Aquaculture Research, 2012, 43, 767–776 doi:10.1111/j.1365-2109.2011.02888.x Effects of substituting dietary fish oil with crude palm oil and palm fatty acid distillate on growth, muscle fatty acid composition and the activities of hepatic lipogenic enzymes in snakehead (Channa striatus, Bloch 1793) fingerling Mohammed Aliyu-Paiko, & Roshada Hashim Laboratory of Feeds and Feed Development, Aquaculture Research Group, School of Biological Sciences, Universiti Sains Malaysia, Penang, Malaysia Correspondence: M Aliyu-Paiko, Laboratory of Feeds and Feed Development, Aquaculture Research Group, School of Biological Sciences, Universiti Sains Malaysia, 11800 Penang, Malaysia. E-mail: moleepaiko@yahoo.com Abstract Three diets were formulated to be iso-nitrogenous (450 g kg  1), iso-lipidic (65 g kg  1) and iso-energetic (18.5 KJ g  1), varying only in their lipid sources and designated as 100% ¢sh oil (FO), 100% crude palm oil (CPO) and 100% palm fatty acid distillate (PFAD). Feed were hand fed to homogenous groups of 12 Channa striatus ¢ngerlings (mean weight 3.5  0.3 g) per tank in triplicate for 12 weeks, in a recirculation system. The growth performance and feed intake in the CPO and PFAD treatments were signi¢cantly (Po0.05) higher than those in the ¢sh fed the control diet (FO), respectively, whereas the feed conversion ratio was better in PFAD than that in the other treatments respectively. The biological indices monitored (hepatosomatic index and viscerosomatic index) as well as carcass yield did not vary signi¢cantly among all the treatments respectively. The muscle fatty acid (FA) pro¢le of ¢sh was in£uenced by the composition of the diets fed, whereas no di¡erences were recorded in the activities of the hepatic lipogenic enzymes monitored (fatty acid synthetase, citrate cleavage enzyme and malic enzyme). Wholebody proximate composition analysis revealed that PFAD treatment, compared with others, contained signi¢cantly higher protein and ash, but lower lipid contents, although the muscle content of these nutrients was similar among all the treatments. Based on the results of this trial, CPO and PFAD could be used to partially substitute FO in the diet for C. striatus © 2011 Blackwell Publishing Ltd ¢ngerling, to achieve good growth performance without any negative e¡ects or compromising the muscle n-3 FA composition (especially in the docosa hexaenoic acid and eicosa pentaenoic acid content). Keywords: Channa striatus, lipogenic enzyme, fatty acid, ¢sh oil, vegetable oil Introduction Currently, the attention of aquaculture in the use of dietary lipid sources is particularly focused on seeking sustainable alternatives to ¢sh oil (FO), the commonly used oil in ¢sh feed globally. This is because the demand for the commodity has increased steadily despite the static (or declining) production levels and it is feared that the supply may not be su⁄cient to meet demand in the near future (Pike 2005; FAO 2007;Tacon & Metian 2008).Vegetable oils (VO) have, however, been identi¢ed as suitable candidates (Caballero, Obach, Rosenlund, Montero, Gisvold & Izquierdo 2002; Turchini, Mentasti, Fryland, Orban, Caprino & Moretti 2003; Bell & Waagbo 2008). The popular strategy currently adopted in the industry is to partially or fully replace FO with di¡erent VO in feeds, depending on the species and the size of ¢sh targeted. Unfortunately,VO are lacking in long-chain, omega-3 polyunsaturated fatty acids (n-3 PUFA), which are abundant in FO (Sargent, Tocher & Bell 767 Substituting FO with CPO and PFAD in C. striatus diet M Aliyu-Paiko & R Hashim 2002) and are essential components of animal cell membranes (Tocher 2003). Therefore, whereas feeding diets containing di¡erent levels of VO was successful in promoting good growth in some species (Bell & Waagbo 2008), the practice was reported to reduce growth and lead to health problems in others (Caballero, Izquierdo, Kjorsvik, Fernandez & Rosenlund 2004; Bell, McGhee, Dick & Tocher 2005) and must be