A feeding trial was conducted to evaluate if gamma-irradiation or fermentation couldincrease the inclusion level of soybean meal (SBM) in the diet of Japanese seabass Lateo-labrax japonicas. A basal diet was formulated to contain 320 g/kg fish meal. In the test diets,25, 50 and 75% of the fish meal in the basal diet was respectively replaced by SBM in threeforms (untreated, fermented or gamma-ray irradiated). Juvenile fish (13.0 ± 0.1 g) werefed with the test diets for 8 weeks. SBM treatment affected weight gain, feed intake, feedconversion ratio (FCR), phosphorus retention efficiency (PRE), phosphorus wastes output,body contents of crude protein and phosphorus, while the level of fish meal replacementaffected weight gain, apparent digestibility coefficient (ADC) of protein, FCR, nitrogen reten-tion efficiency (NRE), PRE, nitrogen wastes output (NW), condition factor, body contents ofmoisture and phosphorus. Weight gain, ADC of protein and NRE decreased, whereas FCRand NW increased with increasing fish meal replacement by SBM, irrespective of SBM treat-ments. No significant differences were found in the weight gain and NRE between fish fedthe basal diet and the diets with 25% fish meal replacement by untreated or fermented SBM,or between fish fed the basal diet and the diet with 50% fish meal replacement by irradiatedSBM. At the end of the feeding trial, no significant differences were found in hepatosomaticindex, viscerasomatic index and proximate body composition between fish fed the basaldiet and the diets with fish meal replaced by untreated, fermented or irradiated SBM. Thisstudy indicates that the use of gamma irradiation provides a novel approach to enhancethe level of fish meal replacement by SBM. Fish meal in the diet for Japanese seabass canbe reduced to 160 g/kg when the gamma-irradiated SBM is used as a fish meal substitute.
Fish meal is a limiting and expensive source of protein that has been used at high levels in fish diets (Tacon and Metian,008). Replacement of fish meal in fish diet with proteins sourced from terrestrial plants is important for sustainable
a Crude protein, crude lipid and ash are expressed on a dry matter basis (n = 2).
aquaculture (Gatlin et al., 2007). Among the terrestrial plant ingredients used for fish diet formulation, soy proteins havebeen recognized as the most promising plant protein source due to its sufficient supply, low price, balanced amino acidsand highly digestible protein (Hardy, 1999; Gatlin et al., 2007). The potential of using soy proteins as a substitute of dietaryfish meal has been evaluated in fish in various studies (McGoogan and Gatlin, 1997; Takagi et al., 2001; Tantikitti et al.,2005). Replacement of fish meal with soy proteins at high levels in fish diets results in decline of growth in many fish species(Boonyaratpalin et al., 1998; Wang et al., 2006; Kikuchi and Furuta, 2009). However, some studies reported that more than90% of the fish meal can be replaced with soy proteins in the diets for rainbow trout (Kaushik et al., 1995), cobia (Salze et al.,2010) and red sea bream (Kader et al., 2012). The determinant mechanisms affecting the replacement of fish meal by soyproteins remain to be tested (Gatlin et al., 2007).
Japanese seabass, Lateolabrax japonicas, is a carnivorous fish species widely cultured in Asia (Wang et al., 2013). When acommercial soybean meal (SBM) was used as a fish meal substitute, the level of dietary fish meal for Japanese seabass canbe reduced to 320 g/kg (Li et al., 2012) or 160 g/kg (Zhang et al., 2014). The presence of anti-nutritional factors (ANFs), suchas protease inhibitors, lectins, phytates, glucosinolates, saponins and tannins has been considered a factor limiting the levelof raw soybean inclusion in fish diet (Francis et al., 2001). Technical removal of ANFs is essential to increase the level of fishmeal replacement by SBM in fish diet (Gatlin et al., 2007). Various processing techniques, such as soaking, dehulling, cookingand fermentation, are used to neutralize the ANFs in plant ingredients (Egounlety and Aworh, 2003; Refstie et al., 2005;Yamamoto et al., 2010). Fish meal replacement by defatted (Catacutan and Pagador, 2004; Tantikitti et al., 2005), dehulled(Choi et al., 2004), heated (Peres et al., 2003), solvent-extracted (Boonyaratpalin et al., 1998) and fermented (Refstie et al.,2005; Yamamoto et al., 2010) SBM in fish diet has been well documented. Besides these techniques, irradiation has beendemonstrated an approach to improve the utilization of plant ingredients by terrestrial animals (DeRouchey et al., 2003;Mani and Chandra, 2003; Ghanbari et al., 2012). To our best knowledge, the effect of gamma-ray irradiation on the suitabilityof plant ingredients as a fish meal substitute in fish diets has been rarely studied. The objective of the present study aimed toevaluate the effect of fermentation and gamma-irradiation on SBM as a fish meal substitute in the diet for Japanese seabass,with emphasis on exploring a novel approach to increase the level of SBM inclusion in fish diet.
