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Aquaculture 273 (

Survival and growth of western rock lobster Panulirus cygnus(George) fed formulated diets with and without fresh

mussel supplement

Danielle Johnston ⁎, Roy Melville-Smith, Blair Hendriks

Western Australia Department of Fisheries, Western Australia Fisheries and Marine Research Laboratories,PO Box 20, North Beach, Western Australia 6920, Australia

Received 2 March 2007; received in revised form 12 September 2007; accepted 14 September 2007

Abstract

Two trials were conducted to compare the growth and survival of western rock lobster Panulirus cygnus post-pueruli and year 1juveniles fed different diets. Trial 1 compared lobsters fed a formulated pelletised feed developed for Panulirus ornatussupplemented with fresh mussels (Mytilus edulis) two days per week, with lobsters fed a daily diet of pellets. Trial 2 comparedlobsters fed the pellet–mussel supplement diet with those fed a daily diet of fresh mussels.

In the first trial, diet treatment did not significantly affect survival, although it was higher in tanks supplemented with mussels.Growth of post-pueruli and year 1 juveniles fed the pellet diet (0.03 g/day; 0.14 g/day, respectively) was significantly lower thangrowth of post-pueruli and year 1 juveniles fed pellet–mussel supplement diets (0.07 g/day; 0.2 g/day, respectively). Year 1 lobstersfed the pellet–mussel supplement diet consumed considerably less pellet (0.27 vs 0.40 g pellet dry matter/day (DM/day)) thanthose fed pellets indicating that they will preferentially favour mussel over pellet diets. Feed conversion ratio (FCR) wassignificantly better for lobsters fed the pellet–mussel supplement diet as a result of the poor growth of pellet-fed lobsters.

In the second trial, survival was significantly higher for lobsters fed mussels only. Growth of post-pueruli fed a mussel diet(0.14 g/day) was significantly higher than those fed pellet–mussel diets (0.11 g/day), but there was no significant difference ingrowth for year 1 juveniles (0.33 g/day). Feed intake of mussel on a dry matter basis was higher than pellet intake for both sizeclasses, with mussel intake being more than double pellet intake for post-pueruli (0.20 vs 0.49 g DM/day).

Poor growth of P. cygnus on a pellet only diet indicates that the current formulation for P. ornatusmay be inadequate for P. cygnus.However, as pellet intake declined dramatically for year 1 lobsters offered a mussel supplement, and pellet consumption wassignificantly lower thanmussel consumption, it is more likely that poor growthmay be attributed to inadequate palatability and intake.The similarly good survival of lobsters fed pellet and pellet–mussel diets indicates that the pellet diet is an acceptable maintenance dietfor P. cygnus, but is not suitable for maximising growth for this species. Further research is needed to improve palatability, intake andpotentially nutritional composition of this pellet diet before its suitability for P. cygnus is assured.© 2007 Elsevier B.V. All rights reserved.

Keywords: Formulated diet; Nutrition; Rock lobster; Mussels; Pellet

⁎ Corresponding author. Tel.: +61 8 92030248; fax: +61 8 92030199.

E-mail address: djohnston@fish.wa.gov.au (D. Johnston).

0044-8486/$ - see front matter © 2007 Elsevier B.V. All rights reserved.doi:10.1016/j.aquaculture.2007.09.020

1. Introduction

Commercial numbers of western rock lobsterPanuliruscygnus pueruli can be collected using sandwich collectors

109D. Johnston et al. / Aquaculture 273 (2007) 108–117

(Phillips et al., 2001), with minimal impact on the wildfishery (Phillips et al., 2003). This has prompted anassessment of the feasibility of P. cygnus culture basedon the collection and ongrowing of wild caught pueruli.Six-month growout trials for post-pueruli, year 1 andyear 2 post settlement juveniles have shown good survival(76–95%) at high densities (up to 100 m−2) without ad-verse effects on growth or captivity-related health prob-lems (Johnston et al., 2006). Although P. cygnus appearswell suited for aquaculture, an effective formulated dietthat will enable juveniles to be reared economically to amarketable size has yet to be developed.

The development of cost effective nutritionally com-plete diets for rock lobsters has been constrained by a poorunderstanding of dietary requirements. Past studies havereported consistently better growth of rock lobsters fedmussels than those fed formulated diets (Crear et al.,2000; Glencross et al., 2001). Consequently mostexperimental rock lobster growth trials and commercialoperations have used mussels (James and Tong, 1997;James et al., 2001), crustaceans, molluscs (Power et al.,2005) or fresh fish (Tuan et al., 2000; Hair et al., 2002) asthe principal diet. However, lobster culture based onfeeding fresh natural foods is unlikely to be permitted byresource managers because of feed wastage and theresulting release of nutrients into the environment (Smithet al., 2003). Commercial scale collection and use ofmussels would be prohibitively expensive and consistentsupply difficult to obtain. Developing a cost effectiveformulated feed, as an alternative to fresh foods likemussels, is a priority for improving the economic outlookand sustainability of rock lobster culture (Crear et al.,2000; Glencross et al., 2001; Smith et al., 2003).

