Nutrient leaching from coated crustacean rations

The use of ethyl cellulose as a coating agent to retain water soluble nutrients in pelleted feeds was investigated. When the entire ration pellet was coated, minimal nutrient leaching occurred, even after 6 h. Inclusion of individually coated micronutrients was less effective than total pellet coating for nutrient retention, but did help prevent losses due to leaching.     

Real‐time measurement of protein leaching from micro‐particulate larval fish feeds

The small size and high surface area to volume ratio of larval fish feed presents challenges for nutrient retention in micro‐particulate diets. A method for the accurate and rapid measurement of nutrient retention or loss from micro‐particulate feed in water is needed to help develop micro‐particulate feeds with good nutrient retention characteristics. The present study developed and validated an instrument method using fibre optic technology that measures protein leaching in real time. Larval fish feed particles of different sizes (100–500 μm) and formulations were measured. Under consistent experimental conditions, a feed could be assayed for the rate of mass loss and the half‐life or time of 50% total soluble mass loss. The results closely approximated natural decay models with coefficients of determination (r²) >0.95. The end result is a fast and accurate method to quantify and provide solid reference data for a feed formulation or particle size. Using this method allows different feeds to be compared and conclusions drawn for relative performance.     

Effects of supplementation of coated crystalline amino acids on growth performance and body composition of juvenile kuruma shrimp Marsupenaeus japonicus

Supplementation of crystalline amino acids (CAA) in shrimp diets is unsuccessful in most cases. In the present study, various pre‐coated CAA were developed to minimize the leaching losses from diets in water and assessed using kuruma shrimp Marsupenaeus japonicus juveniles. Experimental diets were supplemented with coated CAA or non‐coated CAA to simulate the dietary amino acid profile to that found in the whole body protein of shrimp. The four diets contained CAA coated with either carboxymethyl cellulose (CMC) (diet 1), zein (diet 2), k‐carrageenan (diet 3) or agar (diet 4), respectively. Another four diets contained CMC‐coated CAA with the addition of either zein (diet 5), casein‐gelatin (diet 6), zein and k‐carrageenan (diet 7), or casein‐gelatin and k‐carrageenan (diet 8), respectively. The 8 weeks feeding trial demonstrated that the diets containing coated CAA gave significantly higher weight gains than diets containing non‐coated CAA, with the highest value for the diet 6. The diets containing coated CAA also yielded higher feed conversion efficiency, protein efficiency ratio, and specific growth rate than diets containing non‐coated CAA. Leaching trials suggested that shrimp growth performance was improved partly due to the retardation or reduction of CAA leaching by coating them with specific binders.     

The influence of environmental temperature on the apparent nutrient and fatty acid digestibility in Atlantic salmon (Salmo salar L.) fed finishing diets containing different blends of fish oil, rapeseed oil and palm oil

A 12‐week feeding trial was conducted to investigate the interactive effects between water temperature and diets supplemented with different blends of fish oil, rapeseed oil and crude palm oil (CPO) on the apparent nutrient and fatty acid digestibility in Atlantic salmon. Two isolipidic extruded diets with added fish oil fixed at 50% and CPO supplemented at 10% or 25% of total added oil, at the expense of rapeseed oil, were formulated and fed to groups of Atlantic salmon (about 3.4 kg) maintained in floating cages. There were no significant effects (P>0.05) of diet on growth, feed utilization efficiency, muscle total lipid or pigment concentrations. Fatty acid compositions of muscle and liver lipids were mostly not significantly different in salmon fed the two experimental diets but showed elevated concentrations of 18:1n‐9 and 18:2n‐6 compared with initial values. Decreasing water temperatures (11–6°C) did not significantly affect protein, lipid or energy apparent digestibilities of the diets with different oil blends. However, dry matter digestibility decreased significantly in fish fed the diet with CPO at 25% of added oil. Increasing dietary CPO levels and decreasing water temperature significantly reduced the apparent digestibility (AD) of saturated fatty acids. The AD of the saturates decreased with increasing chain length within each temperature regimen irrespective of CPO level fed to the fish. The AD of monoenes and polyunsaturated fatty acids was not affected by dietary CPO levels or water temperature. No significant interaction between diet and water temperature effects was detected on the AD of all nutrients and fatty acids. The results of this study showed that the inclusion of CPO up to about 10% (wt/wt) in Atlantic salmon feeds resulted in negligible differences in nutrient and fatty acid digestibility that did not affect growth performance of fish at the range of water temperatures generally encountered in the grow‐out phase.     

