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Age and growth of Cheilodactylusfuscus, a temperate rocky reef fishMichael Lowry a ba School of Biological Science , University of New South Wales ,Sydney, NSW 2052, Australiab NSW Fisheries , P.O. Box 21, Cronulla, NSW, 2230, Australia E-mail:Published online: 30 Mar 2010.

To cite this article: Michael Lowry (2003) Age and growth of Cheilodactylus fuscus, a temperaterocky reef fish, New Zealand Journal of Marine and Freshwater Research, 37:1, 159-170, DOI:10.1080/00288330.2003.9517154

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New Zealand Journal of Marine and Freshwater Research, 2003, Vol. 37: 159-1700028-8330/03 /3701-0159 $7.00 © The Royal Society of New Zealand 2003

159

Age and growth of Cheilodactylus fuscus,a temperate rocky reef fish

MICHAEL LOWRYSchool of Biological ScienceUniversity of New South WalesSydneyNSW 2052, Australia

Present address: NSW Fisheries, P.O. Box 21,Cronulla, NSW 2230, Australia. email:lowrym@fisheries.nsw.gov.au

Abstract To provide information on age andgrowth of red morwong (Cheilodactylus fuscusCastelnau), populations were sampled from eightlocations over a 2.5-year period with the majority offish sampled from six sites within Sydney Harbour,New South Wales, Australia. Transverse thinsections of otoliths taken from a total of 347 fishwere used to determine age. Age estimates werevalidated using oxytetracycline (OTC) marking andmarginal increment techniques. Validated otolithsindicated that this species forms one annulus per yearover an extended period from April to October. Agevaried from “ 0 ” (<1 year old) to 40 years. Acomparison of otolith weight and otolith radiusdetermined that otolith weight was the more accuratephysical determinant of age. Von Bertalanffy growthestimates based on length (t0 = -1.8, k = 0.32, L =37.64) indicated that growth is most rapid over thefirst 6 years, with fish being close to their asymptoticlength by 7 years. There was no significant dif-ference in length between sexes although femaleswere significantly older than males. Comparisons ofgrowth curves did not indicate any significantdifferences in the rate of growth between sexes.

Keywords Cheilodactylus fuscus; monitor;morwong; age; growth; sagittae; validation

M02014; Published 20 March 2003Received 4 March 2002; accepted 4 November 2002

INTRODUCTION

Cheilodactylus fuscus (Castelnau) communitiesliving adjacent to large population centres areimpacted on by point sources of pollution (LincolnSmith & Mann 1989) and sustained recreationalfishing pressure, particularly from spearfishing(Lincoln Smith et al. 1989). Developing commercialfisheries for the closely related banded morwong(Cheilodactylus spectabilis) have created concernsregarding the vulnerability of this species as initialhigh catch rates have resulted in declines in abun-dance followed by poor recovery in the followingyears (Regulatory Impact Statement NRE 2000).There is currently no commercial fishing for C.fuscus, however existing recreational effort and thepotential for an increase in the commercialexploitation of C. fuscus populations highlight theneed for information on which to base managementplans that will ensure that commercial and re-creational exploitation of the species will be carriedout in a sustainable fashion.

Age related work carried out on this species islimited to one previous study (Lincoln Smith &Mann 1989) based on unvalidated age estimatesfrom thin-sectioned sagittal otoliths. Marginal incre-ment analysis and tetracycline marking methodshave been employed in the current study to validatethe temporal nature of band formation in C. fuscus.

The aims of this study were to: (1) estimate theage of the sample population using validated, thinsections of otoliths; (2) describe the nature of thegrowth curve for this species and estimate the vonBertalanffy growth parameters for C. fuscus; and (3)identify any relationships that exist between physicalparameters of the otolith, i.e., otolith weight or radiusand age.

MATERIALS AND METHODS

A total of 347 fish were captured over a 29-monthperiod. Seventy-four of these fish were collectedfrom local spearfishing competitions, and werelarger, trophy-sized fish (i.e., larger than 35 cm fork

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160 New Zealand Journal of Marine and Freshwater Research, 2003, Vol. 37

length (FL)). To increase the size range of thesample, additional fish were captured on SCUBAusing submerged barrier nets (Lowry & Suthers1998) from a variety of other locations withinSydney Harbour, New South Wales, Australia. Allfish were weighed (rounded to the nearest 0.1 g),measured (FL, rounded to the nearest 0.5 cm), anddissected to verify sex. Heads were removed andfrozen before the removal of the otoliths.