2. Materials and methods
2.1. Feed ingredients and test diets
Poultry by-product meal was supplied by the Hong Kong office of National Rendered Association. Fish meal (anchovymeal), SBM (defatted) and other feed ingredients were purchased from Haihuang Feed Company (Hangzhou, China). TheSBM was irradiated with 60Co gamma-ray at 100 kGy (Zhejiang Yin-Du Irradiation Technology Co., Ltd., Hangzhou, China), orfermented with Lactobacillus spp., Saccharomyces spp. and Bacillus spp. at 40 ◦C (Shanghai Yuan-Yao Biological TechnologyCo., Ltd., Shanghai, China). The proximate composition of feed ingredients is shown in Table 1. Amino acid profiles of fish
meal, poultry by-product meal, SBM with different processing treatment are shown in Table 2.
A 3 × 3 layout included three SBM treatments (untreated, fermented or irradiated) and three levels of fish meal replace-ment (25, 50 and 75%) from a basal diet containing 320 g/kg fish meal. The resulting 10 diets were three untreated SBM diets(S1, S2 and S3), three fermented SBM diets (FS1, FS2 and FS3), three irradiated SBM diets (IS1, IS2 and IS3) and a basal diet
Table 2Amino acid profile (g/kg) of fish meal, poultry by-product meal and soybean meal.
Ingredients Lys Met Thr Phe His Arg Val Ile leu Ser Asp Glu Gly Ala Cys Tyr Pro
a C is the basal diet. In the other diets, 25, 50 and 75% of fish meal in diet C were replaced with untreated soybean meal (S1, S2 and S3), fermented soybeanmeal (FS1, FS2 and FS3), or irradiated soybean meal (IS1, IS2 and IS3).
c Mineral premix composition (mg/kg diet): Ca(H2PO4)2·H2O, 400; calcium lactate, 1000; ferric citrate, 100; MgSO4·7H2O, 400; K2HPO4, 700;N
(adewF
2
sfit4
w(ia
Swwao
es
aH2PO4·H2O, 250; AlCl3·6H2O, 20; ZnCl2, 60; CuSO4·5H2O, 30; MnSO4·4H2O, 20; KI, 20.d Crude protein, crude lipid, ash and phosphorus are expressed on a dry matter basis (n = 2).e Digestible protein were calculated using the crude protein content to multiply the apparent digestible coefficient of protein (Bureau et al., 1999).
C). dl-Methionine and l-lysine were added in the test diets to balance amino acid composition. Chromic oxide was addedt 5 g/kg as an inert marker for measuring apparent digestibility coefficient (ADC) of protein (Wang et al., 2011). The testiets were extruded into slow-sinking pellets (4 mm diameter, 8 mm length) using a SLP-45 laboratory-scale single screwxtruder (Fishery Machinery and Instrument Research Institute, Chinese Academy of Fishery Sciences, Shanghai, China), andere dried under 25 ◦C in an air-conditioned room. Before use, the test diets were stored in sealed plastic bags at −20 ◦C.
ormulation and proximate composition of the test diets are shown in Table 3.
