Evaluation of skate meal and sablefish viscera meal as fish meal

Aquaculture Research, 2012, 1–9

doi:10.1111/j.1365-2109.2012.03151.x

Evaluation of skate meal and sablefish viscera meal as fish meal replacement in diets for Pacific threadfin (Polydactylus sexfilis) Zhi Yong Ju1, Ian P Forster2, Dong-Fang Deng1, Warren G Dominy1, Scott Smiley3 & Peter J Bechtel4 1

Aquatic Feeds and Nutrition Department, Oceanic Institute, Waimanalo, USA

2

Fisheries and Oceans Canada, West Vancouver, Canada

3

Fishery Industrial Technology Center, School of Fisheries & Ocean Sciences, University of Alaska Fairbanks, Kodiak,

USA 4

USDA-ARS, Subarctic Agricultural Research Unit, University of Alaska, Fairbanks, USA

Correspondence: Z Y Ju, Aquatic Feeds and Nutrition Department, Oceanic Institute, 41-202 Kalanianaole Hwy, Waimanalo, HI 96795, USA. E-mail: [email protected]

Abstract

Introduction

The objectives of this study were to investigate the nutritional value of skate meal and sablefish viscera meal from Alaskan fishery processing and to ascertain their suitability as replacements for pollock fishmeal in diets for Pacific threadfin (Polydactylus sexfilis). Test diets were made by replacing 50% or 100% protein from fish meal in the control diet with skate or sablefish viscera meal. The test diets and a commercial feed were each assigned to four tanks with eight juvenile fish (9.7 g) per tank in an indoor flow-through culture system. After 6 weeks, Pacific threadfin fed skate meal-50% and -100% substituted diets exhibited similar weight gains (374%; 369%) and feed conversion ratios (1.29; 1.27) as those fed the control diet (345%; 1.30 respectively) (P > 0.05). In contrast, Pacific threadfin fed the sablefish viscera meal-50% substituted diet exhibited significantly lower weight gain (112%) than fish fed the control diets (P < 0.05). The fish fed the control diet and skate meal substituted diets also achieved significantly higher (P < 0.05) weight gain than those fed the commercial feed (288%). In conclusion, skate meal can fully replace the commercial fishmeal in a Pacific threadfin diet without adversely effecting growth performance.

Pacific threadfin (Polydactylus sexfilis), known in Hawaii as moi, is a popular fish species first cultured in significant quantities at the Oceanic Institute (Ostrowski, Iwai, Monahan, Unger, Dagdagan, Murakawa, Schievell & Pigao 1996), and is now grown in sea cages off the coast of Hawaii. Little is known of the nutritional requirements of Pacific threadfin (Deng, Dominy, Ju, Koshio, Murashige & Wilson 2010). Commercial production of this carnivorous finfish relies on commercial feed formulated with a high level of fishmeal. Commercial fishmeals, such as anchovy meal, menhaden meal or pollock meal, are expensive and in short supply due to expansion of aquaculture (Hardy 2006); the sustainable production of cultured threadfin for the expanding market requires seeking alternative protein ingredients for dietary replacements of fishmeal. Carnivorous fish require substantial quantities of high quality protein ingredients in their diet (Hardy 1996). It is important that ingredients under consideration as replacements for fishmeal be tested for suitability. Many alternative protein sources have been identified as potentially suitable ingredients for fish feeds, including plant proteins (Elangovan & Shim 2000; Venou, Alexis, Fountoulaki & Haralabous 2006; Hardy 2010), terrestrial animal proteins (Williams, Barlow, Rodgers & Ruscoe 2003), fish byproduct meals (Sugiura, Babbitt, Dong & Hardy 2000) and single-cell proteins (Oliva-Teles &

Keywords: replacement, fishmeal, skate meal, sablefish viscera meal, Pacific threadfin, growth © 2012 Blackwell Publishing Ltd

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Replacement of fishmeal with fishery byproducts Z Y Ju et al.