Poor growth of rock lobsters fed formulated feeds hasbeen attributed to a number of factors including leaching ofdietary components when exposed to water, low palatabi-lity, poor feed intake and ineffective feed managementregimes (Crear et al., 2000; Glencross et al., 2001; Thomaset al., 2003). A number of recent studies have aimed toimprove performance by determining the optimal dietaryprotein and lipid specification for P. ornatus (53% protein10% lipid, Smith et al., 2003), P. cygnus (N50% proteinand 6% lipid, Glencross et al., 2001) and J. edwardsii(29% and 31% protein and 5% and 9% lipid, respectively,Ward et al., 2003). The optimum levels of carbohydrateand lipid have also been determined for J. edwardsii (27%and 13.5% respectively, Johnston et al., 2003). Due to poorgrowth of P. ornatus on the pellet diet, Smith et al. (2003)concluded that therewas a need to develop feed resulting inhigher growth, before the nutrient requirements of thisspecies could be determined. Subsequently, Smith et al.(2005) developed a pellet diet for P. ornatus high in

protein and lipid (610 g/kg crude protein and a digestibleprotein to energy ratio of 29.8 mg/kJ) that has achievedsuperior growth and survival to frozen and thawed green-lip mussels (Perna canaliculus). This pellet has beenrecently refined in terms of astaxanthin content and hasachieved superior growth and survival to fresh blue(Mytilus edulis) and green-lipped mussel diets (Barclayet al., 2006). This is a significant breakthrough for formu-lated diet development of rock lobsters as it is the firstpellet to achieve superior growth to fresh mussel diets.

The primary aim of this study was to assess the suit-ability of the successful P. ornatus pellet for P. cygnusgrowout. A six month growth trial was conducted wherepost-pueruli and year 1 post settlement juveniles were fedthe formulated feed as an independent diet, or supple-mented with the generally accepted wild feed fresh bluemussels (M. edulis). Poor growth of P. cygnus fed theformulated feed prompted us to conduct a second growthtrial to compare the performance of the pellet–musselsupplement diet with a fresh blue mussel reference dietwhich has been known to elicit superior growth for thisspecies (Joll and Phillips, 1984; Edgar, 1990).

2. Materials and methods

2.1. Trial 1

Lobsters (P. cygnus) were collected from waters off SevenMile Beach, Dongara, Western Australia, between November2003 and January 2004 using sandwich collectors (Phillips et al.,2001) and baited mesh pots. Animals were transported to theWestern Australian Marine Research Laboratories, Perth, andheld in 250 L tanks with shelter until the trial commenced inMarch 2004. The trial continued for 6 months until September2005. Post-pueruli (mean and standard error 2.06±0.05 g, 13.08±0.12 mmCL) and year 1 post settlement juveniles (mean 58.11±1.9 g, 38.93±0.45 mm CL) were randomly stocked at 50 m−2

and 11 m−2 into 60 L and 250 L tanks, respectively. All tankscontained brick shelters (small individual bricks with circularholes for post-pueruli and large rectangular Besser® bricks foryear 1 juveniles — Johnston et al., 2006) and received ambienttemperature flow-through seawater at a flow rate of 60 L/h. Threereplicate tanks for each size classwere fed a formulated pellet dietdeveloped for the tropical rock lobster Panulirus ornatus (Smithet al., 2005) seven days a week and three replicate tanks for eachsize class were fed a formulated pellet for 5 days per week,supplemented with fresh blue mussels (M. edulis) twice a week.Live weight of all lobsters was measured using an electronicbalance after blotting dry with absorbent towel and carapacelength was measured using vernier callipers.

2.2. Trial 2

Lobsters were collected, transported and held as per Trial 1duringNovember 2004. The trial commenced inDecember 2004

110 D. Johnston et al. / Aquaculture 273 (2007) 108–117

and continued for 12 months until December 2005. Post-pueruli(mean 0.42±0.03 g, 8.75±0.11 mm CL) and year 1 juveniles(mean 51.3±1.7 g, 35.5±0.4 mmCL) were randomly stocked at50 m−2 and 23 m−2 into 60 L and 250 L tanks, respectively. Alltanks contained mesh shelters (2–4 vertical folds of oyster meshjoined by cable ties to rods and plastic lid — Johnston et al.,2006) and received ambient temperature flow-through seawaterat a flow rate of 60 L/h. Three replicate tanks for each size classwere fed fresh blue mussels (M. edulis) seven days a week andthree replicate tanks for each size class were fed a formulatedpellet diet developed for the tropical rock lobster P. ornatus(Smith et al., 2005) five days a week, supplemented with freshblue mussels twice a week.

