SDRP JOURNAL OF AQUACULTURE, FISHERIES & FISH SCIENCE 2016 Short communiction Determintion of n optiml dily dietry rtion for lrge two-yer-old mullowy (Argyrosomus jponicus) using current commercil feed mngement prctices. Jeffrey A. Guy 1, 2 * Stephen D.A. Smith 1, 2 1 Ntionl Mrine Science Centre, Southern Cross University, Coffs Hrour, NSW 2450, Austrli. 2 Mrine Ecology Reserch Centre, School of Environment, Sciencend Engineering, Southern Cross University, Lismore, New SouthWles, Austrli Received dte: 19-01-2015; Accepted dte: 03-03-2016; Pulished dte: 15-03-2016 Open Access Corresponding uthor: Jeffrey A. Guy Address: Ntionl Mrine Science Centre,Southern Cross University, By Drive (P.O. Box 4321), Coffs Hrour, NSW 2450, Austrli. Telephone: +61-2-6648-3913; Fx: +61-2-6656-1580; E-mil: jeff.guy@scu.edu.u Astrct A 30 dy tnk feeding tril ws conducted to determine the optiml dietry rtion for lrge (initil size nd length, 1.7 kg, 54.27 cm) two-yer-old mullowy (Argyrosomus jponicus) grown in sewter during winter (July-August, wter temperture 17.01 20.58 C). Mullowy fed t 0.6% ody weight (BW) dy -1 were underfed while feeding t 1.0% BW dy -1 produced significnt wstge, with up to 25% of the weekly rtion uneten. Differences in growth were lso evident; fish fed t 0.8 nd 1.0% BW dy -1 grew significntly fster (SGR, 0.33 nd 0.34% dy -1, respectively) thn 0.6% BW dy -1 (SGR, 0.23% dy -1 ). Mullowy fed t 0.8% BW dy -1 hd the highest condition index (1.14), feed conversion efficiency (78.6%) with miniml wstge (0.31-2.1% of weekly rtion un-eten). The results of this study suggest tht using feeding rte of 0.8% BW dy - 1 hs the potentil to mximize growth, reduce feed wstge nd lower costs of mullowy production. Keywords: Scienids, Jewfish, Aquculture, optimizing production, Feed costs, Over-under feeding INTRODUCTION Mullowy, Argyrosomus jponicus (Temminck & Schlegel, 1844) re temperte, euryhline, crnivorous finfish of the fmily Scienide, commonly known s drums or crokers (Silerschneider nd Gry 2008). Scienids re ecoming incresingly importnt to glol quculture nd form the sis of significnt quculture industries in the USA (Lee nd Ostrowski 2001), Chin (Hong nd Zhng 2003), Mediterrnen wters round Greece, Itly, Croti nd Spin (Monfort 2010; Kruzic et l. 2016), nd in the Estern Cpe of South Afric (Enviro-Fish Afric Pty. Ltd. 2009). Production of mullowy in Austrli nd NSW ws sed on se-cge culture (Qurtrro 1996; Rimmer nd Poni 2007) ut more recently, n emerging industry is developing using erted rckish-wter prwn ponds in su-tropicl ltitudes (25-30 o ) (Guy nd Cowden 2012, 2014). Pond production techniques hve een developed nd single-tch, three-phse production system involving htchery, fingerlings nd grow-out phses is prcticed with production rtes of 12-14 tonnes h -1 (Guy nd Cowden 2012, 2015). Feed costs ccount for 42.5% of the totl vrile costs (Guy et l. 2014) nd fish re fed formulted, extruded, generic type mrine fish's diet once or twice dily, nd rech mrket size (2 kg live weight) in 22-24 months. To dte, the fish hs found good mrket with top sefood resturnts (Guy nd Nottinghm 2014). One mjor constrint to further industry growth nd profitility is lck of knowledge out feed mngement nd its efficient delivery. Previous studies hve shown tht, in the finl yer of grow-out (>1 kg live weight), food conversion efficiencies re poor (from 37-52%), well elow the industry stndrd for mrine