Effects of defatted soybean protein levels on growth performance and nitrogen and phosphorus excretion in Asian seabass (Lates calcarifer)

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1 Effects of defatted soybean protein levels on growth performance and nitrogen and phosphorus excretion in Asian seabass (Lates calcarifer) C. Tantikitti a, *, W. Sangpong b, S. Chiavareesajja a Abstract The effects of defatted soybean meal protein levels in Asian seabass diets on growth, feed utilization, protein digestibility and nitrogen and phosphorus excretion were investigated. Six isonitrogenous diets were formulated to contain defatted soybean meal to replace fish meal at, 1%, 2%, 3%, 4% and 5% of fish meal protein, respectively. Trash fish was also used in the experiment. The fish were cultured in aerated flow-through 81 l aquaria filled with 54 l of seawater. Each diet was fed twice daily to satiation to three replicate groups of juvenile seabass with an average initial weight of.95 F.4.99 F.2 g/fish for 12 weeks. Growth of fish fed diets 1 and 2 ( and 1%) was significantly higher than that of fish fed diets 3 6 (2 5%) and trash fish. Fish fed diet 6 had the lowest weight gain and specific growth rate but, was not significantly different from those of fish fed diet 5 and trash fish. Feed conversion efficiency (FCE), protein efficiency ratio (PER) and productive protein value (PPV) of fish fed diets 1, 2 and 3 were significantly higher than those of the other diets, particularly the trash fish fed groups. The ammonia excretion of fish fed experimental diets peaked at 1 and 12 h after the first meal and was lowest for fish that were fed diet 1. On the other hand, ammonia excretion of fish fed trash fish was the highest. Fish fed diet 1 had the highest phosphorus excretion, whereas fish fed trash fish had the lowest. Loss values calculated from supply and gain confirmed data obtained through excretion measurements. Furthermore, replacing fish meal with soybean meal in the diets tended to increase nitrogen loss. Feed costs for production of 1 kg of fish was also determined. The cost of diet 2 with soybean meal replacing 1% of fish meal protein was 34.2 baht (US$.81)/kg of fish whereas that of diet 6 with soybean meal replacing 5% of fish meal protein was the highest at 4 baht (US$.95)/kg of fish. The results of the present study indicated that soybean meal can replace fish meal at the level of 1% of fish meal protein in diets for Asian seabass with good growth and feed utilization. In addition, replacing fish meal with soybean meal at the stated levels resulted in a reduction of nitrogenous waste in comparison with trash fish. Keywords: Soybean protein; Fish meal replacement; Growth; Nitrogen and phosphorus excretion; Asian seabass (Lates calcarifer)

2 1. Introduction Asian sea bass or giant sea pearch is an economically important species in Thailand and other Asian countries. Although the fish are cultured in both earthen ponds and sea cages, most are cultured in sea cages located in a river mouth or estuaries (Boonyaratpalin et al., 1989). In the past few years, cage farming has been increasing in different parts of the country. The feed commonly used by sea bass farmers is trash fish. With increasing problems of trash fish supply in terms of both quantity and quality and poor growth of fish when trash fish was used as a feed (Boonyaratpalin et al., 1989), it is predictable that formulated feeds will become necessary in the near future. As with other carnivorous species, an excellent growth performance was obtained when the fish are fed fish meal based diet (Boonyaratpalin et al., 1998). An attempt to replace fish meal with plant protein sources has also been investigated (Pongmaneerat and Boonyaratpalin, 1995; Boonyaratpalin et al., 1998). In line with studies in other fish species, inclusion of soybean meal at high levels resulted in growth reduction (Ballestrazzi et al., 1994; Carter et al., 1994; Robaina et al., 1995; Refstie et al., 1998; Arndt et al., 1999; Carter and Hauler, 2; Kissil et al., 2). Boonyaratpalin et al. (1998) found that diets with soybean meal substituting 37.5% of fish meal protein gave an acceptable growth, though with a slight growth difference in comparison to that of fish fed a fish meal based diet. Studies on replacement of fish meal