Effects of steam pelleting or extrusion on digestibility and performance of silver perch Bidyanus bidyanus

The effects of different processing techniques on apparent digestibility coefficients (ADCs) and performance of silver perch Bidyanus bidyanus were evaluated. Results of a factorial digestibility trial, in which three diets (SP35, 95LC1 and 95LC2) and three processing methods (cold pelleted, steam pelleted and extruded) were evaluated, indicated that extrusion, but not steam conditioning, significantly improved ADCs of dry matter (DM) and energy. ADCs of DM and energy of cold‐pelleted diets were statistically similar to steam‐pelleted diets, and ADCs of nitrogen were unaffected by processing method. No interaction was found between diet type and processing method for DM, energy or nitrogen ADCs. A performance trial indicated that feed intake, weight gain and specific growth rate of fish fed steam‐pelleted diets was greater than those of fish fed extruded diets. Feed conversion and digestible protein efficiency was better in fish fed extruded diets. The results indicated that extruded diets were better utilized than steam‐pelleted diets; however, voluntary intake of extruded diets may have been limited. Fish fed cold‐pelleted SP35 exhibited inferior performance compared with fish fed steam‐pelleted or extruded SP35. Reduced performance of fish fed this diet may relate to poor utilization of digestible protein or reduced palatability. Diets for silver perch with similar formulations to SP35 and 95LC2 should be steam pelleted.     

Evaluation of silver perch (Bidyanus bidyanus, Mitchell) nutritional requirements during grow-out with high and low protein diets at two feeding levels

Silver perch (Bidyanus bidyanus, Mitchell) of 65 g average weight were reared at high density under controlled conditions on diets containing 24.8% and 40.6% protein. Diets were fed at 2% or 4% of the fish biomass day^?1. Both protein concentrations and feeding level of the diet influenced growth and proximate composition of the fish at the end of the 50‐day growth trial. Energy requirement for maintenance for these fish was found to be 77 cal BW^?0.8 and for each unit of energy retained 3.78 cal BW^?0.8 needed to be supplied, and for each gram of protein retained per metabolic body weight 5.04 g were required. The results indicate that it is possible to obtain the same weight increment when feeding a 24.8% protein diet at a level of 4% body weight day^?1 as compared with only 2% body weight day^?1 of a 40.6% protein diet. This study indicates that the nutritional requirements for early grow‐out are similar to those found in a previous study with juvenile silver perch and adds information concerning the required relationships between dietary amino acids. The results provide information required for further refinement of nutrition for this species.     

Heterosis in fingerlings from a diallel cross between two wild strains of silver perch (Bidyanus bidyanus)

Cross-breeding was investigated as a strategy to improve performance of the Australian native freshwater fish, silver perch ( Bidyanus bidyanus Mitchell) through the exploitation of heterosis during the fingerling phase of production. Growth, and mid and best parent heterosis of two wild strains, Cataract Dam (C_♂× C_♀) and Murray River (M_♂× M_♀) and their reciprocal crosses (C_♂× M_♀ and M_♂× C_♀) were evaluated in cages and ponds through summer, and in tanks in a re-circulating aquaculture system during winter. The M × C cross grew significantly faster than the reciprocal cross and pure strains in cages and tanks, had the lowest coefficients of variation of weight and length and was 20.9% and 16.0% heavier than mid-parent and best-parent average, respectively, when grown in ponds. Differences in growth between the reciprocal crosses were also evident, with C × M expressing significantly less heterosis in cages and tanks. Faster growth of M × C was attributed to greater appetite; however, at sizes approaching 250 g this feeding vigour diminished. The results of this study suggest that use of the M × C cross has the potential to reduce the length of the culture period and lower costs of silver perch production.     