Goncalves 2001; McLean & Craig 2004; Zerai, Fitzsimmons, Collier & Duff 2008). However, full replacement of fishmeal in carnivorous fish diets, with no loss of growth or feed efficiency, has not been established with any of the various protein ingredients tested. Reigh and Ellis (1992) found that soybean meal could replace up to 50% fish meal in the diet of red drum without affecting its weight gain. Refstie, Storebakken, Baeverfjord and Roem (2001) also found that moderate replacement of fishmeal by commercial soy protein products was acceptable in diets for Atlantic salmon. Meilahn, Davis and Arnold (1996) tested fish analogue (animal byproduct blend) to replace 50% fishmeal with minimal influence on growth and feed consumption in red drum; whereas 75% replacement caused poor growth performance. Li, Wang, Hardy and Gatlin (2004), confirmed by Whiteman and Gatlin (2005), found that mixed bycatch meals from shrimp trawling could replace 50% of the protein in red drum diets, whereas red salmon head meal could replace only 25%, with no significant reduction in weight gain or feed efficiency. Appropriate use of local or regional protein byproducts could also reduce feed costs by saving on transportation expenses, and has the potential to enhance environmental and economic sustainability. Although landings from the Alaska fishing industry are dominated by Alaska pollock (Theragra chalcogramma) and Pacific salmon (Oncorhynchus sp.), post-harvest processing of other species also generates significant quantities of byproducts. Among these are the skates, including several species in the genera Bathyraja and Raja and sablefish, also known as black cod (Anoplopoma fimbria). Annual harvests of skates of all species since 2003 have ranged from 12 800 t to 8 800 t in Alaska, and from 12 200 t to 16 200 t in the United States. Sablefish harvests since 2003 have ranged from 12 200 t to 18 100 t annually in Alaska, and from 19 400 t to 24 000 t in the U.S. Crapo et al. (1993) estimated total byproduct from skates to be 73% (everything but wings) and for black cod up to 65% (everything but skinless fillets) of the initial weight, leaving approximately 3500 t of these dried materials as byproducts in Alaska annually. These byproducts likely have similar nutritional qualities as the fishmeals currently used in aquafeeds, including: highly digestible, well-balanced proteins, significant quantities of lipids with long chain, highly unsaturated n-3 fatty acids (HUFA), as well as taurine and other growth factors, while

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being low in anti-nutritional factors (e.g., phytase) and carbohydrates. However, little information is published for these byproducts of fish processing in Alaska. The objectives of this research were to investigate the nutritional values of dried meals made from Alaskan skate and sablefish viscera and to ascertain their suitability as replacements for commercial fishmeal in diets for Pacific threadfin. Materials and methods Materials Skate meal (SM) and sablefish viscera meal (SVM) were prepared at the University of Alaska–Fishery Industrial Technology Center (Kodiak, AK, USA). Fresh sablefish (A. fimbria) viscera and long nose skate (Raja rhina) byproducts (body after wings removed) were obtained from commercial processing plants in Alaska and immediately stored at 40°C until thawed for drying. The byproducts were thawed, then ground (Biro grinder 7540; Biro Manufacturing, Marble, OH, USA) and dried over night in a convection oven (Enviropak computer operated dryer with a MP 2500 controller) at 71°C. Meals were mixed with ethoxyquin (MP Biochemicals, LLC) to 150 ppm and stored at 40°C until being shipped to the Oceanic Institute (Waimanalo, HI, USA). Commercial pollock meal (PM) was purchased from Kodiak Fishmeal Company (Kodiak). All fishmeals were analysed for proximate composition, energy and minerals (Table 1), amino acid (Table 2) and fatty acid (Table 3) profiles, as described below. The essential amino acid index (EAAI) of the three meals were also calculated and compared with the Pacific threadfin muscle (Table 2). Organic solvents, including acetone, acetonitrile, methanol and hexane were purchased from Fisher Scientific (Boston, MA, USA). Analytical chemicals, triethylamine was obtained from Fisher Scientific; phenyl isothiocyanate and boron trifluoride-methanol were obtained from Sigma–Aldrich Chemical (St. Louis, MO, USA). Amino acid standards and fatty acid standards were purchased from Sigma– Aldrich Chemical and Nu-Chek Prep (462 standard; Elysian, MN, USA) respectively. Diet formulation and preparation A diet containing PM at 430 g kg1 served as a control diet (Table 4). Three experimental diets © 2012 Blackwell Publishing Ltd, Aquaculture Research, 1–9



Table 1 Proximate and mineral content and gross energy value (on dry matter basis) of skate meal, sablefish viscera meal and commercial fishmeal (pollock meal)

Ingredients

Proximate (g kg1) Dry Matter Crude Protein Crude lipid Ash Gross Energy (kJ g1) Major-Minerals (g kg1) Phosphorus Potassium Calcium Magnesium Sodium Trace-Minerals (ppm) Boron Copper Iron Manganese Zinc

