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Effects of Dietary Supplements on Growth Performance and Phosphorus Waste Production of Australian Catfish, <em>Tandanus Tandanus</em>, Fed with Diets Containing Canola Meal as Fishmeal Replacement
ISSN: 2155-9546
Journal of Aquaculture Research & Development

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Effects of Dietary Supplements on Growth Performance and Phosphorus Waste Production of Australian Catfish, Tandanus Tandanus, Fed with Diets Containing Canola Meal as Fishmeal Replacement

Huy PV Huynh1,2* and Dayanthi Nugegoda1

1Biotechnology and Environmental Biology, School of Applied Sciences, RMIT University, Bundoora West Campus, P.O Box 71, Bundoora 3083 Victoria, Australia

2Faculty of Fisheries, Nong Lam University, Thu Duc Dictrict, Ho Chi Minh City, Vietnam

*Corresponding Author:
Huy P.V. Huynh
Faculty of Fisheries, Nong Lam University. Linh Trung Ward
Thu Duc District, Ho Chi Minh City, Vietnam
E-mail: [email protected], [email protected]

Received Date: September 08, 2011; Accepted Date: November 15, 2011; Published Date: November 22, 2011

Citation: Huynh HPV, Nugegoda D (2011) Effects of Dietary Supplements on Growth Performance and Phosphorus Waste Production of Australian Catfish, Tandanus Tandanus, Fed with Diets Containing Canola Meal as Fishmeal Replacement. J Aquac Res Development 2:117. doi:10.4172/2155-9546.1000117

Copyright: © 2011 Huynh HPV, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

Effects of dietary phytase, amino acid (AA), and inorganic phosphorus (P) in canola meal diets on the growth and P waste production of Australian catfish, Tandanus tandanus were evaluated. Fishmeal protein was replaced by 30% and 45% with canola meal protein in two separate experiments, in which test diets were fortified with phytase, AA, inorganic P, or their combinations. Addition of sole phytase to the 30% replacement diets did improve growth performance and feed utilization of fish compared to those fed with the non-phytase diet. Inclusion of phytase and/ or AAs did not improve the growth and feed utilization of catfish when fishmeal protein was replaced by 45% while adding inorganic P showed significant improvement in the performance of the fish. Ortho-P waste was significantly lower while total P waste was significantly higher in fish fed with canola meal diets at both levels of fishmeal replacement. Phytase did not affect the total P waste of catfish but a combination of phytase and AA resulted in a significant reduction. Dietary inclusion of inorganic P significantly elevated the total P waste of catfish compared to that of the control fish. It was concluded that the use of canola meal in combination with inorganic P in diets for Australian catfish could significantly increase nutrient pollution in aquaculture.

Keywords

Australian catfish; Fishmeal replacement; Canola meal; Phosphorus waste; Phytate

Abbreviations

CM: canola meal; SBM: soybean meal; FM: Fishmeal; P: phosphorus; AA: amino acid

Introduction

Canola meal (CM) is an alternative protein source for fish meal (FM) similar to soybean meal (SBM) in diets for many aquaculture species. Some even believe that CM has a better amino acid profile than SBM [1]. Substitution of FM by CM has also been widely investigated for many fish species, including Chinook Salmon, Oncorhynchus tshawytscha [2-4], Atlantic salmon, Salmo salar L. [5], red sea bream, Pagrus auratus [6], rainbow trout, Oncorhynchus mykiss [1,7,8], tilapia, Oreochromis mossambicus [9], silver perch,Bidyanus bidyanus [10], sunshine bass, Morone chrysops x M. saxatilis [11], turbot, Psetta maxima [1] and channel catfish, Ictalurus punctatus [12-13]. CM has also been incorporated in diets for shrimp, such as white shrimp,Penaeus vannamei [14] and blue shrimp, Litopenaeus stylirostris [15]. However, results from those studies have showed large variations, which were usually attributed to the nutritional quality of the ingredient when derived from different sources [10,16-21].

