The influence of the dietary carbohydrate: lipid ratio on the chronic toxicity of sodium pentachlorophenate to rainbow trout (Salmo gairdneri Richardson)

The influence of diets varying in carbohydrate: lipid ratio on the chronic toxicity of waterborne sodium pentachlorophenate (0 or 50 g NaPCP.l^–1) to rainbow trout (Salmo gairdneri) was examined over a 12 week period. The three diets used were practical salmonid formulations, equivalent in energy and protein content, with cerelose: fish oil ratios of 18.24.7% (high carbohydrate, HC), 9.39.1% (intermediate, INT), and 0.613.8% (low carbohydrate, LC). With increasing levels of dietary carbohydrate trout exhibited enlarged livers, elevated liver glycogen content, reduced liver protein content, reduced body lipid content, reduced weight gain, and elevated feed: gain ratio. For all diet groups, exposure of trout to NaPCP resulted in reduced liver glycogen content, higher liver protein content, reduced levels of plasma total triiodo-L-thyronine and L-thyroxine, increased thyroid epithelial cell height, and increased feed: gain ratios relative to their respective dietary control group. NaPCP exposure led to nominal reductions in weight gain and body lipid content of fish reared on the HC and INT diets. NaPCP exposed fish on the LC diet gained significantly less weight but had a higher body lipid content than control fish. The increasing NaPCP bioconcentration factor (BCF) associated with increasing lipid content of fish (log BCF=2.75 [log % lipid] +0.30; r=0.95) may explain the differences in response. Correction of bioconcentration data for the lipid content of fish reduced the range in BCF from 5- to 2.8-fold.     

Dietary carbohydrate and growth,body composition and heat increment in rainbow trout (Salmo gairdneri)

A study was conducted to determine growth, body composition and heat increment (HI) of rainbow trout reared on isonitrogenous high digestible carbohydrate (HC) and high fat (HL) diets at 15°C. Trout reared on the HC diet had a significantly lower final body weight and carcass lipid content and a significantly higher feed:gain ratio and carcass protein content than trout reared on the HL diet after 12 weeks on the test diets. The lower carcass lipid composition indicates that trout do not readily convert dietary carbohydrates into fat. HI of trout reared on the HC diet was significantly higher than that of fish reared on the HL diet. Considering the poor utilization of dietary carbohydrates as an energy source and the apparently low conversion of dietary glucose into fat, the cause of the higher HI associated with the HC diet is not completely understood. However, it is possible the elimination of excess dietary glucose is an energy dependent process resulting in an increased heat production which would partly account for the increased HI. Furthermore, if the HC diet is a low net energy diet, then the metabolism and utilization of dietary and tissue proteins (amino acids) for energy by the trout may also be partly responsible for the increased HI of the trout reared on the HC diet.     

Influence of dietary protein levels on growth performance, carcass composition and liver lipid classes of juvenile Spinibarbus hollandi (Oshima)

A feeding trial was conducted to investigate the influence of dietary protein levels on growth performance, carcass proximate composition and liver lipid classes of juvenile Spinibarbus hollandi (Oshima), a cyprinid fish. White fish meal was the primary protein source in the study. Eight experimental diets containing 13–55% crude protein were fed to three replicate groups of six fish weighing nearly 8.5 g each for 10 weeks. Both percentage weight gain and feed efficiency ratio increased significantly with increasing dietary protein levels up to 31%, but there was no further increase for protein levels from 31% to 55%. Application of broken‐line regression analysis to the percentage weight gain provided an estimate of 32.7±1.5% dietary protein for maximum growth. The protein efficiency ratio and productive lipid value were inversely correlated with dietary protein level. The hepatosomatic index and the viscerosomatic index were also inversely related to dietary protein level. The carcass protein of fish fed lower protein diets was significantly lower than that of the fish fed higher protein diets. Carcass lipid content decreased with increasing dietary protein levels, whereas moisture was inversely related to lipid content. Both liver glycogen and liver lipid contents decreased with increasing dietary protein levels. Triglyceride was the major component in the liver lipid, and the amount of triglyceride deposited in the liver also decreased with dietary protein levels. The results indicated that both carcass proximate composition and liver lipid class of juvenile Spinibarbus hollandi were affected by dietary treatments.     

