Scholarly article on topic 'Growth performance, feed utilization, body and fatty acid composition of Nile tilapia  (Oreochromis niloticus ) fed diets containing elevated levels of palm oil'

Growth performance, feed utilization, body and fatty acid composition of Nile tilapia (Oreochromis niloticus ) fed diets containing elevated levels of palm oil Academic research paper on "Animal and dairy science"

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Abstract of research paper on Animal and dairy science, author of scientific article — Christian Larbi Ayisi, Jinliang Zhao, Emmanuel Joseph Rupia

Abstract This study was conducted to evaluate effects of dietary palm oil levels on growth performance, feed utilization, body composition and serum metabolites of Oreochromis niloticus. Five isonitrogenous diets, 32% crude protein with increasing palm oil levels of 0 (Control, CTRL), 2%, 4%, 6% and 8% were used as the major lipid source for the trial. The results showed that greatest weight gain, specific growth rate, and protein efficiency ratio occurred at 6% dietary palm oil level. Dietary palm oil levels significantly (P < 0.05) affected lipid, moisture, ash and crude protein contents in muscle and whole body. Serum triglycerides, cholesterol and total protein were significantly affected by elevated palm oil levels. Furthermore, total saturates, total n-3 poly unsaturated fatty acids (PUFA), total n-6 PUFA as well as DHA/EPA in muscle were significantly affected by different levels of palm oil. Fish fed the 6% palm oil level recorded the highest level of whole body docosahexaenoic acid (DHA), which was significantly higher than that of the control. The nutritional quality of O. niloticus was altered by different palm oil levels. The present study suggests that 6% dietary palm oil is the best feed formulation for tilapia, Oreochromis niloticus.

Academic research paper on topic "Growth performance, feed utilization, body and fatty acid composition of Nile tilapia (Oreochromis niloticus ) fed diets containing elevated levels of palm oil"

Aquaculture and Fisheries xxx (2017) 1—11

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Aquaculture and Fisheries

journal homepage: www.keaipublishing.com/en/journals/aquaculture-and-fisheries/

Growth performance, feed utilization, body and fatty acid composition of Nile tilapia (Oreochromis niloticus) fed diets containing elevated levels of palm oil

Christian Larbi Ayisi a, Jinliang Zhao a' *, Emmanuel Joseph Rupia b

a Key Laboratory of Freshwater Fishery Germplasm Resources, Ministry of Agriculture, Shanghai Ocean University, Shanghai 201306, China b Key Laboratory of Exploration and Utilization of Aquatic Genetic Resources, Ministry of Education, Shanghai Ocean University, Shanghai 201306, China

ARTICLE INFO ABSTRACT

This study was conducted to evaluate effects of dietary palm oil levels on growth performance, feed utilization, body composition and serum metabolites of Oreochromis niloticus. Five isonitrogenous diets, 32% crude protein with increasing palm oil levels of 0 (Control, CTRL), 2%, 4%, 6% and 8% were used as the major lipid source for the trial. The results showed that greatest weight gain, specific growth rate, and protein efficiency ratio occurred at 6% dietary palm oil level. Dietary palm oil levels significantly (P < 0.05) affected lipid, moisture, ash and crude protein contents in muscle and whole body. Serum triglycerides, cholesterol and total protein were significantly affected by elevated palm oil levels. Furthermore, total saturates, total n-3 poly unsaturated fatty acids (PUFA), total n-6 PUFA as well as DHA/ EPA in muscle were significantly affected by different levels of palm oil. Fish fed the 6% palm oil level recorded the highest level of whole body docosahexaenoic acid (DHA), which was significantly higher than that of the control. The nutritional quality of O. niloticus was altered by different palm oil levels. The present study suggests that 6% dietary palm oil is the best feed formulation for tilapia, Oreochromis niloticus.

© 2017 Shanghai Ocean University. Published by Elsevier B.V. This is an open access article under the CC

BY license (http://creativecommons.org/licenses/by/4.0/).

Article history: Received 8 April 2016 Available online xxx

Keywords:

Serum metabolites

Growth

Feed utilization Palm oil

Oreochromis niloticus

1. Introduction

The ability of tilapia, Oreochromis niloticus (L.) to tolerate environmental stress, reproduce easily, grow at a fast rate coupled with a high market demand for the species has made it an important fish for aquaculture production (El-Sayed, 2006). Tilapia are omnivorous and feed on a variety of foods ranging from zooplankton to fish food (Olaosebikan & Raji, 1998), and means they can use vegetable oil when it is supplied in the feed (Sala & Ballesteros, 1997).

Dietary lipids serve as a source of fatty acids, phospholipids, sterols and fat-soluble vitamins necessary for proper functioning of physiological processes and to some extent maintenance of biological structure and the function of cell membranes (Ghanawei, Roy, Davis, & Saoud, 2011). An excess of dietary lipids however, can cause a decrease in feed consumption and reduce the utilization of other nutrients leading to reduced growth rates (Ghanawei et al., 2011) and increased fat deposition (Hillestad & Johnsen,

* Corresponding author. 999 Huchenghuan Road, Shanghai 201306, China. E-mail address: jlzhao@shou.edu.cn (J. Zhao).

1994). Therefore, the requirements for lipid and their use for farmed fish should be considered when formulating their diets. In common with other warm water fish, tilapia need higher amounts of n-6 fatty acids as compared to n-3 fatty acids for maximal growth (Aziza, Awadin, & Orma, 2013) and they require approximately 1% of n-6 fatty acids in their diets (Bazaoglu & Bilguven, 2012).

Palm oil (PO) is currently the second most abundant vegetable oil in the world (Ochang, Fagbenro, & Adebayo, 2007b) with the global production of vegetable oil such as palm oil projected to increase by over 30% by 2020 due to the increase in the supply from developing countries. PO is the world's most produced oil and it accounts for about 28.3% and 23.4% of the global production of vegetable and all commercial oils and fats respectively. PO could be an alternative to fish oil in aquafeeds (Ng, Koh, & Zubir, et al., 2006) and it is high in palmitic acid (16:0) and oleic acid (18:1 n-9), which corresponds respectively, to 43.5% and 36.6% of the total lipid fatty acid composition, although it contains relatively low amounts of linoleic acid 18:2 n-6 (9.1%) (NRC, 1993). The fatty acid composition makes PO a good potential source of oil for O. niloticus diets since it provides sufficient energy for growth. Also, palm oil positively affects growth and flesh quality when catfish are fed high levels of

http://dx.doi.org/10.1016/j.aaf.2017.02.001

2468-550X/© 2017 Shanghai Ocean University. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

palm oil in their diets (Lim, Boey, & Ng, 2001).