2.3. Trials 1 and 2

Following stocking, lobsters were acclimated to their newsurroundings for 1 week before the trials commenced. Thepellet diet was made in monthly batches at the WesternAustralia Fisheries and Marine Research Laboratories using apasta maker followed by oven drying at 70 °C. The ingredientsand formulation of the diet are presented in Table 1. Theproximate composition on a % dry matter basis is as follows:protein 55%, lipid 10%, carbohydrate 24%, ash 11%. Anymortalities during the acclimation week were replaced withsimilar sized animals held under similar conditions. Duringthis acclimation period satiation feed rates for pellet and mus-

Table 1Ingredients and formulation of the pelleted dry feed used in the growthtrial

Ingredient g/kg

Wheat flour a 150Fish meal b 360Krill hydrolysate c 20Krill meal d 280Mussel e 100Gluten f 60Carotenoids g 0.5Cholesterol h 2.5Lecithin i 11Vitamin premix j 16a Wheat flour, Manildra Australia, Altona, Victoria.b Anchovy fish meal, 65% CP supplied by Skretting, Cambridge,

Tasmania.c Krill hydrolysate, Specialty Marine Products Pty Ltd, Vancouver,

B.C., Canada.d Antarctic krill, Inual, Santiago, Chile.e Mussel, M. edulis frozen, thawed and homogenised, Sealanes,

Fremantle, Western Australia.f Wheat Gluten, 76% CP, Manildra Australia, Altona, Victoria.g Astaxanthin—Carophyll pink, 80 g/kg, Roche VitaminsAustralia.h Cholesterol 80 g/kg.i Soybean lecithin, 70% lipid, Ridley Agriproducts, Narangba,

Queensland.j Vitamin Premix — Adisseo, Goodna, Queensland.

sels were determined for each tank and a feed rate (expressedas % BW/day) for the trial (90% of the feed rate wheresatiation was reached during the acclimation period) was cal-culated. During the experiment mortalities were not replaceddue to potential long-term differences between lobsters inholding versus treatment tanks.

Lobsters were fed pellet and mussel diets daily in the lateafternoon (1600 h) during the week (pellet approx. 10% and2.5% BW/day for post-puerulus and year 1 lobsters,respectively), with mussel supplement and mussel onlytreatments fed at a similar time on the weekends. Supplemen-tation with mussels was implemented to address any possiblenutritional deficiencies in the pellet diet and hence assessesimpacts on growth and survival. This feeding regime wasselected as the majority of feeding occurs by lobsters at thestart of the dark photophase (Morgan, 1978). More frequentfeeds were not conducted on the basis that no significantdifferences in growth or survival were found in southern rocklobsters fed multiple feeds versus a single feed per day(Thomas et al., 2003). The following morning, the amount offeed left uneaten (as a percentage of food fed) was assessedvisually and the ration adjusted so that N90% of the feed wasconsumed each day. All uneaten pellets or mussel were thenremoved from tanks.

Once a month for 7 consecutive days, the dry weight ofpellet consumed (apparent feed intake) was accuratelymeasured by siphoning uneaten food onto a mesh screen,washing with fresh water to remove salt (Brunson et al., 1997)and drying overnight for 18 h at 70 °C. Apparent feed intake (gpellet dry matter DM/day) and feed conversion ratio (FCR)calculations accounted for leach rates (stability) of the diet.Estimates of feed intake for trial 1 refer only to that of pelletfeed and for 2 out of the 7 days of the week (28% of the time)the lobsters were fed on fresh mussels, the intake of which wasnot quantified. For Trial 2 apparent feed intake of mussel on adry matter basis was calculated for direct comparison to pelletintake. For each of seven consecutive days per month, musselflesh was removed from the shell and accurately weighed priorto feeding the lobsters. Uneaten mussel flesh was collected thefollowing morning and reweighed. The wet weight of musselconsumed was then converted into dry weight using aconversion factor. This conversion factor was standardisedby weighing 3 replicate samples of 10 mussels before and afterdrying in an oven at 65 °C for 12 h.

Each morning, moults and mortalities were removed andrecorded. In trial 1, lobster weight and carapace length wasmeasured every 5 weeks for 6 months and in trial 2 lobsterweight and carapace length was measured every 8 weeks for12 months. Data were used to calculate the mean absolutedaily weight gain and daily growth coefficient (DGC). Ad-justments to feed allocations for the increase in biomass weremade every month following the weight measurements. Ateach weighing the tanks were thoroughly cleaned. Tempera-ture, dissolved oxygen, pH and salinity were monitoredweekly and maintained within recommended levels. Photope-riod was maintained on a 12 h fluorescent light: 12 h darkcycle.

Table 2Survival, growth response and diet utilisation (all expressed as mean±standard error) of P. cygnus post-pueruli and year 1 juveniles in two differentgrowth trials

Size class Parameter Trial 1 Trial 2

Pellet Pellet/mussel Pellet/mussel Mussel

Post-Pueruli Survival (%) 83.3±6.7 83.3±3.3 66.7±20.3 ⁎ 83.3±6.7 ⁎

Initial weight (g) 1.96±0.08 2.15±0.06 0.43±0.04 0.41±0.02Final weight (g) 7.64±0.20 ⁎ 15.68±1.46 ⁎ 42.6±4.9 51.2±0.4Initial CL (mm) 13.05±0.23 13.11±0.15 8.82±0.07 8.67±0.03Final CL (mm) 21.05±0.23 ⁎ 26.13±0.53 ⁎ 36.79±1.13 36.70±1.19Daily weight gain (g/day) 0.03±0.01 ⁎ 0.07±0.01 ⁎ 0.11±0.01 ⁎ 0.14±0.4 ⁎

DGC 0.82±1.52 ⁎ 1.44±0.19 ⁎ 1.27±0.21 1.6±0.05AFI (g DM lobster/day) 0.12±0.04 0.11±0.001 0.2±0.08 ⁎ 0.49±0.05 ⁎