Pollock meal

Skate meal

Sablefish viscera meal

915.4 727.4 86.2 174.7 20.3

976.8 896.4 17.6 83.3 19.6

706.7 519.0 295.6 99.5 26.0

38.2 7.4 64.7 2.1 13.3

18.1 10.0 25.2 1.1 25.2

11.5 9.9 2.7 3.3 14.4

4 3 292 9 64

3 3 73 5 27

3 8 301 4 81

were formulated by adding SM to replace 50% (SM-50%) or 100% (SM-100%) of the PM protein, and by adding SVM to replace 50% (SVM-50%) of the PM protein in the control diet (Table 4). Table 2 Amino acid content (g kg1, on dry matter basis) of skate meal, sablefish viscera meal, pollock meal and Pacific threadfin muscle, and their essential amino acid index (EAAI) based on amino acid profile of Pacific threadfin muscle

Wheat starch and menhaden fish oil were adjusted to balance the diets. The experimental diets were prepared according to methods described in Forster, Dominy, Obaldo and Tacon (2003). A commercial fish feed (Marine Grower, Skretting North America, Vancouver, Canada), nominally containing crude protein (CP) at 500 g kg1, was included as a commercial control diet. The proximate composition and gross energy of the diets are determined as described below (Table 4).

Feeding trial An indoor fish culture facility used in this experiment was located indoors at the Oceanic Institute facility at Waimanalo, HI, USA and was equipped with 20 black high density polyethylene tanks, supplied with 115 L seawater. The tanks were supplied with aeration and seawater from a well at 4 L min1. Juvenile Pacific threadfin were obtained from the Oceanic Institute hatchery and were fed with a commercial feed (Marine Grower) before starting the feeding trial. Each tank was stocked with eight juvenile Pacific threadfin (9.60–9.84 g; Table 5). Each diet was assigned to four tanks using a completely random design. All fish were fed to satiation by hand daily at 08:00, 12:00 and 18:00 hours

Amino acids

Pollock meal

Skate meal


Pacific threadfin muscle

Ala Asp+ASN Cys Glu+Gln Gly Pro Ser Tyr Non Essential AA Arg His Ile Leu Lys Met Phe Thr Val Essential AA Total EAAI Taurine

50.4 40.3 5.7 82.1 65.7 45.2 30.9 25.8 346.0 59.8 17.9 36.4 58.1 55.4 14.6 35.4 34.4 39.9 351.8 697.8 0.97 12.9

92.7 69.2 15.3 109.9 71.5 27.5 38.0 26.5 450.5 66.1 22.3 34.6 66.6 64.3 16.3 34.6 53.1 37.2 395.1 845.5 0.93 20.4

46.7 38.0 6.2 75.5 40.9 7.5 20.7 12.0 247.5 45.5 12.4 20.1 33.4 28.5 9.4 18.2 40.6 30.6 238.6 486.1 0.90 23.9

48.4 75.5 6.7 106.1 41.9 23.0 34.7 27.9 364.3 66.4 17.3 32.1 66.4 62.6 15.8 33.8 36.0 30.6 360.9 725.2 1.00 14.3

© 2012 Blackwell Publishing Ltd, Aquaculture Research, 1–9

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Fatty acids

Code

Tetradecanoic Hexadecanoic Hexadecenoic Octadecanoic Gondic Octadecenoic Octadecadienoic Octadecatetraenoic Eicosanoic Eicosenoic Eicosatetraenoic Eicosapentaenoate Docosapentanoic Docosahexaenoate Identified Unidentified Total fatty acids Saturated FAA Unsaturated FAA

C14:0 C16:0 C16:1n-7 C18:0 C18:1n-9 C18:1n-7 C18:2n-6 C18:4n-3 C20:0 C20:1n-9 C20:4n-6 C20:5n-3 C22:5n-3 C22:6n-3


Pollock meal

Skate meal


2.08 20.55 3.40 4.72 14.76 6.25 0.95 0.60 2.13 1.61 0.39 13.62 1.19 16.08 89.85 10.15 100.00 29.78 60.08

2.14 27.07 4.79 6.72 12.13 5.96 1.37 0.40 1.16 0.98 2.85 7.66 1.88 9.76 87.44 12.56 100.00 37.77 49.67

3.28 12.40 5.52 2.79 21.46 7.50 1.53 1.09 0.10 5.15 0.71 10.56 1.47 8.39 84.03 15.97 100.00 18.91 65.12