Evaluation of commercial catfish, tilapia and salmonid diets for growth promotion of white suckers

In an attempt to identify appropriate diets for use in intensive baitfish culture, the efficacy of three commercial diet formulations, a high-protein, high-lipid, low-carbohydrate diet [a semi-moist salmonid diet (SD)] and two low-protein, low-lipid, high-carbohydrate diets [a catfish diet (CD) and a tilapia diet (TD)] on growth performance of juvenile white suckers, Catostomus commersoni, was examined. All three diets permitted growth during the 16 week trial. The SD promoted highest growth and somatic protein and lipid deposition, whereas the CD and TD formulations promoted markedly higher accumulations of glycogen in the carcass and liver. The high hepatic glycogen content was associated with an elevated hepatosomatic index in the CD- and TD-fed groups. Plasma T3 levels were lower in the CD- and TD-fed groups, possibly a response to the low dietary protein or indicative of dietary insufficiency in these fish. Of the three diets evaluated, the SD was considered to be the best in terms of the growth performance parameters measured, and offers an economical and appropriate diet for intensive culture of juvenile white suckers.     

Effects of chronic exposure to γ-HCH (Lindane) on brain serotonergic and gabaergic systems,and serum cortisol and thyroxine levels of rainbow trout,Oncorhynchus mykiss

Rainbow trout (Oncorhynchus mykiss) were implanted intraperitoneally with 0.5 ml.100 g^–1 body weight of coconut oil alone (controls) or coconut oil contaning 0.05 mg of -HCH (Lindane). After 18 days, changes in brain serotonin and GABA metabolism, as well as in serum cortisol and thyroxine levels, were measured. A lower final body weight was observed in -HCH treated fish when compared with control fish. No significant differences were found for serum thyroxine levels between control and treated fish, but a significantly higher cortisol level was found in the -HCH-implanted trout. Although GABA levels did not differ significantly in any brain region in the two treatment groups, the activity of the serotonergic system was significantly altered by the pesticide in both the hypothalamus and the telencephalon.     

Dose-dependent effects of acute melatonin treatments on brain carbohydrate metabolism of rainbow trout

The levels of glycogen, lactate, acetoacetate and -hydroxybutyrate in brain as well as glycogen and lactate levels in liver, and glucose levels in plasma were evaluated in rainbow trout, Oncorhynchus mykiss, injected with ethanol/saline (5/95; v/v) alone (controls) or containing melatonin at three different doses 0.25, 0.5 and 1 mg kg^-1. The results obtained demonstrate, for the first time in a teleost fish, the existence of changes in brain carbohydrate and ketone body metabolism due to melatonin treatment. Thus, a clear dose-dependent decrease was observed in brain and liver glycogen levels, whereas a clear dose-response increase was observed in brain for lactate, acetoacetate and -hydroxybutyrate levels, and in plasma for glucose levels. CO₂ production from glucose was also tested in brains of pooled fish and these rates were not altered by melatonin treatment. Altogether, these results suggest that melatonin may play an indirect role, possibly through alterations in insulin physiology, in the regulation of carbohydrate and ketone body metabolism in brain of rainbow trout.     

Cryptobia salmositica: cortisol increases the susceptibility of Salmo gairdneri Richardson to experimental cryptobiosis

Abstract. Intraperitoneal implants of cortisol (cortisol suspended in hydrogenated coconut oil) were used to induce a graded hypercortisolism in rainbow trout, Salmo gairdneri Richardson. There was no obvious reduction in circulating lymphocytes in cortisol-implanted rainbow trout (70, 140 or 210μg/g body weight). Cortisol-implanted fish infected with Cryptobia salmositica had significantly higher parasitaemia and lower antibody litres compared with controls infected with haemonagellate but given coconut oil implants. These confirm the immunodepressive effects of the steroid. The parasite was also more readily detected at the early stage of the infection (shorter prepatent period, more infected fish and higher parasitaemia) in cortisol-implanted fish (140 and 210 μg/g body weight) than in controls. The mortality of the infected cortisol-implanted fish was higher than that of the infected fish implanted with only coconut oil, or the cortisol-implanted but non-infected fish. This in vivo study suggests that protective immunity against C. salmositica is, in part, due to a humoral response.     