avoided. Based on their fatty acid (FA) requirements, cultured freshwater ¢sh (including Channel cat¢sh and, possibly, snakeheads) perform well when fed diets containing  5 g kg  1 n-3 FA (National Research Council 1993). This relatively low n-3 FA requirement could be because in general terms, freshwater ¢sh require both the omega 3 (n-3) and the omega 6 (n-6) series of PUFA or the n-6 series alone (De Silva & Anderson 1995; Yildirim-Aksoy, Lim, Shelb & Klesius 2009). This trend is well established in the literature (Manning & Li 2002). Quite notably, freshwater ¢sh are able to regulate the fate of FA formed endogenously and assimilated from the diet (Menoyo, Lo¤pez-bote, Bautista & Obach 2003), such that dietary FA could be incorporated into structural phospholipids, deposited as neutral reserve fat or oxidized to provide energy (Henderson 1996). Nonetheless, concern has also increased in recent times over the incorporation of high dietary non-protein energy (from oils or digestible carbohydrates) into feeds for cultured species; since it could alter body composition, particularly through increased lipid deposition in body tissues (Hillestad & Johnsen 1994). This is because excess levels of certain nutrients, including n-3 and n-6 FA, could signi¢cantly in£uence feed palatability (Boonyaratpalin 1991) and feed consumption (Ling, Hashim, Kolkovski & Chong 2006), leading to adverse e¡ects on the growth and the proper development of cells and tissues (Sargent, Henderson & Tocher 1989). Additionally, a high dietary lipid content has also been reported to a¡ect the activity of several lipogenic enzymes in some species (Arnesen, Krogdahl & Kristiansen 1993), although Dias, Alvarez, Diez, Arzel, Corraze, Bautista and Kaushik (1998) suggested that the inhibition of lipogenesis by the level of dietary fat appears to be less severely controlled in ¢sh than in other terrestrial animals. In spite of available information in the literature showing the positive e¡ect of using VO in feeds for ¢sh and the relative abundance of crude palm oil (CPO) and palm fatty acid distillate (PFAD) (Turchini, Torstensen & Ng 2009) particularly in Asia, reports are scarce on the use of these oils in feeds for Channa 768 Aquaculture Research, 2012, 43, 767–776 striatus, a carnivorous, obligatory air-breathing freshwater species farmed as a valuable food ¢sh in Asia. The culture of this ¢sh has gained increasing importance in recent years, both as an important source of protein and because its ¢llet extract is known to possess pharmaceutical values (Baie & Sheikh 2000). Of signi¢cance is the fact that farmed snakeheads are commonly reared feeding almost exclusively on raw ¢sh (FAO 2009) or on home-made feed composed mainly of marine trash ¢sh and cattle blood mixed with rice bran, wheat £our or spent grains of varying nutrient compositions (Victor & Akpocha 1992). In the present study, we evaluated the e¡ects of the substitution of dietary FO with CPO and PFAD on the growth performance, feed e⁄ciency, muscle FA composition, biological indices and the activity of hepatic lipogenic enzymes in Snakehead (C. striatus, Bloch 1793) ¢ngerling. Materials and methods Experimental ¢sh and rearing conditions Channa striatus (Bloch 1793) ¢ngerlings (purchased from a commercial hatchery in Rawang, Malaysia) were acclimated to laboratory conditions, feeding on commercial post-larval cat¢sh crumbled pellets (post-larva 1 crumbles, Gold Coin Specialties, Johor, Malaysia) containing a minimum of 300 g kg  1 crude protein for 4 weeks before stocking. At the end of this acclimation period, ¢sh (mean initial weight 3.5  0.3 g) were randomly stocked into nine 40 L glass aquaria at a density of 12 ¢sh per aquarium. All tanks (connected to a recirculation system, with the £ow rate set at 1.2 L min  1) were supplied with dechlorinated municipal water, which was continuously aerated and heated throughout the period of the experiment, to overcome temperature £uctuations during periods of heavy