fish nd food wstge is mjor issue (Guy nd Cowden 2012). Excessive nutrient loding from overfeeding cn cuse hrmful dinoflgellte looms within culture systems, nd costl eutrophiction when dischrged, impcting on locl flor nd funl communities (Gliert nd Terlizzi1999; Russell et l. 2005). Current reserch, however, hs focused only on htchery nd juvenile feeding strtegies for this species (Fielder et l. 2010; Pirozzi et l. 2010) despite the fct tht the gretest cost-sving with respect to feed cn e mde t the finl grow-out stges of frming. This is lso evident from the lrge numer of studies, over the lst decde, which Copy rights: This is n Open ccess rticle distriuted under the terms of Cretive Commons Attriution 4. 0 Interntionl License. 13 www. siftdesk. org volume 1: issue 1
SDRP JOURNAL OF AQUACULTURE, FISHERIES & FISH SCIENCE Mrch 15, 2016 pply only to smll, juvenile or fingerling fish (De Silv et l. 1986; Eroldoğn et l. 2004; Fiogé et l. 2003; Hssn nd Jfri 1994; Hung et l. 1995; Khn nd Aidi 2010; Mihelkkis et l. 2002; Oerg et l. 2014; Okorie et l. 2013). The consequence is tht there re lmost no seline dt for lrge fish, nd optiml feeding strtegies nd physiologicl responses to over or under feeding for fish greter thn 1 kg to mrket size remin lrgely unknown for mny species, including mullowy. Reserch to identify suitle restricted rtion for two-yer-old mullowy is therefore high priority for the industry nd our pproch hs een to investigte the current feed mngement on frms while ttempting to optimise existing feeding prctices. In erly spring (wter temperture 18-20 o C), frmers feed nywhere from 0.6% to 1.0% ody weight (BW) dy -1. The more conservtive, keen to economise in high feed cost environment, keep dily consumption to 10 g fish -1 for fish over 1 kg in size or 70kg h -1 while others re convinced tht high feed rtes (1% BW dy -1 ) result in fster growth nd shorter production cycle (Andrew Crroll, frm mnger, Plmers Islnd Mullowy Pty. Ltd., personl communiction). Since there is currently no consensus nd evidence to suggest which feeding strtegy is optiml the ojective of this initil study ws to determine the optimum rtion level in order to support etter industry feed mngement prctices. MATERIALS AND METHODS Commercil diet The feed used ws n off-the-shelf 14 mm imported, formulted, extruded, fishmel-sed, sinking Jpnese sess (Lteolrx jponicus) diet (Groest Austrli, Bry Investment Group Pty. Ltd.). Triplicte smples were nlysed for proximte nlysis y the Nutritionl Biochemistry Lortory, Coopers Plins, Brisne, Queenslnd (Tle 1). We used the frmer s choice of feed in our study to ensure relevnt outcome tht promotes doption y industry. Fish collection nd mintennce procedures Two-yer-old mullowy (n=190) were collected in utumn from commercil fish frm 1.5 months efore the scheduled experiments. Cptured fish were trnsported y rod in n oxygented 900 L trnsport tnk t density of 75kg m -3 to experimentl holding tnks mintined in n outdoor undercover re. The top of the tnks were fitted with drk green cloth to provide cover nd shde nd supplied with high rte (20L min -1 ) of continuously exchnging filtered sewter. Dissolved oxygen ws mintined y delivering pproximtely 10 L min -1 of ir, vi diffusers, to the ottom of these tnks which were sujected to nturl photoperiod nd mient climtic conditions. Fish were hnd-fed the commercil diet (10 g fish -1 ) for two weeks t noon every other