Juro Yamada

Diurnal rhythm in otolith formation in the goldfish, Carassius auratus

Abstract 1. 1. The presence of diurnal rhythm in otolith formation was examined physiologically in the goldfish, Carassius auratus . 2. 2. 45 Ca uptake by otoliths indicated that otolith formation slowed down or stopped at sunrise and resumed in 3 hr. 3. 3. Plasma calcium level increased toward sunrise and fell significantly in the next 3 hr. 4. 4. The increasing phase of plasma calcium corresponded to the period of rapid decrease in 45 Ca in the culture medium.

Scanning electron microscope observations of the organic matrix in the otolith of the teleost fish Fundulus heteroclitus (Linnaeus) and Tilapia nilotica (Linnaeus)

Abstract Scanning electron microscope observations of sagitta otoliths of Fundulus heteroclitus (Linnaeus) and Tilapia nilotica (Linnaeus) have revealed that the “discontinuous zone” is a narrow band of organic matrix consisting of fibers ≈900 A thick, that in turn are composed of thin fibers ≈200 A thick. The “incremental zone” is the crystalline layer with crystals elongated perpendicular to the otolith periphery that are usually terminated at the discontinuous zones. The crystals are embedded in organic matrix fibers that appear similar to and continuous with the fibers of the discontinuous zones. Frequently, these fibers aggregate into matrix sheets. Based on these findings, a possible process of otolith formation is proposed.

Age and growth of larval and juvenile walleye pollock, Theragra chalcogramma (Pallas), as determined by otolith daily growth increments

The validity of otolith increments for determination of age in days in larval and juvenile walleye pollock, Theragra chalcogramma (Pallas), was examined in ground and etched otoliths (sagittae) by scanning electron microscopy. Rearing of larvae from incubated fertilized eggs and a time-marking experiment with reared juveniles showed that the first increment occurred at hatching and increments were then formed on a daily basis. The age of wild fish (11–96 mm in total length) collected from April through August, 1980 and May, 1981 in Uchiura Bay, Hokkaido, was determined by counting increments. The hatching period was estimated to be from early January to late March. Logistic curves were fitted to the body growth and the otolith growth. Both curves showed a maximum growth at ≈ 125 days after hatching when the fish were 61 mm in total length. There was a linear relationship between total length and otolith length in logarithmic scales. The observed interrelationships between total length, otolith length and fish age (number of increments) validated the otolith reading for analyses of the initial growth of walleye pollock. A possibility that otolith microstructure changes can be utilized as information source of some ecological events in the early life history is suggested.

Energetics during embryonic development in kurosoi, Sebastes schlegeli Hilgendorf

Studies on the live-bearing scorpaenid genus Sebastes have recently shown that embryos of one species receive nutrition in addition to that supplied in the yolk. In this large genus, however, reproductive characteristics may differ among species. Energetics of embryonic development in kurosoi, Sebastes schlegeli Hilgendorf, were analyzed to determine the patterns ofembryonic nutrition. The egg of this species is larger and contains over three times the energy content of that in S. melanops, another species which has been studied. Catabolism during the 51 days of embryonic development required 88% of the original energy in the egg, but the embryo at birth contained 93% of the initial egg energy. Thus the total energy required for development from fertilization to birth requires z 1.8 times the initial, endogenous energy supply. Histologi- cal studies demonstrate that uptake occurs through ingestion and absorption of ovarian fluid in the hindgut. Protein and nitrogen budgets during development suggest that the primary substance taken up is nitro- genous. No distinct structures are apparent in the ovarian system to supply nutrients to the developing embryos. Analysis of fecundity-at-length, however, shows that post-fertilization fecundity estimates are significantly lower than pre-fertilization values; the reduction apparently occurs through resorption of ova or early embryos. Along with catabolism, this results in an overall decrease in the energy content of the ovaries during development, but the total amounts of protein and nitrogen remain nearly static. We thus suggest that resorption of unfertilized ova or early embryos which die may enrich the ovarian fluid and supply energy to the surviving embryos. This is a primitive form of embryonic nutrition in viviparous species and may be common in the genus Sebastes.

Effects of calcium deprivation on the metabolism of acellular bone in tilapia, Oreochromis niloticus

1. 1. Effects of calcium deprivation from ambient water or from both diet and ambient water on the metabolism of fish acellular bone were examined by histomorphometry of the pharyngeal bone in tilapia (Oreochromis niloticus). 2. 2. Calcium-deficient ambient water activated bone resorptive cells and suppressed osteoblasts, irrespective of dietary calcium supplementation. 3. 3. Hypercalcemia and decreased contents of body calcium and phosphate were observed only under the combined condition of ambient water and dietary calcium deficiency. 4. 4. Results indicated that the activity of acellular bone cells changed to withdraw calcium from bone into the extracellular fluid. This occurred when fish faced conditions of low calcium stress, such as ambient water calcium deficiency. Dietary calcium alone seemed to be insufficient for normal metabolism of bone in tilapia.

