Mark A. Booth

Replacement of fish meal in diets for Australian silver perch, Bidyanus bidyanus: I. Digestibility of alternative ingredients

Apparent digestibility coefficients (ADCs) for dry matter, nitrogen, energy and individual amino acids for 29 commonly used feed ingredients were determined for silver perch, a native Australian freshwater species currently being cultured in Australia, Taiwan and China. ADCs were determined using faeces collected following settlement. Results from 11 experiments are reported. Each experiment included a reference diet and test diets, which were composed of 69.3% reference diet, 29.7% test ingredient and 1% chromic oxide (inert indicator). Ingredients tested included Australian, Danish and Peruvian fish meals, blood meal, meat and bone meals from beef and lamb, poultry meal, feather meal, soybean and canola meals (both expeller and solvent extracted for each), full fat soybeans, peanut meal, cottonseed meal, linola, two species of lupins, field peas, faba beans, chick peas, vetch, cow peas, wheat gluten, corn gluten meal, two cultivars of wheat, millrun and sorghum. ADCs for dry matter, energy and nitrogen were highest for fish meal, although several other ingredients, including some animal meals and gluten from wheat and corn, had similar ADCs for dry matter and energy. Digestible protein from these ingredients was in the range 52-86% compared with 63-69% for fish meals. Silver perch were capable of digesting protein very effectively in almost all ingredients tested. Amino acid availability reflected nitrogen digestibility except for Peruvian fish meal and the two meat and bone meals, for which the availability of some amino acids was lower, possibly indicating protein damage during processing. Oilseeds and legumes also tended to have lower ADCs for some amino acids (e.g., sulphur amino acids) than for other amino acids. Differences in ADCs for nitrogen and individual amino acids indicate the need for individual amino acid availability data. The data provided a useful starting point for least-cost formulation of diets for silver perch.

Replacement of fish meal in diets for Australian silver perch, Bidyanus bidyanus: IV. Effects of dehulling and protein concentration on digestibility of grain legumes

Three digestibility experiments were conducted using juvenile silver perch. The first factorial experiment evaluated four ingredients; field peas (Pisum sativum), faba beans (Vicia faba), chick peas (Cicer arietinum) and vetch (Vicia sativa) with and without hulls. The second and third experiments determined digestibility of field pea, faba bean and lupin protein concentrates. Apparent digestibility coefficients (ADCs) were determined using indirect procedures. Test diets comprised 29.7% of the test ingredient, 69.3% of a practical reference diet and 1.0% chromic oxide as the inert indicator. Faeces were collected from fish by passive settlement techniques. Two-factor ANOVA of the data from the first experiment revealed a significant interaction between ingredient type and the presence/absence of hulls for dry matter, protein and energy digestibility. Dry matter and energy ADCs for whole grains ranged from 43–58% and 51–59%, respectively. Dehulling significantly improved the dry matter and energy digestibility of all grains except faba beans. Dehulled vetch had the highest dry matter (81%) and energy (81%) digestibility of all grains, but diets containing 30% vetch were poorly accepted by silver perch. Protein digestibility for all legumes was high, ranging from 71% to 91% for whole grains and 80–97% for dehulled grains. Protein digestibility was significantly improved by dehulling field peas, faba beans and vetch, but dehulling did not affect protein digestibility of chick peas. Dry matter and energy ADCs for protein concentrates were much higher than either ADCs for whole or dehulled grains. Protein digestibility was highest for the field pea concentrate (97%), but protein ADCs for concentrates of faba beans and lupins were of a similar value to that of their respective dehulled grains. Silver perch have demonstrated they can efficiently digest the protein from the dehulled and refined legumes evaluated in this study. Further, both dry matter and energy digestibility of most grains was dramatically improved after dehulling or protein concentration, indicating processes such as these are highly desirable for legumes prior to their inclusion in diets for silver perch. The cost effectiveness of using protein concentrates in aquaculture diets requires further evaluation. Of the grain legumes investigated in this study, dehulled field peas appear the most promising for juvenile silver perch.

Effects of grinding, steam conditioning and extrusion of a practical diet on digestibility and weight gain of silver perch, Bidyanus bidyanus