Babalola and Apata (2012) documented that PO can effectively replace fish oil (FO) in the diet of catfish without compromising growth and feed efficiency. Use of PO in the diets of fish such as tilapia, catfish, Atlantic salmon and rainbow trout has been investigated with emphasis on growth and feed utilization efficiency, and changes in tissue FA composition and FA metabolism, giving promising results for; tilapias (Bahurmiz & Ng, 2007; Ng & Wang, 2011; Ochang et al., 2007b), catfish (Babalola & Apata, 2012; Ochang, Fagbenro, & Adebayo, 2007a) and Larmichthys crocea (Duan et al., 2014), Lates calcarifer (Wan, Wan, David, & Kathryn, 2013), Lateolabrax japonicas (Yu-Zhe et al., 2012) and Mystus nemurus (Ng, Tee, & Boey, 2000). Despite these studies, it is still unclear how PO affects serum metabolites as well as PUFA damage and health lipid indices. The aim of this study was therefore to evaluate the effects of elevated dietary palm oil levels on the growth performance, body composition, muscle and whole body fatty acids, serum metabolites as well as PUFA damage and health lipid indices of O. niloticus.

2. Materials and methods

21. Experimental diets

Five isonitrogenous diets of 32% crude protein (CP) with elevated palm oil levels ranging from 0% (CTRL) to 8% were prepared for the experiment. The diet formulation affected lipid and carbohydrate contents as shown in Table 1. Fish meal, soybean meal and rapeseed meal were used as the protein source while palm oil and soybean phospholipids were used as the source of lipid. All dry ingredients (fish meal, soybean meal, rapeseed meal, wheat meal, mineral mix and vitamin mix) were mixed using the progressive enlargement method (Zhou, Zhou, Chi, Yang, & Liu, 2007). The experimental diets were prepared by mixing the dry ingredients with palm oil or soybean phospholipid and distilled water (10%— 12% w/w) in a Hobart mixer and the resulting moist dough pelleted using a meat mincer with a 1-mm die. The 1-mm diameter pelleted

diets were wet extruded and dried in an oven, sealed in plastic bags and stored at room temperature until use. The fatty acid composition of experimental diets is presented in Table 2.

2.2. Experimental procedures

Four hundred and fifty fingerlings of O. niloticus (11.02 ± 0.02 g) obtained from the Tilapia Germplasm Station of Shanghai Ocean University, China. Prior to trials, fish were transported to the aquarium facilities at Shanghai Ocean University, China and acclimated for one week. Fish were fed commercial diets containing 30% crude protein twice daily to apparent satiety for six days. At the beginning of the trial, fingerlings were starved for 24 h, weighed, and randomly distributed into 15 (150 cm x 60 cm x 40 cm) rectangular fibreglass tanks with 25 fish per tank and the water was

Table 2

Fatty acid (FA) composition (% total FA) of palm oil (PO) and experimental diets.

Fatty acid Palm oil levels

0%(CTRL) 2% 4% 6% 8% PO

C14:0 1.32 0.97 0.86 0.85 0.84 0.95

C16:0 17.03 26.78 31.10 31.49 32.83 44.67

C16:1 n-9 1.80 1.13 0.79 0.67 0.56 ND

C18:0 2.78 4.00 4.35 4.87 5.06 2.21

C18:1 n-9 (cis) 20.18 29.44 33.88 36.24 37.09 35.95

C18:1 n-9 (trans) 6.20 4.04 2.55 2.50 1.96 2.02

C18:2 n-6 41.40 28.21 22.47 20.06 18.98 12.65

C18:3 n-3 4.52 2.79 1.81 1.65 1.47 0.66

C20:5 n-3 (EPA) 1.49 0.84 0.64 0.45 0.40 0.27

C22:6 n-3 (DHA) 3.24 1.75 1.16 1.15 0.77 ND

Total saturates 21.13 31.75 36.31 37.21 38.73 47.83

Total MUFA 28.18 34.61 37.22 39.41 39.61 37.97

Total n-3 (PUFA) 9.25 5.38 3.78 3.25 2.64 0.93

Total n-6 (PUFA) 41.40 28.21 22.47 20.06 18.98 12.65

DHA/EPA 2.17 2.08 1.76 2.55 1.92 N/A

n-3/n-6 0.22 0.19 0.17 0.16 0.13 0.07

DHA, decosahexaenoic acid: EPA, eicosapentaenoic acid: MUFA, monounsaturated fatty acid: PUFA, polyunsaturated fatty acid, ND: Not detected or less than 0.1, N/A: Not applicable.

Table 1

Ingredients and proximate composition of experiment diets (% dry weight).

Ingredient Palm oil levels

0%(Ctrl) 2% 4% 6% 8%

Fish mealc 5.00 5.00 5.00 5.00 5.00

Soybean mealc 30.00 30.00 30.00 30.00 30.00

Rapeseed mealc 30.00 30.00 30.00 30.00 30.00

Wheat mealc 31.80 29.80 27.80 25.80 23.80

Soybean phospholipasec 0.50 0.50 0.50 0.50 0.50

Palm oilc 0.00 2.00 4.00 6.00 8.00

Mineral mixd 0.50 0.50 0.50 0.50 0.50

Vitamin mixe 0.20 0.20 0.20 0.20 0.20

Ca(H2PO4)2a 2.00 2.00 2.00 2.00 2.00

Proximate composition

Crude protein 32.11 32.09 32.15 32.15 32.10

Crude lipid 2.09 4.18 6.06 8.03 10.09

Moisture 6.28 6.51 6.42 6.35 6.40

Ash 6.82 6.92 6.97 7.07 7.11

Carbohydratea 52.7 50.66 48.4 46.4 44.3

Estimated available Energy (kJ/g)b 1752.06 1798.85 1835.42 1878.64 1922.50

a Carbohydrates % = 100- (crude protein % + crude lipid % + moisture % + ash %).

b Gross energy estimated according to NRC (1993) using the values of 23.6, 39.5 and 17.2 kJ/g for crude protein, lipid and total carbohydrates respectively.

c Fish meal, soybean meal, wheat meal, soybean phospholipase, palm oil, vitamin premix, mineral mix and Ca(H2PO4)2 were supplied by Shanghai Jin Yuan Trade (Shanghai, China).

d Mineral mix (mg/kg dry diet): Cu (CuSO4), 2.0; Zn (ZnSO4), 34.4; Mn (MnSO4), 6.2; Fe (FeSCU), 21.1; I (Ca (1O3)2), 1.63; Se (Na2SeCh), 0.18; Co (CoCh), 0.24; Mg(MgSO4$H2O), 52.7.

e Vitamin premix (1U or mg/kg diet): vitamin A, 16000 1U; vitamin D, 8000 1U; vitamin K, 14.72; thiamin, 17.8; riboflavin, 48; pyridoxine, 29.52; cynocobalamine, 0.24, tocopherols acetate, 160; ascorbic acid (35%), 800; niacinamide, 79.2; calcium-d- pantothenate, 73.6; folic acid, 6.4; biotin, 0.64; inositol, 320; choline chloride, 1500; l-carnitine, 100.

