Combined effects of temperature and diet on growth and biochemical composition of the Pacific oyster Crassostrea gigas (Thunberg) spat

Temperature and quality of the available food are important factors that influence the physiology of oysters; however, the combined effects have not been well studied. We evaluated the impacts of the temperature and diet on the growth, survival and biochemical composition in the Pacific oyster Crassostrea gigas spat, cultured in the laboratory for 8 weeks at 23, 26, 29 and 32°C and fed Isochrysis sp.‐Pavlova lutheri (IP) and Dunaliella tertiolecta (Dt). The growth and biochemical composition showed a pattern, which changed in response to rising temperature. The shell length was significantly longer, in spat fed the IP diet, except at 32°C, where both diets produced poor growth results. The survival was <50% after 5 weeks at 32°C, whereas at all other temperatures it was >88%. High temperatures directly increased lipids and saturated fatty acids, while the proteins, carbohydrates and unsaturated fatty acids decreased. High temperatures achieved in the environment, as those reached on clear summer days during low tides, are an important stressor in oyster spat, especially when the quality of the available food is poor.     

Finishing diets stimulate compensatory growth: results of a study on Murray cod, Maccullochella peelii peelii

The effective implementation of a finishing strategy (wash‐out) following a grow‐out phase on a vegetable oil‐based diet requires a period of several weeks. However, fish performance during this final stage has received little attention. As such, in the present study the growth performance during both, the initial grow‐out and the final wash‐out phases, were evaluated in Murray cod (Maccullochella peelii peelii). Prior to finishing on a fish oil‐based diet, fish were fed one of three diets that differed in the lipid source: fish oil, a low polyunsaturated fatty acid (PUFA) vegetable oil mix, and a high PUFA vegetable oil mix. At the end of the grow‐out period the fatty acid composition of Murray cod fillets were reflective of the respective diets; whilst, during the finishing period, those differences decreased in degree and occurrence. The restoration of original fatty acid make up was more rapid in fish previously fed with the low PUFA vegetable oil diet. During the final wash‐out period, fish previously fed the vegetable oil‐based diets grew significantly (P < 0.05) faster (1.45 ± 0.03 and 1.43 ± 0.05, specific growth rate, % day⁻¹) than fish continuously fed with the fish oil‐based diet (1.24 ± 0.04). This study suggests that the depauperated levels of highly unsaturated fatty acids in fish previously fed vegetable oil‐based diets can positively stimulate lipid metabolism and general fish metabolism, consequently promoting a growth enhancement in fish when reverted to a fish oil‐based diet. This effect could be termed ‘lipo‐compensatory growth’.     

Growth, survival, lipid and fatty acid profile of juvenile monaco shrimp Lysmata seticaudata fed on different diets

The present work evaluated the effect of three inexpensive diets (frozen minced mussel and edible cockle (MMC), frozen minced squid (MS) and gilthead seabream feed (GSF)) on growth, survival, sex reversal, lipid classes and fatty acid (FA) profile of juvenile ornamental shrimp Lysmata seticaudata. Shrimp fed GSF displayed the highest survival rate (±SD) (85.2±1.8%) and the highest percentage (±SD) of shrimp changing from male to simultaneous hermaphrodite (SH) phase (25.2±2.2%). All diets promoted growth rates superior to those reported in the wild, with SH shrimp displaying higher total lengths (TL). Shrimp in SH phase fed GSF displayed the highest TL (±SD) (40.6±1.2 mm). Cultured shrimp reflected the lipid content of experimental diets, with shrimp fed GSF displaying the highest triacylglycerols and sterols (ST) contents. The higher rearing density induced by lower mortality rates of shrimp fed GSF, and the high ST levels present in the diet, may explain the higher proportion of shrimp in SH phase. The higher levels of highly unsaturated fatty acids (HUFA) displayed by MS did not promote higher survival or growth rates. The low polyunsaturated fatty acids and HUFA content of MMC was not reflected in cultured shrimp, probably because of a selective retention of these FA.     