rains. Water temperature and dissolved oxygen in the culture tanks were monitored bi-weekly by taking measurements of three random samples every other day, and averaged 30  0.5 1C and 5.34  1.3 mg L  1 respectively. Fish were reared under a natural photoperiod of an approximately 12:12 h light:dark schedule, for 12 weeks. Experimental diets, feeding trial and sampling Three practical experimental diets were formulated to be iso-energetic in the gross energy content © 2011 Blackwell Publishing Ltd, Aquaculture Research, 43, 767–776 Aquaculture Research, 2012, 43, 767–776 Substituting FO with CPO and PFAD in C. striatus diet M Aliyu-Paiko & R Hashim (18.5 KJ g  1), iso-nitrogenous (450 g kg  1) and isolipidic (65 g kg  1) as established previously (Aliyupaiko, Hashim & Shu-chien 2009), but di¡ering only in their lipid sources. In the control diet, Peruvian FO (including  32.5 g kg  1 residual oil from ¢shmeal) served as the only lipid source and was designated as FO. In the second diet, the FO added in the control diet was substituted with CPO and the diet was thus designated as CPO, whereas in the third diet, FO was substituted with PFAD and was designated as PFAD. Fishmeal (augmented with casein) was the principal source of protein, corn starch served to adjust the energy in all diets to the same level while a-cellulose was used as the ¢ller. Weighed, dry ingredients and some water were thoroughly mixed in a feed mixer (Tyrone, model TR202; L.J. Stuart & Company, Sydney, NSW, Australia) to make a dough, which was subsequently processed in a meat mincer (Model MH 237, Miao Hsien, Taichung, Taiwan) to make 2 mm diameter spaghetti-like pellets. The pellets were dried in an oven at 50^65 1C, packed separately per treatment and stored at  20 1C until used for the feeding trial after  2 weeks. The ingredients used and proximate compositions of the experimental diets are presented in Table 1, while the FA compositions of the diets fed are presented in Table 2. Fish in three randomly assigned tanks were fed one of the three experimental diets twice daily (09:00 and 16:00 hours) to visual satiation for 12 weeks. The amount of feed consumed was monitored bi-weekly (by calculating the di¡erences in feed weight before the ¢rst and after the last feeding), alongside monitoring ¢sh growth performance accordingly. Once every 2 weeks, the entire culture system was scrubbed and accumulated wastes were siphoned out. Half of the water in the culture system was also replaced, while ¢sh were denied feed during cleaning and sampling, to avoid stress. Fish were weighed individually at the beginning of the experiment but were counted and weighed in groups per aquarium bi-weekly. During sampling, ¢sh were randomly grouped per treatment for the determination of the parameters monitored. Table 1 Ingredients used and proximate compositions of experimental diets Diets FO Ingredients used (g kg  1) 448.4 Fishmeal Casein 142.8 Corn starch 267.9 Fish oilw 28.3 Crude palm oil (CPO)w 0 Palm fatty acid distillate (PFAD)w 0 CMCz 20.0 Vitamin mix‰ 15.0 Vitamin C (ascorbic acid)z 5.0 Minerals mixk 20.0 52.6 Cellulose Proximate composition (g kg  1 dry matter) Protein 452.1 Lipids 65.2 Ash 85.5 Fibre 6.1 Moisture 37.6 NFEww 391.1 18.5 Gross energy (GE) (kJ g  1)zz CPO PFAD 448.4 142.8 267.9 0 28.3 0 20.0 15.0 5.0 20.0 52.6 448.4 142.8 267.9 0 0 28.3 20.0 15.0 5.0 20.0 52.6 451.8 65.4 85.2 6.4 36.8 391.2 18.5 452.2 64.9 85.4 5.9 37.2 391.6 18.6 TripleNine ¢sh protein, Esbjerg, Denmark; containing (g kg  1, DM), protein: 720, total fat:  70, defatted with n-hexane (to reduce crude fat level to  30 g kg  1). wFish oil (Peruvian), CPO and PFAD (from Wilmar edible oils, Penang Malaysia). zCarboxy methyl cellulose (sodium salt), binder. ‰Vitamin premix (Rovimix 6288, F. Ho¡man La-Roche, Basel, Switzerland), contains (kg  1 dry weight): Vit. A 50 million IU, Vit. D3 10 million IU, Vit. E 130 g, Vit. B1 10 g, Vit. B2 25 g, Vit. B6 16 g, Vit. B12 100 mg, Biotin 500 mg, pantothenic