Dietary effect of fish oil and soybean lecithin on growth and survival of juvenile Litopenaeus vannamei in the presence or absence of phytoplankton in an indoor system

This study was conducted to evaluate whether phospholipids have the potential to reduce the level of dietary fish oil inclusion in shrimp feeds in the presence and absence of phytoplankton. To do so, weight gain of juvenile Litopenaeus vannamei stocked at 80 shrimp m^?2 fed different dietary levels of fish oil and soybean lecithin was determined. Six experimental 35% protein diets were formulated to contain 1%, 2% or 3% fish oil combined with either 1% or 4% soybean lecithin. Dietary effects were evaluated using a ‘clear‐water culture system’ without the presence of microalgae in 40‐L aquaria and a ‘green‐water culture system’ in 1.9‐MT tanks. After an 8‐week feeding period, shrimp cultured in both systems and fed diets containing 4% soybean lecithin had greater weight gain than those fed 1%. Thus, diets supplemented with phospholipids improved the efficiency of lipid utilization for growth: diets containing 1% fish oil in combination with 4% soybean lecithin can be used as a cost‐effective combination for commercial shrimp culture feeds. Weight gain in the green‐water system was 1.5–1.7 times greater than that for shrimp reared under clear‐water conditions, suggesting that phytoplankton contributes to shrimp growth through the continuous provision of nutrients.     

Evaluation of lipid sources in diets fed to bull trout,Salvelinus confluentus

To aid in development of nutritionally complete diets, a 12‐week experiment was conducted to identify appropriate sources of dietary lipid for bull trout. The basal diet was top‐coated with marine fish oil (MFO) (pollock liver oil), canola oil (CO), linseed oil (LO) or a mixture of canola and linseed oils (CLO) to produce four treatments. Each diet was fed to triplicate groups of fish initially averaging 1.6 g per fish. Weight gain, feed efficiency, survival and carcass proximate composition were not significantly different among fish fed the dietary treatments. However, whole‐body fatty acid percentages varied significantly among fish fed the four diets. Whole bodies of fish fed diets with vegetable oil (VO) contained significantly higher 18:2n‐6, 18:3n‐3 and total n‐6 polyunsaturated fatty acid percentages and significantly lower 20:5n‐3, 22:6n‐3 and total saturated fatty acid percentages compared with fish fed the MFO diet. Whole‐body fatty acid percentages also varied among fish fed VO diets. Despite similar 18:2n‐6 and 20:4n‐6 percentages in the VO diets, fish fed diet CO contained significantly lower 18:2n‐6 proportions and significantly higher 20:4n‐6 proportions compared with fish fed other VO diets. Results of this study suggest dietary fish oil is not required for short‐term rearing of bull trout.     

Effects of fish oil and partial fish meal substitution with oilseed oils and meals on growth performance, nutrient utilization and health of the rainbow trout Oncorhynchus mykiss

