of these lipids resulted in a greater growth rate and a 0.25:0.75 mixture of trilinolein and trilinolenin produced a greater survival than any other mixture or either purified fatty acid supplement alone. When the 18-carbon polyunsaturated fatty acid supplement was replaced with 1% of the triglyceride of arachidonic acid in the diet fed to prawns, however, the growth was about equal to that of prawns receiving 1% 18:3n−3 and survival was significantly higher than that of prawns fed any combination of 18:2n−6 or 18:3n−3 tested, while being less than that of prawns fed a diet containing 1% of the triglyceride of docosahexaenoic acid (DHA, 22:6n−3). The prawns fed the EFA-deficient control diet or any of the diets with 18:2n−6 or 18:3n−3 supplemented individually had extremely low body lipid levels. Mixtures of these two fatty acids or any combination of the n−6 or n−3 HUFA resulted in more normal body lipid levels, suggesting that both n−3 and n−6 type fatty acids might be required by the Chinese prawn. The fatty acid composition of the total body lipid reflected that of the experimental diets. Though 18:2n−6 and 18:3n−3 were not apparently desaturated and elongated to the physiologically important EFA members of the respective n−6 and n−3 series of fatty acids (20:4n−6, 20:5n−3 and 22:6n−3), there was evidence for elongation of these acids to 20:2n−6 and 20:3n−3. The results indicate that the essential fatty acid values of the fatty acids in the diet of the Chinese prawn increased in the following order 18:2n−6 < 18:3n−3 < 20:4n−6 < 22:6n−3.

The nutritional value of dietary n-3 and n-6 fatty acids for the Chinese prawn (Penaeus chinensis)

Abstract Triacylglycerides of highly purified n -3 and n -6 fatty acids (18:2 n -6, 18:3 n -3, 20:4 n -6 and 22:6 n -3) were each added separately at 1% to a basal diet which contained 4% of an equal mixture of tripalmitin and triolein to make four experimental diets with a control diet which contained 5% of the 16:0 and 18:1 n −9 mixture as the only lipid. Each diet was fed to replicate groups of juvenile Chinese prawn ( Penaeus chinensis ) for 32 days. The prawn fed the control diet without supplemental n -6 or n -3 fatty acids showed poor growth and survival. The addition of 1% of 18:2 n -6, 18:3 n -3 or 20:4 n -6 to the basal diet significantly improved weight gains ( P n -3 or 20:4 n -6 also significantly improved survival rate and molting frequency. The prawn fed the diet containing 1% 22:6 n -3, however, exhibited the highest survival rate, molting frequency and weight gain among the five diets ( P n -6 and n -3 fatty acids have essential fatty acid (EFA) value to the Chinese prawn, and that the EFA value increases in the order 18:2 n -6 n -3≤20:4 n -6 n -3.

Standard experimental diets for crustacean nutrition research. II. Growth and survival of juvenile crayfish Astacus astacus (Linné) fed diets containing various amounts of protein, carbohydrate and lipid

Abstract Nutritional experiments were conducted with individual juvenile freshwater crayfish, Astacus astacus (Linne), using twelve pelleted diets containing various combinations of protein (22, 31 or 40%), lipid (5.5–16%) and carbohydrate (9.2–25.8%) in a 394-day experiment. The diets ranged from 241 to 321 kcal/100 g feed and with protein/energy (P/E) ratios of 69 to 153 mg/kcal. The experiments were carried out in a closed system with constant temperature; dissolved nitrogen, oxygen content, pH and water temperature were monitored. All diets with 40% protein gave a good survival rate. The diet with 31% protein, moderately high carbohydrate (16.6%) and a low lipid content (7%) promoted a high survival rate as well. At the 22% protein level, the feed with high lipid content (16%) gave a poor survival rate. The mean biomass increase was greatest with all diets with 40% protein and those diets with 31% protein, high carbohydrate level and low lipid content. Younger juveniles demonstrated the highest growth rate on 40% protein diets and 31% protein diets, when the latter containedP/E ratios in the range 114 to 153 mg/kcal. At the 22% protein level growth was poor. Optimum biomass gain was obtained withP/E ratios above 114 mg/kcal. Optimum lipid/carbohydrate ratios changed with protein content of the feed. Lipid levels above 10% in diets containing 31 and 22% protein depressed the growth rate of younger animals. With increasing physiological age, the animals responded favourably to higher lipid and carbohydrate levels.