In addition, previous studies revealed that replacing FM with plant protein sources, including soybean meal, reduced phosphorus (P) waste of different fish species, such as Japanese seabass, Lateolabrax japonicus [22], rainbow trout, Oncorhynchus mykiss [23,24], salmonid species [25]. Especially, Huynh and Nugegoda [26] have shown that using soybean meal to replace FM protein did reduce P waste of Australian catfish, T. tandanus. However, information on the effects of dietary CM on waste production of fish is not commonly reported. Since a major fraction of P in CM is bound with phytic acid [27,28], and P digestibility of CM is poor for monogastric animals, including fish [29,30], the use of CM could potentially lead to water pollution due to the excretion of undigested P.

This study therefore evaluated the effects of phytase and nutrient supplement, including limiting AAs and inorganic P, in high CM diets on growth performance, feed and nutrient utilization, and waste production of Australian catfish, T. tandanus. This allowed the determination of the possible use of CM as FM replacement in diet for the fish when both growth performance and waste production of fish were considered in conjunction.

Materials and Methods

Experimental procedures

This study consists of two experiments, Experiment 1 and Experiment 2. The fish used for both experiments were procured from Namoi Valley Aquafarming Pty. Ltd. (Narrabri, New South Wales, Australia). All experimental procedures were conducted in accordance with RMIT Animal Ethics Permit AEC0614. Fish were acclimated for 1 month in 2000 L flow-through fiberglass tanks before being used for experiments. During acclimation, fish were fed twice daily to satiation with Ridley Native Fish Commercial Feed with a crude protein and lipid content of 52% and 12%, respectively. Prior to the experiments, fish were stocked in experimental tanks and acclimated to the experimental feeds and tanks for 2 weeks, during which all experimental fish were fed with a blend of experimental diets This blend was prepared by thoroughly mixing an equal proportion of all diets that were to feed the fish during the experiments. This final acclimation step was to ensure that the fish accepted the experimental diets and conditions and that there was no carry-over of the effects from the initial acclimation.

In Experiment 1, 150 fish with the average body weight (BW) of 6.04 g were randomly stocked into 15 flow-through glass tanks (22cm x 50cm x 30cm), which were randomly assigned to 5 treatments (3 replicate tanks per treatment). Similarly, in Experiment 2, 105 fish with the average BW of 26.62 g were randomly stocked into 21 flow-through glass tanks (36cm x 50cm x 30cm), which were the randomly assigned to 7 treatments (3 replicate tanks per treatment).

During the 84 days of both experiments, fish were fed to approximate satiation, twice daily between 9.00–9.30 and 17.00–17.30, except the days before weighing when fish were fed once. All uneaten feed after 30 minutes was siphoned, dried and recorded to allow for feed-intake calculations. In order to account for the stability of different diets, a correction factor was calculated for each treatment. A predetermined amount (2 g) of each diet was placed in an experimental tank without fish for 30 minutes, the remaining feed were siphoned, dried and weighed. Correction factors were calculated as follow:

C = (F1 – F2)/F1

C: correction factor

F1: dry weight of feed at the beginning

F2: dry weight of feed after 30 minutes

The actual uneaten feed was then calculated as

F1 = F2/(1-C)

Where:

F1: the actual uneaten feed

F2: the amount of feed recovered after each feeding time

C: the correction factor

In order to ensure the maintenance of suitable water quality during the experiment, temperature, dissolved oxygen and pH were measured every other day using a TPS WP-81 pH meter and TPS WP-91 DO and temperature meter; while ammonia and nitrite were monitored weekly using a YSI 9100 photometer and kit chemicals for water analysis. The average dissolved oxygen, pH and temperature of both experiments were about 8.0–8.4 mg/L, 6.7–6.8 and 24.2°C, respectively. Water concentration of ammonia (0.08–0.14 mg/L) and nitrite (0.003–0.004 mg/L) were low and suitable for the optimal growth of fish.

Preparation of experimental diets

Feed ingredients, including Peruvian fishmeal, wheat flour, fish oil, and vitamin and mineral premixes, were provided by Ridley Aquafeed Australia (Narrangba, Queensland, Australia). CM was provided by Riverland Oilseed Processor (Numurkah, Victoria, Australia). Carboxymethyl cellulose (CMC), used as a feed binder, was purchased from Chem-Supply Australia Pty. Ltd. (Port Adelaide, South Australia, Australia). Proximate composition of feed ingredients were analysed prior to diet formulation. The proximate composition and AA profile of feed ingredients are presented in Table 1.