A feeding trial was conducted to investigate the effects of the replacement of dietary fish meal and fish oil with oilseed meals (soybean or canola) and canola oil on growth, nutrient utilization, body composition, diet digestibility and hematological parameters of rainbow trout Oncorhynchus mykiss. Seven diets were used; the control diet (designated FM) contained fish meal and fish oil as the main protein and lipid sources. For the experimental diets, 40% of fish meal protein was substituted with soybean meal, canola meal or a soybean/canola meal mixture, and these diets (designated SM, CM and SCM, respectively) contained fish oil as the lipid source. Three additional diets (SM?+?CO, CM?+?CO and SCM?+?CO) were formulated with the same vegetable protein meals but with fish oil replaced by canola oil. Fish were fed twice daily to apparent satiation for 11?weeks. The growth of fish fed the CM?+?CO diet was significantly lower than that of fish fed the FM, SCM, SM?+?CO and SCM?+?CO diets. The feed conversion ratio (FCR) was significantly better in fish fed the FM and SCM?+?CO diets than in fish fed the CM and CM?+?CO diets. Furthermore, feed intake was significantly lower for fish fed the CM?+?CO diet than in fish fed the SCM diet, and lipid digestibility of the CM?+?CO diet was significantly lower than that of all other diets. No significant differences of body composition were observed. Circulating leukocyte levels, leukocyte ratios and serum lysozyme activity remained unaffected by dietary treatment. However, it was observed that fish fed the CM?+?CO diet displayed hematocrit levels significantly lower (P?<?0.05) than that of fish fed the other diets. The results indicate that when diets contain either fish oil or canola oil, canola meal and soybean meal can be incorporated into rainbow trout feeds at a combined 32% inclusion level (replacing 40% of fish meal protein) without inducing significant negative effects on growth, nutrient utilization or health.     

The problem of meeting dietary protein requirements in intensive aquaculture of marine fish larvae, with emphasis on Atlantic halibut (Hippoglossus hippoglossus L.)

Atlantic halibut (Hippoglossus hippoglossus) achieve a mature gastrointestinal tract approximately 2 months after first feeding (12 °C). The immature digestion may be the reason that compound diets fail to sustain growth and survival in first feeding halibut larvae and in larvae of other marine fish species. On the other hand, larvae fed with live feeds are capable of extraction of sufficient quantities of nutrients to sustain high growth rates. A lower availability of the protein in formulated diets compared with live prey is considered to be an important reason for the low performance of formulated diets. One approach to increase dietary protein availability is supplementation of pre‐digested proteins. Experiments using tube fed individual larvae show that halibut larvae are able to utilize hydrolysed protein more efficiently than intact protein. However, Atlantic halibut in culture did not respond well to dietary supplementation of hydrolysed protein, in contrast to some other species. One reason may be extensive leaching of pre‐hydrolysed proteins from the microparticulate feed. Atlantic halibut are slow feeders and may thus suffer more from nutrient leaching than species eating more rapidly. Feed formulation techniques affect dietary protein leaching, and in this paper, different techniques and their impact on feed properties are described. Microbound diets are most widely used in larval rearing, but show high rates of nutrient leaching. Lipid‐based capsules seem to have the best potential to prevent leaching, however, they are not able to deliver a complete diet. The high need for improvements in larval feed formulation techniques are clearly stated, and some suggestions are given. Among these are production of complex particles, where small lipid‐based capsules or liposomes containing the low molecular weight water‐soluble nutrients are embedded. In such feed particles the water‐soluble molecules are protected from leaching. Techniques for delivery of water‐soluble nutrients that are needed in large quantities, i.e. free amino acids or hydrolysed and water‐soluble protein, remain to be developed.     

Evaluation of Methionine Supplements and Their Use in Grain‐based Feeds for Litopenaeus vannamei

The use of dietary supplements in commercial shrimp production feeds is increasing because of the need to reduce marine meal (e.g., fish meal) content. Our study evaluated leaching and apparent digestibility of artificial methionine supplements and their use in determining appropriate feeding levels of methionine in practical fish meal replacement diets fed to Litopenaeus vannamei. Three forms of methionine were evaluated: dl ‐methionine HCl, various mineral chelates of methionine, and a short‐chain synthetic methionine polymer. Results showed a significant increase (P < 0.05) in leaching loss of methionine from feeds with decreasing salinity and that leaching was significantly higher for dl ‐methionine than other forms in all salinity treatments. No significant difference was shown in apparent digestibility of methionine among digestibility diets, with the exception of diets supplemented with dl ‐methionine HCl. In two 6‐wk clear‐water growth trials, no significant difference in weight gain was shown by shrimp fed diets containing more than 0.4% methionine (1.14%, as percent of protein). This suggests that an appropriate feed level of methionine for practical plant protein‐based feeds is less than 0.4% of the diet. Results also indicated that mineral‐chelated and polymerized forms of methionine are appropriate for supplementation of plant protein‐based feeds.     