银鲈对五种常用药物的敏感性试验

试验银鲈鱼种全长3 0～3 3cm,试验温度(20±2)℃,溶氧4 6～6 4mg/L,pH值7 0～7 4。正式试验前先通过预备性试验,找出银鲈在福尔马林、高锰酸钾、灭虫精、聚维酮碘、硫酸铜中48h内死亡0～100%的范围,然后按寇氏法(Karber)设计分组进行正式实验,求得5种药物对银鲈鱼种的最低致死剂量浓度范围、中间忍受限和安全浓度。结果表明:银鲈对5种药物的敏感性由强到弱依次为:灭虫精;硫酸铜;高锰酸钾;聚维酮碘;福尔马林。     

Carbohydrate utilization by juvenile silver perch, Bidyanus bidyanus (Mitchell). I. Uptake and clearance of monosaccharides following intraperitoneal injection

Abstract Intraperitoneal carbohydrate tolerance tests were done to assess the ability of silver perch, Bidyanus bidyanus, to utilize the predominant monosaccharides in plant ingredients currently being used in the formulation of aquaculture feeds for this species. Preliminary experiments carried out to assess baseline plasma glucose concentrations indicated that blood glucose levels were elevated within 2 min of handling and silver perch required a period of 48 h without feeding before plasma glucose levels remained constant. In the first carbohydrate test, either glucose, galactose or xylose were administered by injection into the intraperitoneal cavity at a dose rate of 1 g carbohydrate kg^?1 body weight (BW). In the second carbohydrate test, glucose was administered at a dose rate of either 2 or 4 g glucose kg BW^?1. Following injection, uptake and clearance rate of the carbohydrates from the blood stream was monitored over a 24‐h period. Silver perch were significantly more efficient at the uptake and clearance of glucose from the blood stream than xylose or galactose. Maximum plasma glucose concentrations (22.2 mmol L ^?1) were recorded at 1 h following injection and basal levels (3.44 mm ) were attained between 6 and 12 h following injection. For both galactose and xylose, maximum concentrations were recorded at 1 and 3 h, respectively, and concentrations of both monosaccharides remained significantly elevated 24 h after the administration. Plasma glucose concentrations of silver perch administered with either 2 or 4 g glucose kg BW^?1 were significantly elevated and peaked at similar levels (30.2 mmol L ^?1 and 30.7 mmol L ^?1 respectively) 3 h after injection. Basal plasma glucose concentrations were attained in silver perch injected with 2 g glucose kg BW^?1 at 24 h following administration. Plasma glucose concentrations remained significantly elevated in fish injected with 4 g glucose kg BW^?1 after 24 h. These findings indicate that silver perch are more efficient at utilizing glucose than either xylose or galactose, and that there are also differing maximum threshold for the inclusion of ingredients rich in glucose, galactose and xylose into the diets of silver perch.     

Use of temperature to manipulate circulus patterns on scales of silver perch, Bidyanus bidyanus (Mitchell), for the purpose of stock discrimination

Abstract  Controlled temperature variation was used to induce marks on scales of silver perch, Bidyanus bidyanus (Mitchell), for stock identification. Genetically similar fish were held in tanks at three temperatures for a period of 4 weeks. Circulus spacing information was acquired using automated video digitizing equipment. Discriminant function analysis was used to classify fish into their respective rearing temperatures. Fish held at 30°C were classified with high accuracy (94–96%). Classification inaccuracies increased in fish held at the lower temperatures. Fish growth at each temperature was examined and classification accuracies were a reflection of growth differences. The use of temperature variables to induce marks on scales offers scope for batch-marking pre-stocked fish.     

Carbohydrate utilization by juvenile silver perch, Bidyanus bidyanus (Mitchell). III. The protein-sparing effect of wheat starch-based carbohydrates

The ability of juvenile silver perch (Bidyanus bidyanus) to utilize dietary raw wheat meal, raw wheat starch, gelatinized wheat starch and dextrin as energy sources to spare protein for growth was quantified. Energy utilization and protein sparing were assessed by comparing the weight gain, energy retention efficiency, protein retention and body composition of silver perch that had been fed a series of diets in which the basal diet (low carbohydrate) was systematically replaced with graded levels of each carbohydrate ingredient or an inert diluent, diatomaceous earth. The protein content decreased as the carbohydrate content increased, giving four different protein to energy ratios for each of the four carbohydrate sources (except for the 60% inclusion level, at which only three carbohydrate sources were tested). Silver perch were efficient at utilizing carbohydrate for energy to spare protein. Silver perch fed diets containing up to 30% wheat meal, raw wheat starch, gelatinized wheat starch or dextrin exhibited similar growth, protein retention and energy retention efficiency to the fish fed the basal diet. Weight gain of silver perch fed diets containing wheat meal or carbohydrates at 45% inclusion content had significantly reduced weight gain when compared with fish fed the basal diet. However, protein retention and energy retention efficiency were similar or better. Whole‐body protein levels of silver perch remained constant regardless of carbohydrate sources, and there was no evidence of increasing whole‐body lipid concentrations for fish fed diets with up to 60% dietary carbohydrate. Silver perch were more efficient at utilizing processed starch (either gelatinized starch or dextrin) than wheat meal or raw wheat starch.     