Content Ingredients
FM (c) CM (c) Wheat flour (c)
Proximate composition(g/kg dry matter)
Protein 715.3 376.2 185.3
Lipid 74.9 22.4 18.5
Ash 164.4 79.4 18.0
Carbohydrate (a) 45.4 522.0 778.2
Phytic acid nd 42.6 12.8
Total P 20.8 14.4 4.5
Energy (kJ/ g) t 20.7 18.8 18.5
In dispensable AA(g/kg dry matter)  
Arginine 45.4 23.7 7.1
Histidine 31.0 10.7 3.5
Isoleucine 32.3 16.8 5.4
Leucine 53.2 28.0 9.8
Lysine 57.4 23.6 4.4
Methionine 20.1 4.4 1.9
Phenylalanine 28.6 15.6 6.8
Threonine 30.3 17.0 4.2
Valine 37.5 21.1 6.5

Table 1: Proximate composition, AA profile (g/kg dry matter) and gross energy (KJ/g) of feed ingredients.

The CM test diets with phytase in experiment 1 were formulated to contain CM to replace 30% FM protein in the control diet prepared with FM as the main protein source. Four CM diets were formulated to provide 390 g/kg crude protein and 20 KJ/g of energy. The test diets were CM30, CM30F1, CM30F2, and CM30F3 supplemented with phytase at the doses of 0, 1000, 2000 and 3000 FTU/kg, respectively. Formulation, proximate composition and estimated AA content of the experimental diets are presented in Table 2.

  Diets
Content Control CM30 CM30F1 CM30F2 CM30F3
Ingredient (g/kg as is basic)        
Fishmeal 500.0 350.0 350.0 350.0 350.0
Wheat flour 310.0 224.3 224.3 224.3 224.3
Canola meal 0.0 305.7 305.7 305.7 305.7
Fish oil 50.0 50.0 50.0 50.0 50.0
Cellulose 80.0 10.0 9.8 9.6 9.4
Phytase(a) 0.0 0.0 0.2 0.4 0.6
Mineral 20.0 20.0 20.0 20.0 20.0
Vitamin 10.0 10.0 10.0 10.0 10.0
CMC 30.0 30.0 30.0 30.0 30.0
Proximate composition (g/kg dry matter)      
Protein 394.0 396.5 385.9 382.9 383.0
Lipid 112.7 105.8 106.4 107.8 107.0
Ash 96.5 96.1 100.3 103.1 98.2
Carbohydrate (b) 396.8 401.6 407.4 406.2 411.8
Phytase activity (FTU/kg) ND ND 954.2 1992.65 2908.56
Total P 14.2 14.8 14.8 14.2 14.7
Gross energy (kJ/ g) (c) 205.9 204.6 203.4 203.0 203.7

Table 2: Ingredient and proximate composition of the experimental diets(*) in Experiment 1 (CM30, CM30F1, CM30F2, and CM30F3 supplemented with phytase at 0, 1000, 2000 and 3000 FTU/kg, respectively).

In experiment 2, in order to test the effect of different combinations of nutrient supplements, CM test diets were formulated to contain CM as replacement of 45% FM protein. FM was the main protein source in the control diet. Six test diets were formulated to provide 390 g/kg crude protein and 20KJ/g of energy. The test diets were CM45, CMF, CMFA, CMPA, CMP, and CMAA. While CM45 contained no nutrient supplement, CMF was supplemented with only phytase at the dose of 1000 FTU/kg. In diet CMFA, phytase and crystal AAs (lysine and methionine) were added in order to balance the AAs profile in the CM diet with the control. These calculations were based on the estimated AA profile of the two diets. CMPA were supplemented with both AAs and inorganic P but not with phytase. The amount of supplemented P was calculated in order to supply the diet with the additional 70% of P constituted by the incorporated CM, which were to be bound in phytate indigestible form, plus to fill the gap in P content between the control and the CM diets. Limiting AAs or inorganic P only was added to the diets CMAA or CMP, respectively, based on the calculations described above. Formulation, proximate composition and estimated AA content of experimental diets are presented in Table 3.