Dietary decontaminated fish oil has no negative impact on fish performance,flesh quality or production‐related diseases in Atlantic salmon (Salmo salar)

Fish oil is the main contributor of persistent organic pollutants (POPs) in fish feed. A combination of active carbon filtration and steam deodourization can remove most of the POPs. However, other fat soluble compounds are also removed, thus possibly affecting the nutritional quality of decontaminated fish oils. Sea water–adapted Atlantic salmon were fed 18 months a commercially relevant diet based on either decontaminated or non‐treated fish oil until market size. The development of production‐related diseases (fin/skin erosion, bone deformity, cataract) and fillet quality parameters (gutted weight, fillet fat soluble vitamin levels and fatty acid composition, colour, gaping, texture and sensory quality) were assessed. No significant differences in growth performances, feed conversion ratio or quality parameters between the two dietary groups were found. The fillet levels of fat soluble vitamins in market size fish remained unaltered, and only marginal differences were observed in fatty acid profiles. There was a significantly lower percentage of deformed vertebrae in the tail region of fish fed the decontaminated fish oil diets, indicating a positive effect of the use of decontaminated fish oil. No apparent negative effects of the use of decontaminated fish oil in Atlantic salmon diets were reported in this study.     

Comparison of effects of vegetable oils blended with southern hemisphere fish oil and decontaminated northern hemisphere fish oil on growth performance, composition and gene expression in Atlantic salmon (Salmo salar L.)

Replacement of fish oil with sustainable alternatives, such as vegetable oil, in aquaculture diets has to be achieved without compromising the nutritional quality, in terms of n-3 highly unsaturated fatty acid (HUFA) content, of the product. This may be possible if the level of replacement is not too high and oil blends are chosen carefully but, if high levels of fish oil are substituted, a fish oil finishing diet prior to harvest would be required to restore n-3HUFA. However, a decontaminated fish oil would be required to avoid increasing undesirable contaminants. Here we test the hypotheses that blending of rapeseed and soybean oils with southern hemisphere fish oil will have a low impact upon tissue n-3HUFA levels, and that decontamination of fish oil will have no major effect on the nutritional quality of fish oil as a feed ingredient for Atlantic salmon. Salmon (initial weight ~ 0.8 kg) were fed for 10 weeks with diets in which 60% of fish oil was replaced with blends of soybean, rapeseed and southern hemisphere fish oil (SVO) or 100% decontaminated northern fish oil (DFO) in comparison with a standard northern fish oil diet (FO). Decontamination of the oil was a two-step procedure that included treatment with activated carbon followed by thin film deodorisation. Growth performance and feed efficiency were unaffected by either the SVO or DFO diets despite these having lower gross nutrient and fatty acid digestibilities than the FO diet. There were also no effects on the gross composition of the fish. Liver and, to a lesser extent flesh, lipid levels were lower in fish fed the SVO blends, due to lower proportions of neutral lipids, specifically triacylglycerol. Tissue lipid levels were not affected in fish fed the DFO diet. Reflecting the diet, flesh eicosapentaenoic acid (EPA) and total n-3 fatty acids were higher, and 18:1n-9 lower, in fish fed DFO than FO, whereas there were no differences in liver fatty acid compositions. Flesh EPA levels were only slightly reduced from about 6% to 5% although docosahexaenoic acid (DHA) was reduced more severely from around 13% to about 7% in fish fed the SVO diets. In contrast, the liver fatty acid compositions showed higher levels of n-3 HUFA, with DHA only reduced from 21% to about 18% and EPA increased from under 8% to 9–10% in fish fed the SVO diets. The evidence suggested that increased liver EPA (and arachidonic acid) was not simply retention, but also conversion of dietary 18:3n-3 and 18:2n-6. Increased HUFA synthesis was supported by increased hepatic expression of fatty acyl desaturases in fish fed the SVO diets. Flesh n-3HUFA levels and desaturase expression was significantly higher in fish fed soybean oil than in fish fed rapeseed oil. In conclusion, partial replacement of fish oil with blends of vegetable oils and southern hemisphere fish oil had minimal impact on HUFA levels in liver, but a greater effect on flesh HUFA levels. Despite lower apparent digestibility, decontamination of fish oil did not significantly impact its nutritional quality for salmon.     