.2. Fish, husbandry and feeding trial
The feeding trial was conducted in the field station of Zhejiang Marine Fisheries Institute (Zhoushan, China). Japaneseeabass fingerlings were purchased from a commercial fish farm in Daishan (Zhoushan, China), and were transported to theeld station in two hours. Upon arrival, the fish were reared in an indoor pond (5 × 3 × 1.2 m) and fed with the basal dietwice daily for 4 weeks. Prior to the feeding trial, 1200 fish of similar size were acclimated in 30 fiberglass tanks (300 L) at0 fish per tank. The acclimation period was two weeks during which the fish were fed the basal diet twice daily.
At the start of the feeding trial, fish were starved for 24 h and then pooled. Thirty groups with 30 fish each were bulkeighed and then randomly distributed into 30 tanks. Each test diet had three replicates. Initial fish weight was 13.0 ± 0.1 g
mean ± S.E., n = 30). Three groups each of 15 fish were sampled from the remaining fish, and condition factor, hepatosomaticndex (HSI) and viscerasomatic index (VSI) of the fish were measured. The sampled fish were preserved at −20 ◦C for thenalysis of initial body composition.
The feeding trial lasted 8 weeks, during which fish were fed the test diets by hand to satiation at 0800 h and 1600 h daily.and-filtered sea water flowed through the tanks at 2 L/min, and water in the tanks was aerated. Environmental conditionsere maintained at temperature 25–28 ◦C, dissolved oxygen >6 mg/L, and salinity 25–28 g/L. Dead fish were accounted andeighed for calibrating the calculation of feed conversion ratio (FCR). At the end of the feeding trial, fish were starved for 24 h,
nd then were captured from each tank and bulk weighed. Three fish were sampled from each tank for the measurements◦
f condition factor, HSI, VSI and final body composition. The sampled fish were preserved at −20 C until analysis.
During the feeding trial, feces were collected from each tank twice daily from week 1 to 8. Feces were siphoned fromach tank about 4 h after feeding, and were filtered on a nylon sieve with pore size of 42 �m. Only the compact feces wereelected for chemical analysis. The feces collected from each tank were pooled, and preserved at −20 ◦C until analysis.
158 Y.Q. Zhang et al. / Animal Feed Science and Technology 197 (2014) 155–163
2.3. Chemical analysis
The fish samples were autoclaved at 120 ◦C for 20 min, homogenized and dried at 105 ◦C for 24 h. Feed ingredients, testdiets and fish were ground with a laboratory mill. Feces were dried at 70 ◦C to constant weight and then ground. Contentsof moisture (dried at 105 ◦C to a constant weight), crude protein (the Kjeldahl method), crude lipid (Soxhlet extraction), ash(combusted at 550 ◦C in a Muffle furnace for 6 h) and phosphorus (a spectrophotometric method) of the feed ingredients,test diets and fish were analyzed using the method recommended by AOAC (1995). The chromium (Cr) content of the testdiets and feces were analyzed with the method described by Furukawa and Tsukahara (1966).
2.4. Calculation and statistics
Feed intake, weight gain, FCR, retention efficiencies of nitrogen (NRE) and phosphorus (PRE), wastes output of nitrogen(NW) and phosphorus (PW), condition factor, HSI, VSI, ADC of protein were calculated as below:
Feed intake(g feed/100 g fish per day) = I[
2 × t
(Wt + W0)
]× 100
Weight gain(g/fish) = Wt
Nt− W0
N0
FCR(
dry feedweight gain
)= I
(Wt − W0)
NRE(g/100 g) =[
(Wt × CNt − W0 × CN0 )(I × CNf
)
]× 100
PRE(g/100 g) =[
(Wt × CPt –W0 × CP0 )(I × CPf
)
]× 100
NW[g N/ (kg fish gain)] = 1000 ×(I × CNf
) × (1–NRE)
[(Wt–W0)]
PW[g P/ (kg fish gain)] = 1000 ×(I × CPf
) × (1–PRE)
[(Wt–W0)]
Condition factor(
g/cm3)
= 100 × Ws
L3s
HSI(g/100 g) = Wl
Ws× 100
VSI(g/100 g) = Wv
Ws× 100
ADC of protein(g/100 g) =[
1–(CCf× CNfecal
)
(CCfecal× CNf
)
]× 100
where I (g) is feed consumed by fish on a dry matter basis; W0 (g) is total body weight of fish at the start of the feeding trialand Wt (g) total body weight at the end; t (d) is duration of the feeding trial; Nt is number of fish at the end of the feedingtrial and N0 at the start; CNt (g/kg) and CPt (g/kg) are contents of nitrogen and phosphorus in fish body at the end of thefeeding trial, CN0 (g/kg) and CP0 (g/kg) at the start; CNf
(g/kg
)and CPf
(g/kg
)are contents of nitrogen and phosphorus of
the test diets; Ws (g/fish), Ls (cm), Wl (g) and Wv (g) are body weight, total length, liver weight and viscera weight of the fishsampled at the start or end of the feeding trial; CCf
(g/kg
)is Cr content of the test diets; CCfecal
(g/kg
)is Cr content of the
feces; CNfecal
(g/kg
)is nitrogen content of the feces; CNf
(g/kg
)is nitrogen content of the test diets.
