600 



Abstract.-The lutjanids Pristipo- 

 moides filamentosus and Aprion vires- 

 cens and the lethrinid Lethnnus malt- 

 sena are commercially important de- 

 mersal bank and deep slope reef fish 

 from the central Indian Ocean. To obtam 

 von Bertalanffy growth parameter esti- 

 mates for management purposes, length- 

 based methods are commonly applied by 

 the fisheries institutions of the region. 

 Because the relatively long-lived, slow- 

 growing nature of these species results 

 in a lack of distinct modal progression in 

 length-frequency data, such estimates 

 are unreliable. In an attempt to obtain 

 more reliable growth estimates, the fea- 

 sibility of age-based methods (where 

 age is determined from annual incre- 

 ments in otoliths) was investigated. 

 Successful validation of annual or daily 

 increments has been reported in two 

 of these species iP. filamentosus and A. 

 virescens). but not for the target areas 

 of our study: the banks of the Seychelles 

 and Mauritius. 



A range of methods was used in an 

 attempt to ensure that the otoliths ful- 

 filled the criteria for use in aging. Two 

 methods are described in this paper: 

 back-calculation and a combination of 

 marginal increment and edge analysis. 

 The results of validation are presented, 

 along with a description of the problems 

 encountered. Marginal increment and 

 edge analysis both indicated that the 

 increments present in the otoliths of L. 

 mahsena are annuli. For A. virescens. 

 no pattern was present in the marginal 

 increment analysis of older individu- 

 als. However, edge analysis offered evi- 

 dence that the increments present in 

 the otoliths were annuli. The combined 

 marginal increment and edge analysis 

 proved inconclusive for P. filamentosus; 

 therefore the increments present in the 

 otoliths of this species could not be vali- 

 dated. Conclusions are drawn regarding 

 the justification of assuming periodic- 

 ity of increments on the basis of valida- 

 tion achieved in other locations. 



Validation of annual growth increments in the 

 otoliths of the lethrinid Lethrinus mahsena 

 and the lutjanid Aprion virescens from sites 

 in the tropical Indian Ocean, with notes 

 on the nature of growth increments in 

 Pristipomoides filamentosus 



Graham M. Pilling 



MRAG Ltd 



47 Prince's Gate 



London SW7 2QA, United Kingdom 



E-mail address: g.pilling@ic.ac.uk 



Richard S. Millner 

 Michael W. Easey 



Fishenes Laboratory 



CEFAS 



Pakelield Road 



Lowestoft NR330HT, United Kingdom 



Christopher C. Mees 



MRAG Ltd 



47 Prince's Gate 



London SW7 2QA, United Kingdom 



Shyama Rathacharen 



Albion Fishenes Research Centre 

 Albion, Petite Riviere, Mauntius 



Roland Azemia 



Seychelles Fishing Authority 



PO Box 449 



Victoria, Mahe, Seychelles 



Manuscript accepted 4 January 2000. 

 Fish. Bull. 98:600-611 (2000). ' 



Examination of hard body parts, such 

 as otoliths, frequently reveals the pres- 

 ence ofrings." Laid down incrementally 

 (whether daily, monthly, or annually), 

 these structures provide a means of 

 aging fish. For tropical species, however, 

 the use of otoliths has become relatively 

 common only since the early nineteen 

 eighties (e.g. Loubens, 1978; Morales- 

 Nin and Ralston, 1990; Ferreira and 

 Russ, 1992; Francis et al., 1992; Milton 

 et al., 1995; see also Manooch, 1987, 

 and Fowler, 1995, for reviews). The 

 lack of studies before this time is fre- 

 quently attributed to the expectation 

 that tropical fish grow consistently in 

 an aseasonal environment. Hence hard 



parts in tropical fish species were not 

 expected to contain internal structures 

 that relate to fluctuations in growth 

 resulting from the environment. 



The physiological basis for the for- 

 mation of distinct zones in calcified 

 structures of tropical species has not 

 been established conclusively (Ferreira 

 and Russ, 1994). The formation of such 

 zones has been associated with both 

 abiotic and biotic factors (Beckman and 

 Wilson, 1995). such as regular seasonal 

 variances in water temperature (e.g. 

 Reay, 1972;Panella, 1980), photoperiod, 

 feeding, reproduction, and spawning 

 period (e.g. Morales-Nin and Ralston, 

 1990) 