by plant protein sources usually concentrate on growth, feed utilization and survival of fish in response to the substitution level. Plant protein sources may not be well digested, contain anti-nutritional factors and have an imbalanced amino acid profile (Tacon, 1991), possibly leading to loss of nutrients either in egesta or metabolic excretion. In the case of seabass cage culture, these waste outputs will affect the surrounding environment directly, as has been reported in salmonid net pen culture in Norway (Bergheim et al., 1991). With an increase in number of farms in the past few years, it can be anticipated that the organic waste output will increase accordingly and will have a negative impact on the surrounding environment, which will in turn affect the production and sustainability of sea bass culture. In order to select an appropriate level of soybean meal to incorporate in a diet with the environmental concerns in mind, data on the amount of waste produced from feeding such diet are necessary. The objective of the present study was to investigate the optimum level of soybean meal replacing fish meal with a good growth and an acceptable waste output. 2. Materials and methods 2.1. Diets Six practical diets containing 4% protein and 1% lipid were formulated to have defatted soybean meal replacing fish meal at, 1%, 2%, 3%, 4% and 5% of fish meal protein, respectively (Table 1). Because of a common practice by seabass farmers, another treatment using chopped headless trash fish as a feed was also included. Ingredients of each diet were mixed and pelleted using a Hobart mixer. The pellets were then dried at 6 8C and kept at 2 8C until feeding. Diets were analyzed for crude protein, crude lipid, ash and phosphorus content according to AOAC (199) Feeding trial Fifteen fish averaging.9 g body weight were distributed into each of l glass aquaria. Each aquarium was then randomly assigned to one of three replicates of the 7 dietary treatments. At this time, 1 g of fish from the same population used in the experiment were sacrificed for determination of initial carcass proximate composition. The fish were fed their respective diet to satiation twice daily at 9: and 15: h for 12 weeks. Satiation was evaluated by the fish slowness in taking pellets. Feed consumption, mortality and gross abnormality were recorded daily. A flow through aquaria system with flow rate of.5 l/min and continuous aeration was used in the study. The experimental units were under natural light and dark cycle. Salinity of water was F.23x and water temperature was 28.4F.1 8C. To ensure that quality of water in the aquaria was suitable for the fish, water samples from

3 Table 1 Composition of experimental diets (as fed basis) Ingredient (g/kg) Diet 1 () 2 (1) a 3 (2) 4 (3) 5 (4) 6 (5) Trash fish Fish meal (63% protein) b Defatted soybean meal (dehulled, 46% protein) b Shrimp head meal Rice bran Fish oil Vitamin premix c Mineral premix d BHT Cooked tapioca starch Rice flour Ground rice hull Proximate composition (as fed basis) e Crude protein Crude lipid Ash Phosphorus Gross energy f a Numbers in brackets indicate levels of soybean substitution for fish meal protein. b Local ingredients. c In mg/kg: Thiamin HCl 6, riboflavin 1, pyridoxine HCl 4, choline chloride 5,, niacin 4, Ca-pantothenate 1, ascorbic acid 5, inositol 2,, biotin 6, folic acid 15, vitamin B 12.1, menadione 5, tocopherol acetate 1, vitamin AD 3 (5 IU of A+1 IU of D 3 /mg) 8. d In mg/kg: CaHPO 4 8, NaH 2 PO 4 d 2H 2 O 15, KH 2 PO 4 1, KCl 5. e Means of three replicate analysis. f In MJ/kg, calculated using caloric values for protein, lipid and carbohydrate according to NRC (1993). each aquarium were collected weekly throughout the experiment and analyzed for NH 4,NO 3,NO 2 and DO according to Strickland and Parsons (1972). At the end of the feeding period, fish in each aquarium were individually weighed after anesthetizing with 2-phenoxyethanol at.5 ml/l of water. Five fish from each aquarium were randomly collected and frozen. The samples were later dried at 6 8C, ground and analyzed for proximate composition and phosphorus content according to AOAC (199). Data on initial weight, final weight, feed intake and proximate composition of diets and carcass were used to calculate specific growth rate, feed conversion efficiency, protein