Assessing the implications of variability in the digestible protein and energy value of lupin kernel meals when fed to rainbow trout, Oncorhynchus mykiss

A series of studies were designed to examine the degree of variability in the digestibility of protein and energy from lupin (Lupinus angustifolius) kernel meals when fed to rainbow trout (Oncorhynchus mykiss) and the potential implications of this variability. The digestibility of protein and energy from 10 different varieties of lupin kernel meal was assessed where the test ingredient comprised 30% of each test diet. Digesta was collected using faecal stripping techniques. Digestible protein value ranged from 331 to 508 g/kg DM and digestible energy values ranged from 10.6 to 13.3 MJ/kg DM. To examine the implications of variability in digestible protein and energy value, two lupin kernel meals from the extremes of the protein digestibility range (Lupin-1: AD_N ~ 70% and Lupin-2: AD_N ~ 100%) were chosen for assessment in two growth studies. Soybean meal and a reference diet with fishmeal as the only protein source were also included in the study. In the first growth experiment the test ingredients were included at equal concentrations (40%) in protein-limiting diets (350 g protein/kg DM) and fed at either of two ration levels (restricted and satiety). Diets were formulated on a crude basis so as to place the test variable on the variability in digestible protein value of the diets. In the restricted-fed treatments growth of fish fed the reference diet was highest, but not significantly better than lupin-H. Growth of fish fed the lupin-L diet was significantly poorer than both the reference and lupin-H diets, but not poorer than the soybean diet. The growth responses observed from this experiment clearly showed that the differences in feed intake and/or digestible protein value could be demonstrated in terms of significant differences in growth outcomes. In a second growth study high-nutrient dense extruded diets (400 g protein/kg and 23.5 MJ/kg) were prepared with a more practical level of 25% inclusion of the same test materials. Again the diets were formulated on crude basis so as to place the test variable on the variability in digestible protein and energy value of the diets. Growth of fish restrictively fed the lupin-H diet was highest, but not significantly better than the soybean, reference or lupin-L treatments restrictively fed. Growth of fish satietal fed the soybean diet was significantly poorer than the reference and lupin-H diets, but not compared to the lupin-L diet. The growth responses observed from this experiment showed that the differences in digestible protein and energy value could not be demonstrated in terms of significant differences in growth outcomes, and that feed intake variability and excess nutrient supply masked the effect of this variability; particularly at the satietal feed intake levels.     

Evaluation of the nutritional value of prototype lupin protein concentrates when fed to rainbow trout (Oncorhynchus mykiss)

This study examines the palatability and discrete nutritional evaluation of some prototype lupin protein concentrates (PC) when fed to rainbow trout. Products were developed from both Lupinus angustifolius and Lupinus luteus kernel meals with an increase in protein of 415 g/kg DM to 690 g/kg DM for L. angustifolius and 545 g/kg DM to 750 g/kg DM for L. luteus, respectively. This study completes a three-phase approach to evaluating the nutritional value of these products. The digestibility of energy, nitrogen, phosphorus and organic matter were determined in earlier studies using the diet substitution approach. The apparent digestibility of the energy from the L. angustifolius PC and the L. luteus PC along with the apparent protein digestibility were used to formulate two series of experimental diets to examine both the palatability and discrete nutritional value of the products. Serial inclusion of either PC at 0%, 10%, 20%, 30% and 40% into a typical salmonid diet specification allowed an examination of the palatability of each product. Additional negative controls, based on the 0% diets with inclusion of sulfamerazine sodium, were included in the experiment to demonstrate the capacity of the experiment to detect significant palatability issues. No significant effects of inclusion of either PC on any fish performance criteria, such as feed intake or growth, were identified. In contrast, significant reductions in feed intake and consequently growth were observed from fish fed either of the negative controls. This experiment demonstrated that each PC was highly palatable at inclusion levels up to and including 40% of the diet. Using a protein-limited-restrictively-fed experimental approach the discrete nutritional utilisation of each PC was defined. Growth of fish fed the PC treatments was not significantly different to that of the 0% reference diet. Two control diets with substitutions of cellulose to an equivalent inclusion level to that of the PC have provided an indication of the net benefit of the test ingredients. This experiment demonstrated that each PC provided equivalent nutritional value to the fish at either of the two inclusion levels (20% and 40%) evaluated. These PCs differed in their viscosity and gelling properties which may allow feed manufacturers the opportunity to manipulate the physical attributes of their feeds. Together, these studies clearly show that the prototype PCs have substantial potential as a prospective feed ingredient for the aquaculture sector.     