Table 3 Fatty acid profiles* (% of total fatty acid) of skate meal, sablefish viscera meal and pollock meal

*Values of less than 1% in the three meals for 13 fatty acids are not included in the table.

for 6 weeks, beginning with a feed rate of 3% of total biomass. On subsequent days, feed amounts were adjusted according to the presence or absence of residual pellets 20 min after the last feeding of the previous day. Feed adjustments increased or decreased the following days ration at a rate of 5% of the total daily ration, providing the fish with a slight excess. Following the last feeding and residual feed observations each day, faeces and all uneaten feed were removed by siphoning. Water temperature (26.0 ± 1.0°C) was monitored daily, and dissolved oxygen concentration (6.30– 6.85 mg L1) was measured weekly in each aquarium using a YSI Model 57 oxygen meter (Yellow Springs Instrument Company, Yellow Springs, OH, USA). Once a week, tank water pH (7.66–7.86) was measured using an Accumet AP61 pH meter (Fisher Scientific, Pittsburgh, PA, USA), and salinity (32.48–32.84 g L1) was measured using a temperature-compensated refractometer (Aquatic Eco-Systems, Apopka, FL, USA). Total ammonia nitrogen concentration was monitored by the automated analysis method of Solorzano (1969) using a Technicon Auto-Analyzer II (Technicon Industry Systems, Tarrytown, NY, USA). At the termination of the trial, all fish in each tank were counted, euthanized in excess anaesthetic (tricaine methanesulfonate, Argent, Red-

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mond, WA, USA), weighed and whole fillets sampled. The fillets were freeze-dried, finely ground (IKA Works, Wilmington, NC, USA) and stored at 80°C until analysis. Sample analysis The ingredients, diets and Pacific threadfin muscle samples were analysed according to AOAC (2000) methods. Moisture was determined by drying a representative 1–2 g sample in an oven with air circulation at 105°C for 16–24 h. Crude protein was determined from total N with a Kjeldahl apparatus using a multiplication factor of 6.25. Crude lipid (CL) was determined by ethyl-ether extraction with an Accelerated Solvent Extractor (Dionex Corporation, Bannockburn, IL, USA). Ash content was determined by incineration of a representative 1 g sample in a muffle furnace at 600°C for 6 h. Gross energy of the diets was determined by bomb calorimetry (Parr 1261 Calorimeter; Parr Inst., Moline, IL, USA). Mineral analysis was done by Agricultural Diagnostic Service Center at the University of Hawaii (Manoa, HI, USA) with an inductively coupled plasma atomic emission spectroscopy (Model Atomscan 16; Thermo Jarrel Ash, Franklin, MA, USA) after combustion at 600°C for 6 h, then dissolved in 3 N HCl (AOAC 2000). © 2012 Blackwell Publishing Ltd, Aquaculture Research, 1–9



Table 4 Formulations of control diet and experimental diets with skate meal (SM) or sablefish viscera meal (SVM) replacing 50% or 100% of fish meal protein in control diet

Ingredient (g kg1)

Control

Pollock meala 430.0 Sablefish viscera mealb 0.0 Skate mealb 0.0 Wheat starch 147.9 50.0 Vital wheat glutend 50.0 Brewers yeaste Soybean mealf 146.0 Squid Meal 34.0 20.0 Soy lecithin (63% phospholipids)g 80.0 Menhaden Oilh Vitamin premixi 4.0 0.6 Mineral premixi 1.2 Choline Chloride (60% Choline)j 0.8 Stay C (35% Vit C)j 22.0 Calcium phosphate (dibasic)k Sodium phosphate (dibasic)k 7.0 6.5 Magnesium phosphate (dibasic)k Total 1000.0 Proximate (g kg1 on dry matter basis) Moisture 951.9 Crude protein 468.74 Crude lipid 147.8 Ash 129.0 21.96 Gross energy (kJ g1)

SM-50%

SM-100%

SVM-50%

215.0 0.0 164.0 182.9 50.0 50.0 146.0 34.0 20.0 96.0 4.0 0.6 1.2 0.8 22.0 7.0 6.5 1000.0

0.0 0.0 327.0 217.9 50.0 50.0 146.0 34.0 20.0 113.0 4.0 0.6 1.2 0.8 22.0 7.0 6.5 1000.0