Effect of dietary mirex and PCB (Aroclor 1254) on thyroid activity and lipid reserves in rainbow trout Salmo gairdneri Richardson

Abstract. Rainbow trout were fed diets contaminated with either PCB (Aroclor 1254, 500 μg/g dry food) or Mirex (500 μg/g dry food). There was no apparent effect of PCB on thyroid histology or on serum thyroid hormone levels. Mire effected significant reductions in serum T₄ ( P <0.05) and T₃ levels ( P <0.01) without apparent change om the histological appearance of the thyroi. Liver weights and total liver lipid content were significantly ( P <0.001) greater in PCB fed fish compared with controls as was the carcass lipid content ( P <0.01). Mirex had no apparent effect on liver size or liver lipid content but there was a decline in carcass lipid content ( P <0.02) which persisted 25 days after returning Mirex-fed fish to the control diet ( P <0.05).     

Effect of increased liver glycogen and liver weight on liver function in rainbow trout, Salmo gairdneri Richardson: recovery from anaesthesia and plasma 35S-sulphobromophthalein clearance

Abstract. Juvenile rainbow trout (initial mean body weight 17 g) reared on practical trout diets containing different levels of available carbohydrate for 8–24 weeks were assayed for liver function based on the time required to recover from the anaesthetics tricaine methanesulphonate (MS222), 2-phenoxyethanol (2PE) and tertiary-amyl alcohol (TAA), as well as plasma clearance of ³⁵S-sulphobromo-phthalein (BSP), Liver/body weight ratios (LBW) and percentage liver glycogen content (LG) increased in a linear manner with increased available carbohydrate. The mean recovery time (MRT) of trout anaesthetized with 2PE and TAA increased linearly with increased LBW and LG. No difference was observed in the MRT of trout anaesthetized with MS222 which is not metabolized in the trout liver. There was a significant linear regression of the biological half-life of plasma BSP on LBW (MR²= 95.7) and LG (MR²= 99.6). The results indicate that increased liver glycogen and liver weight due to higher levels of available carbohydrate affect the liver function of rainbow trout. These liver function tests may be applicable in determining acceptable levels of available carbohydrate in practical trout diets.     

温度胁迫及恢复过程中褐牙鲆幼鱼GH、IGF-I、RNA／DNA比值和糖原的变化

褐牙鲆（Paralichthysolivaceus）幼鱼分别在温度8．5℃（T8.5）、13．0℃（T13.0）、17．5℃（T17.5）、22．0℃（T22.0）、26．5℃（T26.5）下养殖10d后,调整至生长最快的温度22．0℃养殖30d,研究了生长激素（GH）、类胰岛素生长因子I（IGF-I）、RNA／DNA比值和糖原质量分数的变化。除在胁迫阶段T17.5处理血浆IGF-I质量浓度显著低于T22.0处理外,不同处理的血浆GH和IGF-I质量浓度在胁迫和恢复阶段均无显著差异。不同处理的肝脏RNA／DNA比值仅在20-40d阶段有显著差异,不同处理的肌肉RNA／DNA比值在所有时间均无显著差异。胁迫结束时T8.5、T13.0、T26．5处理的肝脏糖原质量分数显著低于T17.5,处理,试验结束时T22.0处理肝糖原质量分数略低于其余处理。胁迫结束时T25.5处理肌肉糖原质量分数最高,而在恢复的第一个10d时T13.0处理肌肉糖原质量分数最高。不同温度下养殖10d导致的生长减缓能够在恢复至22．0℃后的30d内获得完全补偿生长,但此试验中GH、IGF-I和RNA／DNA比值与生长率不存在明显的相关性。     

Metabolic effects of feeding a high protein/low carbohydrate diet as compared to a low protein/high carbohydrate diet to rainbow troutSalmo gairdneri

Groups of trout were fed either a high protein/low carbohydrate (HP/LC) or a low protein/high carbohydrate (LP/HC) diet for 16 weeks. Fish fed the HP/LC diet had significantly higher levels of protein, ninhydrin positive material and tryptophan in plasma as well as lipid and protein in liver, but lower levels of glucose in plasma, glycogen in liver and a lower hepatosomatic index compared with fish fed the LP/HC diet. There were no differences concentrations of tryptophan or serotonin in the brain of fish fed the different diets. Fish fed the HP/LC diet had significantly lower activities of glycolytic enzymes but higher activities of gluconeogenic enzymes compared with the group fed the LP/HC diet. Those enzymes measured concerned with the TCA cycle or initiating amino acid catabolism were generally unaffected by diet although activities of threonine dehydrogenase, alanine aminotransferase and glutamate dehydrogenase were higher in those fish fed the HP/LC diet. The data suggest that rainbow trout show little adaptation in activities of amino acid catabolising enzymes to variations in dietary protein intake.     

