Utilization of digestible nitrogen and energy from four agricultural ingredients by juvenile silver perch Bidyanus bidyanus M.A. BOOTH & G.L. ALLAN NSW Fisheries, Port Stephens Fisheries Centre, Nelson Bay, Australia Abstract Acomparativeslaughter,growthassaywascarriedoutusing 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 balancedbasaldietcomposedmainlyoffishmeal(27%),soya beanmeal(21%),wheat(28%)andsorghum(11%)suchthat between15%and75%ofthebasaldietwaswhollyreplaced bythetestingredient.Inaddition,thebasaldietwasreplaced with 15%, 30% or 45% of an inert filler (diatomaceous earth) in order to compare diets containing test ingredients andtheinertfiller.Fishwerefedrespectivetestdietstwicea 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 thebasaldietwassystematicallyreplacedwithdiatomaceous 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 similarcontentsoftheinertfiller,indicatingsilverperchwere able to utilize these ingredients to support growth. Regres- sion analysis was applied to investigate protein and energy retention and models were fitted with 95% confidence and prediction intervals. Inspection of these relationships indi- cated various outliers which greatly affected the fitted mod- els.Wepostulatethattheseoutliersrepresenttestdietswhich containingredientsthatarepoorlyutilized,orpoorlyutilized at particular inclusion contents. Removal of these outliers greatlyimprovedthefitofeachmodel.Usingthisapproach, the predicted digestible protein (DP) content that gave maximumproteindepositioninsilverperchwas41.1%.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% ormoreofpeanutmealand75%offieldpeaswereremoved from the fitted model. The digestible energy (DE) require- mentformaintenancewas36.79kJkgBW )0.6 day )1 andthe 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 slopeofeachregressionsuggeststhatsilverpercharecapable 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. KEY WORDS KEY WORDS: canola, meat meal, peanut meal, peas, require- ments, silver perch, utilization Received 3 September 2002, accepted 20 February 2003 Correspondence: Mark A. Booth, NSW Fisheries, Port Stephens Fisheries Centre, Private Bag 1, Nelson Bay NSW 2315, Australia. E-mail: boothm@fisheries.nsw.gov.au Introduction Silver perch Bidyanus bidyanus,isanomnivorousAustralian freshwater species that is capable of efficiently digesting a wide range of intact protein and energy sources (Allan et al. 1999, 2000a; Booth et al. 2001). Digestibility for many of these ingredients is additive which has allowed the least-cost formulation of commercial diets based on the protein and energy composition of ingredients and their respective digestibility coefficients (Allan et al. 2000b). The equitable performance of silver perch reared on diets containing meat meal, cereal grains, legumes or oilseeds, compared with fish fed on diets containing significant quantities of fishmeal, demonstrates that this species is also able to utilize the pro- tein and energy from these ingredients (Allan et al. 2000c; 317 Aquaculture Nutrition 2003 9 ; 317^326 .............................................................................................. .............................................................................................. Ó 2003 Blackwell Publishing Ltd