C.L. Ayisi et al. / Aquaculture and Fisheries xxx (2017) 1—11

maintained at 210 L. The dissolved oxygen (DO) concentration, pH and water temperature were monitored on a daily basis using a YSI 556 instrument (YSI, Yellow Springs, Ohio). Ammonia-N and Nitrite-N were analysed spectrophotometrically on a weekly basis using standard methods (APHA, 1998). The water temperature monitored over the feeding trial ranged from 25.3 to 31.3 °C, pH from 7.21 to 7.64 and the dissolved oxygen from 6.62 to 7.94 mg/L. Ammonia and nitrite ranged from 0.02 to 0.40 and 0.000 to 0.023 respectively.

Each diet was randomly offered to replicate tanks of fish and as total of 15 tanks were used. During the experimental period of eight weeks, fish were offered the experimental diets and fed to satiety twice daily at 8:00 and 16:00. Fish were weighed using a Triple Beam Balance (700 series, Ohaus Florham park, N.J. 07932, USA) and the total length measured bi-weekly after a day of fasting.

2.3. Samples collection and chemical analysis

2.3.1. Samples collection

At the beginning of the feeding trial, ten fish were humanly killed and stored at — 20 °C for the determination of initial whole body proximate composition. At the end of the trial, all fish were weighed after starvation for 24 h to evacuate the digestive tract and reduce handling stress. The following fish performance indices were calculated:

Weight gain % = (FW - IW) /IW x 100 (1)

FW and IW for final weight and initial weight respectively.

Specific growth rate (SGR) (%), SGR (%) = (lnFW (g)-lnIW) (g)/T x 100 (2)

T for total number of culture days.

Feed intake (FI) is the total feed consumed (g)

during the 56 days trial. (3)

Feed conversion ratio (FCR), FCR = FI (g)/WG (g) (4)

Protein efficiency ratio (PER), PER = WG (g)/PI (g) (5)

WG and PI are for body weight gain and protein intake respectively.

The hepatosomatic index (HSI), HSI = [LW/BW] x 100 (6)

LW and BW stand for liver weight (g) and total body weight (g) respectively.

Viscerasomatic index (VSI), VSI = VW (g)/BW (g) (7)

VW is for viscera weight (g). VSI = [LW/BW] x 100

Survival rate (SR) %, SR = [TF/TFT] x 100 (8)

TF and TFT are for total number of fish stocked and total number of fish at termination point respectively.

Condition factor (K), K = Total BW (g)/TL (cm) 3 x 100 (9) TL is for total length.

2.3.2. Serum metabolites

At the end of the experiment, five fish per tank were sampled by dip-netting from the tanks and immediately anesthetized with 2-phenoxyethanol (1:300 V/V) in water taken from the experimental system. Blood were collected from the caudal vein using a 1-mL syringe with a 22-gauge x 3.8-cm (11/2 in) needle, from each fish. Serum samples were placed into 1.5-mL heparinized micro centrifuge tubes. After the blood had clotted, the tubes were centrifuged at 6000 r/min for 25 min at 4 ° C. Serum samples were removed from the tubes and stored at -20 °C until used for the analyses described below. Serum levels of cholesterol, total protein and triglycerides (i.e., as triacylglycerol) were measured from pooled serum using a biochemical analyzer (Mindary Chemistry Analyzer BS-200, Shenzhen, Guangdong Province, China).

2.3.3. Assays of water and protein content

The diets, whole body, and muscle were analyzed in triplicate for moisture and protein uing the methods defined by AOAC (1996): moisture was determined by oven drying at 105 °C to a constant weight. Crude protein was determined using the Kjeldahl method with Kjeltec Auto 2300 Analyzer after digestion with concentrated H2SO4. Water content was expressed as a percentage and protein were expressed as percentage of dry weight (% DW).

2.3.4. Analyses of lipid content and fatty acid composition Tissues (liver, whole body and muscle) were freeze-dried and

ground to a powder and then lipid content determined. Total lipid (TL) was extracted from the freeze-dried samples (0.2 g) with 10 mL chloroform—methanol (2:1, V/V), according to the method of (Folch, Lees, & Stanley, 1957). Fatty acid methyl esters (FAME) were prepared by transesterification with 0.4 M KOH-methanol. Rotary evaporation was performed at 40 °C, 90 r/min. 1.5 mL Benzene-Petroleum ether and 1.5 mL KOH-Methanol was then added and allowed to stand for 20 min. The above-mentioned miscible liquids was then transferred to the 10 mL test tube, diluted with distilled water to 10 mL and allowed to stand for 30 min 1.5 mL supernatant was transferred into the EP tube and centrifuged at 3000 r/min for 5min, then the supernatant was collected in a clean EP tube. The fatty acids were then detected by gas chromatograph (GC-7890A, USA). All measurements were performed in triplicate, the fatty acids content was expressed as % total FA.

2.3.5. PUFAs damage and health lipid indices

The Polyene index (PI) was used as a measure of PUFA damage (Lubis & Buckle, 1990) while the Thrombogenic (TI) and Athero-genic Index (IA) were used to assess the nutritional quality of the feed (Ulbricht & Southgate, 1991). These were calculated as follows:

PI: ((C20:5 + C22:6)/C16:0)

Atherogenic Index (IA) = (C12:0 + 4 (C14:0 + C16:0))/(Sum MUFAs + Sum PUFAs)

Thrombogenic Index (TI) = [(C14:0 + C16:0 + C18:0)/(0.5 x Sum MUFAs + 0.5 x Sum n6 PUFAs + 3 x Sum n-3 PUFAs + (n-3/n-6))]

2.3.6. Statistical analysis

All results are presented as mean ± standard error of the mean (SEM). Data were analyzed by one-way Analysis of Variances (ANOVA) to test the effects of the five experimental diets. Where significant differences were found (P < 0.05), a Tukey's test was used to compare all parts of a column and to rank the groups. Statistical analyses were made using GraphPad Prism 5.

Table 3

Growth performance, feed utilization, hepatosomatic and viscera somatic indices (mean ± SEM) for fish fed diets with different palm oil levels.