Preparation and sectioning of otolithsSagittal otoliths were washed in water, dried,weighed (0.001 g) and stored in paper envelopes.Sagittae were embedded between two layers of “Picque” epoxy resin. A thin section (100-200 µm)was cut along the dorso-ventral axis through theprimordium and polished using ebony paper (120,1000) and lapping film (9, 3, 1 µm) to improvereadability. Each section was then fixed to a glassmicroscope slide using “Ultramount” mountingmedium. Structure and measurements were deter-mined by viewing sections with the aid of acompound microscope using transmitted light at 40-lOOx magnification. Image analysis (public domainsoftware NIH Image) provided the means to enhancethe clarity of features and record measurements foranalysis.

Determining otolith ageA readability scale from (1) to (5) using the criteriadescribed by Smith & Robertson (1990), was usedto assess and compare the clarity of each section. (1)Otoliths very clear—good resolution between zones;(2) otoliths clear—resolution reduced but zones stilldiscernible; (3) reduced clarity and or resolution and/or zones still discernible in one area of the otolith;(4) zones could not confidently be interpreted—verypoor resolution; (5) otoliths fragmented or broken—unreadable.

Readers had no knowledge of sample date orlocation or physical characteristics of the fish.Disagreement between readers in all cases was aresult of type 4 and 5 classifications, which wereexcluded from the dataset.

The nomenclature used to describe otolith structureis consistent with Kalish et al. (1995). Annulus isdefined as a continuous opaque zone that can be seenalong the entire structure when viewed throughtransmitted light. Translucent zones separate annuli.To confirm the interpretation of age estimates a sampleof 20 thin sections were examined independently bythe Central Ageing Facility at the Marine andFreshwater Research Institute, Victoria, Australia.

Counts of annuli to determine age were carriedout wherever the preparation revealed the clearestsuccession of concentric zones. Video capturecapability provided the means to magnify andenhance the image to interpret the structure moreclearly and provide on-screen measurement ofsalient features. Otolith diameter and the relativewidths between each annulus were made along astandard axis or standard otolith radius (SOR) (Fig.1). The axis extended from the primordium along acharacteristic saddle located along the ventral sideof the rostrum. This axis corresponds to a “principalgrowth axis” (Gauldie et al. 1989; Francis et al.1992).

ValidationA total of 37 fish were captured on SCUBA using asubmerged barrier net. Weight (g) and FL (cm) weremeasured and sex was visually determined using themethod outlined by Schroeder et al. (1994). A doserate of 1 ml/kg from a 30 mg/ml normal salinesolution was administered via an intraperitonealinjection of “Achromycin”, a pharmaceutical formof oxytetracycline (OTC) (McFarlane & Beamish1987). These fish were then observed for up to 2years in a large (1200 m3) commercial aquarium.Fish were sampled from the aquarium on threeoccasions over the 2-year period. Captured fishexperienced the normal diurnal and seasonalfluctuations in daylight and temperature with filteredwater supplied continuously from Sydney Harbour.Mortalities and any observations of uncharacteristicbehaviour were recorded.

Interpretation of OTC marked otolithsThe position of the OTC mark was resolved byphotographing the thin section under ultraviolet(UV) light. Care was taken to avoid overexposureof the sections to UV light, which can result in adegradation of the mark (Geffen 1987). To determinethe periodicity of annuli formation each section wasalso photographed under normal light. The distancebetween the fluorescent band, the outer edge of theotolith represents the period in captivity betweeninjection and recapture, referred to as “days sinceinjection”. Measurements from the OTC mark andany annulus laid down during the period of captivitysince injection were also calculated. The time ofannulus formation was estimated by the followingrelationship:

Time of annuli formation = D(t0)/D(t) (days sinceinjection)

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Lowry—Age and growth of Cheilodactylus fuscus

POSTERIOR

161

VENTRAL DORSAL

AXIS FOR CUTTINGSECTION

B

Annuli

STANDARD OTOLITHRADIUS (SOR)

Primordium

Fig. 1 A, Whole sagittae showing the axis from which the cross-section is taken; and B, standard otolith radius(SOR) and orientation of the otolith.

Where D(t0) = distance from OTC mark and D(t) =total distance from OTC mark to edge of otolith.