An evaluation of the nutritional value of alternative lipid sources to juvenile southern rock lobster, Jasus edwardsii

Experimental lobster feeds are currently based on fish meal and fish oil formulations, and although survival and growth similar to that of lobsters fed fresh blue mussels has been achieved, varying the protein level in previous experimental feeds has not increased growth beyond that of lobsters fed natural food. This experiment assessed the growth performance of lobsters fed pelleted feeds containing constant amounts of protein, lipid and energy where the lipid was provided by a range of oil-rich ingredients (fish oil, FO; fish oil with added soybean lecithin, FOL; canola oil, CO; tuna oil, TO; mussel meal, MM; and squid meal, SQM). Feed performance was assessed by lobster growth rate, survival, final biochemical composition, nutrient retention and nutrient efficiency. Twenty tanks containing 15 post-larval lobsters each (1.5 ± 0.04 g) were randomly allocated one of six test feeds in triplicate, and the two remaining tanks were fed freshly opened blue mussels (FRM) as a reference feed. Lobsters were fed daily to excess for 10 weeks. Final individual weights of whole body and digestive gland were measured, and tissue chemical composition analysed. There were no significant differences in survival (88.4 ± 3.3%), or specific growth rate (1.3 ± 0.1%.day^− 1) among the formulated feed fed lobsters, which were significantly lower than the survival (100 ± 0.0%) and SGR (2.2 ± 0.1%.day^− 1) of FRM fed lobsters. The SQM fed lobsters had a significantly lower lipid efficiency ratio and lipid productivity value than lobsters fed TO, FOL and MM feeds. The digestive gland lipid content (g.100 g wet tissue^− 1) of lobsters fed the feeds TO (3.7 ± 0.4), FO (3.5 ± 0.3) and SQM (2.2 ± 0.2) were significantly lower than lobsters fed feeds MM (9.9 ± 1.1), FOL (9.0 ± 2.3) and FRM fed lobsters contained most digestive gland lipid (12.3 ± 1.5).     

The potential of dried, low-hatch, decapsulated Artemia cysts for feeding prawn post-larvae

Low-hatch, decapsulated Artemia cysts were assessed as feed for Penaeus indicus post-larvae (PL) 1–15 days old and the problems resulting from the incorporation of decapsulated cysts into compounded feeds were evaluated. Growth and survival of PL fed on decapsulated cysts (AC) were comparable with Artemia nauplii fed PL (control) and significantly (p < 0.05) higher than observed amongst PL fed on two granulated commercial diets (G150 and G300) or a commercial flake feed (AC-F) incorporating decapsulated cysts (80%). PL fed on artificial diets showed poor growth and delay in metamorphosis. However, survival of PL fed on AC-F was significantly higher (p < 0.05) than that observed amongst granulated feeds. Decapsulated cysts processed into a granulated feed (AC-G) or dried at 90°C (AC-90) also resulted in slow growth and survival when fed to PL. Overall, artificial feeds showed poor water stability and significantly higher leaching of soluble protein and carbohydrates than decapsulated cysts. AC-90 cysts also showed a high level of bursting and leaching of material. This indicates that low-hatch Artemia cysts retain a living membrane after commercial decapsulation and drying prevents loss of highly digestible nutrients, which allows PL growth equal to that on PL fed live Artemia nauplii. Survival of PL was negatively correlated with leaching of soluble protein (p < 0.05), but no correlation was observed for leaching of carbohydrates or between growth and loss of both soluble nutrients. Hence, availability of digestible protein is critical and may influence survival of early stages of post-larval development. Water stability of artificial feeds is an essential factor in promoting efficient nutrition of PL, but other aspects related to heating during processing of feeds also appear to have a deleterious effect on nutritional quality of compounded feeds. Commercially dried, encapsulated Artemia cysts from low-hatch strains remain alive and are highly nutritious for feeding early stages of post-larval prawn but even after death may support acceptable survival when incorporated into a flake diet. © Rapid Science Ltd. 1998     