The Effect of Dietary Lipid and Long-chain n-3 PUFA Levels on Growth, Energy Utilization, Carcass Quality, and Immune Function of Rainbow Trout, Oncorhynchus mykiss

The effect of varying dietary lipid and n‐3 polyunsaturated fatty acids (PUFAs) on growth, feed efficiency, protein and energy utilization, carcass quality, and nonspecific immune functions was investigated in rainbow trout reared at two different water temperatures (7.5 and 15 C). Six diets were formulated to contain 47% digestible protein and 21 MJ/kg digestible energy. Three of the diets were formulated to contain increasing lipid levels (10, 16, and 18%) and three additional diets formulated to 18% lipid with different lipid sources. Varying dietary lipid and n‐3 PUFA levels had little effect on growth and on protein and energy utilization. Diet composition only had limited effect on susceptibility of the flesh to rancidity and on the nonspecific immunity of the fish. Increasing lipid levels did not affect fish carcass or fillet proximate composition. Replacing half of fish oil with beef tallow resulted in lower n‐3 PUFAs in fish fillet but did not affect nutrient digestibility or growth performance of fish even at 7.5 C. Increasing dietary n‐3 levels using a fish oil concentrate resulted in significant enrichment of n‐3 PUFAs and elevated n‐3 : n‐6 ratio of the whole body and carcass. Water temperature significantly affected apparent digestibility coefficient (ADC) of protein and energy but did not affect the ADC of lipid, nor did it affect nitrogen and energy retention efficiencies. The study suggests that highly saturated fats, such as beef tallow, can be used to partially replace fish oil without negative effect on digestibility and growth even at low water temperature. High dietary n‐3 PUFAs levels can be used to enrich n‐3 PUFAs of the flesh without negative effect on the immune response.     

Survival of salmonids in seawater and the time-frame of growth hormone action

In salmonids, growth hormone (GH) effectively promotes adaptation of freshwater (FW) fish to seawater (SW), but it has been unclear whether GH has osmoregulatory actions apart from those consequent to an increase in body size. Our objectives were first, to examine the minimum time and dose required for GH to enhance SW adaptation; and second, to optimize the conditions for the acute GH response in developing a convenient GH bioassay based on its plasma ion lowering effect. Trout showed markedly improved SW survival when transferred from fresh water 6, 24, or 48h after a single chum salmon GH injection (0.25 μg/g). Preadapting trout to 1/3 SW enhanced the plasma ion lowering effect of ovine GH (oGH) injected 48h before transfer of the fish to 80% SW. Endogenous plasma GH levels were elevated in control trout switched from low salinities to 80% SW but were depressed in oGH-injected fish after transfer. Under optimal test conditions (1/3 SW preadaptation, 48h pre-transfer injection, and 100% SW final challenge), the reduction in plasma Na⁺, Ca⁺⁺, and Mg⁺⁺ levels of oGH-injected fish was dose-dependent. The oGH doses giving minimum and maximum responses were 50 and 200 ng/g, respectively. In short, GH exerts acute osmoregulatory actions that promote SW adaptation in the absence of changes in body size. Compared with growth GH bioassays, the osmoregulatory assay is superior in economy of time, animal costs, and hormone quantity required and potentially in specificity.     

The response of thick-lipped grey mullet, Chelon labrosus (Risso), to diets of varied protein-to-energy ratio

Six experimental diets were designed containing two lipid levels (approximately 12% and 24%) and three protein levels (approximately 38%, 49% and 59%) with protein-to-energy ratios ranging from 19.72 to 29.83 mg protein kJ^-1 gross energy. At both lipid levels, an increase in the protein content of the diet was achieved by decreasing the carbohydrate input. After 84 days of feeding to appetite, the fish (juvenile thick-lipped grey mullet, Chelon labrosus (Risso)) fed the high-oil diets of low and medium protein content were significantly larger than those fed low-lipid diets containing similar amounts of protein. The greatest weight gain and optimum apparent net protein utilization (ANPU) were recorded for the fish fed the diet with a P:E ratio of 19.72 mg protein kJ^-1 gross energy. At both lipid levels, increasing dietary protein supplementation led to a decrease in voluntary feed consumption and ANPU. Whole-body lipid appeared to increase in response to a higher dietary oil component. At low levels of dietary lipid, the carcass protein content increased in response to elevated protein supply. This trend was less obvious at the higher level of lipid supplementation. Hepatic glycogen deposition was significantly lower amongst the fish fed the low-carbohydrate diets at both levels of supplemental oil. A significant increase in hepatosomatic index was also recorded which was not directly correlated with either dietary carbohydrate or protein:energy level. It can be concluded from the present experiment that the optimum protein-to-energy ratio for C. labrosus juveniles is in the order of 19.72 mg protein kJ^-1 gross energy when fed the present diets containing 37.9% crude protein and 22.8% lipid. Additionally, for this species, lipid was seen as a more effective source of non-protein energy than a corn starch/dextrin mixture.     