Marginal increment analysisMarginal increment analysis was also used as ameans of validating annulus using a method adaptedfrom Anderson et al. (1992). Increment width isdefined as the distance between successive bands.The marginal increment is defined as the regionbeyond the last identifiable annulus. Sections were

classified as: (1) not having a band on the edge buthaving a marginal increment >75% of the previousincrement; (2) having a band on the otolith edge ora marginal increment <25% of the previousincrement; or (3) other than (1) or (2).

Ageing protocolThe conversion of increment counts to age wascarried out using data generated from the marginalincrement analysis. The strong correlation between

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162 New Zealand Journal of Marine and Freshwater Research, 2003, Vol. 37

N =

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

21 25 21 12 49 26 28 10 23 10 21 24

>75% 2:1 <25% 3: EH Other

Fig. 2 Results of the marginal increment analysis. Sections were classified as: (1) not having a band on the edge buthaving a marginal increment >75% of the previous translucent zone; (2) having a band on the otolith edge or a marginalincrement <25% of the previous translucent zone; or (3) other than (1) or (2). Indicated are the % proportions of eachcategory in each monthly sample. Values indicate monthly sample sizes.

each of the independent means of assessingreproductive development indicated that C.fuscus hasa peak spawning period during autumn and earlywinter (Lowry unpubl. data). Other cheilodactylidshave a similar seasonal peak in reproductive conditionwith C. spectabilis spawning in autumn McCormick(1989b) and the more pelagic N. macropterus spawn-ing from March to July (Tong & Vooren 1972). Basedon this information, a birth date of 1 May (the middleof the spawning season) was assigned.

The following ageing protocol was used to inferthe age class of a fish from the number of rings inthe otolith, where AC = age class and N = numberof annuli.

Fish classified as edge type 1 (i.e., not having aband on the edge but having a marginal increment>75% of the previous increment) sampled from Mayto July AC = N + 1. Alternatively, fish classified asedge type 2 (i.e., having a band on the otolith edgeor a marginal increment <25% of the previous incre-ment) sampled from February to May AC = N - 1.

AnalysisRelationships between otolith dimensions andestimated age of fish were investigated using DeltaGraph curve fitting routines. Von Bertalanffy growthcurves were generated using the user-defined curvefitting options in Delta Graph (Delta software).Differences in the growth curves of subgroups werecompared using ANOVA following the methodoutlined by Haskard (1990). Residuals were plottedto check the assumptions of normality and homo-geneity of variance. If the data deviated from theseassumptions then it was transformed accordingly.

RESULTS

Description of the otolithThe clarity and nature of the bands varied betweenindividual fish from clear narrow lines to broaderbands. Older fish had better defined bands towardthe outer margin of the otolith. The shape of the

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Lowry—Age and growth of Cheilodactylus fuscus 163

otoliths varied with age. Younger fish have a regularcross-section and are more oval in shape. Otolithstaken from older fish are more irregular with manydelicate processes and a deeper sulcal groove.

The clarity of thin sections was good with 86%(N = 298) of the total otoliths sectioned classed asthree or higher. These sagittae were used todetermine marginal increments and age estimates.Analysis of the structure of a subset of 20 otolithsections by the Central Ageing Facility confirmedthe interpretation of annuli formation with identicalages in 16 of the 20 sections. In the remaining foursections age estimates differed by a maximum of 3years.

Marginal increment analysisThe classification of the margin with reference to theprevious increment indicated a pattern consistentwith the formation of one band per year (Fig. 2). Themajority of fish sampled from May to Septemberwere classified as (1) (not having a band on the edgebut having a marginal increment >75% of theprevious increment) with a maximum (92%) in June.Annuli became visible in those fish captured duringspring and summer with a maximum of otolithsclassified as (2) (72%) (having a band on the otolithedge or a marginal increment <25% of the previousincrement) in January.

Validation (oxytetracycline)Of the 37 fish injected with OTC only 16 could beidentified and retrieved from the aquarium becauseof tag loss. Tagged fish were recovered after 669,716, and 746 days (22-25 months) after injection.Of the 16 fish, eight produced readable marks for thevalidation of annuli. Interpretations of otolith growth

along the SOR with reference to time are presentedin Table 1. In all the fish examined no more than oneband was laid down over a 12-month period,validating the annual nature of the band structure.Two annuli were apparent in those fish numbered 6,7, and 8 (Fig. 3) that had remained in the aquariumfor 746 days. The position of the second annuli couldnot be clearly determined for the remaining fish heldin the aquarium for 716 days or less (Fig. 3).Correlation with time revealed that the majority ofthe annuli (82%) were laid down over the periodfrom March to August.

