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Although carbon isotopes in fish otoliths are widely utilized to obtain information on environmental records, uncertainty regarding the sources of otolith carbonate, either from fish diet or ambient water, limits detailed determinations. The present study experimentally determined absolute incorporation rates of carbon derived from 2 sources, metabolic CO 2 and ambient water, into otoliths using goldfish under controlled conditions. In addition, the proportions of the 2 sources in otolith daily increments were also determined by the diel variations in the rate of incorporation from the 2 sources. A group of fish was administered with D-[ 14 C-U]-glucose or was exposed to water containing NaH 14 CO 3 , and incubated for 1, 3, 6, 12 and 24 h. Another group was similarly treated with the radiocarbons at 06:00, 12:00, 18:00, 00:00 or again at 06:00 h, and were incubated for 6 h. After incubation, serum and otoliths were collected and were separated into organic and inorganic carbon fractions, and the incorporation rates from the 2 sources were determined. The rates of carbon incorporation from D-[ 14 C-U]-glucose injected and NaH 14 CO 3 water were 0.27 (25.5%) and 0.79 (74.5%) nmol mg -1 otolith h -1 , respectively. During darkness (18:00 to 06:00 h), both the incorporation rate and proportion of metabolic-CO 2 -derived carbon significantly decreased to ~50% of that during daylight. These results suggest that otolith carbonate is mainly derived from ambient water, and the ratio of carbon derived from metabolic CO 2 is lower in the D-zone than that in the L-zone of the otolith daily increments.

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The water-soluble proteins (WSP) of otoliths were electrophoretically and immunochemically stud ied in the tilapia Oreochromis niloticus. WSP were separated into three or more undefined bands by gradient native PAGE and into 14-16 bands with a main band at 52 kDa by gradient SDS-PAGE. The main band was PAS-positive and had a moderate calcium-binding capacity. Proteins extracted from the sacculus showed an intense calcium-binding capacity in a single band in the low molecular region. Immunoelectrophoresis and immunoblotting revealed that anti-WSP rabbit serum was positive to the WSP, serum, and extracts from various tissues, including the sacculus, semicircular canal, heart, liver, gill lamella, and brain. These immunoreactions, except those of the WSP and the brain, disappeared af ter absorption with tilapia serum. Two-dimensional electrophoresis revealed that at least two serum pro teins at 20 kDa and 21 kDa immunoreacted with the antiserum. The amino acid composition of the 20 kDa protein was dominated by Glx but was not necessarily similar to that reported for tilapia otoliths.

Calcium uptake by the gills in goldfish (Curussius uurutus) was observed by electron microscopy using an oxalate-based method which specifically induced electron-opaque precipitates in association with chloride cells in the primary epithelium. EDTA treatment and x-ray microanalysis substantiated that these precipitates are a calcium salt. They were never found in deionized-water-adapted fish. Oxalate-induced calcium precipitates, varying from 0.04 to 0.2 pm in diameter, occurred in the apical crypts of chloride cells and in large vacuole-like structures in the lateral and basolateral regions of the cells. The crypts where the precipitates arose scatteringly had the morphological characteristics similar to the normal morphology of apical crypts: they were 2 to 4 pm in diameter and lined with darker and homogeneous cytoplasm with microridges. The vacuole-like structures containing numerous calcium precipitates were somewhat irregular in contour and had a diameter of about 3 pm. They appeared to contact a densely distributed tubular system, but their limiting membrane was uncertain in the present resolution. The precipitates were concentrated in the central region of the structures. These results suggest that branchial calcium uptake is closely associated with chloride cells in goldfish.

Growth rate effects on the relationship between otolith size and body size were examined in larval and juvenile goldfish. They were kept under the same environmental and feeding conditions , and sampled ad libitum until 154 days after hatching. Therefore, their variations in body size will be explained by internally mediated constraints on growth. After measurement of body size in standard length, three kinds of otolith were dissected under a binocular microscope and their m orphological changes were noted.The asteriscus was too small to be dissected consistently at hatching. The sagitta was considerably deformed with growth. The lapillus was relatively large at hatching and grew steadily from a round to a pear shape. For this reason, lapilli alone were used to measure otolith length (diameter or long axis) and to count the number of otolith increments.Otoliths had three increments at hatching and subsequent increments deposited on a daily basis until at least 154 days after hatching. The relationship between otolith and body length showed an excellent correlation (r=0.92-0.97) within three groups which had different growth rates. However, analysis of covariance revealed a different slope of regression among the groups. This indicates that slow-growing fish have larger otoliths than equal-sized, rapidly growing fish.Otolith reading has been developed from the microstructural and microchemical points of view, and has provided various information about the growth history of the individual fish. Part of such information is the estimation of the previous somatic growth rate with the aid of otolith increments. This is based on the general consensus that otolith growth has a linear relationship to somatic growth. However, recent studies have reported an uncoupling relationship between otolith and somatic growth. Secor and Dean1) found such a relationship in striped bass Morone saxatilis experiencing fast and slow growth due to different pond conditions. Slower growing bass had larger and heavier otoliths, relative to fish length, than did faster growing ones. Similar results were reported in Arctic char Salvelinus alpinus2) and guppies Poecilia reticulata,3) growth rates of which were manipulated by controlling aquatic temperature and food availability, respectively. Therefore, these studies were conducted in relation to externally controlled constraints on growth.It is common that juvenile fish show marked differences in somatic growth even when they are kept under the same environmental conditions. These differences will mostly be due to genetic (internally mediated) events. Therefore, it should be studied how internally mediated variations in somatic growth rate are related to otolith growth. The only study in this field is by Wright et al.4) who presented uncoupling evidence between two groups of Atlantic salmon parr Salmo salar which smolted aged 1+or 2+.Using larval and juvenile goldfish Carassius auratus kept under the same environmental and feeding conditions, the present study was undertaken to provide more i...