A re-evaluation of the lecitihin and cholesterol requirements of juvenile lobster (Homarus americanus) using crab protein-based diets

Abstract Juvenile lobsters (Homarus americanus) were fed purified diets containing three levels of refined soy lecithin, 0, 3 and 6%, each tested in combination with four levels of supplemental cholesterol, 0.00, 0.25, 0.50 or 1.00%. All diets contained 50% purified protein derived from cooked, “deshelled”, whole rock crab (Cancer irroratus). Regardless of the dietary level of lecithin all diets without supplemental cholesterol resulted in total mortality within 14 weeks. There was no significant effect of dietary lecithin on growth or survival at any level of supplemental cholesterol. Implications of these results in light of the previously reported dietary requirement of lobsters for lecithin are discussed.

Distribution of α-and γ-tocopherols in Atlantic salmon (Salmo salar) tissues

Groups of Atlantic salmon parr (mean initial weight 9.5 g) were fed three diets, the first containing no tocopherol supplement, the others supplemented with either all-rac-α-tocopherol (A-T) or RRR-γ-tocopherol (G-T). Tocopherol concentrations in the liver, serum, testes, kidney, brain, gill, muscle, and perivisceral fat were measured after 36 wk. Despite a higher dietary intake of G-T, compared to A-T, deposition of γ-tocopherol (γT) was less efficient than of α-tocopherol (αT) in most tissues except in the perivisceral fat, an adipose tissue. In fish fed the G-T diet, the γT/αT ratio was highest in the perivisceral fat and lowest in the liver, indicating that the liver is the most discriminatory organ for retaining αT as compared to γT, and the perivisceral fat is more suitable for the storage of γT. A negative correlation (P<0.01) was observed between the γT/αT ratio and the corresponding tissue phospholipid content, suggesting that γT is less efficiently deposited compared to αT in the phospholipid-rich membranes which are presumed to be the functional site for lipid antioxidants in vivo. During restricted intake of αT, the liver and muscle exhibited the greatest reduction of this tocopherol among the tissues analyzed. The presence of minimal αT in the muscle from fish fed the tocopherol-unsupplemented diet led to greater susceptibility to lipid peroxidation after frozen storage than was the case for muscle containing higher concentrations of either αT or γT. However, both αT and γT were effective stabilizers of salmon muscle lipids during frozen storage.

The effect of different dietary energy levels in crab-protein-based diets on digestibility, oxygen consumption, and ammonia excretion of bilaterally eyestalk-ablated and intact juvenile lobsters, Homarus americanus

Abstract The fast growth resulting from eyestalk ablation of juvenile lobsters, Homarus americanus , can be attributed to more efficient energy utilization as indicated by lower feeding metabolism, particularly the calorigenic effect of feeding and lower nitrogen excretion than found for intact lobsters. However, there was no difference in standard metabolism between ablated and intact juvenile lobsters. The apparent digestibility of dry matter by ablated lobsters was lower than intact controls when fed low energy (high protein energy ratio) and/or high α-cellulose diets. The apparent lipid digestibility was reduced by eyestalk ablation, whereas there was no effect of ablation on apparent protein digestibility. The apparent digestibilities of dry matter and energy improved with increased dietary energy and/or decreased α-cellulose levels in both ablated and intact lobsters. However, while apparent digestibilities of protein and lipid also increased with dietary energy in ablated lobsters, for intact lobsters the apparent digestibility of protein was relatively constant and apparent digestibility of lipid reached a peak at intermediate levels of dietary energy. The dependence on protein for energy utilization may be greater for ablated lobsters. The energy budget equation of lobsters constructed from the data obtained in this study will be very useful for understanding energy utilization of lobsters.