Age-length relationships andvon Bertalanffy growth estimatesFork length varied between 12 and 46 cm with amean length of 30.8 cm (±0.37 SE). There was nosignificant difference in length between sexes(ANOVA d.f. 1, 269; P > 0.05). Age ranged from aminimum of “0” years to a maximum of 40. Themajority (67.8%) of the 298 fish sampled were <6years of age, with a mean age of 7.6 years (±0.56SE). The sampled population had a larger componentof females (N = 173) than males (N = 98). Analysisof variance indicated that females are significantlyolder than the males (ANOVA d.f. 1,269; P < 0.05).

The L°°, k and t0 parameters were determined forthe total population and for male and female fishseparately (Fig. 4A-C; Table 2). The von Bertalanffygrowth function describes the observed length at agefor the first 5 years (Fig. 4A). The increase in lengthwith age is most rapid over the first 6 years slowingto the asymptotic length at 7. The age-length datacategorised by sex, indicated no significantdifference in the growth between sexes (d.f. 1, 6;P > 0.05).

Table 1 Summary information of eight fish recaptured from the aquarium after initial injection with oxytetracycline(OTC). (Age (years), age of fish at capture estimated from otoliths; days at sea (months), number of days betweencapture and recapture; total (µm), distance measured along the standard otolith radius from OTC mark to edge ofotolith; Dist. 1 and Dist. 2, measurement (µm) from OTC mark to annuli; days, number of days annuli were formedafter OTC tagging.)

Fish no.

12345678

Age (years)

33343534

Days at sea (months)

669 (22.3)669 (22.3)669 (22.3)716 (23.8)716 (23.8)746 (24.8)746 (24.8)746 (24.8)

Total (µm)

127177165191205115121140

Dist. 1

3344666870355567

Dist. 2

89110135

Days

174166268255244227339357

Days

577678719

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iCO

CDII

8

7

6

5

4

3

2

100 200 300

Time

Tetracyclineadministered

400

(days)

500 600 700

Summer Autumn Winter Spring Summer Autumn Winter Spri

800

1 year since injection 2 years since injection

Fig. 3 Results of the oxytetracycline (OTC) validation. Marks represent the position of annuli with reference to theOTC mark laid down when OTC was administered (Day 0). Indicated are the days since injection and passage of

Otolith growth relationshipsA comparison of otolith weights from a subset of 50fish did not reveal any significant differencesbetween the left and right otoliths. Otolith radius andotolith weight measurements correlated well withage showing a linear relationship (Fig. 5). Otolithweight (r = 0.90) provided a better indicator of agethan did otolith radius (r = 0.87). A greater degreeof variation in age relationships for both otolithradius and weight was observed in older fish.

DISCUSSION

ValidationMarginal increment analysis and tetracyclinevalidation confirmed the annual nature of annuliformation. The seasonal patterns of annuli formation

are less clear with general agreement between bothmethods over an extended period from April toOctober.

While the results from the two methods supportthe annual and seasonal patterns of annuli formation,inherent problems associated with marginalincrement analysis, the restriction of the OTC sampleto 3-5-year-old fish and the relatively short time overwhich the validation study was carried out need tobe considered in the interpretation of results.

Campana et al. (2001) emphasises the importanceof distinguishing between the periodicity of a growthincrement and the determination of “absolute age”which relies on validating the periodicity of annuliformation across all age classes. The practicalapplication of determining absolute age requires thevalidation of the oldest and youngest age groups toconfirm that the periodicity of annuli formation isconsistent over the entire age range.

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O

I>

”8

S-S- o

Length (cm) Length (cm) Length (cm) IS S

>(Q

(A

IIo

ON

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166 New Zealand Journal of Marine and Freshwater Research, 2003, Vol. 37

E

ccoM

I

Fig. 5 A, Standard otolith radius(SOR), and B, otolith weight,compared with age. Indicated arelines of best fit.