Parameter Palm oil levels

0% (CTRL) 2% 4% 6% 8%

IBW (g) 11.00 ± 0.06 11.01 ± 0.07 11.06 ± 0.07 11.01 ± 0.05 11.02 ± 0.05

FBW (g) 44.45 ± 1.04a 44.84 ± 0.90a 45.50 ± 1.24a 49.49 ± 0.70b 43.70 ± 0.99a

FBL (cm) 13.31 ± 0.53 13.28 ± 0.56 13.14 ± 0.09 13.50 ± 0.73 13.26 ± 0.56

WG (%) 304.09 ± 0.15ab 307.26 ± 0.09ab 311.39 ± 0.05b 346.97 ± 0.05c 296.55 ± 0.26a

SGR (%) 2.49 ± 0.02ab 2.50 ± 0.02ab 2.52 ± 0.01b 2.68 ± 0.00c 2.45 ± 0.02a

FI (g) 19.66 ± 0.61 19.62 ± 0.57 19.70 ± 0.61 20.12 ± 0.69 20.12 ± 0.63

FCR 1.12 ± 0.01b 1.10 ± 0.00b 1.09 ± 0.00b 1.00 ± 0.00a 1.16 ± 0.00c

PER 2.77 ± 0.02b 2.80 ± 0.01b 2.82 ± 0.00b 3.10 ± 0.01c 2.61 ± 0.02a

CF 1.88 ± 0.01 1.92 ± 0.05 2.00 ± 0.02 2.00 ± 0.02 1.87 ± 0.06

HIS 5.42 ± 0.32 5.40 ± 0.06 5.41 ± 0.12 5.54 ± 0.22 5.47 ± 0.22

VSI 10.27 ± 0.62 10.14 ± 0.13 10.25 ± 0.25 10.42 ± 0.33 10.17 ± 0.34

SURVIVAL (%) 100 ± 0.00 100 ± 0.00 98.67 ± 1.33 100 ± 0.00 100 ± 0.00

Data in the same row with different superscript are significantly different (P < 0.05).

1BW: initial body weight; 1BL: initial body length; FBW: final body weight; FBL: final body length; WG: weight gain; SGR: specific growth weight; F1: feed intake; FCR: feed conversion rate; PER: protein efficiency ratio; K: condition factor; HS1: hepatosomatic index; VS1: viscerasomatic index.

3. Results

3.1. Growth performance and feed utilization

The results showed that final body weight (FBW) and specific growth rate (SGR) were significantly affected by dietary PO levels (P > 0.05). The highest percentage weight gain (WG %), FBW and SGR among all groups occurred in the fish fed 6% PO and the gain was higher than the CTRL fish (Table 3). The feed conversion ratio (FCR) of fish fed diets containing 6% PO was significantly lower than the other groups. The protein efficiency ratio (PER) increased with elevated dietary PO levels up to 6%. However, feed intake (F1), condition factor (CF), Viscerasomatic index (VSI) and hepatosomatic index (HS1) were not significantly different between fish from the different treatments. Survival rate was not affected by palm oil levels.

3.2. Body composition

The effects of elevated dietary PO level on fish whole body, muscle composition and liver lipids at the end of the 8-week feeding trial are presented in Table 4. Crude protein content of fish whole body showed a trend of decreasing values with elevated PO levels. Fish fed the CTRL diet recorded the highest protein content, which was significantly higher than all of the treatments.

The crude lipid content of the fish whole body increased as the dietary PO levels were increased. Fish fed 6% and 8% PO had a significantly higher lipid content than fish fed the CTRL diet whiles

the groups fed 2% and 4% were not significantly higher than the CTRL group. Moisture content of the whole body of fish fed the CTRL diet was not significantly lower than the fish fed 2% and 4% PO but it was significantly higher than fish fed 6% and 8% PO. The highest mean moisture content was observed in fish fed 4% PO with the group fed 8% PO containing the least moisture. The ash content of the whole body showed a trend of increasing levels with elevated PO levels, and was significantly different between groups. Fish fed 8% PO had the highest ash content and was significantly higher than the CTRL group. The groups fed 2%, 4% and 6% PO levels had a similar ash content to the group fed the CTRL diet.

In fish muscle, the elevated PO levels in feed had a significant effect on the crude protein, crude lipid, moisture, ash and the muscle of O. niloticus. The lipid content in the muscle tended to increase with elevated PO levels. Fish fed the CTRL diet recorded lipid levels that were no lower than the fish fed 2% PO levels but higher than those fed 4% PO. Also, fish fed 6% and 8% PO levels had lipid contents significantly higher than the fish fed the CTRL diet. The moisture content of fish fed 8% PO were significantly different from fish fed 4% and 6% but were not different from fish fed 0% and 2% PO. Ash content of the muscle of the fish tended to increase with increasing PO level. Ash content of fish fed 8% PO was significantly higher than fish fed the CTRL and 2% PO but was not significantly different from those of fish fed the 4% PO and 6% PO.

In fish liver, the crude lipid content was significantly affected by the PO and fish fed 8% PO had the highest content of lipid. Fish fed diets containing 2%, 4%, 6% as well as 8% PO had a significantly higher crude lipid content than fish fed the CTRL diet.

Table 4

Major nutrients composition (%DM) of moisture, crude lipid, protein and ash composition of whole body muscle and liver in Nile tilapia fed diets of elevated PO level. Palm oil levels

Initial

0% (CTRL)

Whole Body (%) Crude protein Crude lipid Moisture Ash

Muscle (%) Crude protein Crude lipid Moisture Ash

Liver (%) Crude lipid

57.26 ± 0.17 15.06 ± 0.06 64.95 ± 2.7 4.52 ± 0.02

61.58 ± 0.24c 12.73 ± 0.11a 69.63 ± 0.89ab 4.74 ± 0.02a

83.53 ± 0.07 3.58 ± 0.01a 75.66 ± 0.24al 2.36 ± 0.02a

12.70 ± 0.03a

0.32b 0.01a

59.67 12.89 72.61 ± 1.41b 4.79 ± 0.04ab

84.23 ± 0.26a 3.53 ± 0.10a 75.72 ± 0.24ac 2.40 ± 0.03ab

15.14 ± 0.05

0.33b 0.33a

59.32 12.67 73.75 ± 1.18b 4.81 ± 0.01ab

82.91 ± 0.38a 3.72 ± 0.05a 74.74 ± 0.37al 2.51 ± 0.02abc

16.32 ± 0.34c

0.05a 0.41b

57.74 15.65 69.48 ± 1.05al 4.85 ± 0.02ab

81.82 ± 0.75D 4.28 ± 0.01b 74.54 ± 0.20b 2.57 ± 0.06bc

16.99 ± 0.13c

0.64a 0.05b

57.20 16.60 66.31 ± 0.9a 4.92 ± 0.02b

83.48 ± 0.20ab 4.48 ± 0.01b 76.16 ± 0.12c 2.64 ± 0.03c

17.46 ± 0.17c

Mean ± SEM, in the same row with different superscript are significantly different (P < 0.05).