215.0 390.0 0.0 30.9 50.0 50.0 146.0 34.0 20.0 22.0 4.0 0.6 1.2 0.8 22.0 7.0 6.5 1000.0

950.1 455.62 146.5 108.7 22.09

941.2 475.44 146.2 89.7 22.53

939.9 482.18 196.9 115.0 23.98

a

Kodiak Fishmeal Company, Kodiak, Alaska. Sablefish viscera meal and skate,meal were provided by Kodiak, Alaska. d Hawaii Flour Mill, Honolulu, HI, USA. e Aventine Renewable Energy, Pekin, IL, USA. f Land-o-Lakes, Seattle, WA. g Central Soya Company, Fort Wayne, Indiana. h Omega Protein, Reedville, Virginia. i Research Products Company, Salina, KS, USA. The mineral/vitamin premix had the following composition (mg kg1): for Vitamin premix (kg1): Vitamin A, 3499070.4 IU; Vitamin D3, 799787.52 IU; Vitamin E, 39989.38 IU; Vitamin B12, 10.01 mg; Riboflavin, 14996.02 mg; Niacin, 39989.38 mg; Pantothenic acid, 39989.38 mg; Menadione, 14996.02 mg; Folic acid, 4000.26 mg; D-Biotin, 401.13 mg; Thiamin, 19994.69 mg; Pyridoxine, 19994.69 mg; Vitamin C, 125967.42 mg; Inositol, 149960.16 mg; and for Mineral premix (g kg1): ZnSO4·7H2O, 497.41; FeSO4·7H2O, 281.511; MnSO4·H2O, 58.023; CuSO4·5H2O, 148.09; CoCl2·6H2O, 3.805; KIO3, 3.179; CrCl3·6H2O, 6.438; Na2SeO4, 0.752; MoNa2O4·2H2O, 0.792. j DSM Nutritional Products, Parsippany, NJ, USA. k Sigma Aldrich, St. Louis, MO, USA. b

Fatty acids (FA) were analysed using a Varian 3800 gas chromatograph (Varian Analytical Instrument; GC, Walnut Creek, CA, USA) equipped with a flame ionization detector using an Omegawax 320 column (Supelco, Bellefonte, PA, USA), according to Ju, Forster and Dominy (2009). Amino acid (AA) profiles were analysed using a Beckman System Gold HPLC equipped with a UV detector and a 508 autosampler (Fullerton, CA, USA), as detailed in Ju, Forster, Conquest, Dominy, Kuo and Horgen (2008). The EAAI was calculated as the geometric mean of the essential AA scores


(Penaflorida 1989; Ju et al. 2008). All chemical analyses were conducted in duplicate. Calculation of growth performance and statistical analyses Data from the indoor feeding trial were used to calculate the feed conversion ratio (FCR), percent weight gain (PWG) and specific growth rate (SGR) as follows: PWGð%Þ ¼ ðW2 W1 Þ=W1 100;

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Table 5 Growth and feed conversion ratio of Pacific threadfin fed control diet, commercial feed, and the diets with skate meal (SM) or sablefish viscera meal (SVM) replacing 50% or 100% of fish meal proteins in control diet

Treatment

Initial weight (g)

Final weight (g)

Weight gain (% of initial weight)

Specific growth rate (% day1)

Feed conversion ratio

Control SM-50% SM-100% SVM-50% Commercial feed SEM

9.71a* 9.70a 9.67a 9.84a 9.60a 0.12

43.21c 45.98c 45.39c 20.87a 37.24b 1.40

345c 374c 369c 112a 288b 14.51

3.56c 3.71c 3.68c 1.79a 3.23b 0.16

1.30b 1.29b 1.27b 2.16c 1.07a 0.04

*Means within a column followed by different superscripts are significantly different (Tukey test, P < 0.05; n = 4).