Effects of formalin on water quality and parasitic monogeneans on silver perch (Bidyanus bidyanus Mitchell) in earthen ponds

Infestations of parasitic monogenean trematodes (Lepidotrema bidyana and Gyrodactylus sp.) on freshwater silver perch (Bidyanus bidyanus Mitchell) in earthen ponds were treated with formalin (37% formaldehyde). Concentrations of 30 and 40 mg L^?1 formalin were effective, but fish in ponds treated with 20 or 25 mg L^?1 remained infested. At temperatures of 24.1–26.9°C, concentrations of 30 or 40 mg L^?1 formalin caused dissolved oxygen (DO) to decline from 10.1–11.9 to 3.0–3.3 and 1.2–1.7 mg L^?1, respectively, within 36–42 h of treatment. In addition, pH declined from 7.2–8.4 to 6.3–6.7, within 36 h and turbidity decreased over 48 h. In the ponds where DO was 1.2–1.7 mg L^?1, silver perch showed signs of severe stress, but continuous aeration (10 hp ha^?1) for 3 days and inflow of well‐oxygenated water for 6–8 h prevented mortalities. At temperatures of 13.2–15.7°C, concentrations of 30 or 40 mg L^?1 formalin caused DO to decline from 9.0–10.0 to 6.0–8.1 mg L^?1 and pH from 7.0–7.3 to 5.9–6.6 within 72 h. Total ammonia‐nitrogen increased over 72 h in ponds treated with 30 or 40 mg L^?1 formalin. Fish became re‐infested with L. bidyana in all ponds within 30 days of treatment. A concentration of 30 mg L^?1 formalin is recommended as a treatment for monogeneans on silver perch in ponds, but aeration is necessary to maintain adequate water quality at higher temperatures.     

Carbohydrate utilization by juvenile silver perch,Bidyanus bidyanus (Mitchell). IV. Can dietary enzymes increase digestible energy from wheat starch,wheat and dehulled lupin?

The effects of exogenous digestive enzyme supplements on the digestibility of wheat starch or diets containing either wheat or dehulled lupin (Lupinus angustifolius var. gungurra) by silver perch (Bidyanus bidyanus) were investigated. In the first experiment, Natustarch^® (α‐amylase supplement specific to starch) was added at three nominal concentrations (0, 50, 100 or 150 mg kg^?1 diet) to diets containing either raw or 100% gelatinized wheat starch (30% dietary inclusion content) and fed to silver perch. The apparent digestibility coefficients (ADCs) for dry matter, starch and energy were calculated. The action of Natustarch^® on the diet and in the digestive tract was also investigated. The addition of Natustarch^® to diets containing raw and gelatinized wheat starch led to an average increase in reducing sugar content of diets of 67% and 340% respectively, indicating that the α‐amylase was more efficient at hydrolysing wheat starch in the gelatinized form. Gelatinized wheat starch was digested more efficiently than raw wheat starch. However, although the addition of Natustarch^® at ≥ 50 mg kg^?1 led to a significant increase in digestibility of raw wheat starch; the digestibility of gelatinized wheat starch, which was already high, was not further improved. Leaching due to immersion in water caused a minor loss of α‐amylase activity from diet pellets treated with Natustarch^® (～ 13% after 5 min). The α‐amylase activity in the anterior section of the intestinal tract of silver perch fed diets containing Natustarch^® was not affected, indicating that the α‐amylase had been denatured by the acidic conditions in the stomach of silver perch. In the second experiment, diets containing wheat or lupin (at the 30% inclusion content) were treated with Natugrain‐blend^®[an enzyme supplement containing β‐glucanase and β‐xylanase, specific to non‐starch polysaccharides (NSPs)] at three nominal concentrations (0, 75, 150 or 300 μL kg^?1) and fed to silver perch. ADCs for energy and protein were calculated. The addition of Natugrain‐blend^® had no effect on dry matter, energy or protein digestibility of the diets or ingredients.     