The performance of microbial flocs produced with aquaculture waste as food for Artemia

The performance of microbial flocs as food for Artemia, which were produced using waste from a recirculating aquaculture system stocking European eel (Anguilla anguilla), was investigated in an 18‐day feeding trial. Four dietary treatments were used: Chlorella only (diet 1), flocs only (diet 2), and both Chlorella and flocs offered as mixed diets in different proportions (diets 3 and 4). The survival rate of Artemia fed diets 1 and 4 were significantly higher than those fed diets 2 and 3. The survival rate of Artemia fed diet 4 was the highest among the four diets. Individual length (10.02 ± 2.44 mm) and biomass production of diet 3 (3.2 ± 0.40 g L^–1) were the highest among the four diets. The crude protein contents for Artemia fed diets 2, 3 and 4 were 591.22 ± 30.15, 580.34 ± 22.42 and 533.27 ± 34.19 g kg^–1, respectively, which were significantly higher than that of diet 1 (461.25 ± 10.33 g kg^–1). The concentrations of free amino acids and the fatty acid compositions in the four diets were equal, except for the C24:0 content. The highly unsaturated fatty acid concentration of Artemia fed diet 2 was higher than those of the other three diets. It showed that microbial flocs produced from fish waste can be used for Artemia.     

Effect of dietary energy content on gilthead sea bream (Sparus aurata) feeding behaviour and nutritional use of the diet

We have studied how the diet energy level affects gilthead sea bream (Sparus aurata) daily pattern of demand‐feeding activity and nutritional use of the diet under summer‐ and winter‐like conditions. To that end, animals were kept in a closed circuit under controlled temperature and photoperiod, and fed one of two commercial diets with either high (H: 238 g kg^?1 fat) or low (L: 172 g kg^?1 fat) energy content. In summer conditions (26 °C; 12 : 12 L : D), both diets yielded similar growth rate (0.7 ± 0.0 and 0.7 ± 0.1) and thermal unit growth coefficient values (0.6 ± 0.0 and 0.6 ± 0.0), and although the daily rate of delivered feed was somewhat higher for fish under the high‐energy diet (16 ± 2 g kg^?1 of fish) the difference was not significant. In winter conditions (17 °C; 9 : 15 L : D), on the other hand, no differences were found for any of the parameters evaluated. Thus, the higher lipid content of the diet does not appear to have any protein sparing effect. The ‘summer’ demand‐feeding pattern displayed three daily peaks, which were quite apparent for fish under the low‐energy diet, but rather smoothed for those that ate the energy‐rich diet. This profile was replaced in winter conditions by a single peak around noon, and the animals also displayed a lower overall number of demands.     

A study of the arachidonic acid requirements of the giant tiger prawn, Penaues monodon

This study examined the dietary requirement of arachidonic acid (ARA) when that of linoleic acid (LOA), the natural precursor to ARA, was also satisfied with linolenic acid (LNA) and also with and without the other key dietary highly unsaturated fatty acids (HUFA). Growth by prawns fed diets supplemented with ARA was poorer than in diets where it was not present. Supplementation of ARA to diets with either optimized HUFA or just optimised poly unsaurated fatty acids (PUFA) (i.e. LOA, LNA) resulted in poorer growth. Growth was poorest by prawns (215 ± 13%) fed diets with ARA supplemented at 20% of the total fatty acids but including 7% LOA, 21% LNA and 4% of both eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Growth was best in prawns fed diets devoid of ARA but with 7% LOA and 21% LNA (350 ± 19%). Prawns fed the reference diet (348 ± 21%) and the other diet devoid of ARA but containing about 7% LOA, 21% LNA and 4% of both EPA and DHA (345 ± 18%) had similar growth. The growth responses were not effects of altered lipid or fatty acid digestibilities. Indeed supplementation of ARA to the diet marginally improved the digestibility of the total neutral lipid in the diet and the digestibilities of some other dietary fatty acids. The amount of lipid in the digestive glands of prawns fed with the diets was reduced by the inclusion of ARA in the dietary lipids. Composition of the lipids in the digestive gland (DG) of the prawns was almost directly related to the composition of their dietary lipids. The proportion of ARA in the total fatty acids increased with level of supplementation of dietary ARA. An increased level of dietary ARA reduced the proportion of EPA, DHA in the DG lipid and also the total n‐3 and n‐6 fatty acids in the DG lipid. The results of this study support that addition of ARA to the diet of Penaues monodon when the other key essential fatty acids (EFA) have been optimized, does not improve their growth performance. It is suggested that key cause for this response may lie in the importance of the balance of the n‐3 to n‐6 fatty acids in the diet of these animals.     