3.3. Serum metabolites

Serum cholesterol, total protein and triglycerides are shown in Fig. 1. The concentration of triglycerides, cholesterol and total protein was significantly (P > 0.05) affected by elevated dietary PO. The concentration of cholesterol increased with increasing PO levels with the highest mean recorded in fish fed 8% PO. Fish fed 6% and 8% PO recorded cholesterol levels significantly higher than the control group whiles those fed 2% and 4% PO were similar to the control. Total protein also increased with increasing levels of PO in the diet. Fish fed diets containing 4%, 6% and 8% PO were significantly higher than those fed the control diet. However, fish fed 2% PO were similar to the control group. Similarly, triglycerides increased with increasing dietary PO. Fish fed 8% PO recorded the highest level of triglycerides ian plasma and was significantly higher (P < 0.05) than that of the control group. Fish fed 2%, 4% and 6% PO did not differ from the control.

3.4. Whole body fatty acids

The fatty acid composition of the body is shown in Table 5. The major fatty acids (above 5%) reported in the whole body were palmitic acid (16:0), palmitoleic acid (16:1), stearic acid (18:0), oleic acid (18:1 n-9) and stearidonic acid (18:4 n-3). The 16:0 content of fish fed 8% PO was higher than all other treatments and the value increased with increasing PO in the diets. The 18:0 in fish fed the CTRL diet was significantly higher than the treatment groups, which decreased with increasing POs. 18:4 n-3 in CTRL fish was significantly higher than the treatments. Both arachidonic acid (ARA) and eicosapentaenoic acid (EPA) were not significantly

modified by dietary PO. The docosahexaenoic acid (DHA) recorded for fish fed 6% PO was significantly higher than in all other treatments. Total saturates (SFA) in fish fed 2%, 4%, 6% and 8% PO were not significantly different but were significantly higher than fish fed CTRL diet. Whole body MUFA in fish was not affected by dietary PO. Total PUFA from the n-6 series recorded for fish fed the CTRL diet was significantly higher than all other treatments and decreased with increasing PO. Fish fed 6% PO had the highest DHA/EPA ratio and was significantly higher than fish fed the CTRL diet. However, fish fed diets containing 2%, 4% and 8% PO were not significantly different from fish fed the CTRL diet. The n-3/n-6 ratio was not significantly different.

3.5. Muscle fatty acids

The fatty acid composition of muscle is shown in Table 6. The major fatty acids (above 5%) reported in the muscle were 16:0,16:1, 18:0,18:1(n-9) as well as 18:4(n-3). Fish fed diets containing 2%, 4%, 6% as well as 8% PO had significantly higher fatty acids than those fed the CTRL diet with respect to 16:0. There was an increase in 16:0 content with elevated PO level and those fed 8% PO recording the highest value. The 16:0 content of fish fed the CTRL diet and 2%, 4% and 6% PO was significantly higher than those fed 8% PO. Similarly, the 18:0 values decreased with elevated PO levels. Fish fed the control diet recorded had significantly higher 18:0 values significantly higher than all other groups. Fish fed 8% PO had significantly lower 18:1 n-9 in muscle than those fed the CTRL diet. Fish fed 6% PO had the highest levels of 18:4 n-3 in muscle and was significantly higher than the CTRL group. ARA in muscle was not affected by dietary PO. Fish fed the CTRL diets and 2% PO diet had similar

Table 5

Fatty acid (% total FA) composition of whole body of tilapia fed diets containing different lipid levels for 8 weeks.

Fatty acids Palm oil levels

0% (CTRL) 2% 4% 6% 8%

C14:0 4.61 ± 0.12c 3.15 ± 0.03b 2.75 ± 0.08a 2.58 ± 0.03a 2.17 ± 0.07a

C14:1 0.81 ± 0.02a 0.96 ± 0.07a 0.99 ± 0.10a 1.55 ± 0.21b 1.60 ± 0.09b

C16:0 29.52 ± 0.28c 35.87 ± 0.77a 37.50 ± 0.79ab 38.13 ± 0.00ab 39.26 ± 0.49b

C16:1 6.27 ± 0.19b 5.60 ± 0.02ab 5.5 ± 0.09a 5.40 ± 0.12b 4.64 ± 0.04c

C18:0 9.16 ± 0.07d 9.07 ± 0.12a 8.68 ± 0.09ab 8.65 ± 0.02c 8.58 ± 0.01bc

C18:1 n-9 28.98 ± 0.4a 27.11 ± 0.77ab 27.70 ± 0.50ab 25.82 ± 0.02b 26.08 ± 0.12ab

C18:2 n-6 3.28 ± 0.13a 3.70 ± 0.12b 2.51 ± 0.03a 2.55 ± 0.02a 2.34 ± 0.05a

C18:3 n-3 1.05 ± 0.01ab 0.90 ± 0.04a 0.99 ± 0.00ab 1.09 ± 0.02b 0.98 ± 0.03ab

C18:4 n-3 8.10 ± 0.08d 7.47 ± 0.03c 6.76 ± 0.07b 6.3 ± 0.19b 5.43 ± 0.04a

C20:0 2.96 ± 0.18b 2.20 ± 0.01a 2.17 ± 0.03a 2.35 ± 0.12a 2.20 ± 0.00a

C20:4 n-6(ARA) 1.44 ± 0.04 1.24 ± 0.01 1.18 ± 0.15 1.19 ± 0.15 1.01 ± 0.02

C20:5 n-3 (EPA) 0.56 ± 0.01 0.55 ± 0.01 0.54 ± 0.04 0.51 ± 0.01 0.48 ± 0.00

C22:0 1.65 ± 0.03 1.39 ± 0.05 1.04 ± 0.07 0.92 ± 0.12 1.60 ± 0.28

C22:6 n-3(DHA) 1.61 ± 0.05a 1.72 ± 0.03a 1.63 ± 0.00a 1.80 ± 0.03b 1.59 ± 0.05a

Total saturates 47.90 ± 0.33a 51.68 ± 0.89b 52.14 ± 0.72b 52.63 ± 0.01b 53.81 ± 0.27b

Total MUFA 36.06 ± 0.23 33.47 ± 0.86 34.19 ± 0.71 32.77 ± 0.71 32.32 ± 0.26

Totaln-3 PUFA 11.32 ± 0.00c 10.64 ± 0.10bc 9.92 ± 0.35b 9.70 ± 0.12b 8.48 ± 0.02a