Use of formalin and copper to control ichthyophthiriosis in the Australian freshwater fish silver perch (Bidyanus bidyanus Mitchell)

Infestations of the protozoan parasite, Ichthyophthirius multifiliis, cause the serious disease ichthyophthiriosis in freshwater fish throughout the world. Formalin is a recommended treatment for ichthyophthiriosis in the Australian fish silver perch (Bidyanus bidyanus Mitchell), but the disease is difficult to control in ponds, particularly at low water temperatures. Experiments were carried out to develop an improved treatment regime for formalin and to evaluate copper as a therapeutant. Silver perch fingerlings infested with I. multifiliis were stocked into 55 L aquaria at temperatures of 14.8–17.6 °C and alkalinities of 70–110 mg L^?1. Formalin (34–38% formaldehyde) or copper (24.5% copper sulphate) were added to the aquaria and then monitored and readjusted to nominal concentrations daily. A concentration of 30 mg L^?1 formalin controlled ichthyophthiriosis, but fish treated with 20 mg L^?1 remained infested with theronts and trophonts on day 17; survival at both concentrations was 100%. A concentration of 10 mg L^?1 formalin did not control ichthyophthiriosis and all fish were dead from the infestation by day 17. Fish treated with 0.1 or 0.2 mg L^?1 copper were free of theronts and trophonts by days 17 and 14, respectively, and survival was 100%. Survival at 0.05 mg L^?1 copper was 100%, but fish remained infested. At 0.25 mg L^?1 copper, survival was 82.5% and there were no theronts or trophonts on gill and skin tissues of fingerlings by day 14. There was total mortality of fish treated with 0.5 or 1.0 mg L^?1 copper suggesting these concentrations are toxic to silver perch. All fish in infested‐control treatments died. In earthen ponds containing silver perch, 0.2 mg L^?1 copper was depleted to below 0.1 mg L^?1 within 24 h, and concentrations of 25–38 mg L^?1 formalin were depleted to below 15 mg L^?1 within 48 h. Treatment regimes involving daily applications of formalin or copper controlled ichthyophthiriosis in silver perch in earthen ponds at costs of $US466.37 and $US65.58 hectare^?1 day^?1 respectively. This study has developed a new formalin‐treatment regime for the control of ichthyophthiriosis, and demonstrated that copper sulphate is a potential therapeutant for this serious disease of silver perch.     

Use of salt to control ichthyophthiriosis and prevent saprolegniosis in silver perch, Bidyanus bidyanus

The ciliate protozoan, Ichthyophthirius multifiliis , and the fungus, Saprolegnia parasitica , cause the diseases ichthyophthiriosis and saprolegniosis respectively. Both diseases are difficult to control and can cause high mortalities of freshwater fish, including the Australian silver perch, Bidyanus bidyanus (Mitchell). The efficacy of salt (NaCl) in controlling and preventing these diseases in silver perch was evaluated in aquaria and tanks. Low pH levels were also evaluated as a control for ichthyophthiriosis. Concentrations of 2 or 3 g L⁻¹ salt controlled infestations of I. multifiliis , and fish were free of both theronts and trophonts by day 8 at temperatures of 17.3–21.3 °C and by day 6 at 19.2–23.5 °C. Fish treated with 1 g L⁻¹ salt remained infested and all fish in a control treatment (0 g L⁻¹ salt) died. Although the mean survival rates of infested fish at pH levels of 5 or 6 were only 13.9% and 7.6%, respectively, there were no theronts or trophonts on surviving fish after 12 days. Silver perch harvested from a pond and treated with 2 or 3 g L⁻¹ salt did not become infected with S. parasitica and survival was 100%, whereas 16.6% of untreated (0 g L⁻¹ salt) fish became infected and survival was only 66.7%. A concentration of 2 g L⁻¹ NaCl is recommended for the control of ichthyophthiriosis and the prevention of saprolegniosis in silver perch held in tanks, aquaria and re-circulating aquaculture systems.     