The influence of dehulling efficiency on the digestible value of lupin (Lupinus angustifolius) kernel meal when fed to rainbow trout (Oncorhynchus mykiss)

A single batch of Lupinus angustifolius seed was processed to produce a seed meal and dehulled to produce a pure kernel meal. A series of blends were prepared from the seed and kernel meals. The digestible values of these pure and a series of blended meals were compared when fed to rainbow trout using the diet‐substitution method (700 g kg⁻¹ reference: 300 g kg⁻¹ test ingredient). Improvements were observed for each of dry matter, energy and crude protein digestibilities with increasing dehulling efficiency. The relationship between dry matter digestibility and kernel meal proportion was linear and is described by the equation: y = 0.2147x + 40.929. Dry matter digestibility for the 100% kernel meal was 59.8%. The relationship between crude protein digestibility and kernel meal proportion was curvilinear and is described by the equation: y = −0.0019x² + 0.3948x + 81.9143. Crude protein digestibility for the 100% kernel meal was 102%. The relationship between energy digestibility and kernel meal proportion was linear and is described by the equation: y = 0.158x + 48.77. Energy digestibility for the 100% kernel meal was 65.1%. The findings of this study demonstrate that there are significant benefits from using kernel meals over seed meals.     

Using Near Infrared Reflectance Spectroscopy (NIRS) to predict the protein and energy digestibility of lupin kernel meals when fed to rainbow trout,Oncorhynchus mykiss

This study examined the potential of using near infrared spectroscopy (NIRS) to predict the nutrient composition, energy density and the digestible protein and digestible energy values of lupin kernel meals when fed to rainbow trout. A series of 136 lupin kernel meals were assessed for their protein and energy digestibilities using the diet‐substitution approach in a series of 10 experiments over a 6‐year period from 2002 to 2008. Two reference diets were also included in each experiment. Minimal variance in the digestibility parameters of both reference diets was observed among the experiments ensuring that there was a high degree of robustness in the across‐experiment evaluations. The same lupin kernel meal samples were also scanned using a diode array near infrared spectrophotometer (DA‐NIRS). The spectra obtained by the DA‐NIRS were chemometrically calibrated against both the chemical composition and the digestible value data using multivariate analysis software. The cross validation tests used in this study provide a valid indication of the potential to predict the nutrient composition, energy value and digestible protein and energy values of the lupin kernel meals as used in diets for rainbow trout. That the standard errors of cross validation (SECV) of the parameters investigated were generally commensurate with the cross trial variation seen in the reference sample indicating robust calibrations for the two target parameters of digestible protein and digestible energy. Therefore this study demonstrates that within one raw material type that not only does significant variability in the digestible value of the raw materials exist, but that it is possible to use NIRS technology to provide rapid estimates of the digestible value of those raw materials in near real‐time.     