acid 56 g, folic acid 8 g, niacin 200 g, anticake 20 g, antioxidant 200 mg, Vit. K3 10 g and Vit. C 35 g. zVitamin C-stay (F. Ho¡man La-Roche). kMineral premix, contains (kg  1 dry weight): calcium phosphate (monobasic) 397.5 g; calcium lactate 327 g; ferrous sulphate 25 g; magnesium sulphate 137 g; potassium chloride 50 g; sodium chloride 60 g; potassium iodide 150 mg; copper sulphate 780 mg; manganese oxide 800 mg; cobalt carbonate 100 mg; zinc oxide 1.5 g and sodium selenite 20 mg. a-Cellulose, ¢ller. wwNitrogen-free extract, calculated as 1000  (Protein1Lipid1Fibre1Ash) g kg  1. zzGross energy content, measured in a bomb calorimeter (Model 6200, Parr Instrument, Moline, IL, USA). Activities of hepatic lipogenic enzymes FA analysis The total lipid of diets and ¢sh muscle were extracted according to a slightly modi¢ed, direct fatty acid methyl esters synthesis method of Indarti, Abdul Majid, Hashim and Chong (2005), before FA analyses (as reported previously in Aliyu-Paiko et al. 2009). At the end of the experiment, three ¢sh per tank were randomly chosen and used for the determination of the activities of lipogenic enzymes. Fatty acid synthetase (FAS; EC 2.3.1.85), citrate cleavage enzyme (CCE, EC 4.1.3.8) and malic enzyme (ME; EC 1.1.1.40) activities in ¢sh liver were assayed according to the © 2011 Blackwell Publishing Ltd, Aquaculture Research, 43, 767–776 769 Substituting FO with CPO and PFAD in C. striatus diet M Aliyu-Paiko & R Hashim Table 2 Fatty acid compositions (g 100 g  1 of total FA detected) of experimental diets fed to Channa striatus (Bloch, 1793) ¢ngerlings for 12 weeks Dietary treatments Fatty acids FO CPO PFAD 14:0 16:0 18:0 P SFA 16:1n7 18:1n9w 20:1n9 20:1n11 P MUFAz 18:2n6 18:3n6 20:4n6 18:3n3 18:4n3 20:4n3 20:5n3 22:5n3 22:6n3 P PUFA‰ P n3 PUFAz P n6 PUFAk n3/n6 6.1a 22.5c 3.9b 32.5c 8.0a 19.9b 10.7a 0.4a 39.0a 3.3b 0.2 0.6a 2.6a 0.2 0.8a 6.8a 1.0a 12.2a 27.7a 23.6a 4.1b 5.8 1.4b 37.1b 4.8a 43.3b 4.3b 29.5a 4.3b 0.2b 38.2a 6.9a 0.1 0.4b 1.5b 0.1 0.4b 1.8b 0.2b 6.1b 17.5b 10.1b 7.4a 1.4 1.4b 44.8a 4.6a 50.8a 4.1b 19.5b 4.8b 0.2b 28.6b 5.9a 0.1 0.4b 1.6b 0.1 0.4b 3.8b 0.4b 7.2b 19.9b 13.5b 6.4a 2.1 P SFA- Sum of all saturated FA detected. wContaining 18:1n7. P z MUFA, Sum of all monounsaturated FA detected. P ‰ PUFA, Sum of all polyunsaturated FA detected. P z n3, sum of all n-3 PUFA detected. P k n6, sum of all n-6 PUFA detected. n3/n6, ratio of n3/n6 PUFA. Mean values in the same row with di¡erent superscript letters are signi¢cantly di¡erent (Po0.05). protocols described by Bazin and Ferre (2001), with a slight modi¢cation. Brie£y, ¢sh were killed by a sharp blow to the head, quickly dissected on ice and the livers were removed. Pooled livers per tank were washed gently with a stream of ice-cold distilled water, blotted dry with a ¢lter paper and weighed. The liver samples were homogenized in three volumes (1g of liver in 3 mL bu¡er) of chilled homogenization sucrose bu¡er (0.25 M sucrose containing 1mM DTT, 1mM EDTA and a mixture of several proteases inhibitors, pH 7.4). The homogenate was centrifuged at 30 000 g and 0^4 1C for 1h. The resulting clear supernatant was collected and kept at  40 1C and used as the crude hepatic lipogenic enzyme extract in subsequent assays. The protein concentration of the crude enzyme extract was determined according to the method of Lowry, Rosebrough, Farr and Randall (1951) using BSA as a standard. Speci¢c 770 Aquaculture Research, 2012, 43, 767–776 enzyme activity was expressed as nanomole NADPH oxidized or reduced per milligram soluble protein per minute at 37 1C. In the FAS assay, the oxidation of NADPH at 340 nm was measured for 10 min at 37 1C, as described by Halestrap and Denton (1973); the assay of CCE was based on the measurement of NADH oxidation at 340 nm, according to the procedure described by Cottam and Srere (1969), while the ME assay was performed following Ochoa (1955), but with 100 mM malate. The formation of NADPH was also measured in a spectrophotometer at 