Effects of diets with different plant proteins on the performance of silver perch (Bidyanus bidyanus Mitchell) and on water quality in earthen ponds

As part of a project to develop least‐cost diets with low levels of fish meal, silver perch (Bidyanus bidyanus Mitchell) fingerlings (mean weight, 11.8 g) were stocked at a density of 7500 fish ha⁻¹ into 0.1‐ha earthen ponds and fed one of two diets containing 33% digestible protein, 13 MJ kg⁻¹ digestible energy, similar nutrient specifications, but with different levels of fish meal and plant proteins. The reference diet SP35 had 27% fish meal, 28% wheat, 20% soybean and 11% sorghum, while the diet silver perch least‐cost (SPLC) had 10% fish meal, 20% peanut meal, 19% wheat, 17% lupins, 16% canola, 8% soybean and 5% blood meal; there were three replicate ponds for each diet. Fish were fed a restricted ration up to 5% body weight day⁻¹ and cultured for 10 months. Survival ranged from 85.9% to 94.3% and was not affected by diet. The mean weight (550 g), specific growth rate (SGR; 1.28% day⁻¹), absolute growth rate (AGR; 1.9 g fish⁻¹ day⁻¹) and production rate (4.5 tonnes ha⁻¹ year⁻¹) were significantly higher (P<0.05) and feed conversion ratio (FCR=1.8) was significantly lower for fish fed SP35 compared with fish fed SPLC (413 g, 1.18% day⁻¹, 1.4 g fish⁻¹ day⁻¹, 3.3 tonnes ha⁻¹ year⁻¹, 2.4). From October (spring) to March (autumn), turbidity was significantly lower (P<0.05) in SPLC ponds than in SP35 ponds, and fish were observed avoiding or ingesting and then expelling SPLC pellets. In February and March, infestations of the ectoparasitic copepod Ergasilus sp. were found on silver perch fed SPLC, and there was 5% post‐harvest mortality of these fish. The high inclusion levels of plant proteins, particularly peanut meal and canola in SPLC, may have provided anti‐nutritional factors and/or reduced the palatability and intake of the diet, adversely affecting the performance and health of silver perch, and water quality in the ponds. Our study demonstrates the value of evaluating new aquaculture diets under practical conditions over a complete growing period.     

Effects of extrusion processing on digestibility of peas, lupins, canola meal and soybean meal in silver perch Bidyanus bidyanus (Mitchell) diets

Two experiments were conducted to investigate effects of processing on apparent digestibility coefficients (ADCs) of legumes and oilseeds for juvenile silver perch, Bidyanus bidyanus (～49 g). The first experiment evaluated interactive effects of ingredients (lupins or field peas), processing (whole seed; hulls on or hulls off) and extrusion cooking (raw or extruded) on ADCs for juvenile silver perch (～4 g fish^?1). The second experiment was a three‐fixed‐factor anova designed to evaluate interactive effects of ingredients (soybean meal or canola meal), extrusion cooking (raw or extruded) and inclusion content (30% or 50% of the diet) on ADCs for juvenile silver perch (～4 g fish^?1). Lupin protein was more digestible than that of peas (ADC for crude protein 91% vs. 85% for peas) but the organic matter was less digestible (ADC for organic matter 50% vs. 67% for peas). Dehulling lupins significantly improved ADCs for all indices (dry matter, organic matter, energy and crude protein), but extrusion had no effect because lupins do not contain starch or heat‐labile anti‐nutrients. Conversely, for starch‐rich peas that contain heat‐labile trypsin inhibitors, both dehulling and extrusion significantly improved ADCs. Digestibility of soybean meal was much higher than that of canola meal. For soybean meal, neither processing, content nor their interaction affected digestibility but extrusion improved ADCs for dry matter, organic matter and energy but there was an interaction with content. Although higher overall, digestibility for these indices declined with increasing content for extruded product while there were only minor effects of inclusion for raw product. Benefits of extrusion were attributed to reductions in anti‐nutrients, including phytic acid. For canola, there were no interactions between extrusion and content for any ADC. Increasing content reduced ADCs for crude protein, dry matter and organic matter but did not effect energy. Surprisingly, extrusion of canola also reduced digestibility for all ADCs. Dehulling improved both lupins and peas. Crude protein for all ingredients was well digested with ingredients ranked: lupins>soybean meal>peas>canola meal. Energy digestibility was best for soybean meal and worst for lupins. Extrusion greatly improved digestibility of peas and to a lesser extent soybean meal, gave no benefits to lupins and was detrimental for canola.     