efficiency ratio and productive protein value N and P excretion and waste Nitrogen (N) and phosphorus (P) excretion of fish fed the different diets were measured in the culture water at peak hours after feeding. In order to determine the appropriate peak hour for sample collection, a preliminary study on nitrogen and phosphorus excretion pattern every 2 h over 12 h after feeding was carried out for two consecutive days. During the excretion pattern study, the fish were fed at 2% of body weight twice a day at 9: and 15: h. Since the high excretion occurred at 12 h after feeding, water was sampled at that times. On the sampling day, during the last week of the feeding trial, 1 l of water was collected from each aquarium prior to feeding and at 12 h after feeding. The samples were stored at 2 8C until further analysis for total ammonia nitrogen and phosphorus concentration according to Strickland and Parsons (1972). Calculation for nitrogenous and phosphorus waste was as follows, Nitrogen=Phosphorus waste ðmg=kg fishþ ¼ Peak Conc:n Prefeeding Conc: n 1 : Average wt: of fish at sampling

4 Table 2 Growth and survival of seabass fed experimental diets with soybean meal replacing fish meal protein at different levels Diet Initial weight (g/fish) Final weight (g/fish) SGR 1 (%/day) Survival (%) 1 (Control).95F F1.57 a2 4.28F.1 a 97.78F3.85 a 2 (1) 3.98F F.59 a 4.22F.3 ab 97.78F3.85 a 3 (2).96F F3.13 b 4. F.16 bc 97.78F3.85 a 4 (3).99F F1.97 b 3.93F.1 c 95.56F7.7 a 5 (4).94F F1.99 c 3.58F.12 d 95.56F3.85 a 6 (5).95F F1.9 c 3.4F.16 d 91.11F7.7 a Trash fish.96f.3 2.2F2.36 c 3.62F.18 d 51.11F31.51 b 1 Specific growth rate=(ln W2 ln W1/T2 T1)1. 2 Values are meanfsd (N =3) and means with the same superscript in the same column are not statistical different ( P N.5). 3 Numbers in the bracket indicate levels of soybean substitution for fish meal protein. N and P losses were also determined using biological data on nutrient supply, nutrient gain and fish weight gain as described by Paspatis et al. (2) Statistical analyses All data were subjected to analysis of variance procedure and the differences among means were compared by Duncan s New Multiple Range Test ( P b.5). 3. Results 3.1. Growth and feed utilization Growth response and feed utilization efficiency are given in Tables 2 and 3. The results showed that the higher the level of soybean incorporated in the diets, the lower the growth and feed utilization. Growth and feed intake of fish that were fed diets 1 and 2 ( and 1%) was significantly higher than those of fish fed diets 3 6 (2 5%) and trash fish. A significant decrease of approximately 2% in feed intake was very apparent between diets 2 and 3. Feed conversion efficiency (FCE), protein efficiency ratio (PER) and productive protein value (PPV) of fish that were fed with diets 1, 2 and 3 were significantly higher than those of other diets, particularly the trash fish fed groups. Regression analysis of feed intake, final weight, SGR and FCE against levels of soybean substitution is shown in Fig. 1. At every 1% increment of soybean substituting fish meal protein caused a reduction in SGR and FCE of.18%/day and.42, respectively. In addition, fish fed with diet 6 had the lowest weight gain and specific growth rate which was not significantly different from those of fish fed diet 5 and trash fish. Fish fed pelleted feed had high Table 3 Feed intake (as fed) and feed and protein utilization of seabass fed experimental diets with soybean meal replacing fish meal protein at different levels Diet Feed intake (g/fish) FCE 1 PER 2 PPV 3 (%) 1 (Control) 34.76F1.71 b4.97f.3 a 2.37F.1 a 47.67F.92 a 2 (1) F.23 b.94f.1 ab 2.31F.4 a 45.7F1.6 ab 3 (2) 27.88F3.49 c.96f.4 a 2.33F.9 a 42.62F1.88 bc 4 (3) 28.8F2.17 c.9f.1 b 2.18F.3 b 41.24F1.2 c 5 (4) 21.82F1.66 d.83f.5 c 1.95F.12 c 36.76F3.7 d 6 (5) 2.9F1.39 d.75f.4 d 1.77F.11 d 32.62F1.81 e Trash fish 55.13F5.44 a.35f.2 e.42f.2 e 31.72F1.8 e 1 Feed conversion efficiency=weight gain (g)/feed intake (g). 2 Protein efficiency ratio=weight gain (g)/protein intake (g). 3 Productive protein value=(protein gain (g)/protein intake (g))1. 4 Values are meanfsd (N =3) and means with the same superscript in the same column are not statistical different ( P N.5). 5 Numbers in the bracket indicate levels of soybean substitution for fish meal protein.