dy (M, W, F) nd, two dys prior to experimenttion, ll feed ws withheld. The fish were lso treted twice (two dys prt) with 200 mg L -1 formlin for one hour, two weeks prior to experimenttion to eliminte ectoprsites (Nog 2010). Tle 1 Proximte composition (dry mtter sis) nd pellet chrcteristics of the commercil diet1. Composition (%) Groest diet Moisture 2 5.50± 0.36 Dry mtter 3 94.50 ± 0.36 Ash 4 13.73± 0.29 Nitrogen 5 7.19 ± 0.09 Crude protein 6 44.94 ± 0.59 Gross energy (MJ Kg-1 diet) 7 21.53 ± 0.10 Crude ft 8 17.33 ± 0.85 Crude fire 9 1.17 ± 0.06 Weight (g) 10 0.74 ± 0.01 Dimeter (mm) 11 14.04 ± 0.03 1 Dt re mens (± stndrd error) of triplicte smples. 2 100-dry mtter 3 Dry mtter; y heting to constnt weight t 105 C with Nitrogen using LECO Thermogrvimetric Anlyser 4 Ash; y further heting in the Thermo grvimetric Anlyser t 600 C in n tmosphere of oxygen. 5 Totl Nitrogen; comustion method using n ElementrRpidN III nlyser. 6 Crude protein; totl nitrogen multiplied y fctor, usully 6.25. 7 Gross energy; determined using LECO Automtic Clorimeter. 8 Crude ft; soxhlet extrction using hexne for 16 hours. 9 Crude fier; AOAC method dpted for the Fiertec 2021 Firecp System. 10-11 Weight nd dimeter; from three seprte gs (100 pellets ech). Tnk stocking nd design Lrge mullowy (1.7 kg men weight)with no deformities were stocked rndomly into nine circulr 3200 L tpered ottom polyethylene tnks t stocking density of 11.3 kg m -3 (20 fish tnk -1 ) in triplicte for ech tretment (0.6%, 0.8%, 1.0% BW dy -1 ). At the time of stocking there were no significnt differences in the men weight, length nd condition of fish from the three feeding tretments (P>0.05) (Tle 2). All tnks were supplied with their own intke line for wter nd ir nd two level externl stnd pipe llowed different wter levels to e mintined. A 200 mm x 50 mm round ir diffuser ws positioned inside the tnk, 30 cm ove the 50 mm outlet hole, y fstening it to the metl frme ove. There were Jeffrey A. Guy 14 www. siftdesk. org volume 1: issue 1
Dily feed intke (g) SDRP JOURNAL OF AQUACULTURE, FISHERIES & FISH SCIENCE Mrch 15, 2016 no internl stnd-pipe nd the flow rte ws set t 16 L min -1 for the durtion of the experiment. Feed type, delivery, collection nd djustment Fish were fed the 14 mm commercil diet nd for ech g used 100 pellets (dry weight) were individully weighed to determine men pellet weight (g). Fish were hnd-fed restricted rtion (0.6%, 0.8%, 1.0% BW dy -1 ) t noon, six dys per week using the feeding regime detiled in Guy nd Cowden (2014). All uneten pellets were collected y flushing the contents of the ottom externl pipe into corse nylon net nd then dried prior to counting (Hellnd et l. 1996). Tnks were visully inspected to check tht no pellets remined nd pipes flushed numer of times to ensure they were empty. The inflow wter remined on unless smpling ws to occur nd in these instnces the flow rte ws reset to 16 L min -1 using stopwtch nd 5 L continer. At dy 16 ll fish in ech tnk were nesthetized with AQUIS (15 mg L -1 ), counted, ulk-weighed nd returned to clened tnk. Men weight nd iomss were determined nd the dily rtions djusted to ccount for growth. Wter qulity Wter qulity testing ws conducted twice dily, six dys per week (m nd pm) using U- 52 Hori hnd held multi-meter. Prmeters recorded were ph (rnge 7.77-8.13) dissolved oxygen (6.27-8.76mg L -1 ), slinity (32.9-33.9ppt), conductivity (50.5-51.9mScm -1 ), turidity (NTU) (0.1-1.0mg L -1 ), totl dissolved solids (TDS) (30.3-31.1mg L -1 ) nd this vrition ws common cross ll tretments. Wter temperture (17.01-20.58 C) ws recorded in triplicte t hourly intervls using clirted sumersile temperture loggers (ibcod 22L, Thermodt Pty. Ltd.). Wter smples (100 ml) were collected twice weekly (m nd pm) to determine the totl mmoni nitrogen (TAN) (0.08-0.79 mg L -1 ) using Plintest photometer 7100. Un-ionised mmoni nitrogen (NH3-N) (0.01-0.03mg L -1 ) ws clculted from n online mmoni clcultor using TAN, slinity, ph nd temperture dt.all wter qulity prmeters were within the cceptle limits for mrine finfish, however, these prmeters re likely to vry more in commercil pond grow-out environment (Guy nd Cowden 2012). Dt/sttisticl nlysis At the termintion of the experiment (dy 30), ll fish in ech tnk were nesthetized with AQUIS (15 mg L -1 ), individully counted, weighed nd mesured to determine survivl rte, men weight nd length, condition index (CI =10 5 W/L 3 where W is weight nd L is totl length of the fish), solute growth rte (AGR = (W2-W1)/t2-t1 increment of weight W2-W1 over known time (t); g fish -1 dy -1 ), specific growth rte (SGR= 100 x (loge finl wt.-loge initil wt.)/dys; % dy -1 ), feed conversion rtio (FCR = dry feed intke (g)/wet weight gin (g)), feed conversion efficiency (FCE = wet weight gin(g) x 100/dry feed intke (g)) nd protein efficiency rtio (PER = wet weight gin (g) /protein intke (g)). For sttisticl nlysis the SPSS Version 22 softwre pckge (IBM) ws used to conduct One Wy ANOVAs with three repetitions (n = 3 tnks, men of 20 fish tnk -1 )for growth performnce nd feed efficiency dt. Mens were compred using the Tukeys Honestly significnt difference (HSD) method (P= 0.05). RESULTS Feed utilistion Dily feed intke ws consistent in fish fed t 0.6% nd 0.8% BW dy -1 ut ecme highly vrile (errtic) in fish fed t 1.0% BW dy -1 fter dy 4, nd this trend continued throughout the experiment (Fig. 1). Fish fed t 0.6% BW consumed ll of their food with little to no wstge (<0.5% of ll four weekly totls) (Fig. 2). However, mullowy fed t 1.0% BW dy -1 were overfed with lrge mount of pellets recovered from ech dily feed. On weekly sis, the proportion of rtion uneten ws vrile nd rnged from 8 to 25% (Fig. 2). The 0.8% BW dy -1 ws close to optiml with less thn 1% wstge from weeks 1-3 nd 2% in week 4; there ws no significnt difference etween the 0.6% nd 0.8% BW dy -1 feeding rte. Mullowy fed t 0.8% BW lso hd the lowest FCR nd est feed efficiency nd protein efficiency rtio (Tle 2). Fig. 1 Dily feed intke of mullowy (Argyrosomus jponicus) fed t 0.6 %, 0.8 % nd 1% ody weight (BW)dy -1 in tnkssix dys per weekover 30 dys. Dily dt re mens ± S.E. of three replicte tnks. 400 350 300 250 200 150 100 50 0 0.6%BW 0.8%BW 1.0%BW 1 3 5 7 9 11 13 15 17 19 21 23 25 27 Time (dys) Jeffrey A. Guy 15 www. siftdesk. org volume 1: issue 1
Proportion of rtion uneten (% wstge) SGR (% dy -1 ) SDRP JOURNAL OF AQUACULTURE, FISHERIES & FISH SCIENCE Mrch 15, 2016 Tle 2 Influence of feeding rte: 0.6%, 0.8% nd 1.0% ody weight (BW) dy -1, six dys per weekt noon on growth prmeters, feed efficiency nd condition of mullowy (Argyrosomus jponicus) rered in tnks for 30 dys 1. 