Development of a feeding strategy for silver perch, Bidyanus bidyanus (Mitchell), based on restricted rations

To develop a feeding strategy for the Australian freshwater fish silver perch (Bidyanus bidyanus Mitchell), a series of eight experiments was done in 1 m³ cages in an aerated, earthen pond to determine the effects of feeding rate (% body weight) and feeding frequency (no. of feeds day^?1) on the growth and feed conversion ratio (FCR) of fingerlings and larger fish under ambient water temperatures over the range 13.8–30.6°C. Fish were fed extruded pellets of a silver perch diet containing 34% digestible protein and 14 MJ kg^?1 digestible energy. Commercial silver perch farmers were consulted about feeding practices for large fish (>500 g) and at water temperatures below 12°C, and winter feeding practices for other warmwater species were used to complete the strategy. In the feeding experiments, growth and FCR increased with increasing feeding rates to a level above which only FCR increased. Optimal feeding rates and frequencies were those which resulted in maximal growth, while minimizing effort (feeding frequency) and FCR. The highest feeding frequency required for maximal growth, including that of small fingerlings was twice (2 ×) daily, and the optimal feeding rates varied with water temperature and size of fish. The optimal daily regimes were: small fingerlings (initial mean weight, 2.0 g) 7.5% 2 × at a mean temperature of 23.3°C; fingerlings (14.9–27.7 g) 7.5% 2 × at 27.1°C, 5.0% 2 × at 23.7°C and 2.0% 1 × at 16.8°C; and large silver perch (162.5–510.6 g) 0.5% 1 × daily or 1.0% on alternate days at 15.6°C, 1.0% 1 × at 17.3°C, 3.0% 2 × at 24.1°C and 2.0% 2 × at 27.9°C. It is suggested that regimes of 0.5% 1 × daily for fingerlings (<50 g) and 0.5% 1 × on alternate days for larger fish are used at temperatures of 9–12°C, and 0.5% 3 days week^?1 and 0.5% 1 day week^?1 for fingerlings and larger fish, respectively, at 6–9°C. Feed inputs should not exceed 150 kg ha^?1 day^?1 in ponds less than 0.3 ha and 100 kg ha^?1 day^?1 in larger ponds. Our research has established a feeding strategy for silver perch based on restricted rations.     

Performance and sensory evaluation of silver perch (Bidyanus bidyanus Mitchell) fed soybean or meat meal-based diets in earthen ponds

The performance of silver perch fed a commercially available diet based on meat meal (38%), grain legumes (18%), oilseeds (10%), wheat millrun (20%), fishmeal (5%) and fish oil (3%) was compared with experimental diets based on alternative protein sources in two experiments. In Experiment 1, two experimental diets contained similar contents of fishmeal and fish oil as the commercially available reference diet, but soybean (25%) and wheat millrun (>31%) were used to reduce animal protein meals by approximately 50%. The digestible protein and digestible energy of the two experimental diets was either slightly lower (31.5% and 12.8 MJ kg^?1) or slightly higher (34.9% and 14.3 MJ kg^?1) than the reference diet (32.1% and 13.2 MJ kg^?1). In Experiment 2, the two experimental diets contained no fishmeal but included higher amounts of rendered animal meals (41–48%). One of the diets had similar digestible protein to the reference diet (32%) while the other had only 25% digestible protein. Silver perch (38 g for Experiment 1 and 59 g for Experiment 2) were stocked into each of nine 0.1 ha earthen ponds with fish in three ponds fed each diet for 191 days (Experiment 1) or 187 days (Experiment 2). Survival was >94% in all ponds in both experiments. In Experiment 1, growth rates and feed conversion ratios (FCRs) ranged from 2.1 to 2.4 g fish^?1 day^?1 and 1.7 to 1.9 respectively. Growth rates were significantly (P<0.05) lower for fish fed the experimental diet with the lowest digestible energy content. Growth rates for fish fed the other experimental diet and the reference diet were similar (P>0.05). In Experiment 2, growth rates and FCRs ranged from 2.3 to 2.4 g fish^?1 day^?1 and 1.6 to 1.7. There were no significant differences in fish performance indices for any of the three diets although experimental power was low (power=0.31). A blind consumer sensory evaluation (taste panel) of fish fed the three diets in Experiment 2 rated fish as ‘highly acceptable’. The diet with the lowest digestible protein content produced the best fish in terms of ‘smell liking’, ‘flavour liking’, ‘muddy flavour strength’ and ‘fresh flavour strength’. These results confirm that soybean meal and/or rendered animal protein ingredients including meat meal and poultry offal meal, and wheat can form the basis for high‐performance, low‐cost diets for intensive pond culture of silver perch.     

