OTOLITH ULTRASTRUCTURE OF SMOOTH OREO, PSEUDOCYTTUS 

 MACULATUS, AND BLACK OREO, ALLOCYTTUS SR, SPECIES 



N. M. Davies,' R. W. Gauldie/2 S. A. Crane,' and 

 R. K. Thompson^ 



ABSTRACT 



The ultrastructure of sagittal otoliths from 14 Pseudocyttus maculatiis and 25 Allocyttus sp. individuals 

 were examined to determine their suitability for estimating age in these two species. Scanning electron 

 microscopy revealed high levels of complexity in both external surface topography and internal struc- 

 tural organization in the sagittae of both species. Many different crystal forms were found, including 

 calcite-like prisms. A close similarity in otolith structure exists between the two species. Deposition of 

 check rings analagous to annual and daily growth increments was found to be irregular with the underlying 

 complexity of crystalline growth obscuring the finer (analogous to daily) growth rings, making their 

 periodicity difficult to validate and implying that with present techniques the sagittal otoliths of the oreo 

 species Pseudocyttus maculatus and Allocyttus sp. are not suitable for age estimation. 



The smooth oreo, Pseudocyttus maculatus, and 

 the black oreo, Allocyttus sp., are two related 

 species of the family Oreosomatidae. They are both 

 important commercial species in New Zealand. The 

 black oreo is the most commonly caught oreo in 

 New Zealand waters, while the smooth oreo is the 

 second-most commonly caught oreo. Little is known 

 about the biology of these fish. The black oreo is 

 endemic to New Zealand while the smooth oreo 

 occurs in New Zealand, South Australian, South 

 African, and South American waters (Last et al. 

 1983). In the waters south of New Zealand, the 

 distributions of the two species overlap (McMillan 

 1985). The habitat range of the smooth oreo is be- 

 tween 650 and 1,200 m, and that of the black oreo is 

 between 600 and 1,200 m (McMillan 1985). 



A preliminary examination of the ultrastructure 

 of otoliths [sagittae] of these fish was undertaken 

 as part of a study to establish an ultrastructural 

 basis for a suitable ageing technique. This study 

 describes the external and internal structure and 

 organization of the otoliths in terms of the suitabil- 

 ity of the various check rings of the sagittae for age 

 estimation. 



MATERIALS AND METHODS 



Three otoliths (the sagitta, astericus, and lapillus) 



'Fisheries Research Centre, Ministry of Agriculture and Fish- 

 eries, Greta Point, Evans Bay Parade, P.O. Box 297, Wellington, 

 New Zealand. 



^To whom reprint requests should be sent. 



'Electron Microscope Unit, Kirk Building, Victoria University 

 of Wellington, Private Bag, Wellington, New Zealand. 



are contained in the endolymphatic sac (Fig. la). The 

 sagitta is the largest otolith and is located in the 

 most ventral position in the sac. The arrangement 

 of the three otoliths in the endolymphatic sac ranges 

 between the primitive where a large astericus and 

 sagitta with no lapillus is present (Gauldie et al. 

 1986) and the typical teleost arrangement where a 

 small astericus is located close to the sagitta, and 

 an even smaller lapillus is displaced into the atrium 

 of the semi-circular canal. The oreosomatids are 

 primitive fishes taxonomically, lying in the order 

 Beryciformes (Nelson 1976), and the arrangement 

 of otoliths reflects the taxonomic position of the fish. 

 The orientation of otoliths described here refers to 

 the orientation in situ. The lateral face is the out- 

 ward (antisulcal) surface; the medial face is the in- 

 ward (sulcal) surface. Investigation was restricted 

 to the sagitta primarily because of the difficulties 

 in establishing homologies for daily and annual type 

 check rings in the astericus and lapillus. 



Sagittae were dissected from 14 smooth and 25 

 black oreo individuals caught in bottom trawls off 

 the east coast of New Zealand. These individuals 

 ranged in length from 24.5 to 40.1 cm (black oreo) 

 and 35.1 to 51.2 cm (smooth oreo). 



Whole otoliths were photographed at 6 x to 20 x 

 using a WILD'* photomicroscope. The sagittae were 

 embedded on glass slides in epoxy resin with the 

 antisulcus surface uppermost and finely ground on 

 a Struers Planapol-2 petrographic grinder. The 



^Reference to trade names does not imply endorsement by the 

 National Marine Fisheries Service, NOAA. 



Manuscript accepted April 1988. 



FISHERY BULLETIN: VOL. 86, NO. 3, 1988. 



499 



