PHASE DIFFERENCE BETWEEN CALCIFICATION AND ORGANIC MATRIX 



FORMATION IN THE DIURNAL GROWTH OF OTOLITHS IN 



THE RAINBOW TROUT, SALMO GAIRDNERI 



Yasuo Mugiya' 



ABSTRACT 



The relative role of calcium and organic matrix deposition in the formation of daily increments in 

 otoliths was studied in in vitro preparations of otolith-containing sacculi of rainbow trout, Salmo 

 gairdneri. Sacculi were incubated in a Ringer solution containing both ''•'^Ca and 3H-glutamic acid for 

 2 hours at 6-h intervals throughout a 24-h period and then the uptake of these isotopes was deter- 

 mined for both otolith and saccular tissue fractions. Serum calcium and sodium concentrations were 

 also analyzed for diurnal variations. 



Serum calcium concentrations varied diurnally by 87r in a single phasic pattern, reaching a peak 

 at dusk (1600 hi and a nadir at night <2200 h), while sodium concentrations remained almost constant 

 throughout a 24-h period. Diurnal variation in the otolith's uptake of calcium and glutamic acid 

 showed discrete, antiphasic cycles. The rate of calcium uptake varied in a pattern closely resembling 

 that of serum calcium (the peak at 1600 h and the nadir at 2200 h); glutamic acid uptake remained 

 almost constant during the daytime and peaked at night (2200 h). The results indicate that in rainbow 

 trout daily increments of otoliths are formed by the antiphasic deposition of calcium and organic 

 matrix. 



Teleost otoliths consists of calcium carbonate in 

 aragonite form and an organic matrix in which 

 acidic amino acids dominate (Degens et al. 1969). 

 Concentric rings within the microstructure of 

 otoliths are commonly laid down on a daily basis 

 fCampana and Neilson 1985; Jones 1986). A unit 

 increment comprises one light and one dark ring 

 when observed under transmitted light. These bi- 

 partite structures are also observable by scanning 

 electron microscopy. After etching with weak 

 acids or decalcification with calcium-chelating 

 agents, they usually appear as an alternating 

 pattern of well-calcified zones with elongated 

 crystals perpendicular to the otolith periphery 

 (accretion zone) and narrow grooves which inter- 

 sects the crystal development at right angles (dis- 

 continuous zone). However, some recent studies 

 (Mugiya and Muramatsu 1982; Watabe et al. 

 1982; Takahashi 1982; Morales-Nin 1987) 

 showed that if the etching and subsequent treat- 

 ments were carried out carefully, the organic ma- 

 trix could be preserved in the discontinuous zone, 

 appearing as a raised ridge. After complete decal- 

 cification of the otolith, Dean et al. (1983) and 

 Radtke and Targett (1984) observed incremental 

 features in the remaining matrix. Thus, stated in 



'Faculty of Fisheries. Hokkaido University, Minato-.3, Hako- 

 date, 041 Japan. 



relative terms, the accretion and discontinuous 

 zones appear to be alternatively calcium-domi- 

 nant and matrix-dominant structures. However, 

 Watabe et al. (1982) observed that morphologi- 

 cally similar matrix material extended continu- 

 ously between accretion and discontinuous zones, 

 and proposed a possible mechanism for otolith in- 

 crement formation. For their recently proposed 

 model, Campana and Neilson (1985) also as- 

 sumed continuous matrix formation in diurnal 

 otolith growth. 



Based on these morphological studies, three hy- 

 potheses might account for the formation of the 

 bipartite structure of otolith increments; 1) both 

 organic matrix and calcium deposition show diur- 

 nal variations occurring in antiphase, 2) calcium 

 deposition varies diurnally, while matrix deposi- 

 tion does not, and 3) calcium deposits at a con- 

 stant rate throughout a 24-h period, while matrix 

 deposition varies diurnally. All these would re- 

 sult in the formation of alternate zones where 

 calcium or matrix deposition predominated. Of 

 these, the last possibility can be excluded. Physi- 

 ological studies indicate that the rate of calcium 

 uptake by otoliths varies diurnally in goldfish 

 and rainbow trout (Mugiya et al. 1981; Mugiya 

 1984). 



The present study was undertaken to investi- 

 gate diurnal variation in matrix formation and to 



Manuscript accepted March 1987. 



FISHERY BULLETIN: VOL 8.5. NO. 3. 1987 



395 