Content (g/kg dry matter) Diets
Control CM45 CMF CMFA CMPA CMAA CMP
FM 500.0 275.0 275.0 275.0 275.0 275.0 275.0
Wheat flour 265.0 174.0 173.8 167.8 150.0 168.0 156.0
CM 0.0 426.0 426.0 426.0 426.0 426.0 426.0
Wheat gluten 30.0 30.0 30.0 30.0 30.0 30.0 30.0
Fish oil 50.0 50.0 50.0 50.0 50.0 50.0 50.0
Cellulose 110.0 0.00 0.00 0.00 0.00 0.00 0.00
Mineral 5.0 5.0 5.0 5.0 5.0 5.0 5.0
Vitamin 10.0 10.0 10.0 10.0 10.0 10.0 10.0
Phytase(a) 0.0 0.0 0.2 0.2 0.0 0.0 0.0
L-Lysine-HCl 0.0 0.0 0.0 3.0 3.0 3.0 0.0
L-Methionine 0.0 0.0 0.0 3.0 3.0 3.0 0.0
Na2HPO4 0.0 0.0 0.0 0.0 18.0 0.0 18.0
CMC 30.0 30.0 30.0 30.0 30.0 30.0 30.0
Proximate composition
Protein 381.7 380.8 376.3 387.8 387.8 389.2 383.1
Lipid 96.7 108.7 116.4 117.4 102.9 116.1 109.2
Ash 92.7 91.2 94.8 91.1 106.5 87.9 105.2
Carbohydrate(b) 428.9 419.3 412.5 403.7 402.8 406.8 402.5
Total P 13.2 12.8 12.6 12.7 16.0 12.4 16.1
Phytic acid 3.1 18.8 18.8 18.7 18.5 18.7 18.6
Gross energy (kJ/g)(c) 20.2 20.5 20.6 20.8 20.2 20.8 20.3
Indispensable AA(d)          
Arginine 24.6 23.8 23.8 23.8 23.6 23.8 23.7
Histidine 16.4 13.7 13.7 13.7 13.6 13.7 13.6
Isoleucine 17.5 16.9 16.9 16.9 16.8 16.9 16.8
Leucine 29.2 28.3 28.3 28.2 28 28.2 28.1
Lysine 29.9 26.6 26.6 29.6 29.5 29.6 26.5
Methionine 10.6 7.7 7.7 10.7 10.7 10.7 7.7
Phenylalanine 16.1 15.7 15.7 15.6 15.5 15.6 15.6
Threonine 16.2 16.3 16.3 16.3 16.2 16.3 16.2
Valine 20.5 20.4 20.4 20.4 20.3 20.4 20.3

Table 3: Ingredients, proximate and essential AA composition of the experimental diets in Experiment 2 (CM45: no nutrient supplement; CMF: only phytase 1000 FTU/kg; CMFA: phytase and crystal lysine & methionine; CMPA: AAs and inorganic P; CMAA: only lysine and methionine, CMP: inorganic P only).

Prior to mixing, feed ingredients were ground with a blender and passed through a 400μm sieve. All dry ingredients were first thoroughly hand-mixed. Fish oil was then added and mixed again before adding water to form a dough blend of ingredients for pelleting. Noodle-like feed pellets, which were then broken to make 2-mm diameter pellets, were made using a kitchen meat mincer. Wet pellets were dried at 45°C using a food ventilation dehydrator to produce dry sinking pellets with approximately 8–10% moisture. Experimental feeds were stored at 4°C prior to use.

Chemical Analysis

Proximate analyses of feed ingredients, experimental diets, and whole fish carcass were conducted in duplicate based on the procedures of the AOAC [31]. The analyses include crude protein by the Kjeldahl method; crude fat by petroleum ether extraction using Soxhlet method; moisture by drying to constant weight at 105°C; and ash by incineration at 550°C for 16 hours. AA content of main feed ingredients was analysed by the Australian Proteome Analysis Facility Ltd (Sydney, New South Wales, Australia). The method involved the first step of liquid hydrolyses in 6M HCl at 110oC in 24 hours, followed by Waters AccQTag Ultra chemistry for duplicate analyses of AA. Phytase activity was determined following the method described by Eeckhout and De Paepe [32]. Phytate P content of wheat flour and CM was determined, following AOAC Method 986.11, by Symbio Alliance Laboratory Service (Eight Mile Plains, Queensland, Australia).