The differences in survival, final body weight (FBW), weight gain, feed intake, ADC of protein, FCR, NRE, PRE, condition
factor, HSI, VSI, proximate composition (moisture, crude protein, crude lipid, ash and phosphorus) of whole body, NW andPW were examined with ANOVA for a 3 × 3 design. The differences between the treatments were examined with Tukey’shonestly significant difference (HSD) test. Survival, feed intake, NRE, PRE, ADC of protein, HSI, VSI and body componentswere arcsine and logarithm transformed prior to ANOVA. The differences in survival, FBW, weight gain, feed intake, FCR,
Y.Q. Zhang et al. / Animal Feed Science and Technology 197 (2014) 155–163 159
Table 4Survival, body weight, feed intake and feed utilization of Japanese seabass fed the test diets for 8 weeksb.
Dieta IBW (g/fish) FBW (g/fish) Weight gain(g/fish)
ADC, apparent digestibility coefficient; FBW, final body weight; FCR, feed conversion ratio; FL, fish meal level; IBW, initial body weight; NRE, nitrogenretention efficiency; PRE, phosphorus retention efficiency; SBMT, soybean meal treatment; SEM, standard error.
a C is the basal diet. In the other diets, 25, 50 and 75% of fish meal in diet C were replaced with untreated soybean meal (S1, S2 and S3), fermented soybeanmeal (FS1, FS2 and FS3), or irradiated soybean meal (IS1, IS2 and IS3).
b Data are presented as mean value (n = 3). The superscript present the results of Tukey’s honestly significant difference test between fish fed diets S1,S(
NalwS
3
3i
FPImtNt
(orcnl(
3fi
VIc
2, S3, FS1, FS2, FS3, IS1, IS2 and IS3 (the small letters) or the results of Dunnett test between fish fed diet C and diets S1, S2, S3, FS1, FS2, FS3, IS1, IS2 or IS3the capital letters), respectively. The data with different superscript within same column are significantly different at P < 0.05.
c SBMT include untreated, fermented or gamma-irradiated.
RE, PRE, condition factor, HSI, VSI, proximate composition (moisture, crude protein, crude lipid, ash and phosphorus), NWnd PW between fish fed diets S1, S2, S3, FS1, FS2, FS3, IS1, IS2, IS3 and diet C were examined with Dunnett test. Significantevel was set at P < 0.05. Hierarchical cluster analysis was performed based on weight gain, FCR, condition factor and NW,
hich were used to evaluate production performance in marine fish farming. The statistical analysis was performed withPSS (version 18.0, Chicago, Illinois, USA).