10 15 20 25 30 35 40

Age (years)

60 •

50 -

40 -

3 0 •

20

1 0 •

B

•iijiiMr *

•: '/'-'

. :'

r=0.90

10 15 20 25 30 35 40

Age (years)

Table 2 Number and mean length and age data used to determine the von Bertalanffy parameters for the populationgrouped by sex.

Group

All fishMalesFemales

N

29898

173

Length (cm)

mean (SE)

30.75 (0.37)32.28 (0.55)31.51 (0.41)

Age (years)mean (SE)

7.62 (0.56)4.92 (0.54)7.62 (0.56)

L

37.6445.4137.56

k

0.320.130.22

to (years)

-1.80-5.39-3.60

Of the 16 fish retrieved from the tetracycline trial,eight fish aged between 3 and 5 years old provideduseful validation marks. The results of this studyappear to validate increment formation in C.fuscusup to 5 years of age. Further work is needed to

validate the periodicity of annuli formation acrossolder age classes.

The failure of the OTC to mark 50% of the samplepopulation indicates that the dose rate of 30 mg/kgwas too low and a higher dose may have resulted in

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Lowry—Age and growth of Cheilodactylus fuscus 167

a larger sample and improved the quality of the mark.Further work is required to determine a dose rate thatoptimises marks while minimising mortalities.

Age and growthResults of validated age estimates of C. fuscusindicate that age can be accurately determined fromannuli counts of sagittal otoliths. Age-length dataindicates a long-lived and initially fast growingspecies that has a clear annual pattern of incrementdeposition.

The von Bertalanffy growth curve adequatelydescribes growth with close agreement betweenobserved and calculated length at age. C. fuscus is arelatively long-lived species with a maximumsampled age of 40 (FL = 42 cm), although maximumlength and weight values fall well below the reportedmaximum of 65 cm and 3.5 kg (Hutchins &Swainston 1986) indicating that these larger fish mayhas an even longer lifespan. C. spectabilis occupiessimilar habitat type to that of the red morwong andhas maximum recorded ages of 86 for females and81 years for males (Murphy & Lyle 1999).

Cheilodactylus fuscus females are older thanmales with no significant difference in size; theseresults reflect previous work carried out on tarakihi(Nemadactylus macropterus) (Tong & Vooren 1972;Smith 1982). Tarakihi mature at 4-6 years, femalesare significantly older, grow faster than males, withno significant difference in size between sexes.

A comparison of C. fuscus with the available datafor other closely related species indicatedsimilarities. Growth curves are characterised by low

k values and large negative t0 values (Table 3). Thelarge negative value of t0 indicates that the growthhistory of the juveniles is dissimilar to that of theadult fish most likely as a result of the extendedpelagic post larval or “paperfish stage” of c. 8-12months (Vooren 1972). Results of this study indicatethat C. fuscus juveniles experience rapid growth overthe first 12 months reaching a mean length of14.6 cm. N. macropterus juveniles reach a meanlength of 12.7 cm over the same period (Vooren1973).

Relationship between otolithcharacteristics and growthContinued growth of the otolith is essential for theband formation to continue with age. Analysis ofotolith weight and radius indicate that the accuracyof these relationships as an indicator of age isdependent on the variable being compared and theage of the fish making up the sample.

The consistency of the relationship betweenotolith radius and age varies between species. Manyresearchers have found a close relationship betweenotolith radius and age (Rosenberg & Haugen 1982;Neilson et al. 1985; Jenkins 1987; Secor & Dean1989; May & Jenkins 1992), whereas others havefound this not to exist (Neilson 1982; Brothers et al.1983; Mosegaard et al. 1988; Reznick et al. 1989;Hovencamp 1990; Milicich & Choat 1992; Radtke& Shafer 1992; Lombarte & Lleonart 1993).

Otolith radius measurements of C. fuscus indicatea linear relationship between radius and age withotolith radius explaining 87% of the variation, with

Table 3 Age estimates and von Bertalanffy growth parameters for the genus Cheilodactylidae. (F, female; M, male.)

Species

Jackass morwong(Nemadactylus macropterus)Vooren (1973)Smith (1982)

Banded morwongCheilodactylus spectabilisLeachman et al. (1978)Murphy & Lyle (1999)

Red morwong(Cheilodactylus fuscus)Lincoln Smith & Mann (1989)Lowry

Tmax. (years)

55F:16M:11

59F:86M:81

27F:40M:33

L (cm)

50.351.145.5

no von43.251.2

no vonF: 37.6M: 41.2

k

0.100.120.17

Bertalanffy parameters0.010.16

Bertalanffy parameters0.220.13

0 (years)

0 .30-3.17-3.51

reported-11.30-2.70

reported-3.60-5.39

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error increasing with increasing otolith radiusmaking age prediction using otolith radius moreaccurate for younger age classes.