逆流运动及葵花籽油替代鱼油对吉富罗非鱼生长和体成分的影响

选取初始体质量（73．81±9．02）g的雄性吉富罗非鱼（GIFFOreochromisniloticus）,分别投喂含100％鱼油（A）、50％葵花籽油＋50％鱼油（B）和100％葵花籽油（C）的饲料,每种饲料设置2个流速运动水平（0BL·s-1、1．5BL·s-1）（BL,体长）,共6个试验组合（0A、1．5A、0B、1．5B、0C、1．5C）,饲养42d后测定试验鱼生长和体成分变化。结果显示各组合吉富罗非鱼的成活率没有显著性差异（P〉0．05）。1．5B组合的特定生长率（4．96±0．02）％·d-1显著高于其他各组合（P〈0．05）。逆流运动后红肌和白肌蛋白质含量分别最高增加10．25％和7．74％（P〈0．05）。逆流运动对全鱼和肌肉多不饱和脂肪酸（PUFA）含量没有显著影响（P〉0．05）,但饲料B组和c组鱼体红肌PUFA含量显著高于A组（P〈0．05）,而B组和c组之间则没有显著差异（P〉0．05）。研究结果表明,葵花籽油替代鱼油对吉富罗非鱼的生长和体成分没有显著影响,而逆流运动能够显著提高肌肉蛋白质含量。     

Palm oil-laden spent bleaching clay as a substitute for marine fish oil in the diets of Nile tilapia, Oreochromis niloticus

A 8‐week feeding trial was conducted to determine the effect of substituting fish oil with palm oil‐laden spent bleaching clay (SBC), a by‐product from crude palm oil (CPO) refining, on growth, feed utilization, fatty acid composition and heavy metal accumulation in the muscle of Nile tilapia, Oreochromis niloticus. Four isonitrogenous and isolipidic practical diets were formulated to contain 0, 100, 200 or 300 g kg^?1 SBC. Growth performance of Nile tilapia was significantly better in fish fed the 100 g kg^?1 SBC diet compared with fish fed the 0, 200 or 300 g kg^?1 SBC diet. Growth and feed utilization efficiency of fish fed 200 or 300 g kg^?1 SBC were similar to fish fed the control diet without added SBC. Whole‐body composition, body‐organ indices and haematocrit of tilapia were not affected by dietary treatments. Fatty acid compositions in the muscle lipid of Nile tilapia were strongly influenced by dietary treatments with progressively elevated levels of total saturates and n‐6 PUFA because of the dietary influence of these fatty acids from residual CPO adsorbed onto SBC. A gradual decrease in total n‐3 PUFA concentrations were also observed with the ratio of n‐3 to n‐6 fatty acids in muscle lipids decreasing from 4.75 to 4.41, 3.23 or 2.37 after 8 weeks on the 0, 100, 200 or 300 g kg^?1 SBC diet, respectively. The arsenic, cadmium and lead concentrations in the experimental diets increased with increasing dietary levels of SBC but the concentrations of these heavy metals in the whole body and bone of Nile tilapia were not significantly different among fish fed the various diets. The present 8‐week study showed that in fishmeal‐based diets for Nile tilapia, palm oil‐laden SBC can totally replace added fish oil. The use of this presently discarded waste product from palm oil refining in tilapia diets will greatly contribute to reducing the impact of rising feed costs in the culture of tilapia in many tropical countries. Other potential benefits may include acting as a feed binder, removal of mycotoxins in fish feeds as well as adsorbing toxic substances present in the culture water.     