Totaln-6 PUFA 4.72 ± 0.08b 3.94 ± 0.13a 3.70 ± 0.11a 3.74 ± 0.12a 3.35 ± 0.03a

DHA/EPA 2.86 ± 0.03a 3.12 ± 0.11a 3.03 ± 0.25a 3.52 ± 0.03b 3.30 ± 0.06ab

n-3/n-6 2.39 ± 0.04 2.71 ± 0.11 2.68 ± 0.01 2.59 ± 0.05 2.53 ± 0.03

PUFAs/SFAs 1.08 ± 0.01d 0.92 ± 0.01c 0.91 ± 0.00c 0.87 ± 0.02b 0.82 ± 0.01a

PUFAs/n-3 1.41 ± 0.00 1.37 ± 0.03 1.37 ± 0.00 1.38 ± 0.01 1.39 ± 0.00

IA 1.09 ± 0.02a 1.22 ± 0.01ab 1.19 ± 0.02ab 1.25 ± 0.05ab 1.28 ± 0.05b

IT 0.74 ± 0.01a 0.90 ± 0.01b 0.95 ± 0.00bc 0.98 ± 0.01c 1.09 ± 0.02d

PI 0.07 ± 0.00c 0.06 ± 0.00b 0.05 ± 0.00ab 0.06 ± 0.00b 0.05 ± 0.00a

Mean ± SEM, in the same row with different superscript are significantly different (P < 0.05). DHA, docosahexaenoic acid: EPA, eicosapentaenoic acid: MUFA, monounsaturated fatty acid: PUFA, polyunsaturated fatty acid.

muscle EPA and were significantly higher than those fed 4%, 6% and 8% PO. DHA in muscle of fish fed 2%, 6% and 8% PO was significantly higher than the CTRL. Fish fed the CTRL diet had significantly less saturated lipids in muscle than those fed 4% PO, although fish fed 2%, 6% and 8% PO were not significantly different from the CTRL group. Fish fed the CTRL diet had significantly higher total MUFA

than fish fed diets containing PO. Total PUFA of the n-3 series in muscle of fish fed the CTRL diet was significantly higher than the fish fed diet with 2%, 4% and 6% PO. The DHA/EPA ratio was significantly modified by elevated PO with higher levels in fish fed 8% PO and lowest levels in fish fed the CTRL diet (2.07). The n-3/n-6 ratio was not significantly different between groups.

Table 6

Fatty acid (% total FA) composition of muscle of tilapia fed diets containing different lipid levels for 8 weeks.

Fatty acids Palm oil levels

0% (CTRL) 2% 4% 6% 8%

C14:0 4.06 ± 0.04c 3.55 ± 0.02b 3.50 ± 0.14b 2.63 ± 0.02c 2.57 ± 0.01c

C14:1 0.50 ± 0.04a 0.62 ± 0.00a 0.68 ± 0.05a 0.76 ± 0.04ab 1.03 ± 0.10b

C16:0 26.10 ± 0.13a 28.28 ± 0.33b 30.61 ± 0.12c 31.91 ± 0.12d 32.97 ± 0.02e

C16:1 5.84 ± 0.08b 5.23 ± 0.06ab 5.21 ± 0.00ab 5.02 ± 0.07ab 4.91 ± 0.02a

C18:0 10.47 ± 0.07d 9.87 ± 0.01c 9.39 ± 0.03b 9.07 ± 0.01a 8.97 ± 0.02a

C18:1 n-9 33.14 ± 0.10b 32.54 ± 0.17ab 31.74 ± 0.37ab 31.66 ± 0.37ab 31.32 ± 0.24a

C18:2 n-6 3.80 ± 0.04e 3.57 ± 0.04d 3.37 ± 0.00c 3.19 ± 0.00b 2.90 ± 0.01a

C18:3 n-3 0.70 ± 0.03a 0.70 ± 0.01a 0.73 ± 0.01a 1.00 ± 0.02b 1.31 ± 0.05c

C18:4 n-3 8.22 ± 0.02b 8.07 ± 0.05ab 8.00 ± 0.04ab 7.80 ± 0.02a 7.83 ± 0.14ab

C20:0 2.39 ± 0.06b 2.79 ± 0.02c 2.46 ± 0.03b 1.71 ± 0.01a 1.68 ± 0.00a

C20:4 n-6(ARA) 1.48 ± 0.03 1.35 ± 0.01 1.31 ± 0.07 1.24 ± 0.00 1.23 ± 0.08

C20:5 n-3 (EPA) 0.66 ± 0.00c 0.59 ± 0.01abc 0.55 ± 0.01ab 0.53 ± 0.01ab 0.49 ± 0.01a

C22:0 1.93 ± 0.15b 1.71 ± 0.01b 1.63 ± 0.02b 1.16 ± 0.01a 1.15 ± 0.00a

C22:6 n-3(DHA) 1.37 ± 0.01a 1.55 ± 0.00b 1.38 ± 0.01a 1.81 ± 0.00c 2.03 ± 0.03c

Total saturates 45.95 ± 0.53a 47.20 ± 0.20ab 47.59 ± 0.20b 46.43 ± 0.30ab 47.34 ± 0.11ab

Total MUFA 39.48 ± 0.03d 38.39 ± 0.09c 37.63 ± 0.03b 37.44 ± 0.03ab 37.26 ± 0.02a

Totaln-3 PUFA 9.58 ± 0.03b 9.36 ± 0.06a 9.28 ± 0.01a 9.33 ± 0.01a 9.66 ± 0.02b

Totaln-6 PUFA 6.65 ± 0.05b 6.47 ± 0.01b 6.06 ± 0.02a 6.24 ± 0.04a 6.16 ± 0.01a

DHA/EPA 2.07 ± 0.03a 2.62 ± 0.01b 2.50 ± 0.05a 3.41 ± 0.03c 4.14 ± 0.04d

n-3/n-6 1.44 ± 0.02 1.45 ± 0.03 1.53 ± 0.03 1.49 ± 0.03 1.56 ± 0.01

PUFAs/SFAs 1.21 ± 0.00b 1.14 ± 0.02ab 1.11 ± 0.00a 1.14 ± 0.02ab 1.12 ± 0.02a

PUFAs/n-3 1.69 ± 0.00b 1.69 ± 0.00b 1.65 ± 0.00a 1.66 ± 0.00ab 1.63 ± 0.01a

IA 0.76 ± 0.03a 0.96 ± 0.01b 1.01 ± 0.02b 0.97 ± 0.01b 0.98 ± 0.01b

IT 0.76 ± 0.01a 0.80 ± 0.01a 0.84 ± 0.01b 0.84 ± 0.02b 0.85 ± 0.00b

PI 0.07 ± 0.00b 0.07 ± 0.00b 0.06 ± 0.00a 0.07 ± 0.00b 0.07 ± 0.00b

Mean ± SEM, in the same row with different superscript are significantly different (P < 0.05). DHA, docosahexaenoic acid: EPA, eicosapentaenoic acid: MUFA, monounsaturated fatty acid: PUFA, polyunsaturated fatty acid.