Variability in the chemical composition of different cottonseed and sunflower meals influences their digestibility when fed to grass carp (Ctenopharyngodon idella)

In the present study, it was examined whether variability in chemical composition of different cottonseed (Nazilli‐M39, Nazilli‐84 and Çukurova‐1518) meals (CSMs) and sunflower (Sanbro, Isera and Coban) meals (SFMs) had any effects on digestibility when fed to grass carp. Protein and energy digestibility of CSMs (83.2–86.8%; 88.7–92.5%) and SFMs (78.9–83.1%; 88.4–92%) had a coefficient of variation of 1.96% (CSMs) and 1.52% (SFMs) for protein and 1.93% (CSMs) and 1.82% (SFMs) for energy digestibility. Sum of amino acids digestibility of CSMs (83.1–86.5%) and SFMs (78.9–83.4%) had a coefficient of variation of 1.85% and 2.47%, respectively. Protein and energy digestibility of CSMs and SFMs was significantly positive affected by a range of compositional features including protein or sum of amino acids and phosphorus content, and significantly negative affected by fiber and carbohydrate contents in the test ingredients. This suggested that fiber and carbohydrate contents of CSMs and SFMs may also be influencing the nutritional value of its own protein or sum of amino acids. In conclusion, the relationship between plant protein meals protein content and its digestible value provides a good support for the development of a system of grain segregation by protein content and ingredient pricing according to that protein content.     

A comparison of the growth performance of rainbow trout (Oncorhynchus mykiss) when fed soybean,narrow‐leaf or yellow lupin meals in extruded diets

This study compared the effect of increasing dietary inclusion of soybean, narrow‐leaf lupin or yellow lupin kernel meals when fed to rainbow trout. Each meal was formulated into a test diet to create a series of inclusion levels of 0, 100, 200, 300 and 400 g kg^?1. Each diet was formulated to the same digestible protein and energy specifications. The diets were fed to apparent satiety to 30.0 ± 0.71 g rainbow trout for 28 days. After this period, fish in the reference (0 g kg^?1) treatment attained a weight of 93.2 g. Growth of the fish among the treatments was observed to be improved by the addition of either variety of lupin meal. In contrast, growth of fish fed the soybean meal was equivalent to that of the 0 g kg^?1 fish meal reference, but was poorer at the 400 g kg^?1 inclusion level. Feed intake with the lupin meals was marginally improved with lupin inclusion, but at the higher soybean meal inclusions, feed intake was reduced relative to the fish meal reference diet. The inclusion of the different grains also had significant effects on the physical properties of the pellets.     

A comparison of the digestibility of lupin (Lupinus sp.) kernel meals as dietary protein resources when fed to either, rainbow trout, Oncorhynchus mykiss or red seabream, Pagrus auratus

The nutritional value of the kernel meals of three species of lupin (Lupinus albus, L. angustifolius and L. luteus) was compared against each other and solvent extracted soya bean meal and wheat gluten, when fed to either rainbow trout or red seabream. The digestible nutrient and energy values were determined for each ingredient, based on the diet substitution digestibility method. Each test ingredient was included in test diets at 300 g kg^?1. As different faecal collection methods were used on each species, only ingredient comparisons within each fish species study are valid. Protein digestibility for all lupin kernel meals was significantly better than for soya bean meal when fed to red seabream, although only numerically so when fed to rainbow trout. The highest protein digestibility in both fish species was that from the wheat gluten (100.0% for both rainbow trout and red seabream). Energy digestibility for each of the lupin kernel meals (range 62.4%–64.9% in rainbow trout and 60.9%–69.5% in red seabream) was less than that obtained from soya bean meal (75.1% and 81.0% for rainbow trout and red seabream, respectively). However, the higher gross energy content of the lupin kernel meals still resulted in both L. albus and L. luteus providing equivalent levels of digestible energy as that of soya bean meal. Organic matter digestibility was generally poorer for each of the lupin kernel meals relative to that for the soya bean meal and particularly compared with the wheat gluten. Phosphorus digestibility was significantly better in all lupin kernel meals than that from both the soya bean meal and wheat gluten. Highest phosphorus digestibility was that obtained from L. albus kernel meal (100.0% for both rainbow trout and red seabream) although notably the phosphorus digestibility of all lupin kernel meals when fed to rainbow trout was determined at 100%. Similarly the digestibility of phosphorus from lupin kernel meals fed to red seabream was also very high. This study supported the good nutritional value to both rainbow trout and red seabream of kernel meals of all three species of lupin, although the digestible nutrient attributes of kernel meal from L. luteus were particularly favourable.     