FCR 4.68±0.54 ⁎ 1.77±0.17 ⁎ 1.6±0.77 3.1±0.27Year 1 Survival (%) 90.0±3.3 93.3±6.7 68.3±6.0 ⁎ 76.7±1.7 ⁎

Initial weight 60.84±3.62 55.37±1.67 71.4±3.2 ⁎ 31.2±0.3 ⁎

Final weight 88.78±5.01 ⁎ 94.78±1.76 ⁎ 195.9±2.4 ⁎ 155.1±3.0 ⁎

Initial CL (mm) 39.71±0.97 38.15±0.33 41.04±0.76 30.39±0.12Final CL (mm) 45.43±1.14 46.42±0.47 59.06±0.32 ⁎ 54.56±0.51 ⁎

Daily weight gain (g/day) 0.14±0.02 ⁎ 0.20±0.04 ⁎ 0.33±0.007 0.33±0.009DGC 0.79±0.33 0.74±0.09 0.66±0.22 ⁎ 0.52±0.16 ⁎

AFI (g DM lobster/day) 0.40±0.03 0.27±0.02 0.31±0.09 0.48±0FCR 3.13±0.18 ⁎ 1.56±0.24 ⁎ 0.8±0.27 1.27±0.32

⁎ Indicates parameters that are significantly different (Pb0.05) between diet regime.

111D. Johnston et al. / Aquaculture 273 (2007) 108–117

2.4. Data processing

Apparent feed intake of pellet was calculated by subtract-ing the dry weight of uneaten feed from the dry weight of pelletfed, after taking into account the proportion of feed lost intothe water. The percentage of pellet lost into the water wascalculated by immersing samples into 3 replicate tanks withlightly agitated/aerated water for 19 h. The feed remaining wascollected into a sieve, washed with fresh water to remove salt(Brunson et al., 1997) and dried in an oven overnight at 70 °C.A mean 20% of pellet weight was lost into water (80% of pelletwas available for ingestion by the lobsters).

To compensate for mortalities the number of lobster days offeeding was calculated (based on survivors at each weighing)and used to calculate daily weight gain (weight of deadlobsters subtracted from the tank biomass, lobster weightbased on mean weight of lobsters in the tank) and feed intakefor each lobster.

Absolute dailyweight gain

¼ final mean lobster weight� initial mean lobster weightð Þ=duration of the trial in days

Apparent Feed Intake g drymatter DM lobster=dayð Þ¼ Dryweight of pellet fed gð Þ40:8ð Þ

� dryweight of uneaten pellet gð Þ=lobster days of feedingð Þ

DailyGrowthCoefficient DGCð Þ¼ 100� time 2 tank total weight1=3 � time 1 tank total weight1=3

� �

=number of days

2.5. Statistical analyses

Data from trial 1 and trial 2 were analysed separately, butthe same statistical methods were applied. Three tanks wereused as replicates for the two treatments being compared ineach trial. One-way analysis of variance (ANOVA) was usedto test for differences in measured variables between thetreatments at the completion of the trials (significance levelPb0.05). For each analysis, the assumptions of ANOVAwere checked using residual plots. Tukey's HSD post hoc testwas used to identify differences between means for eachtreatment. To compare how measured variables for differenttreatments varied over time throughout the trial, a split-plotdesign (Insightful, 2001) was used. This design is suitable for arepeated measures experiment when the “circulatory condi-tion” holds, as well as the usual conditions required forANOVA. The circulatory condition means that the variances ofall pair-wise differences of the observations at each point intime are equal (Insightful, 2001). Estimating the variance of allpair-wise differences and comparing using multiple F-testsassessed the validity of this assumption. To test the effects ofdiet on the proportion of lobsters surviving over time, a logisticregression was used: Si(t)=exp(−At) /1+exp(−At), where Si(t)is the proportion of lobsters (necessarily between 0 and 1) thathave survived over time t in tank i and A is a linear combinationof dummy variables that have been used to model the maineffects and interaction terms of the variables being considered. Alogistic regression was seen as being appropriate since it forcespredicted values (and their confidence intervals) to be between 0and 1, whereas the split-plot design does not. Regressions werealso used to assess significant differences in survival as the trend

Fig. 2. Apparent feed intake of P. cygnus post-puerulus and year 1lobsters fed pellet diet 7 days per week or pellet diet 5 days per weekand mussel supplement for 2 days per week after 6 months. Data aremean and standard error of pellet intake. Time period: D1-2, 5 weekperiod between consecutive measurements.

112 D. Johnston et al. / Aquaculture 273 (2007) 108–117

in survival over time was seen as important, rather than just thefinal survival data at the completion of the trial.

3. Results

3.1. Trial 1 — pellet only versus pellet–mussel supplementdiets

Survival of post-pueruli and year 1 juveniles fed on pelletonly and pellet–mussel supplement diet regimes after 6 monthsranged from 83.3% to 93.3%. Diet regime did not significantlyaffect survival, although survival was similar or higher in tankssupplemented with mussels (Table 2).