. Results
.1. Effects of SBM treatment and fish meal replacement level on survival, feed intake, growth, feed utilization, morphologicalndices, body composition and wastes output
Final body weight, weight gain, feed intake, FCR, PRE and PW were dependent on SBM treatment (ANOVA, P < 0.05, Table 4,ig. 1), while FBW, weight gain, ADC of protein, FCR and NRE were dependent on the level of fish meal replacement (ANOVA,
< 0.05). No significant differences were found in the survival and feed intake among fish fed diets S1, S2, S3, FS1, FS2, FS3,S1, IS2 and IS3 (ANOVA, P > 0.05). Weight gain decreased, whereas FCR and NW increased, with increasing the level of fish
eal replacement, irrespective of fish meal replacement with untreated, fermented or irradiated SBM (Table 4, Fig. 1). Athe same level of fish meal replacement, no significant differences were found in the weight gain, ADC of protein, FCR, NRE,W and PW between fish fed the diets with untreated SBM, fermented SBM or irradiated SBM as a fish meal substitute (HSD
est, P > 0.05).At the end of the feeding trial, body contents of crude protein and phosphorus were dependent on SBM treatment
ANOVA, P < 0.05, Table 5), while condition factor, body contents of moisture and phosphorus were dependent on the levelf fish meal replacement (ANOVA, P < 0.05). Only body content of phosphorus was affected by SBM treatment × fish mealeplacement level (ANOVA, P < 0.05). Condition factor, HSI and body lipid content tended to decrease, whereas body moistureontent tended to increase with increasing the level of fish meal replacement. At the same level of fish meal replacement,o significant differences were found in the condition factor, HSI, VSI and body composition (moisture, crude protein, crude
ipid and ash) between fish fed the diets with untreated SBM, fermented SBM or irradiated SBM as a fish meal substituteHSD test, P > 0.05).
.2. Feed intake, weight gain, feed utilization efficiency, morphological indices, body composition and wastes output betweensh fed the basal diet and diets with fish meal replaced by SBM in three forms
No significant differences were found in the weight gain, ADC of protein, FCR, NRE, PRE, NW, PW, condition factor, HSI,SI and body composition between fish fed diets C and S1, or between fish fed diets C and FS1, or among fish fed diets C,
S1 and IS2 (Dunnett test, P > 0.05, Tables 4 and 5, Fig. 1). The production performance (evaluated with weight gain, FCR,ondition factor and NW) of fish fed diet C was close to fish fed diets IS1, IS2 and FS1 (Fig. 2).
160 Y.Q. Zhang et al. / Animal Feed Science and Technology 197 (2014) 155–163
Fig. 1. Wastes output of nitrogen (NW) (a) and phosphorus (PW) (b) of Japanese seabass fed the test diets for 8 weeks. C is the basal diet. In the other diets,25, 50 and 75% of fish meal in diet C were replaced with untreated soybean meal (S1, S2 and S3), fermented soybean meal (FS1, FS2 and FS3), or irradiatedsoybean meal (IS1, IS2 and IS3). The columns represent mean value, and the error bars represent SEM (n = 3). The small letters present the results of Tukey’sHSD test between fish fed diets S1, S2, S3, FS1, FS2, FS3, IS1, IS2 and IS3, and the capital letters present the results of Dunnett test between fish fed diet Cand diets S1, S2, S3, FS1, FS2, FS3, IS1, IS2 or IS3, respectively. The data with different letters are significantly different at P < 0.05.
Fig. 2. Average linkage dendrogram for distances between Japanese seabass fed the test diets. C is the basal diet. In the other diets, 25, 50 and 75% offish meal in diet C were replaced with untreated soybean meal (S1, S2 and S3), fermented soybean meal (FS1, FS2 and FS3), or irradiated soybean meal(IS1, IS2 and IS3). Weight gain, feed conversion ratio, condition factor and nitrogen wastes output were used as variables in hierarchical cluster analysis.Abbreviations refer to Fig. 1.
Y.Q. Zhang et al. / Animal Feed Science and Technology 197 (2014) 155–163 161
Table 5Condition factor, hepatosomatic index, viscerasomatic index and proximate composition of Japanese seabass fed the test diets for 8 weeksb.
FL, fish meal level; HSI, hepatosomatic index; SBMT, soybean meal treatment; SEM, standard error; VSI, viscerasomatic index.a C is the basal diet. In the other diets, 25, 50 and 75% of fish meal in diet C were replaced with untreated soybean meal (S1, S2 and S3), fermented soybean
meal (FS1, FS2 and FS3), or irradiated soybean meal (IS1, IS2 and IS3).b Data are presented as mean value (n = 3). The superscript present the results of Tukey’s honestly significant difference test between fish fed diets S1,
S2, S3, FS1, FS2, FS3, IS1, IS2 and IS3 (the small letters) or the results of Dunnett test between fish fed diet C and diets S1, S2, S3, FS1, FS2, FS3, IS1, IS2 or IS3(
4
acfisbw(raadPrTbc
mpeaeicINlof
ae
capital letters), respectively. The data with different superscript within same column are significantly different at P < 0.05.c Crude protein, crude lipid, ash and phosphorus are expressed on a wet weight basis.d SBMT includes untreated, fermented or gamma-irradiated.