340 nm. All determinations were performed in triplicate and the results are expressed as mean  SD. Analytical methods/statistical analysis The feed ingredients, experimental diets and ¢sh carcass and muscles were analysed for dry matter (DM) proximate composition of crude protein, lipid and ash contents following the standard methods of AOAC (1997); DM was determined by oven drying at 100 1C to a constant weight. The crude protein content was estimated according to the Kjeldahl procedure (crude protein 5 nitrogen  6.25). Samples were extracted with chloroform:methanol (2:1, v/v) to determine crude lipid; crude ash was measured by heating in a mu¥e furnace for 5 h at 550 1C. Nitrogen-free extract was calculated by subtracting the sum of crude protein, crude fat, crude ¢bre and ash from the total DM content. Samples of liver and viscera were removed and weighed for the estimation of the hepatosomatic index (HSI) and the viscerosomatic index (VSI), while carcass yield (CY) was calculated as a percentage of total ¢sh weight by subtracting visceral weight from whole-body weight. Di¡erent parameters were calculated using the following formulae where applicable: Specific growth rate ðSGR %Þ ¼ ½ðln Wf  ln Wi Þ=T  100 Feed conversion ratio ðFCRÞ ¼ total feed intakeðgÞ=total wet weight gainðgÞ Feed intakeðFIÞ ¼ total feed intake=number of fish HSI % ¼ 100  ðliver weight=body weightÞ VSI% ¼ 100  ðviscera weight=body weightÞ CY % ¼ ðweight of eviscerated carcass= weight of whole carcassÞ  100 © 2011 Blackwell Publishing Ltd, Aquaculture Research, 43, 767–776 Aquaculture Research, 2012, 43, 767–776 Substituting FO with CPO and PFAD in C. striatus diet M Aliyu-Paiko & R Hashim where Wf refers to the mean ¢nal weight, Wi is the mean initial weight and T is the feeding trial period in days. Results are presented as mean  SD of three replicate determinations (n 5 3). All data were analysed statistically by1-way ANOVA, using the general linear model. Where di¡erences in mean were recorded, a subsequent comparison was made using Duncan’s Multiple Range Test. Values of P  0.05 were considered to be signi¢cant at a 0.05 probability level. All analyses were performed using SPSS software, version 12. Results No ¢sh mortality was recorded throughout the period of the trial. The results of growth performance (¢nal body weight and SGR) and feed e⁄ciency (FI and FCR) as well as the biological indices (HSI and VSI) monitored are shown in Table 3. From the results, similar growth performance was recorded among ¢sh fed the CPO and PFAD dietary treatments, which was signi¢cantly (Po0.05) higher than that in the control (FO) respectively. Feed intake was also similar among the CPO and PFAD treatments and signi¢cantly (Po0.05) higher than in FO. However, FCR was noted Table 3 Growth, feed e⁄ciency and biological indices of Channa striatus (Bloch 1793) ¢ngerlings fed experimental diets for 12 weeks Dietary treatments Parameters monitored FO Initial weight (g) Final weight (g) SGR FIw FCRz HSI (%)‰ VSI (%)z CY (%)k 3.5 21.5 2.2 27.9 1.6 1.3 4.0 94.7 CPO         PFAD 0.8 3.4  0.6 3.4  0.5 1.3c 23.5  1.1b 26.2  2.3a 0.0c 2.3  0.1b 2.4  0.1a 1.3b 30.3  1.5a 31.1  2.1a 0.6b 1.6  0.9b 1.4  0.4a 0.1 1.4  0.1 1.6  0.3 1.1 2.6  0.6 3.9  0.7 1.2 96.4  0.8 94.5  1.5 Speci¢c growth rate (SGR, %/day) 5 [(ln W  ln W )/T]  100. f i wFeed intake (FI) 5 total feed intake (g)/number of ¢sh. zFeed conversion ratio (FCR) 5 Total feed intake (g)/total wet weight gain (g). ‰Hepatosomatic index (HSI, %) 5 (weight of liver/¢sh weight)  100. zViscerosomatic index (VSI, %) 5 (weight of viscera/¢sh weight)  100. kCarcass yield (CY, %) 5 (weight of eviscerated carcass/weight of whole carcass)  100. Values are mean  SD of triplicate determinations (n 5 3). Mean values in the same row with di¡erent superscript letters are signi¢cantly di¡erent (Po0.05). to be better in the PFAD than in the other two treatments (and ranged between1.39 and1.57 for all treatments). In the biological indices monitored, no