Effect of arachidonic acid supplementation on reproductive performance of tank‐domesticated Penaeus monodon

The reproductive performance of domesticated Penaeus monodon was assessed when fed on two experimental semi‐moist maturation diets varying in their arachidonic acid content for 21 days before ablation and throughout a 17‐day reproductive assessment. The biochemical composition of the two semi‐moist two diets was similar with the exception of arachidonic acid (ARA) content; the basal diet (BAS) consisting of 0.9 g kg^?1 DM ARA (1.1% of total fatty acids) and the supplemented diet (ARA‐SUP) consisting of 5.0 g kg^?1 DM ARA (5.8% of total fatty acids). ARA/EPA and ARA/DPA ratios were 0.1 in the BAS diet and 0.5 in the ARA‐SUP diet. Fatty acid composition of the spawned eggs was comparable between diets with the exception of ARA concentration, which was higher in the ARA‐SUP (8.95 ± 0.44 g kg^?1 DM) than the BAS (3.23 ± 0.17 g kg^?1 DM) (P < 0.0001). The cumulative percentage of females spawning (mean ± SE after 17 days) (31.9 ± 7.0%; 24.1 ± 1.3%), number of spawnings per female (0.48 ± 0.1; 0.29 ± 0.02), and eggs per female (62 520 ± 16 935; 44 521 ± 9914) was significantly (P < 0.0001) higher for the ARA‐SUP than the BAS. Results of this study suggest that arachidonic acid plays a key role in promoting egg development and spawning in P. monodon.     

Effects of fishmeal replacement with soybean meal as protein source, and protein replacement with carbohydrates as an alternative energy source on sharpsnout sea bream, Diplodus puntazzo, fatty acid profile

The effect of replacing fishmeal with soybean meal in the diet and also partial dietary protein replacement with carbohydrates, on sharpsnout sea bream (Diplodus puntazzo) total lipid fatty acid profile was studied. A group of sharpsnout sea bream of 200 g were fed a diet containing either 0%, 20%, 40% or 60% of protein from soybean meal. In a second experiment, fish (126 g) were fed diets with reduced protein and increased carbohydrate percentages. Fishmeal replacement with soybean meal increases the fish polyunsaturated fatty acids (PUFA) content, mainly due to linoleic acid, which is present in high quantities in soya. But as a consequence, the inclusion of soybean meal produces a significant decrease of the n‐3/n‐6 relationship (from 2.21±0.07 to 1.66±0.05). Replacement of protein with carbohydrate hardly modifies the diet fatty acid profile. As the fishmeal content decreases, there is a slight reduction of saturated fatty acids, the diet with lowest protein percentage having the highest monounsaturated fatty acids and lowest PUFA proportions. Fat quality indices are similar to those reported in previous studies, and in the case of fish under soy‐containing diets, they are favourables. However, fishmeal replacement causes a loss of n‐3 fatty acids that is important to compensate using other sources rich in this type of fatty acids.     