Growth of post-pueruli fed the pellet–mussel supplement dietwas significantly higher than those fed pellets seven days a week(ANOVA: final weight F(1,4)=10.32; P=0.03; final carapacelength F(1,4)=85.53, Pb0.01; Split plot: DGC F(1,3)=18.45,P=0.05; g/day F(1,3)=10.29, P=0.03) (Table 2; Fig. 1). Post-pueruli fed the pellet–mussel supplement diet had a linear rate ofgrowth over the 6month trial,whereas growth of post-pueruli fedpellets slowed significantly to plateau in the final month of thetrial (Fig. 1).

Fig. 1. Growth of P. cygnus post-pueruli and year 1 juveniles fed pelletdiet 7 days per week, or pellet diet 5 days per week and musselsupplement for 2 days per week after 6 months. Data are mean weightand standard error. Weight gain in grams per day is indicated.

Fig. 3. Differences in survival of P. cygnus post-puerulus and year 1juveniles fed mussels 7 days a week, or pellet diet 5 days per week andmussels 2 days per week after 12 months. Data are mean and standarderror and analysed by logistic regression (see Table 2).

Fig. 4. Growth ofP. cygnus post-pueruli and year 1 juveniles fed mussels7 days a week, or pellet diet 5 days per week andmussels 2 days perweekafter 12 months. Data are mean and standard error. Weight gain in gramsper day between consecutive measurements is indicated.

Fig. 5. Apparent feed intake of P. cygnus post-pueruli and year 1juveniles fed mussel 7 days per week or pellet 5 days per week andmussel 2 days a week after 12 months. Data are mean and standard errorof pellet versusmussel intake. Time period: D1-2, 8week period betweenconsecutive measurements. The average feed intake over the 12 monthperiod for each temperature treatment is indicated. Mussel intake wasdirectly comparable to pellet intake by conversion to dry weight.

113D. Johnston et al. / Aquaculture 273 (2007) 108–117

Growth of year 1 juveniles fed pellet–mussel supplementdiet was also significantly higher than those fed pellets sevendays a week (ANOVA: final weight F(1,4)=7.7; P=0.05; finalcarapace length F(1,4)=10.03, P=0.03; split plot: % weightgain F(1,3) =6.33, Pb0.01; g/day F(1,3) =8.08, P=0.05)(Table 2; Fig. 1). Weight gain of year 1 lobsters fed the pelletand pellet–mussel diet was negligible for the months of July,August and September (100+ days) due to a seasonal reductionin tank water temperatures from 21.9 °C in March to 15.9 °C inSeptember.

Feed intake of pellets did not differ significantly betweenpost-pueruli fed either diet regime. However, feed intake ofpellet was lower in year 1 lobsters fed pellet–mussel supple-ment diet compared to pellet diet (F(1,6)=6.08, P=0.05)(Table 2; Fig. 2). Feed intake declined steadily in year 1 lobsters(and to a lesser extent post-puerulus) over the course of the trial,which corresponded with seasonal declines in water tempera-tures. Feed conversion ratios (FCR) were significantly better(lower) for post-pueruli and year 1 juveniles fed the pellet–mussel supplement diet than those fed pellets seven days perweek (ANOVA post-pueruli F(1,4)=11.86, P=0.03; year 1juveniles F(1,4)=48.25, Pb0.01) (Table 2).

3.2. Trial 2 — pellet–mussel supplement versus fresh musseldiets

Survival of post-pueruli and year 1 juveniles ranged bet-ween 66.7% and 83.3% when fed on pellet–mussel supple-ment and mussel only diet regimes after 12 months (Table 2).Diet regime significantly affected survival, with higher sur-vival for post-pueruli (Pb0.01) and year 1 lobsters (Pb0.01)fed mussel only diets (Table 2; Fig. 3).

Growth of post-pueruli fed mussel only diet was signifi-cantly higher than those fed pellet–mussel supplement (splitplot: % weight gain F(1,2)=54.84, P=0.02, F(1,2)=266.42,Pb0.01) (Table 2; Fig. 4). However, final weight and carapacelength were not significantly different between the two dietregimes. Diet regime did not significantly influence the growthof year 1 juveniles, with growth rates relatively similar bet-ween lobsters fed the pellet–mussel supplement and musselonly diets over the 12 month period (Table 2; Fig. 4). How-ever, final weight and carapace length were significantly

114 D. Johnston et al. / Aquaculture 273 (2007) 108–117

different between year 1 lobsters fed pellet–mussel supple-ment and mussel only diets (ANOVA: Final weight F(1,4)=112.23, P=0.0004; Final carapace length F(1,4) =56.64,P=0.0017). This was due to the significantly different initialweight andcarapace lengths between the two treatments(ANOVA: Initial weight F(1,4)=157.09, P=0.0002; Initialcarapace length F(1,4)=191.1, P=0.0016) (Table 2).