SGRð%day1 Þ ¼ lnðW2 =W1 Þ=t 100; FCR ¼ Total feed intake=ðW2 W1 Þ Where the W2 is final weight (g) of fish, W1 is initial weight (g) and t is the number of days of growth. The data were analysed using one-way ANOVA. Where significant treatment effects were detected, mean separations were performed using Tukey’s significant difference test. All statistical analyses were carried out using computer software (SigmaStat for Windows v3.5, Systat Software, San Jose, CA, USA), with 5% error rate for significance. Results and discussion Growth trial of Pacific threadfin All fish survived until harvest. Fish fed the SM50% and SM-100% diets exhibited similar weight gain (374%; 369%), SGR (3.71% day1; 3.68% day1) and FCR (1.29; 1.27) as those fed the control diet (345%; 3.56% day1; 1.30) (Table 5), suggesting that SM could completely replace the fishmeal in Pacific threadfin diets without affecting growth. Also, the fish fed SM-substituted diets and the control diet both achieved significantly higher (P < 0.05) weight gain than the fish fed the commercial feed (288%). In contrast, Pacific threadfin fed the SVM-50% diet had much lower weight gain (112%) and higher FCR (2.16) than those fed the control diets (P < 0.01). The fish fed the commercial feed had better (lower) FCR (1.07) than fish fed all other diets (P < 0.05, Table 5). There are a number of potential reasons for the low nutritional quality of SVM, and although there is insufficient information to definitively assign a cause, some are more likely than others.

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For example, the amino acid balance of the SVM is unlikely to contribute to the poor nutritional quality, since the essential amino acids, except lysine, occur at or in excess of the level in the Pacific threadfin (when expressed as a proportion of total amino acids). Lysine at 5.86% of total amino acids is less than that of the muscle protein (8.63%), but still above the 5.1% requirement value for this species (Deng et al. 2010). Also, as noted, the EAAI values were high for all the products tested, including SVM (Table 2). The bioavailability of the amino acids in the various products is unknown, and if low in the SVM this could explain its low nutritional value. High dietary lipid or saturated fatty acids can reduce protein digestibility and reduce fish growth (Giri, Sahoo, Sahu & Mukhopadhyay 2000; Torstensen, Lie & Froyland 2000). The SVM diet contained high lipid which may have interfered with protein digestibility. Testing will be required to determine if bioavailability is an issue with SVM. Essential fatty acid deficiency is unlikely, as there is more n-3 HUFA in the SVM than in the SM. High dietary lipid content in the diets may reduce the pellet hardness and decrease pellet stability due to the reduction in the compression capacity of the press pellet machine. However, it was observed that the pellets of the SVM diet were strong enough to remain intact in water for sufficient duration for complete consumption, 5–10 min. The degree of fatty acid oxidation was not tested directly, but is unlikely to have been extensive, given the high level of n-3 HUFA and the absence of visual or olfactory indication. It is possible that some characteristic of the meal inhibited feed consumption, which would result in reduced growth. The higher FCR experienced by the fish fed the SVM diet is not easily explained by reduced © 2012 Blackwell Publishing Ltd, Aquaculture Research, 1–9



growth. The introduction of pathogenic material from the SVM is unlikely, given the general good health of the animals, other than the poor growth and FCR. Finally, the presence of biogenic amines (histamine, gizzerosine, etc.) or some other growth inhibitor could explain the poor performance of Pacific threadfin fed the diet containing SVM. The raw viscera was frozen (40°C) immediately after being obtained during processing and the material was dried at 71°C, which is considerably below the temperatures associated with biogenic amine generation. Forster, Babbitt and Smiley (2005) reported that fishmeals produced under different heating conditions had greatly differing nutritional

Table 6 Proximate composition of wet muscle weight of Pacific threadfin fed different diets for 6 weeks

Diet

Moisture %

Crude protein %

Crude lipid %

Ash %

Control SM-50% SM-100% SVM-50% Commercial feed SEM

77.77a* 77.38a 77.89a 78.05a 77.86a

17.07a 17.08a 16.95a 17.14a 17.09a

2.11bc 1.98b 2.22c 1.67a 1.97b

1.41a 1.43a 1.37a 1.43a 1.35a

9.33

1.42

0.44

0.32

*Means within a column followed by different superscripts are significantly different (Tukey test, P < 0.05; n = 4).

quality for Pacific threadfin. Additional testing is needed to ascertain whether or not SVM contains biogenic amines of known activity for fish. The results of this study found that the skate meal ingredient made from the Alaska fish processing industry can be applied as a reliable alternative protein ingredient to replace fish meals in feeds for Pacific threadfin production. Proximate composition and fatty acid profiles of Pacific threadfin muscle Fish in the different dietary treatments had similar fillet moisture, protein and ash contents (P > 0.05) but small differences (P < 0.05) in lipid contents were observed (Table 6). The SVM-50% diet for Pacific threadfin resulted in significantly (P < 0.05) lower CL content (16.7 g kg1) in muscle than the other diets (19.7–22.2 g kg1), although the SVM-50% diet had the highest CL of the five diets tested (Table 4), which might be due to small sizes of the fish from feeding of SVM-50% Diet, which might also be due to the small size of fish feeding on the SVM-50% Diet. Fish basically eats to its energy requirements therefore; feed intake could be lower for a diet with a higher energy content. This may result in poor growth as well as a low lipid content in the muscle of fish fed the SVM-50% diet. Pacific threadfin was observed to grow well with diets with medium lipid levels