The effects of dietary digestible protein and digestible energy content on protein retention efficiency of juvenile silver perch Bidyanus bidyanus (Mitchell)

Effects of varying dietary digestible protein (DP) and digestible energy (DE) on protein retention efficiency (PRE), weight gain, protein deposition and carcass composition for silver perch (Bidyanus bidyanus, Mitchell) were studied. Using digestibility data for silver perch, we formulated three series of diets with different DE contents (13, 15 or 17 MJ DE kg^?1). For each series, a ‘summit’ diet containing an excess of protein for silver perch (based on previous research) and a ‘diluent’ diet with only 10–13% DP were formulated. By blending the summit and diluent diets together in different ratios, five diets with different DP contents were produced for each DE series. A commercial diet was also included to give 16 experimental diets in total. Eight juvenile fish (mean initial weight 1.2 g) were stocked into each of 64 × 70‐L acrylic aquaria and then each of the 16 diets was randomly allocated to four replicate aquaria. Tanks were supplied with partially recirculated water (75%) at 25–27°C. Fish were fed restrictively, twice per day, based initially on 3.5% body weight day^?1 with 40% of the ration given at 08:30 hours and 60% given at 15:00 hours for 59 days. Quadratic functions were fitted to each energy series to describe the relationship between DP content of diets and PRE (the asymptote of these functions were used to predict maximum PRE). For low DE (13 MJ kg^?1), mid‐DE (15 MJ kg^?1) and high DE (17 MJ kg^?1), the dietary DP contents to give maximum PRE were 24.7%, 26.1% and 30.1% respectively. Carcass fat decreased with increasing DP and increasing DP:DE ratio. Varying the dietary protein and DE also influenced other indices of fish performance. ‘Optimum’ dietary protein therefore depends on several factors. For fish fed, restrictively, the protein content needed to maximize PRE is lower than the content needed to maximize weight gain or minimize carcass fat. For fish fed to satiation, the lowest protein content for maximum weight gain is lower than for fish fed restrictively.     

Utilization of digestible nitrogen and energy from four agricultural ingredients by juvenile silver perch Bidyanus bidyanus

A comparative slaughter, growth assay was carried out using juvenile silver perch to evaluate different inclusion contents of peanut meal, canola meal, meat meal and dehulled field peas. Each ingredient was combined with a nutritionally balanced basal diet composed mainly of fishmeal (27%), soya bean meal (21%), wheat (28%) and sorghum (11%) such that between 15% and 75% of the basal diet was wholly replaced by the test ingredient. In addition, the basal diet was replaced with 15%, 30% or 45% of an inert filler (diatomaceous earth) in order to compare diets containing test ingredients and the inert filler. Fish were fed respective test diets twice a day for 56 days under a slightly restricted feeding regime (90% of apparent satiation) to negate any palatability problems. Weight gain of silver perch decreased steadily as the basal diet was systematically replaced with diatomaceous earth, confirming the limiting contribution to weight gain from the basal diet under a restricted feeding regime. Silver perch fed diets containing a mixture of the basal diet and either peanut meal, meat meal, canola meal or up to 60% field peas gained more weight than fish fed diets containing similar contents of the inert filler, indicating silver perch were able to utilize these ingredients to support growth. Regression analysis was applied to investigate protein and energy retention and models were fitted with 95% confidence and prediction intervals. Inspection of these relationships indicated various outliers which greatly affected the fitted models. We postulate that these outliers represent test diets which contain ingredients that are poorly utilized, or poorly utilized at particular inclusion contents. Removal of these outliers greatly improved the fit of each model. Using this approach, the predicted digestible protein (DP) content that gave maximum protein deposition in silver perch was 41.1%. The DP requirement for maintenance was 0.61 g DP kg BW^?0.6 day^?1 and the efficiency of DP for growth above maintenance was constant (0.45) after diets containing 45% or more of peanut meal and 75% of field peas were removed from the fitted model. The digestible energy (DE) requirement for maintenance was 36.79 kJ kg BW^?0.6 day^?1 and the efficiency of digestible energy for growth above maintenance was constant (0.68) after diets containing 75% of field peas and 75% of canola were removed from the fitted model. Adherence of other diets containing test ingredients to the slope of each regression suggests that silver perch are capable of utilizing any of the protein sources tested at all but the inclusion contents described above. Confirmation of this approach under different feeding regimes is required.     