Phosphorus utilization in rainbow trout (Oncorhynchus mykiss) fed practical diets and its consequences on effluent phosphorus levels

Excessive dietary phosphorous (P) concentrations in effluents from aquaculture present a major environmental problem. We therefore studied the effect of dietary P and vitamin D₃ on P utilization by rainbow trout-fed practical diets and on P concentrations in the soluble, particulate and settleable components of the effluent from fish tanks. Rainbow trout (average weight: 78 g, initial biomass: 13 kg in 0.7 m³ tanks) were fed for 11 weeks, practical diets that varied in total P, available P, and vitamin D₃ concentrations. Soluble, particulate (10–200 μm) and settleable (>200 μm) P in the effluent were sampled every 0.5–6 h for 1–3 days in the third and eleventh weeks of the experiment. Trout in all diets more than doubled their weight after 11 weeks. Increasing the concentrations of available dietary P from 0.24% to 0.88% modestly enhanced growth rate. Feed conversion ratio (FCR) and biomass gain per gram P consumed decreased as dietary P concentrations increased. Carcass P, daily P gain, and plasma P concentrations were lower in fish fed with low P diets. Soluble P concentrations in the effluent peaked immediately after and again 4–6 h after feeding, and is a linear function of available dietary P. No soluble P would be produced during consumption of diets containing less than 0.22±0.02% available P. Above this dietary concentration, soluble P would be excreted at 6.9±0.4 mg/day/kg for each 0.1% increase in available dietary P. Particulate P concentrations in the effluent were independent of dietary P concentrations. Settleable, presumably fecal, P concentrations tended to increase with dietary P concentrations. In trout fed with low P (0.24% available P, 0.6% total P) diets, 60% of total dietary P were retained by the fish and the remaining 40% were excreted in the effluent as settleable P (20–30%) and particulate or soluble P (10–20%). In trout fed with high P (0.59–0.88% available P; 0.9–1.2% total P) diets, 30–55% of total dietary P was retained by fish, and the remaining 15–25% appeared in the effluent as settleable P, 20–55% as soluble P, and 5–10% as particulate P. Vitamin D₃ did not affect fish growth nor effluent P levels. Physicochemical management of aquaculture effluents should consider the effect of diets on partitioning of effluent P, the peaks of soluble P concentration following feeding, and the contributions of particulate P to total P in the effluent. Increasing our understanding of how dietary P is utilized and is subsequently partitioned in the effluent can contribute significantly towards alleviating this important environmental and industry problem.     

黄鳝生长差异基因发掘及其调控机制初步研究

该研究对体质量为 (25.03±0.02) g 的健康黄鳝 (Monopterus albus) 进行了10 周的养殖实验,探究了低鱼粉饲料中添加牛磺酸对黄鳝生长、消化率及肠道酶活性的影响。实验设置了高鱼粉组 (42%, FM)、低鱼粉组 (22%, T₀) 以及在低鱼粉饲料中分别添加0.2% (T_0.2) 和0.5% (T_0.5) 牛磺酸的4个处理组,每组5个重复。结果显示,与FM组相比,T₀组黄鳝的增重率、蛋白质效率、干物质消化率和蛋白质消化率显著下降 (P<0.05),饲料系数显著上升 (P<0.05)。添加适量牛磺酸可显著提高黄鳝的增重率、蛋白质效率和干物质消化率,降低饲料系数 (P<0.05),但T_0.5组黄鳝的增重率、蛋白质效率和饲料系数与T₀组相比无显著性差异 (P>0.05)。此外,T₀组肠道肌酸激酶 (CK)、钠钾ATP酶 (Na⁺-K⁺-ATPase)、碱性磷酸酶 (AKP)、胰蛋白酶 (TRYP) 和脂肪酶活性显著低于FM组 (P<0.05),T_0.2组的上述肠道酶活性均显著升高 (P<0.05),T_0.5组肠道Na⁺-K⁺-ATPase、AKP、TRYP和脂肪酶 (LPS) 活性虽高于T₀组,但无显著性差异 (P>0.05)。综上,低鱼粉饲料中添加0.2%牛磺酸可提高黄鳝的生长,改善肠道消化吸收功能,但添加过量牛磺酸 (0.5%) 效果不明显。     