Optimization of vacuum coating conditions to improve oil retention in Trout feed

This work describes a process approach to study the oil leakage phenomenon in feeds for large Trout. Using a pilot vacuum coater, four experimental coating parameters were studied (stirring speed, pressure, filling rate, and time needed to restore atmospheric pressure) through an experimental design. The properties measured on the coated pellets were the oil leakage rate and three other important usage properties, i.e. durability, hardness, and floatability. The coating conditions had a significant influence on oil leakage rate, varying at 40 °C from 2.7 % to 1.2 % depending on the coating conditions used. Finally, the vacuum level was the most effective factor in reducing leakage. Indeed, a progressive reduction in oil leakage rate was observed as the pressure inside the coater was reduced during coating.     

Effect of different oil cake sources on growth, nutrient retention and digestibility, muscle nucleic acid content, gut enzyme activities and whole-body composition in silver barb, Puntius gonionotus fingerlings

Six iso‐nitrogenous (30% crude protein) and iso‐energetic (15 kJ g⁻¹) diets were prepared using different oil cake sources, viz. groundnut, soybean, sunflower, sesame, mustard and mixed oil cakes as major ingredients, and protein sources along with a minimum of 5% fish meal in each diet and were fed to silver barb Puntius gonionotus fingerlings (16.20±0.11 g) ad libitum four times a day close to an apparent satiation level for a period of 60 days to determine the effect of diets on growth, nutrient utilization, apparent digestibility coefficient (ADC) of the nutrients in the diets, gut enzyme activity, muscle nucleic acid content and whole‐body chemical composition of fish. Significantly higher (P<0.05) weight gain, specific growth rate, protein efficiency ratio, nutrient retention, ADC of nutrients in the diets, DNA:RNA ratio, protease and amylase activity with lower (P<0.05) feed:gain values were recorded in fish‐fed groundnut and soybean oil cake‐based diets than other diets tested. Among the dietary treatment groups, significantly higher (P<0.05) whole‐body protein, lipid and energy were also found in groundnut oil cake‐ and soybean oil cake‐based diets. The study suggests that the groundnut and soybean oil cake‐based diets, which led to significantly higher (P<0.05) growth and nutrient utilization than the other oil cake‐based diets in P. gonionotus fingerlings, may be used for pond culture of this species.     

Potential of local agricultural by-products for the rearing of African catfish Clarias gariepinus in Rwanda: effects on growth, feed utilization and body composition

This study was performed to evaluate the effect of replacing fish meal with local by‐products on Clarias gariepinus growth performance, feed utilization and body composition. A control diet contained 50% of fish meal. In four other diets, fish meal was partially replaced by vegetable and animal protein blend composed of sunflower oil cake, soybean oil cake, groundnut oil cake, bean meal, chicken viscera and blood meal. The study was conducted in a recirculating water system at a mean temperature of 23.6°C. The five test diets were compared with a commercial diet developed for African catfish. All diets were balanced to be equal in gross energy (19 kJ g⁻¹) and crude protein (40%). The experimental groups were fed in triplicate for 8 weeks, increasing fish weight from about 6.2 g at start to 52.3 g in the end. Best specific growth rate (SGR=3.4), feed efficiency (FE=1.3) and protein efficiency ratio (PER=3) were obtained with the control diet (diet 50% fish meal), although there were no significant differences between the group of fish fed the control diet and those fed diets based on groundnut oil cake or bean meal, whereas SGR (2.17), FE (0.85) and PER (1.95) were significantly (P<0.01) lower in fish fed diet containing sunflower oil cake. No significant differences (P<0.05) were found in fish fed commercial diet and diets containing bean meal or groundnut oil cake. Groundnut oil cake or bean meal can thus replace at least 50% of fish meal in the diet of Clarias fingerlings without amino acid supplementation. Because of its economic importance and its potential in animal nutrition sunflower oil cake is still an interesting feed ingredient, but its efficiency should be improved by various processing techniques. African catfish can utilize efficiently a diet with low percentage of animal protein without growth reduction.     