5 Final weight (g/fish) a) = Final weight y = x R 2 =.8951 = Feed intake y = x R 2 = Feed intake (g/fish) SGR (%/day) b) Level of soybean substitution (%) = FCE y = x R 2 =.7466 = SGR y = x R 2 = FCE Level of soybean substitution (%) Fig. 1. Changes in feed intake, average final body (a) and SGR and FCE (b) with increasing levels of soybean substituting fish meal protein in diets for Asian seabass. survival in the range of % whereas survival of fish that were fed with trash fish was only F 31.51%, significantly lower ( P b.5) than those of the former groups with high variation among the replications. Proximate composition of fish showed a slight but significant reduction in protein content of fish fed diets 3 6 and trash fish (Table 4). A decrease in lipid content of fish was associated with increasing levels of soybean meal particularly at 4 5% of fish meal protein replacement. On the contrary, phosphorus content of the fish fed diets with high levels of soybean was significantly higher than those of the other diets, particularly the trash fish fed group. For water quality in the aquaria, temperature varied between 28.2 and C, ph between 8.13 and 8.15 and DO between 6.15 and 6.29 mg/l N and P excretion and loss The results on nitrogen excretion pattern showed that ammonia excretion of fish fed experimental diets peaked at 12 h after the first meal (Table 5). Ammonia concentration at 12 h in the last week of feeding trial revealed that fish fed diet 1 (fish meal based diet) had low ammonia excretion (Tables 5 and 6). On the other hand, ammonia excretion in the trash fish fed group were the highest ( P b.5).

6 Table 4 Body composition (% wet weight) 1 of Asian seabass fed experimental diets with soybean meal replacing fish meal protein at different levels Diet Composition (%) Protein Lipid Ash Phosphorus Moisture Initial Fish 14.81F F F F.14 1 (Control) 2.19F.29 a 4.9F.17 a 5.9F.19 a.99f. bc 69.47F.15 e 2 (1) F.76 a 4.25F.55 ab 5.77F.12 a.98f.2 bc 7.32F.71 de 3 (2) 18.19F.14 b 4.48F.53 ab 5.65F.21 a.96f.1 c 71.16F.32 cd 4 (3) 18.78F.55 b 4.11F.24 b 5.75F.12 a.97f.2 c 71.56F.44 c 5 (4) 18.6F.65 b 3.26F.54 c 5.94F.7 a 1.6F.2 a 72.8F.6 bc 6 (5) 18.23F.39 b 3.2F.15 c 5.8F.26 a 1.1F.2 b 72.88F.62 ab Trash fish 18.14F.2 b 4.27F.34 ab 3.69F.6 b.61f.1 d 73.71F.51 a 1 Values are meanfsd (N =3) and means with the same superscript in the same column are not statistical different ( P N.5). 2 Numbers in the bracket indicate levels of soybean substitution for fish meal protein. Furthermore, it was noticed that ammonia excretion of fish with an average weight of during the pattern study was higher than those of the last week of the experiment when the fish were of a larger size. For phosphate excretion, fish fed diet 1 was the highest with a noticeable value at 12 h after feeding (Tables 5 and 6). Fish fed diet 2 also excreted a considerably high concentration of phosphate which was not statistically different from that of fish diet 1. Table 7 shows N and P intake and loss of fish fed different diets. It was found that nitrogen loss of fish fed diet 1 was the lowest, whereas that of the trash fish fed group was the highest. Furthermore, replacing fish meal with soybean meal in the diets tended to increase nitrogen loss, while decreasing loss of phosphorus. N loss was also highly correlated with the intake in that the higher intake resulted in a greater loss (Fig. 2). An estimation of feed cost for production of 1 kg of fish was also made. The cost of diet 2 with soybean meal replacing 1% of fish meal protein was 34.2 baht (US$.81)/kg of fish, trash fish was baht (US$.86)/kg of fish, and diet 6 with soybean meal Table 5 Ammonia and phosphate concentrations at every 2 h over 12 h sampling after feeding diets containing different levels of soybean meal replacing fish meal protein Time (h) Diet 1 (Control) 2 (1) a 3 (2) 4 (3) 5 (4) 6 (5) Trash fish Ammonia concentrations (mgnh 3 N/kg of fish) F11.46 b 7.47F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F Phosphate concentrations (mgpo 4 P/kg of fish) F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F F.24 a Numbers in the bracket indicate levels of soybean substitution for fish meal protein. b Values are meanfsd (N =2).