Antioxidant processes are affected in juvenile rainbow trout (Oncorhynchus mykiss) exposed to ozone and oxygen-supersaturated water

Two groups of juvenile rainbow trout (Oncorhynchus mykiss) were exposed for 4 h to either hyperoxic (>40 mg O₂/l) or ozonised (5.2 μg O₃/l) water containing supersaturated oxygen. Gill, liver, blood cells and plasma were taken 1, 5, 12, 24 and 48 h following the exposure periods and antioxidant responses and oxidative damage studied in terms of, respectively, antioxidant enzyme activities/glutathione status and lipid peroxidation. Observed biochemical changes were significant at p<0.05. Ozonation elevated oxidised glutathione (GSSG) levels, increased lipid peroxidation and decreased reduced glutathione (GSH) levels in gills 1 h following exposure, which indicate oxidative stress. However, the longer-term effects (48 h) following ozone exposure resulted in increased GSH levels in both gills and liver and, measured as oxidative stress index (OSI), were indicative of enhanced potential of tissues to resist oxidative stress. Ozonation also resulted in elevated activity of superoxide dismutase (SOD) at 5–12 h following exposure in gills compared to 24–48 h in liver, indicating either differential regulation and time-courses of response, or an earlier impact of ozonolysis products on gills than liver. In contrast, catalase activity was elevated in both gills and liver at 24 h by the effects of hyperoxia alone. Hyperoxia also decreased GSSG levels in both gills and liver, but had no effect on lipid peroxidation. Increases were seen in the activities of selenium-dependent glutathione peroxidase as a result of ozonation (gills; 5 and 24 h) and hyperoxia (liver; 1 h), and in total GPX (Se-dependent and independent) as a result of ozonation (both tissues; 48 h), but no effects were seen on glutathione reductase (GR) in either tissues. Levels of GSH were increased in blood cells at various times following hyperoxia. Overall, the results show (i) differential antioxidant and pro-oxidant effects of ozonation compared to hyperoxia, (ii) gills and possibly blood as the first line of impact and defence, with later effects on liver, and (iii) that even after 24–48 h following ozone exposure, all antioxidant defences had not returned to pre-exposure values.     

斑节对虾Chitinase-2基因的克隆及其在蜕皮和幼体发育过程中的表达分析

该研究以高氨氮和淡水胁迫致死时间为衡量指标,估计了斑节对虾(Penaeus monodon)耐氨氮和淡水应激性状的遗传参数。以斑节对虾“南海1号”和非洲品系为亲本,建立了27个全同胞家系,含5个半同胞家系。利用单性状动物模型和ASReml软件估计斑节对虾幼体阶段的耐氨氮和淡水应激性状的方差组分和遗传参数。通过最佳线性无偏预测法估计所有个体和家系耐氨氮和淡水应激性状的育种值。斑节对虾耐氨氮和耐低盐的遗传力分别为0.11±0.04和0.29±0.08,且统计检验达到显著水平。斑节对虾耐氨氮和淡水应激性状的家系表型值相关系数为0.15,表现为低度线性正相关。斑节对虾耐氨氮和淡水应激性状的家系育种值相关系数为0.57,表现为中度线性正相关。因此在进行斑节对虾耐氨氮性状选育时,耐淡水应激性状也能得到一定的改良。

     

Depletion of isoeugenol residues from the fillet tissue of AQUI-S™ exposed rainbow trout (Oncorhynchus mykiss)