di¡erence was noted in the HSI and VSI values among all the treatments. Similarly, CY was not signi¢cantly varied between the control and the other two treatments. The muscle FA composition of all treatments (as reported in Table 4) generally re£ected that of the experimental diets fed (refer to Table 2). Similar muscle content of SFAwas recorded in ¢sh from the CPO and PFAD treatments, which was signi¢cantly (Po0.05) higher than for ¢sh in the control. SFAwas composed principally of 16:0. The total muscle content of MUFA in the ¢sh fed the control diet was signi¢cantly higher than that in ¢sh fed the CPO and PFAD diets respectively. Similar to the trend observed in the diets, the muscle of ¢sh fed the control diet contained signi¢cantly (Po0.05) the highest content of n-3 and the lowest content of n-6 PUFA relative to the other treatments. The muscle n-3 PUFA content contained principally 22:6n-3 [docosa hexaenoic acid (DHA)] Table 4 Muscle fatty acid compositions (g 100 g  1 of total FA detected) of Channa striatus (Bloch, 1793) ¢ngerlings fed experimental diets for 12 weeks Dietary treatments Fatty acids FO CPO PFAD 14:0 16:0 18:0 P SFA 16:1n7 18:1n9w 20:1n9 20:1n11 P MUFA 18:2n6 20:4n6 18:3n3 18:4n3 20:4n3 20:5n3 22:5n3 22:6n3 P PUFA P n3 P n6 n3/n6 6.9a 24.7b 9.2 40.8b 11.9a 10.6a 8.7a 0.1 36.3a 4.2c 1.0a 0.1b 0.5a o0.01 4.5a 1.7 10.8 22.8 17.6a 5.2b 3.4a 4.7b 32.1a 10.1 46.9a 15.2b 8.8b 4.8b 0.1 28.9b 8.4a 0.7b 0.2b o0.01b o0.01 3.1b 1.5 10.2 24.1 15.0b 9.1a 1.7b 5.1b 33.6a 10.4 49.1a 15.8b 6.0b 5.3b 0.2 27.3b 7.5b 0.6b 0.7a o0.01b o0.01 3.4b 0.5 10.8 23.5 15.4b 8.1a 1.9b See Table 2 for details of the abbreviations used. wContaining 18:1n7. Mean values in the same row with di¡erent superscript letters are signi¢cantly di¡erent (Po0.05). © 2011 Blackwell Publishing Ltd, Aquaculture Research, 43, 767–776 771 Substituting FO with CPO and PFAD in C. striatus diet M Aliyu-Paiko & R Hashim Aquaculture Research, 2012, 43, 767–776 Table 5 Whole body and muscle proximate compositions (g kg  1) of Channa striatus (Bloch, 1793) ¢ngerlings fed experimental diets for 12 weeks Dietary treatments Parameters monitored FO CPO PFAD 1 dry matter) Whole-body composition (g Kg Dry matter 713  7 712 Protein content 575  8b 579 Fat content 157  10b 182 Ash 162  2b 161 NFE 106 78 Muscle composition (g kg  1 dry matter) Protein content 767  8 787 Fat content 71  3 68 Ash 57  5 57 NFE 105 88     9 4b 5c 1b  12 2 1 718 612 135 180 73     3 3a 4a 5a 762  13 65  4 55  3 118 Mean values in the same row with di¡erent superscript letters are signi¢cantly di¡erent (Po0.05). and 20:5n-3 [(eicosa pentaenoic acid (EPA)], whereas n-6 PUFA composed of 18:2n-6 [linoleic acid (LA)]. The muscle content of n-3 and n-6 PUFA in£uenced the n-3:n-6 ratio signi¢cantly, being relatively higher in the control (3.4) and lower in the others (1.7 in CPO and 1.9 in PFAD), similar to the trend recorded in the diets fed. Interestingly, although the level of DHA detected in the control diet was about twice that in the other diets, the muscle content in all the three treatments was similar. The result of the whole body and muscle proximate composition analysis is shown in Table 5. The wholebody contents of protein and ash were signi¢cantly (Po0.05) higher in the PFAD treatment than in the other two treatments, respectively, whereas the lipid content varied signi¢cantly among all the treatments. On the other hand, the muscle proximate analysis for protein, lipid and ash did not reveal any signi¢cant di¡erences among the treatments. The activities of the lipogenic enzymes monitored (FAS, CCE and ME) are reported in Fig. 1. The activity of all lipogenic enzymes monitored was generally low and not signi¢cantly (Po0.05) varied among the treatments respectively. However, the activity of CCE was  twice that of FAS, while the activity of ME was about two to three times that of FAS in all the treatments. Discussion In this trial, the growth performance, feed intake and e⁄ciency of