7 Table 6 Ammonia, and phosphorus concentrations 1 at 12 h after feeding diets containing different levels of soybean meal replacing fish meal protein for 12 weeks Diet replacing 5% of fish meal protein was the highest at 4 baht (US$.95)/kg of fish. 4. Discussion Ammonia (mgnh 3 N/kg fish) Phosphorus (mgpo 4 P/kg fish) 1 (Control) 53.65F82.86 c 25.1F3.24 a 2 (1) F1.63 b 18.67F.33 ab 3 (2) F2.58 b 1.96F1.9 c 4 (3) 14.21F26.98 b 13.4F7.6 bc 5 (4) F6.3 b 1.17F.63 c 6 (5) F14.92 b 11.86F2.9 bc Trash fish 33.99F58.6 a 9.93F2.54 c 1 Values are meanfsd (N =3) and means with the same superscript are not statistical different ( P N.5). 2 Numbers in the bracket indicate levels of soybean substitution for fish meal protein. Fish fed diets 2 (1% substitution for fish meal protein) showed good growth, feed consumption, feed conversion efficiency, PER and PPV comparable to that of fish fed fish meal based diet. A linear reduction in feed intake, growth and nutrient utilization in response to higher substitution levels was observed. Substitution at 2% and 3% of fish meal protein resulted in a significant decrease in feed intake, final weight, SGR and PPV as compared with those of fish fed diets 1 and 2. A more pronounced effect on growth and feed utilization was observed at 4% Nitrogen loss (g/kg weight gain) Nitrogen intake (g/kg weight gain) 1 Fig. 2. Correlation of nitrogen intake and loss in fish fed trash fish and diets containing different levels of soybean meal replacing fish meal protein. and 5% substitution levels. The results are in agreement with those studied in different carnivorous species fish such as rainbow trout, Atlantic salmon and red drum (Alexis, 199; Reigh and Ellis, 1992; Carter et al., 1994; Olli et al., 1995). Asian seabass seems to be very sensitive to soybean meal in that only 2% replacement caused a significant decrease in intake and growth. Arndt et al. (1999) obtained a similar result in coho salmon in that inclusion of heat-treated soy defatted flour greater than 15% substitution of herring meal protein resulted in reduced weight gain Table 7 N and P intake and loss of seabass fed experimental diets with soybean meal replacing fish meal protein at different levels Diet Weight gain (g/fish) N intake 1 (g/kg wt. gain) N loss P intake P loss (g/kg wt. gain) 2 (%) (g/kg wt. gain) (g/kg wt. gain) (%) 1 (Control) 33.56F1.61 a F.22 c 35.4F.65 d 51.85F.84 e 25.79F.8 a 15.5F.3 a 6.11F.7 a 2 (1) F.59 a 69.2F1.1 c 37.58F1.2 cd 54.3F1.6 de 24.77F.39 ab 14.22F.14 b 57.44F.34 b 3 (2) 26.84F3.14 b 68.79F2.63 c 39.49F2.76 cd 57.37F1.88 cd 23.79F.91 bc 13.95F.34 b 58.65F.82 ab 4 (3) 25.91F1.98 b 73.45F1.14 c 43.52F.42 c 59.26F.42 c 22.79F.35 c 12.4F.13 c 52.85F.25 c 5 (4) 18.9F1.97 c 82.8F4.92 b 52.1F5.62 b 63.24F3.7 b 24.57F1.47 ab 11.49F.52 d 46.8F.7 d 6 (5) 15.7F1.92 c 9.6F5.54 a 61.11F5.35 a 67.38F1.82 a 25.41F1.55 ab 11.39F.43 d 44.87F1.2 d Trash fish 19.7F2.39 c 93.68F5.56 a 64.36F5.49 a 68.62F1.78 a 1.15F.6 d 1.44F.12 e 14.19F2.2 e 1 Nutrient intake (g/kg wt. gain)=1[feed consumption (g/fish)feed nutrient content (%)/Weight gain (g/fish)]. 2 Nutrient loss (g/kg wt. gain)=1[nutrient intake (g/fish) Nutrient gain (g/fish)/weight gain (g/fish)]. 3 Values are meanfsd (N =3) and means with the same superscript in the same column are not statistical different (P N.5). 4 Numbers in the bracket indicate levels of soybean substitution for fish meal protein.