Effects of dietary lipid and environmental salinity on growth,body composition,and cold tolerance of juvenile red drum (Sciaenops ocellatus)

Simultaneous, 6-week feeding trials were conducted in which diets containing menhaden, corn, coconut and hydrogenated menhaden oil at 7.0%, plus a diet containing 14% menhaden oil, were fed to triplicate groups of juvenile red drum (Sciaenops ocellatus) at two different salinities (5 and 32%.). Weight gain was significantly (p < 0.05) affected by diet and salinity. Fish fed the diet containing 14% menhaden oil had the greatest weight gain; whereas, fish fed the diet containing coconut oil gained the least weight. Fish in brackish water had significantly greater weight gain than fish in full-strength seawater over the 6-week period, although fish fed coconut and saturated menhaden oil in brackish water had reduced survival. Dietary lipid also significantly affected muscle and liver total lipid, hepatosomatic index (HSI), and intraperitoneal fat (IPF) ratio, as fish fed the diets containing 14% menhaden oil had higher values for all of these body condition indices.After the feeding trial, fish were subjected to a chronic cold tolerance assay. In the chronic trial, where temperature was gradually reduced over a 3-week period, fish fed the diets containing menhaden oil had significantly lower median lethal temperatures (MLT) than those fish fed the diets containing coconut, corn and saturated menhaden oils. No significant effects of cold exposure were observed on muscle and liver total lipid. Cold exposure prompted a modification in lipid metabolism by lowering total saturated fatty acids and raising (n – 3) highly unsaturated fatty acids (HUFA) in the neutral lipid of liver. Fish with the lowest MLT in the chronic assay exhibited signs of conserving (n – 3) HUFA and depleting (n – 6) fatty acids [primarily 18:2 (n – 6)], resulting in higher (n – 3)/(n – 6) ratios in the polar lipid of liver. These data suggest that the lower lethal temperature of juvenile red drum can be reduced through dietary manipulation involving the inclusion of high levels of dietary lipid rich in (n – 3) HUFA.     

Fasting combined with long catch duration modifies the physio‐metabolic response and flesh quality of rainbow trout

Pre‐slaughter handling involves fasting fish and catching them, which can affect fish welfare and flesh quality, but few studies have considered their combined effects. In this study, adult rainbow trout (320 ± 10 g average weight) were fasted for 7 days (135.6 degree days) and subjected to a long catch duration (20 min), compared with controls (no fasting or short catch duration). Condition factor, organ weight indexes and carcass yield decreased with fasting but not catch duration. Plasma concentrations of cortisol, glucose and lactate increased after a long catch, while plasma triglycerides decreased with fasting. Liver glycogen concentration was lower in fasted fish, and liver luminosity and chroma were higher after fasting with a long catch. Regarding flesh quality, rigor mortis resolved more slowly and final muscle pH at 48 hr post‐mortem was higher for fasted fish with a long catch time. Muscle glycogen concentration was higher in fasted fish, where chroma was also lower. Fasted fish had lower lipid oxidation, but there were no differences in fat content in muscle. Fasted fish with a long catch duration also had less monounsaturated and more saturated fatty acids. In conclusion, a long catch triggered a stress response that had negative effects on flesh quality, independently of fasting.     