3.6. Health lipid indices and nutritional quality

Health lipid indices and nutritional quality of O. niloticus fed feed with PO are shown in Figs. 2—6. Different PO levels affected the Polyene index (PI) value significantly in both whole body and muscle with fish fed the CTRL diet recording the highest value in the whole body (0.07 ± 0.00) (Fig. 2). The index of thrombogenicity (IT) values were significantly different among treatments in both whole body and muscle (Fig. 3). The index of atherogenicity (1A) in both whole body and muscle was not significantly different between treatments (Fig. 4). The PUFAs/n-3 ratio in muscle was significantly different in fish fed different PO diets but was not modified in the whole body (Fig. 5). The PUFAs/SFAs ratio was significantly modified by different PO levels in both whole body and muscle, with fish fed CTRL diets recording the highest values (1.08 and 1.21 for whole body and muscle respectively) Fig. 6.

4. Discussion

The present study revealed that different dietary PO levels affected FBW, WG, SGR and FCR of O. niloticus. This result is in agreement with previous reports for Nile tilapia (Ochang et al., 2007b) where dietary lipid levels affected the growth index of fish. In contrast, in the tropical bagrid catfish Mytus (Ng et al., 2000) and Clarias gariepinus (Ochang et al., 2007a) the FBW, WG, SGR and FCR were not affected by dietary PO levels. Fish fed 6% palm oil levels had the best FBW, WG, SGR and FCR but a further increase of dietary palm oil level resulted in a decline in FBW, WG, SGR and

FCR. Normally, fish have an optimum dietary lipid requirement and above the optimum dietary lipid has the tendency to cause a reduction in growth (Du et al., 2005). In this study, a growth reduction was observed in fish fed diets with 8% PO. Higher level of lipids might compromise with ability of the fish to digest, absorb food and also interfere with metabolic activities (Wang et al., 2005). In this study PER was significantly affected by elevated PO levels, although this differs from what was observed by El —Kasheif et al. (2011) (Nile tilapia). It was expected that the highest PER would occur at 8% dietary PO rather than 6% PO as occurred because utilization of protein by most aquaculture fish can be improved by increasing dietary energy levels (Cho & Kaushik, 1985).

Feed intake increased with increasing PO levels, although previously it was observed that feed intake is reduced with diets rich in lipids (Wang et al., 2005). This notwithstanding, Du et al. (2005) reported that feed intake seems to adjust to protein intake instead of energy intake. The present results are in agreement with this assertion that feed intake adjusts to protein intake instead of energy intake. The results of this present study revealed that HS1 was not significantly affected by elevated dietary PO as previously reported (Chatzifotis et al., 2010; Ghanawei et al., 2011). This is in contrast with other studies in which H1S was higher when diets contained a high lipid content (Lopez, Torres, Durazo, Drawbridge, & Bureau, 2006; Ochang et al., 2007b) such as occurs with white sea bass fingerling. This trend was also observed in Japanese sea bass (Luo, Xu, Teng, Ding, & Yan, 2010) and cobia (Wang et al., 2005) and presumably highlights species differences but also the lipid sources and protein content of the diets.

C.L. Ayisi et al. / Aquaculture and Fisheries xxx (2017) 1—11

Fig. 4. Mean Index of atherogenicity level of O. niloticus fed diets with 0% CTRL, 2%, 4%, 6% and 8% palm oil levels. (A) Whole body (B) Muscle. Figures with different superscript are significantly different (P < 0.05).

Fig. 5. Mean PUFAs/n-3 ratio of O. niloticus fed diets with 0% CTRL, 2%, 4%, 6% and 8% palm oil levels. (A) Whole body (B) Muscle. Figures with different superscript are significantly different (P < 0.05).

Fig. 6. Mean PUFAs/SFAs ratio of O. niloticus fed diets with 0% CTRL, 2%, 4%, 6% and 8% palm oil levels. (A) Whole body (B) Muscle. Figures with different superscript are significantly different (P < 0.05).

1n the present study a higher lipid content was reported in the fish fed higher lipid (PO) levels and this is comparable to reports by Martin, Valente, and Lall (2007) and dietary lipid levels have previously been correlated with an increase in whole body lipid content (Song, An, Zhu, Li, & Wang, 2009). 1n the present study, the results showed that CP levels of the whole body of fish fed elevated PO levels were significantly different and decreased with increasing dietary PO level. This was also documented in other fish species

(Song et al., 2009; Wang et al., 2005). However, El —Kasheif et al. (2011) (Oreochromis niloticus) indicated that the crude protein content of the whole body increased with increasing dietary lipid. The reason why the O. niloticus fed high dietary PO had low CP levels may be due to dilution of CP with lipid (Page & Andrews, 1973). Also, the lipid level in the whole body increased with elevated PO levels confirming the results obtained by El —Kasheif et al. (2011) on O. niloticus. There was an increase in hepatic lipid

C.L. Ayisi et al. / Aquaculture and Fisheries xxx (2017) 1—11

levels with increasing dietary PO. Higher lipid in the liver occurred in fish fed higher dietary PO and suggests that high lipid intake may cause lipid deposition in the liver and visceral cavity (Song et al., 2009).