0.6% BW 0.8% BW 1.0% BW P-vlue Initil Wt. (kg) 1.70 ± 0.03 1.70 ± 0.02 1.69 ± 0.01 0.986 Finl Wt. (kg) 1.87 ± 0.03 1.95 ± 0.02 1.95 ± 0.02 0.104 Initil L (cm) 54.31 ± 0.40 54.22 ± 0.12 54.31± 0.21 0.962 Finl L (cm) 55.31 ± 0.33 55.48 ± 0.03 55.62 ± 0.31 0.707 Initil CI 2 1.06 ± 0.01 1.06 ± 0.01 1.05 ± 0.01 0.780 Finl CI 1.10 ± 0.01 1.14 ± 0.02 1.13 ± 0.01 0.280 Survivl (%) 3 100 100 100 TWG (kg) 4 3.42 ± 0.12 5.06 ± 0.19 5.17 ± 0.23 0.001** AGR (g fish -1 dy -1 ) 5 4.07 ± 0.15 6.02 ± 0.22 6.15 ± 0.27 0.001** SGR(% dy -1 ) 6 0.23 ± 0.01 0.33 ± 0.01 0.34 ± 0.01 <0.000** Feed eten (kg) 4.76 ± 0.03 6.43 ± 0.07 6.76 ± 0.12 <0.000** FCR 7 1.39 ± 0.05 1.27 ± 0.03 1.31 ± 0.04 0.182 FCE (%) 8 71.88 ± 2.43 78.62 ± 2.10 76.40 ± 2.33 0.188 PER 9 1.60 ± 0.05 1.75 ± 0.05 1.70 ± 0.05 0.188 Feed wstge (kg) 10 0.01 ± 0.01 0.06 ± 0.02 1.37 ± 0.07 <0.000** 1 Dt re mens (± stndrd error) of three replicte tnks (20 fish ech) for ech feeding rte (n=180). Rows with different letters (, ) re significntly different (P < 0.01; Tukey test). P is proility vlue nd ** highly significnt. 2 Fulton s condition index (CI) =10 5 W/L 3 where W is the weight nd L is the totl length of the fish. 3 Survivl (%) = n 2/n 1 x 100 where n 2 is the remining numer of fish nd n 1 is the originl numer of fish. 4 Totl weight gin (kg) = (finl weight -initil weight) 5 Asolute growth rte (g fish -1 dy -1 ) = (w 2-w 1/ t 2-t 1) increment of weight W 2-W 1 over known time (t) intervl 6 Specific growth rte (% dy -1 ) = 100 x (log e finl wt.-log einitil wt.)/dys. 7 Feed conversion rtio = dry feed intke (g)/wet weight gin (g). 8 Feed conversion efficiency (%) = wet weight gin(g) x 100/dry feed intke (g) 9 Protein efficiency rtio = wet weight gin/protein intke. 10 Feed wstge (kg) = numer of uneten pellets (wet) x men dry weight (g) of pellets Fig. 2 Percentge of weekly rtion uneten y mullowy (Argyrosomus jponicus) fed t 0.6 %, 0.8 % nd 1% ody weight (BW)dy -1 in tnks over 30 dys. Dt re mens ± S.E. of three replicte tnks. Columns with different letters (, ) within ech week re significntly different (P < 0.01; Tukey test). Fig. 3 Specific growth rte (SGR % dy -1 ) of mullowy (Argyrosomus jponicus) fed t 0.6%, 0.8% nd 1% ody weight (BW) dy -1 in tnks over three smpling periods; 0 16 dys, 17-30 dys nd overll (0-30 dys). Dt re mens ± S.E. of three replicte tnks. Columns with different letters (, ) within ech smpling period re significntly different (P < 0.05; Tukey test). 30 0.6%BW 0.8%BW 1.0%BW 0.5 0.6%BW 0.8%BW 1.0%BW 20 0.4 0.3 10 0.2 0.1 0 1 2 3 4 Time (weeks) 0 Strt-mid (16 dys) Mid-end (14 dys) Strt-end (30 dys) Smpling period Jeffrey A. Guy 16 www. siftdesk. org volume 1: issue 1
SDRP JOURNAL OF AQUACULTURE, FISHERIES & FISH SCIENCE Mrch 15, 2016 Growth performnce Fish fed t 0.6% BW dy -1 hd significntly slower growth nd weight gin thn fish fed t 0.8 % nd 1.0% BW dy -1, ut this ws not reflected in their condition or feed efficiency (Tle 2). Mullowy fed t 1.0% BW dy -1 showed the highest initil growth from 0-16 dys (0.39% dy -1 ), ut this declined from 17-30 dys (0.26% dy -1 ) (Fig. 3). Mullowy fed 0.8% BW dy -1 hd the highest condition index (1.14) nd less vrition in growth rte over the smpling period (0.34 nd 0.32 % dy -1 fter 0-16 nd 17-30 dys, respectively). DISCUSSION Determining the optimum rtion for est growth is one of the most difficult nd importnt spects of quculture (De Silv nd Anderson 1995). The results of our preliminry study indicte tht the optimum feeding rte for lrge mullowy (1.7-1.9 kg) grown in sewter (33.5 ppt) t men wter temperture of 18.8 C (rnge 17-20.6 C) lies close to 0.8% BWdy -1. Here