Carbohydrate utilization by juvenile silver perch, Bidyanus bidyanus (Mitchell). II. Digestibility and utilization of starch and its breakdown products

Abstract The ability of silver perch ( Bidyanus bidyanus ) to digest and utilize dietary starch or starch breakdown products was investigated. For experiment 1 the ability of silver perch (2.7 ± 0.01 g) to digest wheat starch at two dietary inclusion levels (30% or 60%), each at four levels of gelatinization (0%, 25%, 50% or 80%), was investigated over a 31-day period. For experiment 2, the ability of silver perch (15.9± 0.25 g) to digest wheat starch, dextrin (at three levels of dextrinization), maltose, glucose and pea starch, all at the 30% inclusion level, was investigated over a 41-day period. Water temperature for both experiments was 25 ± 1 °C. Apparent digestibility coefficients (ADCs) for starch, dry matter (DM) and energy were affected by both degree of gelatinization (80% > 50% > 25% = 0%) and inclusion level (30% > 60%). Specific growth rate (SGR) was unaffected by the inclusion of 30% starch; however, it was reduced at the 60% starch content level. Degree of gelatinization had no effect on SGR. For experiment 2, there were significant differences between carbohydrate and DM ADCs for the test ingredients. The carbohydrate, DM and energy ADCs were ranked as follows: dextrin (Fieldose 9) = dextrin (Fieldose 17) = dextrin (Fieldose 30) = gelatinized wheat starch = maltose = glucose > raw wheat starch > raw pea starch. The protein ADC of the diets, postprandial plasma glucose concentration and SGR were all unaffected by ingredient type. For both experiments, HSI tended to increase with carbohydrate inclusion. Liver glycogen concentrations were also elevated, but muscle glycogen and liver and muscle triacylglycerol concentrations were unaffected. Digestibility of starch by silver perch is clearly affected by inclusion content and processing.     

Replacement of fishmeal in diets for Australian silver perch Bidyanus bidyanus (Mitchell). II. Effects of cooking on digestibility of a practical diet containing different starch products

Abstract The interactive effects of cooking and starch type on the dry matter, gross energy and protein digestibility of diets fed to fingerling silver perch were examined. Nine experimental diets were made: a reference diet either uncooked or cooked, six other diets comprising uncooked reference diet supplemented with 30% uncooked or cooked wheat, maize or potato starch and one diet comprising uncooked reference diet supplemented with 15% pregelatinized maize starch. Cooking involved autoclaving at 121 °C for 15 min. The indirect method was used to calculate apparent digestibility coefficients, and chromic oxide (1%) was used as the inert indicator. Both ingredient type and cooking influenced dry matter and gross energy digestibility of diets. All diets had significantly different digestibility coefficients in the following order (from most to least digestible): reference > wheat > maize > potato, for both dry matter and gross energy. Cooking significantly increased the apparent digestibility of diets for both dry matter and gross energy. There was no significant effect of ingredient or cooking or their interaction on protein digestibility. Dry matter and energy digestibility of the diet containing pregelatinized maize starch were significantly higher than for diets containing cooked or uncooked starch products. Ingredient digestibility followed the same trend as diet digestibility. The results from this study indicate that the successful use of starch in practical diets for silver perch is dependent on the origin and processing of the starch. The significant benefits of cooking in the reference diet suggest that pelleted diets should be cooked (e.g. steam conditioned or extruded).     

银鲈胚胎和仔、稚鱼发育观察

实验对银鲈受精卵的胚胎及仔、稚鱼发育进行连续跟踪观察,结果表明:银鲈受精卵具有在淡水鱼类中比较少见的油球,水温25.4～27.8℃条件下,24小时胚胎破膜而出.出膜仔鱼3日龄开始平游,消化道形成,已能开口摄食;35日龄全长2.3～3.0cm,全身已布满鳞片,形态已具备成鱼特征.