Abstract As processing can affect the digestibility and utilisation of diets by fish, we examined the effects of grinding, steam conditioning and extrusion of a commercially available diet (SP35) on weight gain and performance of silver perch. SP35 (35% protein, 18 MJ/kg gross energy) with approximately 80% of particles between 710 and 1000 μm was either left (unground) or finely ground to 500 μm (ground). Both unground and ground fractions were made into sinking pellets in a commercial steam pelleting mill with or without the addition of steam (90°C) A fifth diet was processed by pelleting finely ground material in a single-screw extruder (after the addition of approximately 5% fish oil) at a temperature of 120°C. The extruded diet floated or sank slowly. Each diet was fed to 50 juvenile silver perch (mean initial weight 17.8 g) in each of three replicate 10 000-l tanks for 113 days. Fish gained between 55 and 71 g/fish during the experiment, and feed conversion ratio (FCR) ranged from 1.5:1 to 2.0:1. Steam conditioning significantly improved weight gain and FCRs while neither grinding nor the interaction between grinding and steam conditioning had any effect. Fish were reluctant to consume the extruded diet and grew less on this diet than on the steam-conditioned diets, although FCR was better than for all other diets. Ground diets, uncooked and steamed, and the extruded diet were subsequently reground and 1% chromic oxide was added as an inert indicator. Each of these three diets was fed to juvenile silver perch (mean initial weight 2.5 g) in 170-l cylindroconical tanks from which faeces were collected by settlement to determine digestibility coefficients for dry matter, energy and nitrogen. Digestibility coefficients for dry matter and energy were higher for the extruded diet but similar for the unsteamed and steamed diets. Protein digestibility was unaffected by processing. These results indicate that for silver perch fed diets similar to SP35, diets should be steam-conditioned, but the additional expense associated with fine grinding is unwarranted with respect to gains in either fish performance or improvements in pellet stability. Extrusion significantly improved digestibility and FCR but consumption of floating extruded pellets was reduced in our facility. Sinking, extruded diets deserve evaluation.

The routine metabolic rate of mulloway (Argyrosomus japonicus: Sciaenidae) and yellowtail kingfish (Seriola lalandi: Carangidae) acclimated to six different temperatures

This study compared the mass-specific routine metabolic rate (RMR) of similar sized mulloway (Argyrosomus japonicus), a sedentary species, and yellowtail kingfish (Seriola lalandi), a highly active species, acclimated at one of several temperatures ranging from 10-35 degrees C. Respirometry was carried out in an open-top static system and RMR corrected for seawater-atmosphere O2 exchange using mass-balance equations. For both species RMR increased linearly with increasing temperature (T). RMR for mulloway was 5.78T-29.0 mg O2 kg(-0.8) h(-1) and for yellowtail kingfish was 12.11T-39.40 mg O2 kg(-0.8) h(-1). The factorial difference in RMR between mulloway and yellowtail kingfish ranged from 2.8 to 2.2 depending on temperature. The energetic cost of routine activity can be described as a function of temperature for mulloway as 1.93T-9.68 kJ kg(-0.8) day(-1) and for yellowtail kingfish as 4.04T-13.14 kJ kg(-0.8) day(-1). Over the full range of temperatures tested Q10 values were approximately 2 for both species while Q10 responses at each temperature increment varied considerably with mulloway and yellowtail kingfish displaying thermosensitivities indicative of each species respective niche habitat. RMR for mulloway was least thermally dependent at 28.5 degrees C and for yellowtail kingfish at 22.8 degrees C. Activation energies (Ea) calculated from Arrhenius plots were not significantly different between mulloway (47.6 kJ mol(-1) and yellowtail kingfish (44.1 kJ mol(-1).

The effect of temperature and body weight on the routine metabolic rate and postprandial metabolic response in mulloway, Argyrosomus japonicus.

Specific dynamic action (SDA) is the energy expended on the physiological processes associated with meal digestion and is strongly influenced by the characteristics of the meal and the body weight (BW) and temperature of the organism. This study assessed the effects of temperature and body weight on the routine metabolic rate (RMR) and postprandial metabolic response in mulloway, Argyrosomus japonicus. RMR and SDA were established at 3 temperatures (14, 20 and 26 degrees C). 5 size classes of mulloway ranging from 60 g to 1.14 kg were used to establish RMR with 3 of the 5 size classes (60, 120 and 240 g) used to establish SDA. The effect of body size on the mass-specific RMR (mg O(2) kg(-1) h(-1)) varied significantly depending on the temperature; there was a greater relative increase in the mass-specific RMR for smaller mulloway with increasing temperature. No statistical differences were found between the mass exponent (b) values at each temperature when tested against H(0): b=0.8. The gross RMR of mulloway (mg O(2) fish(-1) h(-1)) can be described as function of temperature (T; 14-26 degrees C) as: (0.0195T-0.0454)BW(g)(0.8) and the mass-specific RMR (mg O(2) kg(-1) h(-1)) can be described as: (21.042T-74.867)BW(g)(-0.2). Both SDA duration and time to peak SDA were influenced by temperature and body weight; SDA duration occurred within 41-89 h and peak time occurred within 17-38 h of feeding. The effect of body size on peak metabolic rate varied significantly depending on temperature, generally increasing with temperature and decreasing with increasing body size. Peak gross oxygen consumption (MO(2): mg O(2) fish(-1) h(-1)) scaled allometrically with BW. Temperature, but not body size, significantly affected SDA scope, although the difference was numerically small. There was a trend for MO(2) above RMR over the SDA period to increase with temperature; however, this was not statistically significant. The average proportion of energy expended over the SDA period (SDA coefficient) ranged from approximately 7-13% of the total DE intake while the proportion of total energy expended on SDA above RMR ranged from approximately 16-27%.