There is a critical need in U.S. public aquaculture and fishery management for an approved sedative that allows for the immediate release of fish after sedation. AQUI-S^TM is a fish anesthetic/sedative approved for use in several countries and until recently was being developed in the U.S. as a sedative for immediate release of fish after sedation. The U.S. National Toxicology Program reported that isoeugenol (the active ingredient in AQUI-S^TM) exposed male mice showed clear evidence of carcinogenicity, therefore efforts within the U.S. Department of Interior to develop AQUI-S^TM as a sedative that allows for immediate release ceased. Despite the ruling, AQUI-S^TM still has the potential to be approved as an anesthetic with a short withdrawal time. Among the data required to gain approval for use in the U.S. are data describing the composition and depletion of all AQUI-S^TM residues from fish fillet tissue. A total residue depletion study for AQUI-S^TM was conducted by exposing market-sized rainbow trout, Oncorhynchus mykiss (mean weight, 502.7 ± 54 g; s.d.) to 8.9 mg/L of ¹⁴C-[URL]-isoeugenol for 60 min in 17 °C water. The ¹⁴C-[URL]-isoeugenol was mixed with a surfactant resulting in a mixture that mimicked AQUI-S^TM. Groups of fish (n = 6) were sampled immediately after the exposure (0-h sample group) and at 0.5, 1, 2, and 4 h thereafter. Total isoeugenol-equivalent residue concentrations in the fillet tissue were determined by oxidizing triplicate subsamples of homogenized skin-on fillet tissue from each fish to ¹⁴CO₂ and enumerating the radioactivity by static liquid scintillation counting. Isoeugenol concentrations in fillet tissue were determined by extracting homogenized fillet tissue with solvents and determining the isoeugenol concentrations in the extracts with high performance liquid chromatography techniques. The mean total isoeugenol-equivalent residue concentrations in the 0, 0.5, 1, 2, and 4-h sample groups were 55.4, 32.0, 19.8, 11.3, and 4.9 µg/g, respectively. The primary chemical residue in fillet tissue from all exposed fish was isoeugenol. The mean isoeugenol concentrations in the 0, 0.5, 1, 2, and 4-h sample groups were 48.9, 26.5, 15.3, 7.2, and 2.2 µg/g, respectively. The percents of the total radioactivity classified as isoeugenol in the 0, 0.5, 1, 2, and 4-h tissue extracts were 95, 73, 73, 64, and 48%, respectively.     

Feeding high inclusion of whole grain white lupin (Lupinus albus) to rainbow trout (Oncorhynchus mykiss): effects on growth,nutrient digestibility,liver and intestine histology and muscle fatty acid composition

The effect of dietary inclusion of whole grain white lupin (Lupinus albus) on growth performance, histology, muscle fatty acid composition and nutrient digestibility was investigated in an 11‐week growth and a 4‐week digestibility trial with rainbow trout (initial body weight of 54.0 ± 6.2 and 181.9 ± 3.4 g respectively). Four experimental extruded diets were formulated to contain 0%, 30%, 40% and 50% of whole grain lupin and fed to triplicate groups of fish twice a day until apparent satiation. Faeces were collected daily from each digestibility tank by decantation. No significant trends were observed with respect to growth, feed utilization, apparent digestibility coefficients or whole‐body composition (P>0.05). Conversely, increasing levels of dietary lupin led to significant decreases in the Hepatosomatic index (R²=0.75, P<0.05) and slight lipid infiltration into hepatocytes and enterocytes. Muscle fatty acid compositions were slightly affected by the dietary treatment. Polynomial regression of dietary inclusion of lupin and muscle fatty acid concentrations showed an increase in C18:1n‐9, C18:2n‐6 and C18:3n‐3 and a decrease in C20:5n‐3 with increasing dietary lupin level. These results demonstrated that whole grain lupin can be included up to 50% in commercial rainbow trout diets without negative effects.     

