FISHERY BULLETIN: VOL. 86, NO. 3 



crystals on the central lateral surface are com- 

 parable with those in the oyster shell described as 

 individual laths (Carriker et al. 1980). The leaflike 

 crystals in the sulcus of the black oreo otolith are 

 similar to the chalky crystal forms in the oyster shell 

 (Carriker et al. 1980). Such a variety of crystalline 

 forms is uncommon in teleost otoliths. The low legi- 

 bility of structures of various kinds in the otolith may 

 reflect this complex crystallinity. However, the com- 

 plex crystallinity of the mollusc shell is thought to 

 reflect changes in both the external and internal 

 milieu of the organism (Wilbur and Saleuddin 1983). 

 Thus the difficulties of reading the oreo otolith in 

 the conventional sense may be offset by the life 

 history record (albeit difficult to translate) provided 

 by its complex crystallinity. 



The broken sections of the otolith reveal the in- 

 ternal structure organization, and development of 

 crystals. Epitaxial crystal grov^h in the oreo otolith 

 results in columnar, monoclinal crystals of ara- 

 gonite. However, the presence of calcite-like prisms 

 has not been described for other otoliths. Calcite 

 occurs on the antisulcal surface of some otoliths 

 apparently by simple crystallization out of the fluid 

 of the endolymphatic sac (Morales-Nin 1985), but 

 calcite has never been described from within an 

 aragonite otolith (Carlstrom 1963). In molluscs, 

 calcite replacement of aragonite results in an orderly 

 alignment of calcite crystals following the alignment 

 of the original aragonite crystals. The disorderly 

 appearance of the calcite-like hexagons in the 

 smooth oreo otolith may be due to a diagenetic 

 transformation of aragonite to calcite with depth. 

 The compensation depth for the aragonite/calcite 

 transformation is about 3,000 m (Fyfe and Bischoff 

 1965) well beyond the known range of the smooth 

 oreo which has a maximum recorded depth of 1,300 

 m. However, there may be enough variation in 

 either the kind or amount of stabilizing protein in 

 the smooth oreo otolith to allow crystal changes to 

 occur at shallower depths than 3,000 m. 



The complex, and often coarse, crystal structure 

 of the oreo otolith obscures the sequences of incre- 

 ments when they do occur. As a result, large rings 

 observed at low magnification become indistinct at 

 higher magnification when many finer increments 

 appear. The large rings could be assumed to be 

 annual check rings, but the difficulties in differen- 

 tiating between the fine and large rings create am- 

 bivalence in one's interpretation. The finer micro- 

 scopic growth increments, analagous to daily growth 

 rings, have no uniform width and occur intermit- 

 tently making accurate counting impossible. 



The suitability of an otolith for determining the 



age of a fish depends on the pattern of both annual 

 and daily check rings inferred from the structure 

 of the otolith. The hyaline/opaque zones observed 

 in the regular lobe (using transmitted light) had a 

 similar mean width to the concentric ridges found 

 by SEM on the lateral surface. The ^statistic we 

 obtained accepts the null hypothesis that no sig- 

 nificant difference exists between the two means. 

 Mel'nikov (1981) regarded these opaque/hyaline 

 zones as annual check rings in the otolith of Allo- 

 cyttus verrucosus. However, because no evidence ex- 

 ists for a relationship between the surface ridges and 

 fish age, it is possible that Mel'nikov's (1981) ages 

 are incorrect. Furthermore, the width of the opaque/ 

 hyaline zones (0.34 mm) would indicate daily growth 

 increments less than 1 \xm wide. There are no 

 reports in the literature of validated daily growth 

 rings of such small size. In addition, the microscopic 

 growth increments which we have observed in the 

 oreo otolith are 3 to 5 ^m wide, which is a size range 

 commonly observed in other species. 



With the techniques available we have been unable 

 to use either annual- or daily-type structures to 

 develop a technique for age estimation for Pseudo- 

 cyttus maculatus and Allocyttu^ sp. The reasons for 

 these difficulties may lie in the crystal morphology 

 of the otoliths which are more complex than any so 

 far described in the literature. 



ACKNOWLEDGMENTS 



All otoliths were supplied by Peter McMillan (Fish- 

 eries Research Centre). All 35 mm photographs 

 were processed by Alan Blacklock (Fisheries Re- 

 search Centre). SEM photographs were taken at the 

 SEM Unit, Zoology Department, Victoria Univer- 

 sity of Wellington. 



LITERATURE CITED 



Carlstrom, D. 



1963. A crystallographic study of vertebrate otoliths. Biol. 

 Bull. (Woods Hole) 125:441-463. 

 Carriker, M. R., R. E. Palmer, and R. S. Prezant. 



1980. Functional ultra-morphology of the dissoconch values 

 of the oyster Crassostrea virginica. Proc. Natl. Shellfish. 

 Assoc. 70:139-183. 

 Degens, E. T. 



1976. Molecular mechanisms of carbonate, phosphate and 

 silica deposition in the living cell. Top. Curr. Chem. 64: 

 1-112. 

 Degens, E. T., W. G. Deuser, and R. L. Haedrich. 



1969. Molecular structure and composition of fish otoliths. 

 Mar. Biol. 2:105-113. 

 Fyfe, W. S., and J. L. Bischoff. 



1965. The caJcite-aragonite problem. In L. C. Pray and R. C. 

 Murray (editors), Dolomitization and limestone diagenesis, 



514 