Dietary utility of enzyme-treated fish meal for juvenile Pacific bluefin tuna <Emphasis Type="Italic">Thunnus orientalis</Emphasis>

ABSTRACT:   In order to develop an artificial diet, the dietary utility of enzyme-treated fish meal was investigated for juvenile Pacific bluefin tuna Thunnus orientalis (PBT). Diets containing each 63% of Chilean fish meal (FM), enzyme-treated Chilean fish meal (EC) and enzyme-treated Peruvian fish meal (EP), with 10% bonito oil and raw sand lance Ammodytes personatus (SL) were fed to juvenile tuna six times per day for one week. In a different trial, diets EC and SL were fed to tuna six times per day for 2 weeks. Only diet EC sustained similar growth or caused lower survival and higher feed efficiency, hepato- and enterosomatic indices and final carcass lipid content as compared to those of SL. Diets FM and EP led to lower specific growth rate (SGR) but similar feed efficiency, survival and hepatosomatic index, yet higher enterosomatic index. Moreover, PBT fed diet EC for 2 weeks led to similar growth performance but higher final carcass and hepatic lipid contents, and plasma cholesterol and phospholipid levels than those fed SL. Carcass fatty acid composition of diet EC group had lower 20:5  n -3 and 22:6  n -3 levels than the SL group. These results revealed that EC, as a suitable dietary protein source, could sustain growth of PBT, while dietary bonito oil led to higher carcass lipid but lower accumulation of n -3 highly unsaturated fatty acids.     

Partial replacement of fish oil by soybean oil on lipid distribution and liver histology in European sea bass (Dicentrarchus labrax) and rainbow trout (Oncorhynchus mykiss) juveniles

A 12‐week feeding trial was conducted to evaluate the effects of fish oil replacement by soybean oil, on lipid distribution and liver histology of two commercially important finfish species: rainbow trout (Oncorhynchus mykiss) and European sea bass (Dicentrarchus labrax). Sea bass (16.2 ± 0.5 g; mean ± SD) and rainbow trout (52.1 ± 0.5 g) juveniles were fed one of three isonitrogenous (500 g kg^?1 CP) and isoenergetic (19 kJ g^?1) diets, containing 0% (control, diet A), 25% (diet B) and 50% (diet C) soybean oil. At the end of the experiment, lipid deposition was evaluated in muscle, liver and viscera. Cholesterol and triglycerides levels were also determined in plasma. Tissue total, neutral and polar lipid composition (g kg^?1 total lipids) showed no significant differences within species, regardless the dietary treatment. The same trend was observed for plasma parameters (P > 0.05). Viscera were the preferential tissue of lipid deposition, with 252–276 and 469–513 g kg^?1 total lipid content in trout and sea bass, respectively. Dietary fish oil replacement had no effect on either hepatic lipid droplets accumulation or degree and pattern of vacuolization in the observed liver sections. These data suggest that both sea bass and trout can be fed diets containing up to 50% soybean oil without adverse effects on tissue lipid composition or liver histology.     

Stocking density and cohort sampling effects on endocrine interactions in rainbow trout

Studies were conducted to explore the effect of cohort sampling and stocking density on the interactions between plasma growth hormone (GH), thyroid hormone and cortisol concentrations in rainbow trout. Depending on the experimental design, plasma GH concentrations were either suppressed, or elevated by sequential removal of cohorts from the holding aquarium. Since plasma cortisol concentrations consistently increased during cohort sampling, regardless of experimental design, it would appear that the apparent correlation (direct or inverse) is the result of concomitant changes, i.e. not necessarily a cause-effect relationship. Plasma GH concentrations of rainbow trout were not correlated with eviscerated body weight.Trout stocked at 150 kg m^–3 exhibited a significantly lower mean growth rate, hepatosomatic index, hepatic lipid reserve, plasma triiodo-l-thyronine (T₃) concentration andin vitro hepatic T₃ production than trout stocked at 60 kg m^–3. These observations are consistent with the former group being food deprived or ration restricted. Stocking density appeared to have no effect on plasma GH or cortisol concentrations, or on the pituitary-interrenal axis response to stressor challenge, or the thyroid tissue response to exogenous TSH challenge.     

The effect of dietary lipids on the trout erythrocyte membrane

Rainbow trout were fed either a commercial diet or semi-purified diets containing 8% by weight of either cod liver oil, grape seed oil or hydrogenated coconut oil. Important changes in the fatty acid composition of erythrocyte membrane phospholipids were induced by these dietary fats. No changes were seen in the cholesterol/phospholipid ratio and in the cellular ATP level. Shape changes (crenation of cell margin and shrinkage) were only seen in trout fed hydrogenated coconut oil in connection with an accumulation of high amounts of (n-9) fatty acids including 20:3 (n-9) phospholipids. The compositional changes affect the stability of the erythrocyte membrane. An increased rate of osmotic hemolysis appeared to be associated with an increased unsaturated fatty acid content of the membranes.