Evaluation of the influence of Lupinus angustifolius kernel meal on dietary nutrient and energy utilization efficiency by rainbow trout (Oncorhynchus mykiss)

This study examined the utilization efficiencies of three diets when fed to rainbow trout in a 28‐day growth study. Each of the diets was fed at one of three ration levels, and an additional starved treatment was also included. The diets differed by an increasing concentration of lupin (Lupinus angustifolius cv. Myallie) kernel meal (MKM) inclusion. Two lupin kernel meal inclusion levels of 15% (MKM15%) and 30% (MKM30%) were studied. The diets were formulated to equivalent digestible protein and energy specifications based upon the predetermined digestibility values for each of the ingredients used. There were no significant differences in digestible protein level among the diets. However, a significantly higher level of digestible energy of both MKM diets was measured, as well as a significantly higher level of digestible phosphorus in the MKM30% diet. No significant differences between the diets were observed with respect the utilization of dietary digestible energy. Over the full data range, the energy utilization efficiency was described by the linear equation of; y = 0.747x ? 26.174, R² = 0.985. Efficiency of protein utilization over lower digestible protein intake levels was also linear (y = 0.599x ? 0.142, R² = 0.905), but over the full range was better described by a nonlinear function. The comparison of the three diets in this study shows that the dietary inclusion of lupin kernel had no significant effect on the gain of either protein or lipid energy relative to protein or lipid energy intake, respectively. Protein energy use efficiency constants varied depending on the feed intake level, but were not significantly affected by diet type. The efficiency of use of lipid energy for lipid energy retention was also not affected by diet type. The findings of this study demonstrate that the inclusion of lupin kernel meal, at up to 30% of the diet, does not affect the ability of rainbow trout to utilize the dietary digestible protein and energy of diet in which it is included.     

Growth performance,nutrient digestibility and intestinal morphology of rainbow trout (Oncorhynchus mykiss) fed graded levels of the yeasts Saccharomyces cerevisiae and Wickerhamomyces anomalus

In a 10‐week study, we evaluated the effects of replacing 20%, 40% or 60% of fishmeal (present in control diet at 300 g/kg) on a digestible protein basis with yeast Saccharomyces cerevisiae or a yeast mixture of Wickerhamomyces anomalus and S. cerevisiae on growth performance, nutrient digestibility, nutrient retention and intestinal health of rainbow trout (Oncorhynchus mykiss). Triplicate tanks with 35 rainbow trout (144.7 ± 25.1 g mean ± SEM) were fed rations of 1.5% of total biomass per tank. Replacement of 60% of fishmeal with yeast mixture resulted in lower specific growth rate of 1.0% versus 1.2%/day for other diets. Apparent digestibility coefficients for crude protein and most amino acids were highest in fish fed fishmeal‐based diet, with similar values for fish fed the diet with 20% replacement with yeast mixture. Diet with 20% replacement with yeast mixture resulted in highest phosphorus digestibility. Replacement of 60% of fishmeal with S. cerevisiae resulted in oedematous mucosal fold tips in the proximal intestine. The results of this study suggest that these yeasts can replace up to 40% of fishmeal under current inclusion levels in diets for rainbow trout without compromising growth performance, nutrient digestibility or intestinal health.     

Effect of enzyme supplementation to dehulled lupin-based diets on growth, feed efficiency, nutrient digestibility and carcass composition of rainbow trout, Oncorhynchus mykiss (Walbaum)