Partial replacement of fishmeal with sunflower cake and corn oil in diets for tilapia Oreochromis niloticus (Linn): effect on whole body fatty acids

The objective of this study was to determine the effect of replacing fishmeal with high‐fibre and low‐fibre sunflower cakes (HFSC and LFSC) on whole body fatty acid composition in tilapia Oreochromis niloticus (Linn). Sex‐reversed O. niloticus males with an initial weight of approximately 16g ± 0.95 (SD) were used. A control diet based on herring meal and soybean meal was formulated. Six test diets were formulated such that low‐fibre (LF) and high‐fibre (HF) sunflower cakes (SC) contributed 30%, 60% and 80% of the dietary protein, and the diets were designated as LFSC‐30, LFSC‐60, LFSC‐80, HFSC‐30, HFSC‐60, and HFSC‐80 respectively. All fish were held at 25–28°C. They were fed three times daily their prescribed experimental diets for 70 days. At the end of this period they were starved for 24 h and weighed. Five fish representing the average weight of each replicated group (n=3) were frozen in plastic bags at –22°C for determination of fatty acid composition. Fatty acids in the fish were significantly influenced by diet. Palmitic, oleic and linoleic acids were the most abundant fatty acids in both the diets and the fish. Linoleic acid (18:2 ω6) was the most abundant fatty acid in diets based on sunflower cake. The levels of this fatty acid were also higher in fish fed diets with high contents of the sunflower cakes (LFSC‐60, LFSC‐80 and HFSC‐80) (31.3%, 34.7% and 29.7% respectively) than fish fed the control diet (13.8%). Percentages of long chain polyunsaturated acids of the ω‐3 family viz., docosahexaenoic (22:6 ω3) and eicosapentaenoic (20:5 ω3) were low in the diets and in the fish bodies. Fish fed the control diet had a higher level of 22:6 ω3 than those fed the other diets. The possible implications of the preceding findings for human health will be discussed.     

Bacterial colonization of winter flounder Pseudopleuronectes americanus fed live feed enriched with three different commercial diets

The proliferation of bacteria in intensive aquaculture systems may be responsible for poor growth and mass mortality of marine fish larvae. Essential fatty acids provided in the diet could protect larvae by modulation of the immune response via arachidonic acid (AA) and eicosapentaenoic acid (EPA). Winter flounder Pseudopleuronectes americanus larvae were fed rotifers Brachionus plicatilis enriched with three commercial diets containing different fatty acid profiles. Bacterial colonization on the gills and skin and in the intestinal lumen was evaluated at the end of the rotifer feeding period (day 26), and growth was surveyed until metamorphosis. At 26 days post hatching, larvae fed rotifers containing the higher AA content and with a higher docosahexaenoic acid (DHA) to EPA ratio showed better growth and the lowest bacterial colonization of the intestinal lumen compared to larvae fed rotifers with the lowest AA and DHA : EPA levels. AA had been selectively incorporated into the polar lipids of larvae fed the rotifers enriched with the three diets. This is the first study in winter flounder larvae to report a link between different commercial rotifer enrichments and bacterial density in intestinal lumen.     

Glucose tolerance in Atlantic salmon, Salmo salar L., dependence on adaption to dietary starch and water temperature

Individually tagged Atlantic salmon, Salmo salar L., were fed three different adaptation diets containing low, medium or high levels of extruded starch, before intraperitoneal injection of glucose. The injections were done at winter and at summer temperatures. This was to investigate whether the tolerance for glucose varied according to adaption diet and/or according to season. The results showed a temperature-dependent response. At winter temperatures (2°C) the Atlantic salmon had problems adapting to both medium and high levels of dietary starch. This was indicated by lower growth response in the adaptation period, as well as by delayed glucose regulation. At summer temperatures (12.5°C) the Atlantic salmon could tolerate and utilize both medium and high levels of dietary starch. In summer also all groups responded evenly to the tolerance tests with respect to blood glucose regulation. Incorporation of liver glycogen was higher at summer than at winter temperatures in the high- carbohydrate group. No effect was found on haematocrit values as a response to diet or season.     