growth (SGR 0.33 % dy -1 ) ws s good s fish fed to stition (1.0% BW dy -1, SGR 0.34 % dy -1 ), ut more consistent, nd feed wstge ws low (0.31-2.1% of the weekly rtion uneten). This study lso shows tht two-yer-old mullowy grow well t lower wter tempertures (down to 18 C) thn reported to e optiml for this species, lthough much of this work is only for smll fish. Therml studies on Juvenile mullowy y Berntzeder nd Britz (2007), Collett et l. (2008) nd Pirozzi nd Booth (2009) demonstrted finl preferred temperture rnge of 25 26.4 C, 23.9-26.3 C nd 28.5 C for 20g, 24g nd 182g fish, respectively, with food conversion efficiency mximized t lower temperture (21.7 C) thn the optiml temperture for growth (Collett et l. 2008). We propose tht lrger mullowy hve lower temperture rnge for optiml metolic function (Guy nd Cowden 2014), however this remins to e tested. Hndelnd et l. (2008) study showed tht the optimum temperture for fed conversion efficiency vried mong size clsses of Atlntic slmon (Slmo slr); lrger fish (170-300g) hd much lower (11.0 C) optiml growth temperture thn smller (70-150g) fish (13.4 C).This hs implictions for the quculture of mullowy, prticulrly in terms of the sesonl temperture profiles t loctions for culture, mking colder wter more ttrctive for lrge fish grow-out to mrket size nd highlights the importnce of doing reserch withmrket size fish. This hs lso een the experience with the megre (Argyroso musregius), Mediterrnen species from the sme fmily with est reported growth etween 17-21 C nd reduced feeding ctivity t 13-15 C (Monfort 2010). There is very little pulished informtion for comprison with our results: most previous studies hve focused on smll or juvenile mullowy rnging in size from 7-40 g (3-5.1% BW dy -1 ) (Collett 2007; Collett et l. 2008; Dniel 2004; Doroudi et l. 2004, 2006) nd plte-sized fish (400-677 g, 1.1-1.75 % iomss dy -1 ) grown in se- cges nd ponds (Alln et l. 2008; Mosig 2007; Qurtrro 1996). As such, this study provides the first experimentl dt on feed optimistion in lrge mullowy nd this hs importnt implictions for industry. This study clerly demonstrtes tht strtegy imed t mximising growth through high feeding rtes (1.0% BW dy -1 ) will e inefficient, led to significnt wstge (8-25%) nd highly vrile dily intke. At the other end of the scle feeding well elow this rte (such s 0.6% BW dy -1 ) will negtively impct growth nd extend the production cycle. Our pst work hs identified tht round 4.8 tonnes of feed pond -1 (six dys week -1 ), worth AU$9,600 (AU$2 kg -1 ), is consumed in the eight weeks of spring grow-out to mrket size with poor feed conversion nd serious wter qulity issues (Guy nd Cowden 2012). At this delivery rte dense phytoplnkton looms developed, leding to dissolved oxygen depletion nd high mmoni levels when they senesced, cusing stress nd mortlity of fish (Hrgreves nd Tucker 2005). By contrst, frmers dopting n industry stndrd of 0.8% BW dy -1 t spring deliver only 3.84 tonnes of feed pond -1, sving of 120 kg week -1 pond -1 in direct feed costs worth AU$1, 920 ponds -1. Indirect svings on ertion nd wter exchnge (pumping) use re lso likely, s wter qulity improves nd looms ecome mngele. While this is n importnt initil finding it remins to e tested under commercil culture conditions nd the vlidtion of this rte, through series of on-frm feeding trils, would e n venue for future work. This initil work in tnks, however, hs