Mean apparent feed intake of mussel (on a dry matter basis)by post-pueruli was significantly greater (almost double) thanthat of pellets (split plot:F(1,2)=20.84,P=0.04) (Table 2; Fig. 5).In contrast there was no significant difference between feedintake of pellets versus mussels on a dry matter basis for year 1lobsters. Feed intake of pellet declined steadily to be negligibleover the winter months for year 1 lobsters whereas mussel intakeremained relatively constant. Intake of all mussel and pelletincreased in the last 2months of the trial for both post-pueruli andyear 1 lobsters, which corresponded with increasing summerwater temperatures (Fig. 5). There was no significant differencein feed conversion ratios (FCR) for post-pueruli and year 1juveniles fed the pellet–mussel supplement diet and mussel onlydiets (Table 2). However FCR was better (lower) for lobsters fedthe pellet–mussel supplement diet.

4. Discussion

Successful P. cygnus culture requires a formulateddiet that meets the nutritional requirements of the spe-cies (i.e. supports adequate growth) and is cost effectiveto produce and supply. Our first trial was designed to testthe effectiveness of an “ideal” situation (a pellet onlydiet) against an alternative option, a feeding regimewhere the pellet was supplemented with additional feedin the form of mussels. Mussels are an excellent diet fora range of spiny lobsters (Rayns, 1991; James and Tong,1997; Crear et al., 2000; Ward et al., 2003; Power et al.,2005) and P. cygnus juveniles are known to prefer andgrow extremely well on mussels in the wild (Joll andPhillips, 1984; Edgar, 1990) and in the aquaria(Chittleborough, 1974; Phillips et al., 1977).

Under the conditions used in this study, the highprotein, high lipid formulated diet (protein to energyrequirement of 28–30 mg/kJ) that has shown suchpromise for P. ornatus culture (Smith et al., 2005)produced sub-optimal growth in P. cygnus post-pueruliand year 1 juveniles. Growth of P. cygnus post-pueruli(0.03 g/day,) and year 1 juveniles (0.14 g/day,) fed thepellet only diet was significantly lower than the growthof post-pueruli (0.07 g/day, WG) and year 1 juveniles(0.2 g/day,) fed pellet–mussel supplement diets, with themost marked difference between the post-puerulitreatments (Fig. 1; Table 2). By comparison, smalljuvenile P. ornatus showed superior growth when fedformulated feed compared to fresh and thawed mussels,a diet known to perform extremely well for rock lobsters

(Smith et al., 2005; Barclay et al., 2006). The poorgrowth response recorded in this study for P. cygnus fedpellet only diet, has also been reported for J. edwardsiipost-pueruli fed the P. ornatus pellet compared with apellet–mussel supplement diet and a mussel only diet(Bruce et al., 2004). Our results and those of Bruce et al.(2004) clearly show that there are species-specificrequirements for rock lobster formulated feeds. Thereare three potential reasons why the pelleted dietperformed so well for P. ornatus culture but failed toproduce adequate results here.

Firstly, it is possible that pellet palatability wasundesirable for P. cygnus so that insufficient volumeswere consumed to maintain adequate growth. Accurateintake of supplemented mussels was not determined soit is difficult to confirm whether superior growth oflobsters fed the pellet–mussel supplement diet was dueto consumption of mussels, rather than poor intake ofpellets. The fact that pellet intake by both size classeswas not significantly different between the two dietregimes suggests this scenario is likely. Pellet consump-tion by year 1 juveniles fed the pellet–musselsupplement diet (AFI 0.27) was much lower thanthose fed the pellet only diet (AFI 0.40), but growth wassignificantly higher, further confirming that musselscontributed significantly to the growth of these lobsters.However, this trend also indicates that pellet palatabilityis not acceptable for year 1 juveniles when offered analternative food source of mussels, hence the decline inpellet intake. Although feed intake of pellet (and feedconversion ratios) of P. cygnus appears similar to thatreported for other spiny lobsters fed formulated diets(Crear et al., 2000; Glencross et al., 2001; Johnstonet al., 2003; Smith et al., 2003; Ward et al., 2003), it isclear that pellet consumption could be increasedsignificantly by improvements in palatability, particu-larly for older juveniles. Pellet consumption was notquantified for P. ornatus (Smith et al., 2005) so higherpellet intake by that species compared with P. cygnuscannot be ruled out as the factor responsible for itssuperior performance on the pelleted diet. Smith et al.(2005) believe that considerable improvement in growthon the revised formulated feed compared with theirprevious study (Smith et al., 2003) is attributed tochanges in the basal feed formulation, namely the ad-dition of krill hydrolysate to improve attractiveness andpalatability and increased lipid content. Clearly theseimprovements in feed formulation and palatability forP. ornatus, although possibly contributing to good sur-vival of P. cygnus, were not sufficient to promote op-timal growth and further work is needed to improvepellet palatability and intake for this species.

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Secondly, it is possible that the physical size of thepellet diet may have contributed to poor ingestion andgrowth, particularly for recently settled P. cygnus post-pueruli (Moyle, Recfishwest, Western Australia pers.comm.). However, similar patterns of pellet consump-tion between the two size classes of P. cygnus on thepellet only diets suggest that this has not been a problemhere. Moyle (Recfishwest, Western Australia pers.comm.), used much smaller post-pueruli (0.3 g) thanthis trial (1.96 g), which suggests that pellet size isparticularly important for recently settled animals. Bruceet al. (2004) believed that inappropriate pellet size wasresponsible for the reduced growth of J. edwardsii post-pueruli fed the P. ornatus diet. Tailoring pellet size tolobster size should therefore be considered in future trialsinvolving post-pueruli not only to increase consumptionbut to also reduce wastage (Sheppard et al., 2001).