Effects of varying dietary docosahexaenoic acid levels on growth,proximate composition and tissue fatty acid profile of juvenile silver pomfrets,Pampus argenteus (Euphrasen, 1788)

This study investigated the effects of varying dietary levels of decosahexaenoic acid (DHA) on growth performance, proximate composition and whole body fatty acid profiles of juvenile silver pomfret, Pampus argenteus. Triplicate groups of fish (30.55 ± 0.08 g) were fed diets containing 5.2%, 9.31% and 13.38% DHA (% of total fatty acids) or 0.85%, 1.52% and 2.18% DHA on dry diet weight for diets 1, 2 and 3 respectively. Survival was not affected by dietary DHA levels. The growth performance and feed utilization parameters of fish fed diets 2 and 3 were significantly (P < 0.05) higher than those fed diet 1, although these parameters in diets 2 and 3 did not differ significantly (P > 0.05). Whole body lipid and fatty acid profiles were influenced by dietary DHA levels. Significantly higher n‐3 fatty acids particularly DHA, DHA:EPA(eicosapentaenoic acid) ratios and n‐3:n‐6 ratios were observed in fish fed diets 2 and 3 compared to those fed diet 1. Better growth performance and higher whole body DHA:EPA (2.31, 2.29) ratios and n‐3:n‐6 ratios (2.17, 2.12) observed in fish fed diets 2 and 3, respectively, suggests that silver pomfret juveniles have a higher requirement for n‐3 fatty acids, notably DHA for optimum growth and survival.     

Effects of dietary lipid level and vegetable oil on fatty acid metabolism in Atlantic salmon (Salmo salar L.) over the whole production cycle

Changes in fatty acid metabolism in Atlantic salmon (Salmo salar) induced by vegetable oil (VO) replacement of fish oil (FO) and high dietary oil in aquaculture diets can have negative impacts on the nutritional quality of the product for the human consumer, including altered flesh fatty acid composition and lipid content. A dietary trial was designed to investigate the twin problems of FO replacement and high energy diets in salmon throughout the entire production cycle. Salmon were grown from first feeding to around 2 kg on diets in which FO was completely replaced by a 1:1 blend of linseed and rapeseed oils at low (14–17%) and high (25–35%) dietary oil levels. This paper reports specifically on the influence of diet on various aspects of fatty acid metabolism. Fatty acid compositions of liver, intestinal tissue and gill were altered by the diets with increased proportions of C₁₈ polyunsaturated fatty acids and decreased proportions of n-3 highly unsaturated fatty acids (HUFA) in fish fed VO compared to fish fed FO. HUFA synthesis in hepatocytes and enterocytes was significantly higher in fish fed VO, whereas β-oxidation was unaltered by either dietary oil content or type. Over the entire production cycle, HUFA synthesis in hepatocytes showed a decreasing trend with age interrupted by a large peak in activity at seawater transfer. Gill cell prostaglandin (PG) production showed a possible seasonal trend, with peak activities in winter and low activities in summer and at seawater transfer. PG production in seawater was lower in fish fed the high oil diets with the lowest PG production generally observed in fish fed high VO. The changes in fatty acid metabolism induced by high dietary oil and VO replacement contribute to altered flesh lipid content and fatty acid compositions, and so merit continued investigation to minimize any negative impacts that sustainable, environmentally-friendly and cost-effective aquaculture diets could have in the future. Abbreviations: FO - fish oil; HUFA - highly unsaturated fatty acids acids (carbon chain length ≥C ₂₀ with ≥3 double bonds); LO - linseed oil; RO - rapeseed oil; VO - vegetable oil. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of Different Dietary Lipid Sources on the Survival, Growth, and Fatty Acid Composition of South American Catfish, Pseudoplatystoma fasciatum, Surubim, Juveniles