een crucil in nrrowing the rnge of vlues for further experimenttion nd refinement. This study lso provides importnt seline informtion tht lrge mullowy respond, in similr wy to other crnivorous fish, to the reported reltionships etween feeding level, growth rte nd feed efficiency (Kim et l. 2007; Kloudtos nd Apostolopoulos 1986; Li et l. 2004; Ozorio et l. 2009). Our results indicte tht the optimum feed efficiency in mrket size mullowy (FCE 78.62% t 0.8% BW dy -1 ) is chieved t feeding rtes elow stition (FCE 76.40% t 1.0% BW dy -1 ). This hs een reported in other fish species such s the lck porgy, (Sprus mcrocephlus), minnows (Phoxinus phoxinus), southern ctfish (Silurus meridionlis) nd Europen se ss (Dicentrrchus lrx) (Cui nd Wootton 1988; Li et l. 1997; Russell Jeffrey A. Guy 17 www. siftdesk. org volume 1: issue 1
SDRP JOURNAL OF AQUACULTURE, FISHERIES & FISH SCIENCE Mrch 15, 2016 et l. 1996; Xio-Jun nd Ruyung 1992). In ech of these cses, the conversion efficiencies incresed with incresed rtion size, from zero vlue t the mintennce rtion to pek t the optimum rtion size, then decresed with further increses in rtion size. One unexpected result, however, ws the significnt drop in specific growth rte of fish fed t 1.0% BW dy -1 from dy 17-30 (Fig. 3), despite eting more food thn fish fed t 0.6 % nd 0.8% BW dy - 1 over this period.a possile explntion is tht excessive eting (to stition) cuses progressive gstrointestinl issues in mullowy, overloding the stomch nd intestine, nd decresing the efficiency of digestion nd sorption, which limits the supply of energy destined to growth (Brett nd Grove 1979; Hrdy 1998). For exmple, in gilthed se rem (Sprus urt), incresed feed uptke led to rise in oxygen consumption (Guine nd Fernndez 1997) nd such responses cn decrese the efficiency of feed sorption y up to 15% (Elliott 1982; Joling 1994); lthough we found no evidence of lower dissolved oxygen levels in the 1.0% BW dy -1 fed tnks. Lower levels re, however, common occurrence in sttic wter ponds with dissolved oxygen levels of 3 mg L - reported in mullowy ponds (Guy nd Cowden 2012). Lrge mullowy my therefore e prticulrly sensitive to overfeeding with one symptom or negtive effect reduced growth nd there ppers to e rtion threshold ove which the digestion physiology lters, however this remins to e tested. Du et l. (2006) reported tht when feeding rte exceeded 2% BW dy -1 in juvenile grss crp (Ctenophryngodon idell) the pprent digestiility coefficient decresed quickly nd growth reduced. Negtive effects hve lso een reported for Africn ctfish (Clris griepinus) (Henken et l. 1985) nd rown trout (Slmo trutt) (Elliott 1976) ut the effect of feeding rte on pprent digestiility hs een shown to e species specific with positive nd no effect demonstrted in southern ctfish (Xie nd Sun 1993) nd wlleye (Stizostedion vitreum) (Kelso 1972), respectively. Future work to monitor the pprent digestiility of the food, y collecting the feces of lrge mullowy would provide more insight into the digestion nd utiliztion of the feed t different levels of feeding. In conclusion, the successful doption of these results hs the potentil to mke mullowy production more efficient, environmentlly friendly nd sustinle. ACKNOWLEDGEMENTS This work formed prt of project (PRJ-005806) funded y the Austrlin Governments Rurl Industries Reserch nd Development Corportion (RIRDC) New Animl Products R&D progrm. This work hd ethics pprovl for reserch involving nimls (SCU pprovl numer ARA 12-13/01). REFERENCES 1. Alln GL, Hesmn H, Bennison S (2008) Development of industril-scle inlnd sline quculture: Coordintion nd communiction of R nd D in Austrli. FRDC Project No. 2004/241, p235. 