Sampling Procedures

Ten fish were sampled at the start of each experiment to allow for initial fish carcass analysis. At the end of each experiment, 5 fish from each tank were sampled and stored frozen for carcass proximate analysis. Specimens for carcass analysis were ground and dried at 80°C for proximate analysis. All fish carcass samples were stored at −20°C until analysis. Small specimens were dried at 105°C to estimate moisture content.

All fish were weighed at the beginning and the end of the experiment and fish growth was calculated. The pooled weight of the fish in each tank was monitored bi-weekly during the whole course of the experiment in order to monitor the growth of fish as well as to estimate feed intake.

Final body weight (BW), apparent net protein utilization (ANPU), feed conversion ratio (FCR), phosphorus efficiency ratio (PhER), daily ortho P waste, and daily total P waste were used as indices to evaluate the effect of treatments on growth, nutrient utilization, and waste production of experimental fish. FCR, ANPU, and PhER were calculated using the method described by Huynh and Nugegoda [26].

The specific growth rate (SGR) of fish was calculated as follow

SGR (%/day) = [ln(Wt/Nt) – ln(W0/N0)]/t

Where: W0 and Wt (g) were the total final body weight of fish at the beginning and the end of the experiment. N0 and Nt was the number of fish at the beginning and at the end of the experiment.

Water assessment for P waste production

At the end of each of the growth experiments, fish were retained in static tanks for a further 3 days in order to determine the P excretion of fish. During this period, the fish were fed once daily in the morning. Water was then changed and water samples were taken for analysis of initial P concentrations. Tank water was then kept static for 24h and samples were again taken for 24h P measurements. P discharged per tank per day was calculated as the difference between the total amount of P in tanks after 24h and total amount of P in tanks at initial measurements. Ortho and total P concentration in water was determined following the methods described by Boyd and Tucker [33]. P discharged was expressed as mg of ortho or total P per kg of fish per day, which was calculated using the method described by Huynh and Nugegoda [26].

Statistical Analysis

Statistical analyses were conducted using SPSS for Windows software version 16.0. One way analysis of variance (ANOVA) was used to test the statistical significance of the differences between the experimental treatments. The Levene’s test was used to test homogeneity of variances. The test was not significant at 95% of confidence suggesting that variances were homogenous and thus the statistical test could be performed accordingly. The Tukey’s

HSD tests were performed to test the differences between the means at P < 0.05. Means were treated as significantly different from each other if P < 0.05.

In experiment 1, the growth performance and FCR of catfish fed with diet CM30 (Table 4) were significantly poorer than those of the control fish (P = 0.016). The growth of catfish on diet CM30F1, supplemented with 1000FTU/kg, was not significantly different from that of fish on the control diet while those on the CM30F2 and CM30F3 diets grew significantly less than the control fish (P = 0.018 and 0.048, respectively). FCR of fish fed with all CM diets was not significantly different from each other (P > 0.05) and was significantly poorer than that of the control fish (P < 0.05) except fish fed with the CM30F1 diet that had comparable FCR to the control fish (P > 0.05). There was no significant difference in ANPU of fish in all treatments. PhER of fish fed with all CM diets was significantly lower than that of the control fish (P < 0.05) but was not significantly different from one other (P > 0.05).