Thirdly, it is possible that rock lobsters have species-specific dietary requirements and whilst the formulatedfeed promotes excellent growth in P. ornatus (Smith et al.,2005), the nutritional composition of this diet is notadequate for P. cygnus. Glencross et al. (2001) also foundthat a pelleted feed, similar to that used in this study, hasrelatively poor nutritional value for P. cygnus comparedwith freshmussels and concluded that considerable work isstill required to improve the value of formulated feeds forP.cygnus. Significantly higher feed conversion ratios inlobsters fed pellet only diet (4.68 and 3.13) than the pellet–mussel supplement diet regime (1.77, 1.56) reflect the poorgrowth of lobsters fed the pellet only diet compared withthose fed the mussel supplement diet. It is difficult toidentify what component of the P. ornatus pellet diet islacking as the protein and lipid composition of supple-mented mussels (70% and 6% of dry matter respectively,Glencross et al., 2001) suggests that grossly inadequatesupply of these nutrients is not the reason for poor per-formance. It is likely that poor consumption; palatabilityand inadequate nutritional composition have all contribut-ed in part to unacceptable growth on the pellet diet. At thisstage, optimal growth of P. cygnus can only be achievedthrough the provision of fresh mussel supplement.

Although growth rates were significantly lower,survival of P. cygnus fed the pellet only diet (83%post-pueruli, 90% year 1) was very good after 6 monthsand not significantly different to animals fed the pellet–mussel supplement diet (83% post-pueruli, 93% year 1).This is somewhat promising because survival of otherrock lobster species fed a pellet only diet is often lowerthan that observed in this study. For example, only 79%survival of P. ornatus fed pellet diet over 8 weeks(Smith et al., 2005), 60–73% survival over 16 weeks(Crear et al., 2000), 65–95% over 12 weeks (Ward et al.,

2003) and 72–88% over 12 weeks (Johnston et al.,2003) of J. edwardsii fed pellet diets. Furthermore,survival of P. cygnus on the pellet–mussel supplementdiet is also considerably higher than has been previouslyreported for species on pellet fresh food diet combina-tions. For example, only 53% survival of P. ornatus feda pellet, prawn flesh diet after 39 weeks (Jones et al.,2001). This suggests that despite poor growth rates, P.cygnus appears to survive quite well on the pelleted dietfor relatively long periods (6 months) in captivity indi-cating that it is an adequate maintenance diet for thisspecies. These findings are consistent with previous stud-ies where P. cygnus post-pueruli fed formulated diets over7 weeks exhibited 75–100% survival (Glencross et al.,2001). Good survival combined with reasonable feedintake and utilisation on the P. ornatus formulated dietgive us confidence for the ongoing development of thepellet diet, which is essential for the long-term success of aspecies in culture.

Having shown in trial 1 that the pellet diet was in-adequate for optimising growth of P. cygnus, we con-ducted a second trial that compared the supplementaryfeeding ofmussels conducted in trial 1, with amussel onlydiet. From a cost perspective, a combination of musselsand pellets would be more desirable than a mussel onlydiet if it could be shown to generate sufficient growthcompared to the more expensive mussel only option.

There was no significant difference in the growth ofyear 1 juveniles fed pellet–mussel supplement (0.33 g/day)and those fed only fresh mussels (0.33 g/day). This is asignificant finding as it suggests that P. cygnus juvenileswill perform equally well on the combination pellet–mus-sel diets, compared to mussel only diet. Bruce et al. (2004)also reported similar growth of J. edwardsii juveniles fedthe same P. ornatus pellet supplemented with fresh greenmussels (P. canaliculus) to those fed onmussels only. Bothstudies confirm that the nutritional composition of the P.ornatus diet may in fact be adequate for P. cygnus and J.edwardsii juveniles and that pellet palatability andconsumption may be the underlying problem for poorgrowth. The findings of Bruce et al. (2004) supports thisconclusion and states for J. edwardsii that increasing thedurability of the pellet and improving water stability willpromote greater consumption and minimise wastage. Thecapacity to provide the P. ornatus formulated feed as partof a combination diet with fresh mussels for the culture ofjuveniles, in the short term, has obvious economic benefitsover a mussel only diet. In the longer term, the P. ornatusdiet will serve as a starting point for future optimisation offormulated feeds specifically designed forP. cygnuswhichmay further reduce the reliance onmussels as a componentof the diet.