C. striatus ¢ngerlings were higher with 772 Figure 1 Activities of hepatic lipogenic enzymes in Channa striatus (Bloch, 1793) ¢ngerling fed diets containing ¢sh oil (FO) substituted with crude palm oil (CPO) and palm fatty acid distillate (PFAD) for 12 weeks. FAS, fatty acid synthetase; CCE, citrate cleavage enzyme; ME, malic enzyme; IU, enzyme activity units, de¢ned as nanomoles of substrates converted to products per milligram protein per minute under assay conditions at 37 1C. the CPO and PFAD diets compared with the control diet (FO). This is consistent with reports of several other studies with freshwater ¢sh, indicating that VO could be used to successfully replace FO in ¢sh feeds without a¡ecting survival and growth (Subhadra, Lochmann, Rawles & Chen 2006). Ng (2002) also reported that dietary palm oil (PO) produced growth similar to cod liver oil, corn oil and soybean oil in tropical bagrid cat¢sh (Mystus nemurus). In climbing perch (Anabas testudineus) fed a diet in which 200 g kg  1 dietary FO was substituted with PO, Varghese and Oommen (2000) reported that the ¢sh grew as well as those fed a similar level of dietary coconut oil or cod liver oil. In the diet of bagrid cat¢sh (M. nemurus), it was demonstrated that 900 g kg  1 of FO could be replaced by CPO without a¡ecting the growth, feed utilization e⁄ciency or body composition (Ng, Tee & Boey 2000). Concurrent with our result, Ng, Lim and Boey (2003) also showed better growth when African cat¢sh (Clarias gariepinus) was fed semi-puri¢ed diets containing 100 g kg  1 PO as the sole dietary lipid compared with ¢sh fed cod liver oil-based diets. The comparable or higher growth performance recorded when FO was substituted with CPO or PFAD in the present study is additional evidence demonstrating that PO is a good lipid source for ¢sh, due to its content of metabolic energy. In vitro mitochondrial b-oxidation studies in ¢sh by Henderson and Sargent (1985) demonstrated that there exists a preference for SFA and MUFA over PUFA for metabolic energy. PO is a rich source of SFA ( 480 g kg  1) and MUFA ( 420 g kg  1) © 2011 Blackwell Publishing Ltd, Aquaculture Research, 43, 767–776 Aquaculture Research, 2012, 43, 767–776 Substituting FO with CPO and PFAD in C. striatus diet M Aliyu-Paiko & R Hashim (Chong1993) and PFAD is composed of  640 g kg  1 SFA and 300 g kg  1 MUFA (Ng et al. 2003). In another development, an improvement in growth and feed utilization by ¢sh has been reported to be due to the protein-sparing e¡ect of dietary lipid (Chaiyapechara, Liu, Barrows, Hardy & Dong 2003), which was demonstrated with CPO in African cat¢sh (Lim, Boey & Ng 2001). This may be the explanation for the better growth performance observed in the VO-substituted diets in the present study. The observation of no signi¢cant di¡erences in the HSI and VSI values (as well as CY) among all the dietary treatments in this study was not surprising, given that the gross energy content of all diets was about the same. This agrees with the results obtained by other authors in di¡erent species: Atlantic salmon (Menoyo et al. 2003; Bendiksen, Berg, Jobling, Arnesen & Masoval 2003), turbot (Regost, Arzel, Robin, Rosenlund & Kaushik 2003), grouper (Luo, Liu, Mai, Tian, Liu & Tan 2004), Pike perch (Schulz, Knaus, Wirth & Rennert 2005) and cuneate drum (Wang, Guoj, Li & Bereau 2006). HSI is often used to indicate the condition and nutritional status of ¢sh, where an increasing HSI level is often associated with an increased intake of dietary lipids (Rueda-jasso, Conceicao, Dias, De Coen, Gomes, Rees, Soares, Dinis & Sorgeloos 2004). The in£uence of the dietary FA composition on the muscle FA pro¢le observed in this study is consistent with observations already established in the literature by several authors (Rosenlund, Obach, Sandberg, Standal & Tveit 2001; Caballero et al. 2002; Piedecausa, Mazo¤n, Garc|¤ a Garc|¤ a & HernaŁndez 2007). The higher muscle contents of SFA in the PFAD and CPO treatments compared with the