The present study examines the effect of four semi‐purified diets (casein–gelatin based) where the source of fatty acids was free (esterified) oleic acid and linoleic acid (LA) (LOA diet), linseed and olive oil (predominantly LA and linolenic acid) (LO diet), cod liver oil (rich in highly unsaturated fatty acids) (CLO diet), and soybean lecithin (phospholipids; mostly LA) (LE diet) on the growth of juvenile South American catfish (surubim, Pseudoplatystoma fasciatum, Pimelodidae) (0.98 ± 0.04 g individual weight). Fish were fed at a restricted–readjusted feeding rate for 8 wk. At the end of the experiment, LE‐diet‐fed fish grew significantly larger than those of the other three groups (P < 0.05). Considerable cannibalism was observed in all the treatments. It is suggested that the quantitative growth performance may possibly change under other conditions, with less or no cannibalism. Survival did not differ significantly among the fish fed four different diets. Muscle and liver lipid contents did not vary among dietary treatments (P > 0.05), but whole‐body lipid concentrations were affected by dietary treatments. Fish fed LE diet contained significantly lower lipid level than those fed three other diets (P < 0.05). Muscle and liver fatty acid profiles reflected dietary fatty acid composition. Arachidonic acid level was significantly higher in muscle and liver of fish fed LOA and LE diets than in those fed LO and CLO diets. The results suggest that the efficiency of elongation and desaturation of 18C fatty acids depends on the dietary lipid source, and South American catfish has considerable capacity to transform linoleate to arachidonate.     

Restoration of the fatty acid composition of red seabream (Pagrus auratus) using a fish oil finishing diet after grow-out on plant oil based diets

This study evaluated the potential for manipulating the fatty acid composition of juvenile red seabream, Pagrus auratus. Prior to the start of the study, three groups of fish had been reared for 3 months on a fish oil based diet or diets where the added fish oil had been replaced with either canola or soybean oil. In the present study, fish that had previously been fed either the canola or soybean oil diets were fed a fish oil based diet. Three additional treatments included fish being maintained on their original diets of fish oil, canola oil or soybean oil. Fish were fed their respective diets twice daily to apparent satiety for 32 days. Samples of fish from each treatment were collected after 0, 1, 2, 4, 8, 16 and 32 days. Composition and growth of the fish were determined at each sample point. Most treatments showed no differences in growth performance, although fish fed a fish oil diet after previously being fed a soybean oil diet showed slightly better growth. No significant differences among treatments were observed in proximate composition of the fish, although there was a significant increase in total fat and individual fatty acid (g kg^?1 live‐weight) content of the fish from all treatments over the period of the study. No significant changes in the relative fatty acid composition (% of total fatty acids) over time were observed in the three treatments where fish were maintained on their original diets. In contrast, fish that were previously fed either the canola or soybean oil diets and were then fed a fish oil diet had significant changes in both the relative (% of total fatty acids) and absolute (g kg^?1 live‐weight) fatty acid content. Key changes observed included a decrease in the relative levels of polyunsaturated fatty acids (PUFA) such as 18 : 2n ? 6 and 18 : 3n ? 3. Increases in the relative levels of the long‐chain polyunsaturated fatty acids (lcPUFA) 20 : 5n ? 3 and 22 : 6n ? 3 were also observed in both treatments. The rates of absolute (g kg^?1 live‐weight) change/accumulation of these fatty acids followed an exponential equation that differed for each fatty acid in each treatment. Examination of the retention efficiency of specific fatty acids also showed marked differences between fatty acids within treatments and also differences between treatments. Biologically important fatty acids such as 20 : 5n ? 3 and 22 : 6n ? 3 had only moderate retention efficiencies and these were unaffected by treatment. In contrast, the retention efficiencies of 18 : 2n ? 6 and 18 : 3n ? 3 suggested selective retention of these fatty acids when fed fish oil diets, but moderate catabolism when fed the plant oil diets. There were also high retention efficiencies of most saturated and monounsaturated fatty acids suggestive of active retention and/or active synthesis of these fatty acids by the fish. The results of this study, particularly the increases in lcPUFA, support the usefulness of a fish oil based finisher diet for fish raised predominantly on plant oil based diets.     