8 compared to fish fed the control diet. The poor performance of fish fed diets with increasing levels of soybean meal beyond 1% of fish meal protein was most likely due mainly to poor palatability and amino acid imbalance of soybean meal. A reduction in feed intake of approximately 2% in the group of fish fed diets 3 and 4, and 4% in the group of fish fed diets 5 and 6 as compared to that of fish fed diet 2 was observed. Hajen et al. (1993) also found a reduction in feed intake when chinook salmon fry were fed diets containing soybean meal at 15% and 3% of diet. Unpalatability of diets 2 and 3 was possibly the main cause of growth depression in fish fed these diets, the same phenomenon as those found by Boonyaratpalin et al. (1998) in the same fish species when solvent extracted soybean meal was incorporated at 21% of diet. If the diets were improved by attractant supplementation, feed intake of these fish would be improved resulting in a good growth because the fish showed a high efficiency in nutrient utilization with high FCE, PER and PPV as compared with that of either the control and diet 1 fed group. The very low growth performance and nutrient utilization observed in the groups of fish fed diets 5 and 6 was not only affected by a low feed intake, but likely also by the poor amino acid balance of these diets. Soybean meal, though considered as the best plant protein source with regard to amino acid profile, may have insufficient methionine for meeting the essential amino acid requirements of seabass. Substitution at 4% and 5% of fish meal protein in the present experiment without any amino acid supplementation possibly caused methionine deficiency resulting in slower growth, and reduced feed conversion efficiency and protein utilization. A similar response was observed in olive flounder when the diet contained more than 2% dehulled soybean meal (Choi et al., 24), and in young tin foil barb when fed with a diet containing soybean meal replacing 5% of fish meal (Elangovan and Shim, 2). If the diets were supplemented with amino acids and attractants, Choi et al. (24) found that olive flounder could utilize higher soybean meal level at 3% of fish meal. Unfortunately, the amino acid composition of the experimental diets was not analyzed. However, growth and protein utilization of fish would possibly be improved if the diets were supplemented with amino acids which were present at below requirement levels. Results on N excretion and loss correlated well with those of growth and dietary utilization. Fish fed the control diet had the best growth and nutrient utilization, and exhibited the lowest amount of ammonia excretion and N loss. Generally, substituting fish meal with soybean meal resulted in significantly higher N excretion. This finding was in accordance with those found in rainbow trout, gilthead seabream fed with soybean meal and European seabass fed diet corn gluten meal, in comparison with fish meal based diet (Ballestrazzi et al., 1994; Robaina et al., 1995; Medale et al., 1998). Within the soybean substitution groups, N excretion and loss increased as the level of substitution increased. This consequently resulted in an increase in N intake required to obtained 1 kg weight gain. Both amino acid imbalance and digestibility may play important roles in low utilization of diets and nutrients in the groups of fish fed the mentioned diets resulting in high N excretion and loss. In the case of the trash fish fed groups, which exhibited the highest excretion and loss, this correlates well with other nutritional parameters and was most likely due to the deterioration of trash fish during storage. Although trash fish is not recommended for use solely as feed for aquatic animals, most seabass farmers in Thailand are still using it because of its low price (US$.24/kg) and convenience. Excretion and loss of phosphorus was noticeably associated with dietary levels and intake. Fish fed diet 1 (fish meal based diet) exhibited the greatest excretion and loss of phosphorus, corresponding to the highest amount of dietary phosphorus. Diets with soybean meal substituting for fish meal led to lower phosphorus excretion than that of diet 1. Fish meal is the richest source of phosphorus among common feedstuffs used in fish feed formulation (Lall, 1991). Differences in phosphorus levels in experimental diets were clearly associated with contribution of fish meal in the diets. Moreover, increasing levels of soybean meal in the diets resulted in a decrease in phosphorus excretion and loss. These results were in line with those observed in European seabass and rainbow trout (Ballestrazzi et al., 1994; Vielma et al., 2). Furthermore, low levels of P loss in the groups of fish fed diets 5 and 6 related well with significantly high phosphorus content in these fish. The results of the present study showed that soybean meal can replace fish meal up to 1% of fish

9 meal protein in diets for Asian seabass with good growth, feed utilization and reasonable cost (34.2 baht (US$.81)/kg of fish) when local ingredients were used. In addition, replacing fish meal with soybean meal at the stated level resulted in reduction of nitrogen waste in comparison with trash fish, a common feed used by seabass farmers in Thailand. Acknowledgements The authors wish to thank Government of Thailand for funding the study and Department of Fisheries, Ministry of Agriculture and Cooperatives, for providing experimental spaces. We would also like to gratefully extend our appreciation to Ian Forster and B.R. Moss for reviewing the manuscript. References Alexis, M.N., 199. Comparative evaluation of soybean meal as dietary ingredients for rainbow trout fingerlings. Aquat. Living Resour. 3, AOAC, 199. Official Methods of Analysis. Association of Official Analytical Chemists, Fifteenth edition. 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