Table 7 Fatty acid profile* (% of total fatty acid) of muscle of Pacific threadfin fed control diet, commercial feed, and the diets with skate meal (SM) or sablefish viscera meal (SVM) replacing 50% or 100% of fish meal proteins in control diet

Fatty acids Tetradecanoic Hexadecanoic Hexadecenoic Octadecanoic Gondic Octadecenoic Octadecadienoic Eicosanoic Eicosenoic Eicosapentaenoate Docosahexaenoate Identified Unidentified Total fatty acids Saturated FA Unsaturated FA

Code C14:0 C16:0 C16:1n-7 C18:0 C18:1n-9 C18:1n-7 C18:2n-6 C20:0 C20:1n-9 C20:5n-3 C22:6n-3

Control

SM-50%

SM-100%

SVM-50%

Commercial feed

6.36 30.75 8.82 12.10 14.72 6.92 2.33 1.35 1.02 1.42 1.99 90.95 9.05 100.00 52.01 38.93

7.16 33.38 9.69 11.57 12.80 6.13 2.28 0.91 1.44 1.30 1.80 91.68 8.32 100.00 54.62 37.06

8.29 33.55 10.57 11.56 11.43 5.94 2.05 0.95 1.53 1.17 1.74 91.59 8.41 100.00 55.47 36.13

4.21 26.07 5.94 9.09 21.53 8.30 4.17 0.68 2.24 1.77 2.56 89.21 10.79 100.00 40.50 48.71

5.84 31.75 7.15 11.29 20.40 6.03 1.79 1.50 1.72 1.75 1.61 92.97 7.03 100.00 51.09 41.88

*Values of less than 1% in all muscle samples for 13 fatty acids are not included in the table.


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(10–15%) (Deng, Ju, Dominy, Murashige & Wilson 2011), and the lipid content (19%) in SVM-50% might be too high for digestion of the finfish and will warrant additional research. The CP contents of the muscle tissue in the various treatments were about 8–10 times that of the CL levels (Table 6), indicating the high protein and low fat composition of Pacific threadfin muscle. The fatty acids (FA), docosahexaenoic (DHA, 22:6n-3), eicosapentaenoic (EPA, 22:5n-3) and arachidonic acid (ArA 20:4n-6), are important or essential nutrients for marine fish (Castell, Bell, Tocher & Sargent 1994; Sargent, Bell, McEvoy, Tocher & Estevez 1999; Tocher 2003). The FA profile of Pacific threadfin muscle was influenced by the profile of the test diets (Table 7). DHA contents varied from 1.61% to 2.56%, EPA varied from 1.17% to 1.77%, and ArA varied from 0.20% to 0.52% of total FA content in the muscle samples. The SVM-50% diet produced the highest amounts of the three essential FA and total unsaturated FA, whereas SM-100% diet was lowest among the five diet treatment groups of Pacific threadfin muscle. Diet has been shown to affect the lipid level and fatty acid profile of fish, including tilapia (Ng, Lim & Sidek 2003), sea bass (Lanari, Poli, Ballestrazzi, Lupi, D’Agaro & Mecatti 1999), catfish (Mohammad & Jafri 1995) and Atlantic salmon (Bell, Tocher, Henderson, Dick & Crampton 2003). Conclusion Skate meal is rich in protein with a balanced essential AA profile relative to Pacific threadfin muscle and can fully replace the commercial fishmeal in Pacific threadfin diets without adverse effect on growth performance. The replacement of the commercial fishmeal by the skate meal did not affect the composition of Pacific threadfin muscle in this study. SVM replacing 50% pollock meal did not support growth equal to that of pollock meal. The replacement of the fishmeal by sablefish viscera meal resulted in increased values for DHA and EPA content in the Pacific threadfin muscle. Acknowledgments Support for this study from the U.S. Department of Agriculture, Agricultural Research Service (USDAARS), Grant No 59-5320-2-712, and the University of Alaska Fairbanks, Sub-award Agreement

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