Otolith weight provided a better indicator of agethan did otolith radius. The relationship betweenotolith weight and age (r = 0.90) was very close tothe value attained independently by Lincoln Smith& Mann (1989) (r = 0.89) for the same species. Agreater degree of error was also observed in olderfish.

The variance in the relationship between age andthe two otolith variables, weight and radius, arisefrom two sources. Inaccuracies in the measurementof the radius arose from difficulty in determining theposition and length of the SOR. Growth of the otolithis not radially symmetrical and measurements of theradius may have been accentuated in some of the ageclasses. Otolith weight provides a more accuratepredictor of age than otolith radius as otolith growthmay not be linear along the radial axis, therefore,using radius as an estimator may not be as sensitiveas weight which will detect growth in any plane.

Management implicationsRed morwong are a popular spearfishing targetmaking up the largest proportion of the catch at spearcompetitions with similar catches reported fromexperienced and inexperienced divers (LincolnSmith et al. 1989). The diver neutral nature of thisspecies, limited home range and tendency foraggregations to structure local populations inrelatively shallow water (Lowry & Suthers 1998)provides the opportunity for even marginal increasesin an effort to have significant impact on localpopulations of this long-lived, resident species.

Cheilodactylus spectabilis occupies a similarniche to the red morwong. Size and sex relateddistribution patterns structure the population with thejuveniles and females occupying the shallow areasand males dominating the deeper areas of the reef(Leum & Choat 1980; McCormick 1989a). Adultshave a limited home range forming small groups orlarger aggregations with overlapping ranges.

Concern over the depletion of banded morwongas a result of recreational fishing resulted in a localban on this “long-lived attractive and significantmember of New Zealand's northern reefcommunity” (Leachman et al. 1978). Bandedmorwong have proven to be highly vulnerable tocommercial fishing with initial high catch ratesfollowed by serious declines in abundance followedby little, if any, signs of recovery in the followingyears (Regulatory Impact Statement NRE 2000).

Proposals to develop similar high value live fishmarkets for red morwong should recognise thepotential for even marginal increases in effort toresult in long-term impacts on existing populations.

AKNOWLEDGMENTS

Financial support was provided by Sydney Water and theAustralian Research Council. The use of aquariumfacilities was generously permitted free of charge by theDarling Harbour Aquarium. I thank C. Rogers, A. Smith,and M. Lockett for assistance in the field. I particularlythank Dr David Rissik for his assistance in the field andvaluable comments in reviewing the paper, Dr. IainSuthers for assistance and advice in the development ofthis paper, and the two anonymous reviewers for the manyconstructive comments on the manuscript. This researchwas carried out with the authorisation of the Animal Careand Ethics Committee.

REFERENCES

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Brothers, E. B.; Williams, B.; Sale, P. F. 1983: Length oflarval life in twelve families of fishes at “OneTree Lagoon”, Great Barrier Reef, Australia.Marine Biology 76: 319-324.

Francis, R. I. C. C. 1996: Do herring grow faster thanorange roughy? Fishery Bulletin 94: 783-786.

Francis, M. P.; Williams, M. W.; Pryce, A. C.; Pollard,S.; Scott, S. G. 1992: Daily increments in otolithsof juvenile snapper, Pagrus auratus (Sparidae).Australian Journal of Marine and FreshwaterResearch 43: 1015-1032.

Gauldie, R. W.; West, I. F.; Davies, N. M. 1989: Kselection characteristics of orange roughy(Hoplostethus atlanticus) stocks in New Zealandwaters. Journal of Applied Ichthyology 5: 127-140.

Geffen, A. J. 1987: Methods of validating daily incrementdeposition in otoliths of larval fish. In: Summerfelt,R. C.; Hall, G. E. ed. The age and growth offish.Ames, Iowa, Iowa State University Press. Pp.223-240.

Haskard, K. A. 1990: Simple and robust comparison ofgrowth in different populations, using ANOVA.Bureau of Rural Resources Proceedings 12: 174-181.

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