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In contrast to year 1 juveniles, growth (0.14 g/day) ofpost-pueruli fed a mussel only diet was significantlyhigher than those fed pellet–mussel supplement (0.11 g/day) suggesting that this combination diet is less accep-table for post-pueruli (Table 2; Fig. 4). Although theprovision of superior nutrition (macro or micronutrients)frommussels is a key factor contributing to higher growthof post-pueruli fed mussel only diets, the difference ingrowth responses between the post-pueruli and year 1juveniles suggests that other factors are at play. The mostlikely factor is the significantly lower pellet consumptioncompared with mussel by this size class (AFI 0.20 vs0.49), resulting in the superior growth of post-pueruli fedthe mussel only diet. In contrast, feed intake of musselsversus pellet was comparable for year 1 juvenilesaccounting for the similar growth rates between musselsand pellet–mussel supplement diets. Glencross et al.(2001) also concluded that low feed intake of the pelleteddiet was a more likely explanation for poor performanceof P. cygnus as consumption of mussel was a lot higherthan pellet (unpublished data). There are two likelyreasons for poor consumption of pellet compared withmussels by post-pueruli. Firstly, poor palatability of thepellet compared with fresh mussels and secondly, the sizeof the pellet for recently settled post-pueruli may beinappropriate. We believe that pellet size may be the mostimportant issue here, at least initially, as Moyle (Recfish-west, Western Australia pers. comm.) reported poorconsumption of the same pellet by similar sized P. cygnuspost-pueruli (0.3 g vs 0.4 g in trial 2) for the first month ofgrowth, after which pellet consumption increased. Pelletintake did not differ between the diet regimes for post-pueruli in Trial 1 as animals were considerably older andtherefore larger at the commencement of that trial (1.96 g;13.05mmCL) compared with trial 2 (0.43; 8.82mmCL),which supports the conclusion that pellet size is extremelyimportant for early post-pueruli. Nevertheless, palatabilityand stability of the diet require improvement as pelletconsumption by older year 1 juveniles remain lower thanthat of mussels (AFI 0.31 vs 0.48).

Differences in nutritional requirements of post-pueruli and year 1 juveniles are also potentially res-ponsible for differences in the performance of musselonly versus pellet–mussel supplement diets between thetwo size classes. It has been shown that small versusolder juvenile rock lobsters have different protein re-quirements (Crear et al., 2001) which potentially reflectsignificant ontogenetic shifts in wild diets (Edmunds,1995). This is the first study to examine the response ofolder year 1+ juvenile P. cygnus to formulated feeds,despite the fact that requirement data of older animalsare perhaps more important, as they ingest a larger part

of the total feed required for production (Guillaume,1997). Differences in growth responses between the sizeclasses in trial 2 strongly indicate that age specificnutritional studies are warranted.

Although the P. ornatus formulated feed appears to bean adequatemaintenance diet forP. cygnuswith respect tosurvival (Trial 1), fresh mussel diets promoted signifi-cantly better survival of post-pueruli (83%) and year 1juveniles (77%) than pellet–mussel combination diets(67% and 68%, respectively) after 12 months (Table 2).However, it should be noted that survival of post-puerulifed pellet–mussel supplement diets was similar to thosefed fresh mussels until approximately 10 months, afterwhich survival plummeted from 86% to 67% (Fig. 3).Superior survival of P. cygnus post-pueruli fed fresh bluemussels (100% after 7 weeks) compared with formulateddiets (mean 87%) has also been reported by Glencrosset al. (2001), as well as for J. edwardsii (98% after16 weeks Crear et al., 2000; 80.42% after 12 weeks Wardet al., 2003). This suggests that although a musselsupplemented pellet diet improves growth, a diet of freshmussels is optimal for minimisingmortalities ofP. cygnusjuveniles over long periods in captivity. Nevertheless, itshould be noted that survival ofP. cygnus post-pueruli fedpellet–mussel supplement after 6 months (trial 1, 83%)and 12 months (trial 2, 67%) was significantly better thanthe survival of P. ornatus fed formulated diet supplemen-ted with fresh food (52.5% after 39 weeks, Jones et al.,2001). This shows considerable promise for the use ofP. ornatus pellet–mussel supplement diets, in the shortterm, for potential P. cygnus growout.

5. Conclusions

The P. ornatus pellet diet appears to be an adequatemaintenance diet for P. cygnus, achieving relativelygood survival for both post-pueruli and year 1 juvenilesover extended time periods. However, it is clearly un-acceptable for optimising growth for this species. Im-provements in nutritional composition, pellet stabilityand palatability would increase pellet intake and po-tentially solve this problem. The fact that similar growthrates were achieved between pellet–mussel combinationdiets and mussel only diets indicates that the P. ornatuspellet diet is an excellent platform on which to basefuture development of formulated diets for P. cygnus.Until a formulated feed tailored to P. cygnus is achieved,the pellet–mussel combination diets used in this studymay provide a relatively cost effective alternative tomussel only diet regimes, whilst achieving good growthand survival over long periods. Investigation of thefrequency and quantity with which mussels are

117D. Johnston et al. / Aquaculture 273 (2007) 108–117

supplemented to P. cygnus, together with determiningthe economics of each dietary regime, is warranted.

Acknowledgements

This study was an additional component to researchconducted in the Fisheries Research and DevelopmentCorporation, Rock Lobster Enhancement and Aquacul-ture Subprogram project FRDC 2003/213 “Establishingpost-pueruli growout data for western rock lobsters”. Theauthors thank Adrian Thomson for advice and assistancewith statistical analyses.We thankDrsAndrew Jeffs, BradCrear and Brett Glencross for helpful comments through-out the trial and Drs Brett Glencross and Kevin Williamsfor the critical review of the manuscript. We sincerelythank the many countless volunteers who assisted usthroughout the trial.

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