2. Berntzeder A, Britz PJ (2007) Temperture preference of juvenile dusky ko Argyrosomus jponicus (Pisces: Scienide). Afr J Mr Sci 29:539 543. 3. Brett JR, Grove TDD (1979) Physiologicl energetics. In: Hor WS, RndllDJ, Brett JR (eds) Physiology. Bioenergetics nd Growth. Acdemic Press, New York, pp279 352. 4. Collett PD (2007) Towrd the development of rering protocol for juvenile dusky ko, Argyrosomus jponicus (Pisces: Scienide). MSc thesis, Rhodes University, South Afric, p 60. 5. Collett PD, Vine NG, Kiser H, Bxter J (2008) Determintion of the optiml wter temperture for the culture of juvenile dusky ko Argyrosomus jponicus Temminck nd Schlegel 1843. AqucRes 39:979-985. 6. 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SDRP JOURNAL OF AQUACULTURE, FISHERIES & FISH SCIENCE Mrch 15, 2016 47. Oerg EW, Fulk CK, Fuimn LA (2014) Optiml dietry rtion for juvenile pigfish, Orthopristis chrysopter, grow-out. Aquculture 433:335-339. 48. Okorie OE, Be JY, Kim KW, Son MH, Kim JW, Bi SC (2013) Optimum feeding rtes in juvenile olive flounder, Prlichthys olivceus, t the optimum rering temperture. Aquc Nutr 19:267-277. 49. Ozorio ROA, Andrde C, Timoteo VMFA, Conceico LEC, Vlente LMP (2009) Effects of feeding levels on growth response, ody composition, nd energy expenditure in Blckspot Serem, Pgellus ogrveo, Juveniles. J World Aqucult Soc 40:95-103. 50. Pirozzi I, Booth MA (2009) The routine metolic rte of mullowy (Argyrosomus jponicus: Scienide) ndyellowtil kingfish (Seriol llndi: Crngide) cclimted to six different tempertures. Comp Biochem Physio 152A:586 592. 51. Pirozzi I, Booth MA, Alln GL (2010) The interctive effects of dietry protein nd energy on feed intke, growth nd protein utiliztion of juvenile mullowy (Argyrosomus jponicus). Aquc Nutr 16:61-71. 52. Qurtrro N (1996) Grow-out of snpper nd mullowy in se cges. In: Qurtrro N. (ed) Mrine Finfish Frming. Proceedings of Workshop, 23 June 1995, NSW Fisheries Reserch Institute, Cronull, pp 37 70. 53. Rimmer MA, Poni B (2007) A review of cge quculture: Oceni. In: Hlwrt M, SotoD, Arthur JR (eds) Cge quculture - Regionl reviews nd glol overview. FAO Fisheries technicl pper no. 498,pp 208 231. 54. Russell B, Elsdon T, Gillnders B, Connell S (2005) Nutrients increse epiphyte lods: rod-scle oservtions nd n experimentl ssessment. MrBiol. 147:551-558. 55. Russell NR, Fish JD, Wootton RJ (1996) Feeding nd growth of juvenile se ss: the effect of rtion nd temperture on growth rte nd efficiency. JFish Biol 49:206-220. 56. Silerschneider V, Gry C.A (2008) Synopsis of iologicl, fisheries nd quculture-relted informtion on mullowy Argyrosomus jponicus (Pisces : Scienide), with prticulr reference to Austrli. J Appl Ichthyol 24:7-17. 57. Xio-Jun X, Ruyung S (1992) The ioenergetics of the southern ctfish (Silurus meridionlis Chen): growth rte s function of rtion level, ody weight, nd temperture. J Fish Biol 40:719-730. 58. Xie X, Sun R (1993) The fecl production nd digestiility of the southern ctfish (Silurus meridionlis Chen) in reltion to rtion level, ody weight nd temperture. Ocenol Limnol Sin 24:627 633. Jeffrey A. Guy 20 www. siftdesk. org volume 1: issue 1