Treatment IW  (g) FW (g) WG (g) SGR FCR ANPU PhER
Experiment 1              
Control 6.03 26.8a 20.7a 1.77a 1.52a 0.22 46.3a
CM30 6.07 23.2c 17.2c 1.60c 1.69c 0.19 39.8b
CM30F1 6.08 25.4ab 19.3ab 1.70ab 1.59ab 0.21 42.6b
CM30F2 5.95 23.3c 17.3c 1.62c 1.68c 0.19 41.8b
CM30F3 6.08 24.8bc 18.7bc 1.67bc 1.66bc 0.21 41.3b
Pooled S.E. 0.02 0.63 0.48 0.02 0.02 0.006 0.72
Experiment 2              
Control 26.7 90.1a 63.4a 1.44a 2.17a 0.16ae 35.2a
CM45 26.5 71.6c 45.1c 1.18c 2.72c 0.13cd 28.7c
CMF 26.5 74.4c 47.9c 1.23c 2.51c 0.14bce 31.6ab
CMFA 26.5 77.6bc 51.1bc 1.28bc 2.38bc 0.16ae 33.3ab
CMPA 26.5 90.5a 64.0a 1.46a 2.12a 0.17a 29.5bc
CMAA 26.7 73.7c 47.0c 1.21c 2.58c 0.12d 31.1bc
CMP 27.2 87.4ab 60.2ab 1.39ab 2.19ab 0.15ab 28.4c
Pooled S.E. 0.10 2.05 2.02 0.03 0.08 0.004 0.67

Table 4: Growth and feed utilization indices of Australian catfish fed with CM diets with various nutrient supplements, CM30, CM30F1, CM30F2, and CM30F3 supplemented with phytase at 0, 1000, 2000 and 3000 FTU/kg, respectively; CM45: no nutrient supplement; CMF: only phytase 1000 FTU/kg; CMFA: phytase and crystal lysine & methionine; CMPA: AAs and inorganic P; CMAA: only lysine and methionine, CMP: inorganic P only. (Conducted at 24oC for 84 days under 12:12 light regime). IW = initial weight, FW = final weight, WG = weight gain.

Results

Growth and feed utilization of fish

In experiment 1, the growth performance and FCR of catfish fed with diet CM30 (Table 4) were significantly poorer than those of the control fish (P = 0.016). The growth of catfish on diet CM30F1, supplemented with 1000FTU/kg, was not significantly different from that of fish on the control diet while those on the CM30F2 and CM30F3 diets grew significantly less than the control fish (P = 0.018 and 0.048, respectively). FCR of fish fed with all CM diets was not significantly different from each other (P > 0.05) and was significantly poorer than that of the control fish (P < 0.05) except fish fed with the CM30F1 diet that had comparable FCR to the control fish (P > 0.05). There was no significant difference in ANPU of fish in all treatments. PhER of fish fed with all CM diets was significantly lower than that of the control fish (P < 0.05) but was not significantly different from one other (P > 0.05).

Results from experiment 2 (Table 4) revealed that the growth of the control fish was significantly better than that of fish fed with all non-P supplemented CM diets (P < 0.02). Fish fed with CMPA and CMP diets had similar growth performance with the control fish (P > 0.05). FCR and ANPU of fish fed with the CMPA, CMP, and control diets were not significantly different from one other (P > 0.05) and were significantly better than that of fish fed with all other CM diets (P < 0.02). ANPU of fish on CMF and CMAA diets was comparable to that of fish on the CM45 diet (P > 0.05) but significantly higher ANPU was observed in fish fed with CMFA diet in comparison to that of fish on the CM45 diet (P < 0.03). Table 4 also showed that PhERs of fish fed with CM45, CMPA, and CMP diets were significantly lower than that of fish fed with the control diet (P < 0.01) and were not significantly different from each other. Catfish on diets CMF and CMFA had comparable PhERs to the control fish (P > 0.05) but only fish fed with the CMFA diet, supplemented with both phytase and AAs, had significantly higher PhER than fish fed with the CM45 diet (P < 0.03).

Effects of dietary treatments on daily P waste of fish

Data in Figure 1 demonstrated that ortho-P waste of fish fed with all CM diets was significantly lower than that of fish fed with the control diet (P < 0.01) but the total P waste of fish on these diets was significantly higher than that of the control fish (P < 0.04). There was no significant effect of dietary phytase on ortho and total P waste of the fish (P > 0.05).

aquaculture-research-development-daily-ortho-phytase

Figure 1: Daily ortho-P and total P waste (mg/kg fish) of Australian catfish fed with phytase supplemented CM diets (CM30, CM30F1, CM30F2, and CM30F3 supplemented with phytase at 0, 1000, 2000 and 3000 FTU/kg, respectively), conducted at 24oC (mean ± S.E., n=3 replicate tanks/treatment). In the same data series, (*) denotes the significant difference from the control (P < 0.05)