Cholesterol and total protein concentration in O. niloticus serum were significantly affected by dietary PO levels. Cholesterol concentrations are known to vary depending on the nutritional status of fish (Regost et al., 2001). The increase in cholesterol content with increasing dietary PO is similar to the trend reported by El —Kasheif et al. (2011) (Nile tilapia). The range in the concentration of cholesterol with dietary PO is in agreement with previous results in GIFT Tilapia (Wang et al., 2011) and grass carp (Du et al., 2005). Contrary to the present studies results was the concentration of serum cholesterol in meagre (Argyrosomus regius) juveniles (Chatzifotis et al., 2010). The inconsistency of the results reported by different scientists could be possibly due to the difference in species and nutritional status of the fish (Regost et al., 2001). Similarly, the total protein concentration values of the present study were affected by elevated dietary PO levels which were much lower than the values reported for juvenile meagre (Chatzifotis et al., 2010) and Atlantic salmon (Hamre et al., 2004). The concentration values of triglycerides reported in this study were not significantly affected by dietary PO and the values were similar to that of grass carp (Du et al., 2005) in which significant differences were observed. The values were also similar to the values reported by (Chatzifotis et al., 2010) for juvenile meagre. Both serum triglycerides and protein increased with increasing PO levels. This is contrary to the reports by Kikuchi, Furuta, Iwata, Onuki, & Noguchi (2009) who reported a trend for increasing serum triglycerides with decreasing protein levels. The trend in the present study is therefore considered as a sign of increasing health condition of the fish. This trend again is in contrast to the undesirable effects of increasing dietary lipids on triglycerides and protein levels as documented for Japanese flounder (Kikuchi, Sugita, & Watanabe, 2000). According to Wang et al. (2011) internal and external environments affects the serum biochemical characteristics, with these environments indirectly reflecting the metabolic health status of the fish and can therefore be used to give an indication whether the fish is sick or not. According to Wang et al. (2014) cholesterol and triglycerides are the main parts of lipids. Cholesterol usually increases or decreases with increasing or decreasing triglycerides levels, respectively (He, 2000, pp. 95—123). In the present study, the concentration values of both cholesterol and triglycerides increased with increasing PO levels which is in agreement to the assertion made by Wang et al. (2014). Also, Kotaro, Takeshi, Nakahiro, Kazue, and Tamo (2009) documented that the serum triglycerides of tiger puffer increased as dietary lipid levels increased. This is in agreement to the result of this present study where the concentration values of triglycerides increased with elevated dietary palm oil levels. Again there was an increase in both Triglycerides and Cholesterol concentrations with increasing dietary PO levels. This is an indication of a more active endogenous lipid transport in response to the higher dietary lipid/palm oil levels (Du et al., 2005).

The higher amount of 16:0 and 18:1(n-9) in the whole body and muscle is linked to the abundance of these fatty acids in PO (Olsen, Henderson, & McAndrew, 1990), since the fatty acid composition of fish depends on the dietary fatty acid profiles (Luo et al., 2010). In the whole body and muscle, the amount of EPA was much less than DHA. This is because EPA is easily oxidized, hence less is retained relative to DHA (Luo et al., 2010; Wang et al., 2005). We found that the values of n-6 decreased with increasing dietary PO levels, which is in line with the decrease in the concentrations of n-6 HUFA in fish fed high levels of vegetable oil (Kaushik, 2004). The n-6 series reported in the present study for the whole muscle were reduced significantly as compared to that of the feed. This is possibly due to

the fact that n-6 is an intermediate in pathways of desaturation and elongation of fatty acids (Teoh, Turchini, & Ng, 2011).

The docosahexaenoic acid (DHA) in the whole body recorded for fish fed 6% PO level was significantly higher than all other treatments, and that in muscle recorded for fish fed 2%, 4% and 8% PO levels were significantly higher than the CTRL, while DHA in diet decreased with increasing PO level. This selective retention of DHA could be related to the higher beta-oxidation of eicosapentaenoic acid (EPA) compared to DHA (Madsen, Froyland, Dyroy, Helland, & Berge, 1998) due to the complex catabolism of this fatty acid (Bell et al., 2001). This probably indicates a selective catabolism of EPA over DHA when dietary levels decrease, possibly to meet the requirement for tissue membrane composition and function. The higher values of DHA recorded in fish fed PO shows that tilapia has the ability to bio-convert EPA and most SFAs to maintain levels of LC-PUFAs (Teoh et al., 2011) when FO is replaced with PO. The PUFAs/SFAs ratio was affected by different levels of dietary PO with a decreasing PUFAs/SFAs ratio with increasing PO levels in the whole body of the fish. The value in all the fish of the PUFAs/SFAs ratio was higher than of 0.45, which is considered beneficial for human health (FAO/WHO, 1994), since it may protect from coronary heart diseases (Simat, Bogdanovic, Poljak, & Petricevic, 2015). Similarly, n-3/n-6 ratio is a good index for assessing nutritional value of fish since higher ratios are crucial for preventing coronary heart disease and reduces the risk of cancer (Kinsella, Broughton, & Whelan, 1990).

In the present study, elevated palm oil levels did not affect n-3/ n-6 ratio in either whole body or muscle. Therefore, PO levels have a limited effect on the nutritional value of the fish. Notably, there was a higher level of n-3/n-6 ratio in muscle than in the diets. This could indicate that a threshold level in the muscle was obtained, probably adjusted to a narrowly defined physiological level (Turchini et al., 2003). The index of atherogenicity (IA) indicating the relationship between the sum of the main saturated fatty acids and that of the main classes of unsaturated, the former being considered pro-atherogenic and the latter anti atherogenic was higher with PO (Ghaeni, Ghahfarokhi, & Zaheri, 2013; Ulbricht & Southgate, 1991). The index of thrombogenicity (IT) indicates the tendency to form clots in the blood vessels (Garaffo, Vassallo-Agius, Nengas, Lembo, & Rando, 2011). Index of atherogenicity and index of thrombogenicity takes into account the different effects that a single fatty acid might have on human health and in particular on the probability of increasing the incidence of pathogenic phenomena, such as atheroma and/or thrombus formation (Garaffo et al., 2011). This study revealed that increasing PO levels resulted in increased IT levels in both WB and Muscle with a similar trend recorded for IA in both WB and Muscle. These values recorded for IA are similar (0.9—1.09) to those found in tilapia fed diets supplemented with soybean oil for a period of 90 days (Tonial et al., 2014). Polyene index(PI)is used to assess the damage of PUFA with reduced PI a sign of PUFA being decomposed or damaged (Simat et al., 2015). This study revealed that PI seemed to have decreased when PO levels were increased. This is an indication that the PUFA in the whole body had been damaged.

5. Conclusion

In conclusion, the results obtained in the present study showed that PO levels affects growth performance, feed utilization and body composition of O. niloticus. The higher WG, FBW and SGR, all occurred in fish fed 6% lipid level. The results therefore suggest that 6% PO is the best for maximum weight gain, SGR and FCR. Again our results show that the whole body and muscle fatty acid composition of fish were affected by the amount of PO provided in the diet. The fatty acids reported in the present study reflect that of the

C.L. Ayisi et al. / Aquaculture and Fisheries xxx (2017) 1—11

experimental diet since the major of fatty acids reported in both the liver and the whole body were related to the level of PO in the diets. Furthermore, the PO levels affected serum metabolites, cholesterol, triglycerides and total protein in the fish. From the nutritional quality perspective, it is evident from the results that feeding tilapia with different levels of PO. Palm oil has the tendency to influence the quality of fish produced in aquaculture and their nutritional quality indices.

Acknowledgements

This work was financially supported by the China Agriculture Research System (CARS-49) and Shanghai Collaborate Innovation Center for Aquatic Animal Genetics and Breeding (ZF1206) to J L Zhao.

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