. Discussion
The results of the present study reveal that the weight gain and FCR were dependent on both the method of SBM treatmentnd the level of fish meal replacement. No significant differences were found in the weight gain, FCR, NRE, PRE, NW, PW,ondition factor, HSI, VSI and body composition between fish fed diets C, S1 or FS1, suggesting that the level of dietarysh meal for Japanese seabass can be reduced to 240 g/kg when the untreated or fermented SBM are used as a fish mealubstitute. No significant differences were found in the weight gain, FCR, NRE, PRE, NW, PW, condition factor, HSI, VSI andody composition among fish fed diets C, IS1 and IS2, suggesting that the level of dietary fish meal can be reduced to 160 g/kghen the irradiated SBM is used as a fish meal substitute. The multivariate analysis confirms that production performance
weight gain, FCR, condition factor and NW) of fish fed the basal diet was close to fish fed diets IS1, IS2 and FS1 (Fig. 2). Theseesults reveal that gamma irradiation has benefits to increase the level of fish meal replacement by SBM. When SBM is useds a fish meal substitute, the lowest level of dietary fish meal can be reduced to 420 g/kg for olive flounder (Choi et al., 2004),nd 300–320 g/kg for rainbow trout (Kaushik et al., 1995), mangrove red snapper (Catacutan and Pagador, 2004) and cuneaterum (Wang et al., 2006), and 250–280 g/kg for Asian seabass (Boonyaratpalin et al., 1998; Tantikitti et al., 2005) and Tigeruffer (Kikuchi and Furuta, 2009). Previous studies reported that the level of dietary fish meal for Japanese seabass could beeduced to 320 g/kg (Li et al., 2012) or 160 g/kg (Zhang et al., 2014) if a commercial SBM was used as a fish meal substitute.he results of the present study reveal that the level of fish meal for Japanese seabass fed the diets with fish meal replacedy SBM is 160–240 g/kg, which is lower than that in Asian seabass (Boonyaratpalin et al., 1998; Tantikitti et al., 2005) anduneate drum (Wang et al., 2006).
Growth rate and feed utilization efficiency usually decline in fish fed the diets containing high levels of SBM as a fisheal substitute (Romarheim et al., 2006; Wang et al., 2006). The factors limiting fish meal replacement by SBM include the
resence of ANFs, low digestibility of protein, and deficiency in essential amino acids in SBM (Francis et al., 2001; Gatlint al., 2007). Refstie et al. (1998) indicated that the lowered growth rate of Atlantic salmon fed the SBM-based diets isttributed to the decrease of dietary ADC. Romarheim et al. (2006, 2008) reported that feed intake and nitrogen retentionfficiency decreased in rainbow trout when dietary fish meal level was reduced from 487–591 g/kg to 293–325 g/kg bynclusion of 249–300 g/kg SBM. Takagi et al. (2001) reported that the supplementation of crystalline methionine and lysinean improve growth and feed utilization of red sea bream fed the diets with fish meal replaced by soy protein concentrate.n the present study, the test diets were formulated to contain same contents of digestible protein, methionine and lysine.itrogen retention efficiency decreased, while feed intake and ADC of protein did not significantly change, with increasing the
evel of fish meal replacement by the untreated SBM. These results reveal that the lowered dietary palatability, digestibilityf protein and methionine content are not the factors negatively affecting growth and feed utilization of Japanese seabass
ed the diets with fish meal replaced by SBM.