control can also be attributed to the dietary SFA content of PFAD and CPO, both of which contained a high level of palmitic acid (16:0). On the other hand, the comparatively higher or lower muscle SFA content than the level in the diets is consistent with the suggestion of Menoyo et al. (2003) that ¢sh are able to regulate the fate of FA formed endogenously or assimilated from the diet. The similar muscle content of DHA recorded in all treatments, in spite of the di¡erences in the levels detected in the diets, may suggest that C. striatus ¢ngerling is able to chain elongate and desaturate short-chain PUFA to long-chain HUFA as was speculated previously (Aliyu-Paiko et al. 2009). On the other hand, it also implies that DHAwas preferentially accumulated. Almaida-pagaŁn, HernaŁndez, Garc|¤ a Garc|¤ a, Madrid, De Costa and Mendiola (2007) suggested that dietary 22:6n-3 would, for the most part, be preserved and rapidly stored in tissue membranes. Substituting FO with CPO and PFAD in the diet of C. striatus did not signi¢cantly alter the activities of the hepatic lipogenic enzymes monitored. This is consistent with the recorded observations of Regost et al. (2003) in gilthead seabream, Menoyo, Izquierdo, Robaina, Gines, Lopez-bote and Bautista (2004) in turbot and Torstensen, Froyland and Lie (2004) in Atlantic salmon, where the use of di¡erent VO to partially substitute FO did not lead to signi¢cant di¡erences in the activities of lipogenic enzymes. Richard, Mourente, Kaushik and Corraze (2006) speculated that such an observation (which they also recorded in European sea bass) was probably because the differences in the dietary contents of EPA, DHA and linolenic acid or the mixture of VO between the treatments were not enough to induce modi¢cations in lipogenesis. The de novo synthesis of long-chain FA from acelylCoA and malonyl-CoA is catalysed by FAS, a multifunctional enzyme complex, whose activity is correlated with the rate of endogenous FA synthesis (Bazin & Ferre 2001). The relatively lower activity of FAS recorded in the present trial could be due to the low concentration of the enzyme, which, according to Volpe and Vagelos (1976), is highly sensitive to both nutritional and hormonal regulations. This is likely the result of the adequate amount of lipid supplied in the diet. In studies with rainbow trout, Henderson and Sargent (1981) and Brauge, Corraze and Me¤dale (1995) separately concluded that FA synthesis was inhibited by a dietary fat level above 50 g kg  1. This may explain why the inhibitory e¡ects of dietary EPA, DHA and LA on the activities of FAS as reported by Alvarez, Diez, Lopez-bote, Gallego and Bautista (2000) were not observed in the current study, because dietary lipids in all treatments were included above 60 g kg  1. Additionally, Iritani, Ikeda, Fukuda and Katsurada (1984) reported that the activities of the preliminary enzymes in lipogenesis were extremely low in poikilotherms (¢sh and frog). The activity of CCE (also called ATP-citrate lyase) recorded was also low, but was twice that of FAS. In analysing body proximate composition, Houlihan, Mathers and Foster (1993) explained that the retention of ingested proteins suggested reduced degradation and, thus, low turnover rates in growing animals, as observed in the present trial. In conclusion, the present feeding trial has clearly demonstrated that C. striatus ¢ngerling tolerates the substitution of dietary FO with CPO and PFAD © 2011 Blackwell Publishing Ltd, Aquaculture Research, 43, 767–776 773 Substituting FO with CPO and PFAD in C. striatus diet M Aliyu-Paiko & R Hashim without any negative e¡ects on growth performance and feed e⁄ciency. The experiment also demonstrated no signi¢cant (P40.05) e¡ect on biological indices (HSI, VSI and CY) and the activity of lipogenic enzymes (FAS, CCE and ME) when dietary FO was substituted with CPO and PFAD and fed to C. striatus ¢ngerlings for a period of 12 weeks. 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