Growth and fatty acid composition of juvenile Cerastoderma edule (L.) fed live microalgae diets with different fatty acid profiles

The importance of dietary 20:5n‐3 (EPA), 22:6n‐3 (DHA) and 20:4n‐6 (ARA) for growth, survival and fatty acid composition of juvenile cockles (Cerastoderma edule) was investigated. Cockles of 6.24 ± 0.04 mm and 66.14 ± 0.34 mg (live weight) were distributed into three treatments where live microalgae diets were fed constantly below the pseudofaeces production threshold, for three weeks. Diets had distinct fatty acid profiles: high EPA (53% Chaetoceros muelleri + 47% Pyramimonas parkeae), no DHA (47% Brachiomonas submarina + 53% Tetraselmis suecica) and low ARA concentrations (73% P. parkeae + 27% Phaeodactylum tricornutum). Growth was positively affected by high EPA and low ARA diets, whereas no significant growth was observed for the no DHA diet. High mortality of cockles fed no DHA diet raises questions about its suitability for cockles. In balanced diets with EPA and DHA, lower concentrations of ARA do not limit growth. The impact of dietary fatty acids was evident in the fatty acids of neutral and polar lipids of cockles. In polar lipids of all cockles, there was a decrease in EPA, in contrast to an increase in DHA. The combination of EPA and DHA in a live microalgae diet was beneficial for the growth and survival of juvenile cockles.     

Rearing of pike-perch larvae using formulated diets – first success with starter feeds

The present study evaluated the performance of two commercial diets: AgloNorse (AN) and BioKyowa (BK), and two experimental, formulated diets based on casein (C) or casein plus casein hydrolysates (CH) in rearing of pike‐perch larvae (Sander lucioperca L.). All fish were 5 day old and control group was fed live Artemia nauplii. Fish were sampled periodically for histological comparison of morphological changes in the digestive tracts. Survival of fish fed Artemia nauplii, BK and AN was similar: 54.4%, 50.8% and 52.4%, respectively, while the fish fed formulated diets C and CH showed considerably lower survival: 28.4% and 21.6% respectively. After 5 weeks of rearing, the average body mass of fish ranged from 212±32 mg in Artemia fed group to 53.8±6.8 mg in C diet fed group. A considerable vacuolization of supranuclear zone in enterocytes of posterior intestine was observed in the larvae fed commercial diets. No anomalies in liver development were found. Hepatocytes of fish fed BK diet showed larger glycogen storage areas, compared with those occupied by lipids. The highest zymogen accumulation of pancreatic cytoplasm was observed in fish fed Artemia. In fish fed C and CH diets, anomalies in digestive system development were indicated by lower and less numerous intestinal folds, smaller hepatocytes, retarded development of gastric glands, and in CH group – also local fatty degeneration of liver.     

Effects of canola meal on physiological and biochemical parameters in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (initial body weight 4.16 ± 0.25 g) were fed diets [crude protein 420 g kg^?1; gross energy 18.7 MJ kg^?1 dry matter (DM); crude fat 110 g kg^?1] containing graded levels of either a canola meal (crude protein 350 g kg^?1 DM) supplemented with DL‐methionine as partial fish meal protein. A growth trial was conducted over 16 weeks at a water temperature of 12 ± 1 °C. At the end of the growth trial, in addition to body composition analyses, plasma tri‐iodothyronine (T₃) and thyroxine (T₄), cholesterol and liver fatty acid composition were measured. Replacement of fish meal with canola meal (100–570 g kg^?1 replacement) did not affect on growth performance. At 16th week, plasma cholesterol levels were reduced in fish fed all diets in comparison with 8th week. Plasma T₄ levels were significantly higher in the canola meal‐fed fish sampled after 16 weeks, but no significant differences in T₃ levels were obtained (P > 0.05). Proximate compositions were affected by dietary treatments. The liver fatty acid composition reflected that of the diet with a higher level of polyunsaturated (n‐6) fatty acids in fish fed diet canola meal and a higher content in n‐3/n‐6 ratio in fish fed diet without canola meal. These studies show that canola meal has potential to replace substantial levels of fish meal in diets for carnivorous fish without compromising performance.     