The daily ortho P and total P waste of fish fed with nutrient supplemented CM diets are shown in Figure 2. Catfish on the CM45 diet had significantly lower ortho P and higher total P compared to those of the control fish (P < 0.01 and P < 0.05, respectively). In addition, ortho P waste of fish fed with all non-P supplemented CM diets was significantly lower than that of fish fed with the control diet (P < 0.02). Catfish fed with the CMFA diet had a significantly lower total P waste compared to fish on the CM45 diet (P < 0.05). However, dietary phytase did not affect ortho P waste of the fish. The ortho P waste was significantly higher in fish fed with the CMPA diet than in fish fed with all other diets, including the control (P > 0.05). Catfish fed with CMP had significantly higher ortho P waste than fish fed with all other CM diets. The total P waste of fish on the CMP and CMPA diets were significantly elevated compared to that of the fish on all other diets (P < 0.05), except the CM45 diet.

aquaculture-research-development-daily-ortho-nutrients

Figure 2: Daily ortho-P and total P waste (mg/kg fish) of Australian catfish fed with CM diets supplemented with different combination of nutrients (CM45: no nutrient supplement; CMF: only phytase 1000 FTU/kg; CMFA: phytase and crystal lysine & methionine; CMPA: AAs and inorganic P; CMAA: only lysine and methionine, CMP: inorganic P only), conducted at 24oC (mean ± S.E., n=3 replicate tanks/treatment). In the same data series (*) indicates significant difference from the control and (**) indicates significant difference from fish fed CM45 diet (P < 0.05).

Discussion

Results from the 2 experiments indicated that only 30% FM protein was replaceable by CM in diets of Australian catfish. At the higher CM inclusion level of 45% FM protein replacement, the use of phytase as a sole treatment or in combination with lysine and methionine failed to improve the growth performance, P utilization, and P waste production of the fish. Although supplementation of inorganic P showed a significant positive effect on growth, it resulted in high P waste from fish which posed a potential negative impact on the environment.

The low acceptance of dietary CM has been reported in many fish species, such as 15% in Chinook salmon, Oncorhynchus tshawytscha [2,4]; 15% in tilapia, Oreochromis mossambicus [9]; and 36% in channel catfish, Ictalurus punctatus [12]. It would therefore suggest that dietary CM is accepted at low inclusion by most fish. In the current study, replacement of 30% of FM protein with CM did not affect the total P content of the diets, but lysine and methionine content of the replacement diets were decreased by about 6% and 18%, respectively, compared to those of control diet. However, the growth of fish was improved and similar to that of the control fish when phytase was added without the need for supplementing with AAs. Therefore, the low AAs may not be the main cause for the poor growth of fish but phytate since AAs in CM could be bound with phytate and became unavailable and caused significant impairment in the growth of the experimental fish.

Addition of AA to plant protein based diets is a very common practice to improve the growth of fish [34-37]. However, supplementation of lysine and methionine into CM diets in the present study failed to improve the growth of Australian catfish when 45% of dietary FM protein was replaced. In addition, a combination of both phytase and AAs did not enhance the growth performance of the fish. Moreover, while methionine supplement was estimated according to the content in raw ingredients, obtained from AA analysis, the results indicate that a significant proportion of methionine was possibly destroyed during AA analyses. This could imply that the difference in methionine content between the control and canola meal diets was over-compensated. Despite this over-compensation, methionine had no response to the growth of the experimental fish. Although the effects of dietary free AAs are often varied among fish species [38-39], the significant improvement in growth of Australian catfish fed with AAs supplemented SBM diets in the previous study [26] proved the significance of dietary AAs for the species. Therefore, the poor performance of catfish fed with CM diets supplemented with both phytase and AAs particularly suggested that AAs may not be the most important limiting factor in CM.