High inclusion levels of dehulled lupin (Lupinus angustifolius) in salmonid diets significantly decrease growth rates. This may be caused by the high concentrations of non‐starch polysaccharides including oligosaccharide (OS) in lupin. The antinutritive effects of OS have not yet been fully investigated in fish. The objective of this study was to determine the effect of enzyme supplementation of dehulled lupin‐based diets on the fish performance. There were two control diets: a fish meal‐based diet with no plant protein (FM) and a diet that contained 50% dehulled lupin (L). Four experimental diets based on diet L and containing four different exogenous enzyme supplements were used: diet L(E) (Energex^™); diet L(B) (Bio‐Feed^™ Pro); diet L(α) (Alpha galactosidase^™); and diet L(Mix), which contained all the enzymes. Fish were randomly stocked into tanks in duplicate groups of 38 fish, 16.58±0.169 (SE) g, and were fed twice a day for 6 weeks. The supplemented enzymes did not improve weight gain in fish fed lupin‐based diets. However, mixed enzyme significantly improved Protein Efficiency Ratio (PER). Apparent digestibility of DM, CP and GE significantly improved in fish‐fed L(E) diet. None of the supplemented enzymes affected digestive tract indices or carcass composition. Surprisingly, weight gain was significantly higher in fish‐fed L(α), L(E) and L(Mix) diets as compared with FM diet. Feed intake was significantly higher in fish‐fed L, L(α) and L(E) diets compared with the FM diet. It is concluded that storing of lupin kernel under a suitable condition may have partially hidden the positive effects of exogenous enzymes through activating the endogenous enzymes.     

Vitamin B6 supplementation increases the docosahexaenoic acid concentration of muscle lipids of rainbow trout (Oncorhynchus mykiss)

Fish fillet quality is influenced by feed quality. In particular, vitamin B₆ availability improves growth rate and nutritional value, because it is related to protein and lipid metabolism. The present study investigates the effect of increasing amounts of vitamin B₆ on growth, fatty acid composition and lipid peroxidation of muscle tissue of rainbow trout (Oncorhynchus mykiss). Quadruplicate groups of trout of a mean initial weight of 110 g were fed commercial diets supplemented with four different quantities of vitamin B₆ (0, 10, 25 and 50 mg kg^?1 diet). Over the experimental period, there were no significant differences in weight gain and feed intake, while vitamin B₆ concentration of muscle was affected by dietary intake, even though its increase was not proportional to the concentrations in the feed. The fatty acid composition of muscle lipid showed differences between the four groups. The percentage of long‐chain unsaturated fatty acids, in particular docosahexaenoic acid, increased significantly in vitamin B₆‐supplemented groups. However, despite the increased fatty acid unsaturation index, lipid peroxidation parameters such as vitamin E content, malondialdehyde production, glutathione reductase and glutathione peroxidase activities did not show significant differences, meaning that the higher level of long‐chain unsaturated fatty acid did not increase the muscle susceptibility to oxidative stress.     

The use of AquaMats® to enhance growth and improve fin condition among raceway cultured rainbow trout Oncorhynchus mykiss (Walbaum)

AquaMats® are a type of artificial seaweed designed to provide structure in ponds used for fish culture and as a substrate for the growth of aquatic plants and invertebrates which in turn are a source of nutrition to cultured species. In two separate tests AquaMats® were placed into raceways used to rear rainbow trout Oncorhynchus mykiss (Walbaum) to evaluate their effect on fish growth and fin condition. In the first test, the AquaMats® were placed perpendicular to the raceway length similar to a baffle design. One treatment consisted of AquaMats® that were cleaned on a regular basis, and the other treatment consisted of AquaMats® that were not cleaned throughout the test. By the end of the test no differences were found between treatments with respect to final fish weight, specific growth rate, or feed conversion ratio. The use of AquaMats® did not improve fin condition, in fact several fins measured were significantly better among control fish. In the second test AquaMats® were placed on the raceway bottom parallel to their length and to the water flow. AquaMats® were also hung from the side of the raceway to provide cover. At the conclusion of this test no differences were found between treatments with respect to final fish weight, specific growth rate, or feed conversion ratio. The placement of AquaMats® did have a transitory impact on fin condition. Mid‐way through the test, treatment fish generally exhibited longer fins compared with the controls. However, by the end of the test, these differences were no longer detectable. The results from both tests indicate that fish were not provided with additional nutrition to the extent it improved growth. However, the use of AquaMats® did make a significant, albeit transitory, impact on fin condition.