Pond‐raised Hybrid Catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus,Do Not Respond to Microbial Phytase Superdosing

Two experiments were conducted in consecutive years to evaluate the responses of hybrid catfish, ♀ Ictalurus punctatus × ♂ Ictalurus furcatus, to “superdosing” of 6‐phytase added to existing commercial catfish feeds. In each experiment, two diets with or without a phytase superdose (2500 and 5000 phytase units/kg, respectively) were compared. In Experiment 1, fingerlings (mean weight: 59 g/fish) were stocked in 17 0.4‐ha earthen ponds at 17,290 fish/ha and were fed once daily to apparent satiation for 198 d. In Experiment 2, fingerlings (mean weight: 47 g/fish) were stocked in 10 0.4‐ha ponds at 24,710 fish/ha and were fed for 128 d. In both experiments, there were no significant differences in total feed fed, gross yield, final fish weight, survival, or Blood packed cell volume between fish fed diets with or without phytase. The diets also had no significant effects on pond water column total phosphorus or chlorophyll a concentrations, but soluble reactive phosphorus concentrations were significantly higher in ponds receiving the phytase diet in Experiment 2. Phytase superdosing of nutritionally complete feeds does not appear to have additional benefits beyond the standard phytase dose on production characteristics or packed cell volume of pond‐raised hybrid catfish and had no beneficial effects on water quality.     

橡胶籽油替代豆油对草鱼(Ctenopharyngodon idellus)生长性能、消化酶活性及部分生化指标的影响

为研究橡胶籽油替代豆油对草鱼(Ctenopharyngodon idellus)生长性能、消化酶活性、血脂水平、蛋白质代谢及抗氧化功能的影响,分别以橡胶籽油替代0(对照组)、25%、50%、75%和100%豆油配制5种等氮等能饲料,进行10周饲养实验。实验显示,0~50%替代组草鱼增重率、日增重系数显著高于100%替代组(P<0.05)。随着橡胶籽油替代豆油比例的升高,饲料系数呈先下降后上升的趋势,其中,25%替代组饲料系数最低,显著低于50%~100%替代组(P<0.05);25%替代组蛋白质效率最高,显著高于其他处理组(P<0.05)。随着橡胶籽油替代比例的升高,肠道胰蛋白酶、脂肪酶活性呈先上升后下降的趋势,其中,25%替代组脂肪酶活性最高,显著高于其他处理组(P<0.05),50%替代组胰蛋白酶活性最高,显著高于对照组、75%和100%替代组(P<0.05)。0~50%替代组肝胰脏胰蛋白酶活性显著高于75%和100%替代组(P<0.05)。25%~100%替代组血清总胆固醇(TC)含量显著低于对照组(P<0.05)。随着橡胶籽油替代比例的升高,肝胰脏天门冬氨酸氨基转移酶(AST)、丙氨酸氨基转移酶(ALT)活性呈先下降后上升的趋势,其中,25%替代组AST、ALT活性最低,显著低于对照组和100%替代组(P<0.05)。0~25%替代组血浆总抗氧化力(TAC)显著低于75%和100%替代组(P<0.05)。对照组血浆、肝胰脏丙二醛(MDA)含量显著高于100%替代组(P<0.05)。由此可知,橡胶籽油替代25%~50%豆油对草鱼生长性能、饲料利用率、血脂水平、抗氧化功能指标均无不良影响;但替代超过50%时显著降低草鱼生长性能和消化酶活性。