Optimizing the essential fatty acids, eicosapentaenoic and docosahexaenoic acid, in the diet of the prawn, Penaeus monodon

The dietary requirements of Penaeus monodon for eicosapentaenoic (20:5n‐3; EPA) and docosahexaenoic (22:6n‐3; DHA) acids were examined. These requirements were examined when dietary levels of linoleic (18:2n‐6; LOA) and linolenic acids (18:3n‐3; LNA) were also provided at previously established optimal levels of 14 and 21% respectively of the total lipid fatty acids. A 5 × 5 factorial design was used with incremental amounts (0, 4, 8, 12 and 16% of total fatty acids) of EPA and/or DHA. An additional diet containing cod‐liver oil was provided as a reference diet. The total lipid content of all of the 25 treatments and reference diets was maintained at the same level of 75 g kg^?1. Growth of prawns fed with the reference diet after 50 days was 244 ± 21%. The greatest response to singular additions of EPA or DHA was with a 12% inclusion of either fatty acid, resulting in 287 ± 21 and 293 ± 18% weight gain, respectively. Growth was generally better when combinations of EPA and DHA were used, the optimal combination being EPA 4% and DHA 4%, resulting in 335 ± 25% weight gain. Addition of high levels of either of the highly unsaturated fatty acids (HUFA) in the diet had a negative effect on growth. Digestibilities of the total neutral lipid and specific fatty acids were examined during the growth trials. The digestibility of total neutral lipid was usually higher when either or both HUFA were present, however there were few significant differences between treatments that contained either or both HUFA. Following the growth trials, digestive glands (DG) of prawns fed with the various diets were analysed to determine the total lipid content and fatty acid composition. Total lipid in the digestive gland increased with the inclusion of DHA, but was not significantly affected by the addition of EPA. The fatty acid composition of the digestive gland lipid generally reflected that of the diet. However, the maximum retention of EPA (11.1% of total DG fatty acids) and DHA (10.7% of total DG fatty acids), was not directly proportional to the amount of either fatty acid present in the diet. These results demonstrate that both EPA and DHA have considerable growth promoting capacity. This growth promoting capacity is enhanced when an optimal balance of both fatty acids are incorporated into the diet.     

Experiential legacies of early-life dietary polyunsaturated fatty acid content on juvenile Walleye: Potential impacts from climate change

Climate-induced shifts in plankton blooms may alter fish recruitment by affecting the fatty acid composition of early-life diets and corresponding performance. Early-life nutrition may immediately affect survival but may also have a lingering influence on size and growth via experiential legacies. We explored the short- and longer-term performance consequences of different concentrations of polyunsaturated fatty acids (PUFA) for juvenile Walleye (Sander vitreus, Mitchill 1818). For the first 10 days of feeding, juveniles were provided Artemia enriched with: oleic acid (low PUFA), high docosahexaenoic acid and high eicosapentaenoic acid (high PUFA), or high PUFA and a form of vitamin E (high PUFA + E). After 10 days, all fish were fed a high-quality diet and reared for an additional 27 days. Juveniles fed either high PUFA diet were 1.15-fold larger (PUFA mean ± SD = 20.0 ± 3.3 mg; PUFA + E = 19.8 ± 3.3 mg) than those fed the low PUFA (17.3 ± 2.8 mg) diet after 10 days of feeding. After 27 days, juveniles initially fed the high PUFA diet were still 1.10- to 1.20-fold larger (PUFA = 407.0 ± 61.6 mg; PUFA + E = 422.7 ± 58.7 mg) than those initially fed the low PUFA diet (356.5.0 ± 39.5 mg). Our findings demonstrate that fatty acid composition of juvenile Walleye diets has immediate and lingering size effects. As changes in climate continue to alter lower trophic levels, fish management and conservation may need to consider short- and long-term effects of temporal or spatial differences in early-life diet quality.