Fermentation can enhance nutrient digestibility and reduce antinutritional factors in SBM (Hong et al., 2004). Egounletynd Aworh (2003) reported that the content of trypsin inhibitor slightly increases during soybean fermentation. Refstiet al. (2005) reported that lactic acid fermentation can eliminate the ANFs in SBM and improve dietary digestibility of
162 Y.Q. Zhang et al. / Animal Feed Science and Technology 197 (2014) 155–163
protein, lipid and carbohydrate for rainbow trout. Yamamoto et al. (2010) indicated that nutritive value of fermented SBMis dependent on fermentation conditions, and fish meal in diets for rainbow trout can be completely replaced by well-fermented SBM. In the present study, no significant differences were found in the weight gain, ADC of protein and nitrogenretention efficiency between fish fed the diets with fish meal replaced by the fermented or untreated SBM across all levelsof fish meal replacement, suggesting that fermentation under the conditions used in the present study cannot significantlyimprove nutritive value of SBM as a dietary fish meal substitute for Japanese seabass.
Gamma-irradiation can inactivate some ANFs in plant ingredients (Abu-Tarboush, 1998; De Toledo et al., 2007; Dixit et al.,2011) since irradiation increases the surface hydrophobicity of proteins via exposing to non-polar groups by promoting theunfolding of the protein structures and denaturation (Gaber, 2005). Gamma-irradiation can improve the digestibility onplant ingredients in pig (DeRouchey et al., 2003) and ruminant (Taghinejad et al., 2009; Ghanbari et al., 2012), and increasethe nitrogen retention efficiency in Babari male kids (Mani and Chandra, 2003). Thongprajukaew et al. (2011) reported thatthe use of a diet containing gamma-irradiated SBM at 200 g/kg can improve the growth of Siamese fighting fish. However, theeffect of gamma-irradiation on a single feed ingredient has not been evaluated. In the present study, production performanceof fish fed the diets with fish meal replaced by irradiated SBM was better, compared with fish fed the diets with fish mealreplaced by untreated SBM. This result reveals that inactivating ANFs in SBM may be the mechanism to improve growth andfeed utilization of fish fed the diets with fish meal replaced by SBM. Therefore, the presence of ANFs may be the primaryfactor limiting SBM inclusion in fish diets.
Replacement of dietary fish meal with SBM results in the decrease of body lipid content in mangrove red snapper andcuneate drum (Catacutan and Pagador, 2004; Wang et al., 2006), but has no significant effect on body lipid content in rainbowtrout and red sea bream (Kaushik et al., 1995; Romarheim et al., 2006; Kader et al., 2012). In the present study, the conditionfactor, hepatosomatic index and body lipid content tended to decrease with increasing the level of fish meal replacement,regardless of the use of untreated, fermented or irradiated SBM as a fish meal substitute. These results are consistent with thetrends in the weight gain and nitrogen retention efficiency, suggesting that the lowered nutrient deposition is a mechanismresponsible to poor growth of fish fed the diets with fish meal replaced by SBM.
In the present study, the nitrogen wastes output increased with increasing the level of fish meal replacement, regardlessthe inclusion of untreated, fermented or irradiated SBM as a fish meal substitute. This result is consistent with the conclusionthat the replacement of fish meal with SBM in fish diets can result in the increase of nitrogen wastes output (Kaushik et al.,2004). Therefore, environmental impact must be considered in evaluating the level of fish meal replacement by SBM in fishdiets.
5. Conclusion
The present study reveals, for the first time, that gamma-irradiation is a novel approach to enhance the level of fishmeal replacement by SBM in fish diets. The dietary fish meal level for Japanese seabass can be reduced to 160 g/kg if thegamma-irradiated SBM is used as a fish meal substitute.
Conflict of interest statement
We declare that all the listed authors meet the following criteria:
1. This study is original and has not been published elsewhere.2. All data involved in the manuscript are checked and reliable.3. All the authors have read and accepted the manuscript as it is submitted.4. All the authors approve the version to be published.
We declare that nobody who qualifies for authorship has been excluded from the list of authors.
Acknowledgements
This research was funded by the Major State Basic Research of China (Grant no. 2009CB118705) and National NaturalScience Foundation of China (Grant no. 30771673). We thank Serge Dossou, Tao Zhou and Han Zhang for their helps inpreparing the test diets.
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