The negative effects could then be attributed to the other antinutrients in the meal. While the total P content of the CM45 diet was similar to that of the control diet, the growth performance and P utilization of fish fed with former was significantly poorer than that of fish fed with the latter. This may suggest that a significant proportion of dietary P from CM could be bound in phytate form, which has been previously proved to be poorly digestible for many fish species, such as rainbow trout, Oncorhynchus mykiss [1,40]; and turbot, Psetta maxima [1]. Therefore, the direct cause of the low acceptance of CM in fish diets could be the phytate content rather than the nutritional quality. In fact, this assumption was supported by the low P utilization efficiency (PhER) of catfish fed with non-phytase CM diets and the significantly improved PhER of fish on those diets supplemented with phytase (the CMF and CMFA diets). Furthermore, dietary supplementation of inorganic P significantly improved the growth performance of the fish, demonstrating the importance of dietary P when CM was used as FM replacement. Despite the use of inorganic P as a supplement CM diets significantly impaired the P efficiency ratio of the fish, this negative effect would be partially attributed the CM content, which constituted a high proportion of poorly digestible P in the form of phytate, of these diets.

Dietary treatments showed different effects on ortho and total P waste of fish. While the daily ortho-P waste was significantly lower in fish fed with CM diets at both inclusion levels, the ortho-P waste was significantly higher in fish fed with P supplemented diets. The highest ortho P waste was observed in fish on the CMPA diet, which was supplemented with inorganic P as well as lysine and methionine. The low ortho-P waste of fish fed with CM diets suggested the low availability of dietary P in these diets. The effects of dietary CM on total P waste of catfish were completely contrary to that of the effect on ortho-P waste. Catfish fed with CM diets at either 30 or 45% FM replacement had significantly higher daily total P waste compared to that of fish fed with the control diet. The addition of phytase, either solely or in combination with limiting AAs, significantly reduced total P waste of catfish fed with diets containing CM as replacement of 45% FM protein. The enhancement of P utilization and reduction of total P waste of fish fed with phytase supplemented plant-based diets have been reported in previous studies [17,5,41-44]. The common explanations for the improvement of dietary P utilization were: (1) the liberation of chelated phytate-P by phytase leading to higher availability of dietary P [45]; and (2) the promotion of P deposition in fish by dietary phytase leading to higher P utilization and low P waste discharged by fish [46]. In the current study, phytase only showed a significant effect on total P waste of fish when CM replaced 45% dietary FM protein and only when used in combination with supplemented AAs. Fish fed with all non-P supplemented CM diets released significantly higher P waste compared to that of the control fish. This once again supported the assumption that a large fraction of P in CM was in the phytate-bound form, poorly available and thus mostly discharged by the fish.

Dietary supplementation of inorganic P significantly increased both ortho and total P waste of catfish. This negative effect could be attributed to the elevated content of readily available P of the diet which may decrease the efficacy of P retention in fish [46]. In addition, the positive correlation between dietary P and P waste of fish has been reported in previous studies [24,47-51]. The practical use of dietary inorganic P to improve growth performance of catfish is therefore not recommended despite the significant improvement in the growth of the fish.

Conclusions

Only 30% of FM protein could be replaced with CM in diet of catfish, with no detrimental effects on growth and nutrient utilization, when 1000 FTU/kg feed was supplemented. The use of phytase, limiting AAs, or combination of these supplements did not improve the growth of catfish when 45% FM protein was replaced with CM. Replacement of 30% or 45% of FM protein with CM significantly reduced the daily ortho P waste while significantly elevated the daily total P waste of catfish. Dietary phytase had no effect on P waste of catfish when CM replaced 30% FM protein of the fish. At 45% FM protein replacement, adding both phytase and AAs into CM diets significantly lowered the total P waste of the fish. Supplementation of P into CM diets significantly improved the growth of catfish but it significantly impaired P utilization efficiency and increased both ortho-P and total P waste of the fish thus supplementation of diets with inorganic P is also not a recommended practice.

Acknowledgements

The authors would like to thank the Vietnamese Overseas Scholarship Program (Project 322) for sponsorship of the PhD scholarship given to the first author. We are grateful to RMIT Research and Innovation for partial financial support to the first author. We thank James Oliver for technical support. We express our special appreciation of contribution of raw materials for the research by Ridley Aquafeed Australia and Riverland Oilseed Processor.

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