Changes of the fatty acid composition in smolts of masu salmon (Oncorhynchus masou), associated with desmoltification and sea-water transfer

Abstract 1. 1. Tissue lipid compositions of desmoltified yearlings of masu salmon (Oncorhynchus masou) obtained by keeping smoltified fish in fresh water, were examined and compared to those of smoltified fish before and after transfer to sea-water (SW). 2. 2. Lipid contents of muscle, liver, gut and gills of desmolts tended to increase compared to those of initial smolts. 3. 3. The increased proportion of triacylglycerol (TG) and decreased proportion of phospholipids (PL) characterized the tissue lipids of desmolts. 4. 4. Liver and muscle lipids showed no distinct differences both in content and proportion between initial and SW smolts, but gut and gill lipids of SW smolts decreased in content accompanied by a decrease of TG and an increase of PL in proportion. 5. 5. Excepting muscle non-polar lipids, tissue lipids of desmolts contained more mono-unsaturated fatty acids and saturated fatty acids and less polyunsaturated fatty acids (PUFA), especially (n-3) PUFA such as 22:6(n-3), than those of initial and SW smolts. 6. 6. No large differences in fatty acid composition were seen between initial and SW smolts except for the gut. 7. 7. The proportion of (n-3) PUFA in the gut of SW smolts was higher than that of initial smolts. 8. 8. The results indicated that masu salmon smolts can modify their lipid metabolism to adapt to ambient salinity changes. The proportion of (n-3) PUFA particularly in polar lipids, or in osmoregulatory organs such as gut and gills, was seen to be critical in lipid types of freshwater- or sea-water-adapted fish.

Oxygen consumption of gestating femaleSebastes schlegeli: Estimating the reproductive costs of livebearing

SynopsisDuring gestation, live-bearing fishes incur physiological energy costs, including provision of energy and respiratory gases to the developing embryos and removal of waste products. Fecundity in the genusSebastes is high, and the ovaries represent a significant portion of the weight of gestating females. In this study, we compare oxygen consumption of gestating females with non-gestating females and males of kurosoi,Sebastes schlegeli, to estimate these costs. Oxygen consumption by pregnant females is significantly higher than that of males and immature females at similar sizes and weights. We estimate that a 1.5 kg gestating female consumes 68% more oxygen than a non-gestating fish during the 51.5-day period of gestation. Such an increase in oxygen consumption rates may have important implications to the metabolic scope of gestating alone, suggesting that costs of increased gill ventilation, ionic and osmotic regulation and cardiac output are relatively high. Such energetic costs represent a quantifiable expense of the viviparous mode of reproduction inSebastes as compared with oviparous species.

Effects of growth hormones on bone formation and resorption in rainbow trout (Oncorhynchus mykiss), as examined by histomorphometry of the pharyngeal bone

Effects of salmon and eel growth hormones (GHs) on bone metabolism in rainbow trout (Oncorhynchus mykiss) were studied using histomorphometry of their pharyngeal bones. When salmon GH (sGH) was injected intraperitoneally at a dose of 0.01 or 0.1 microgram/g/week for 10 times into fed trout, body growth in both length and weight was accelerated. Formation and resorption of bone were enhanced only by the higher dose of sGH. When a cholesterol pellet containing recombinant eel GH (reGH-pellet) was implanted subcutaneously into starved trout for 1 week (37 micrograms reGH/18 g fish), formation and resorption of bone increased, although activity of bone formation was low. The results indicate that the GHs increased both formation and resorption of bone, regardless of the nutritional status of the fish.

Ultrastructure of the epidermis and digestive tract in Sebastes embryos, with special reference to the uptake of exogenous nutrients

SynopsisUltrastructural features of the epidermis and rectum were studied inSebastes schlegeli andS. melanops during the late stages of embryonic development, to confirm uptake of maternal substances. Ruthenium red (RR) and horseradish peroxidase (HRP) were used at fixation and in live embryos, respectively. Epidermal tissue of embryos after developmental stage 24 comprised two squamous cell layers. The outer, thinner cells and their intercellular spaces were easily infiltrated with RR, but the inner cells had no RR deposition. The HRP was not incorporated into the epidermis except in a few outer cells, which had well-developed microvillous projections of cytoplasm. Sacciform cells, chloride cells, and mucous cells distributed in the inner layer but protruding to the epidermal surface had no intracellular RR and HRP depositions. The rectal cells of embryos at about developmental stage 28 had many globular inclusions containing electron-dense substances. The rectal cells were found to take up and digest HRP actively. It is suggested that the embryonic epidermis is structurally loose and takes up low weight molecules, while rectal cells, after the opening of the mouth, actively ingest exogenous, high weight molecules.

Changes in metabolism of acellular bone in tilapia, Oreochromis niloticus, during deficiency and subsequent repletion of calcium

Abstract 1. 1. Young tilapia, Oreochromis niloticus, were reared under calcium-deficient condition for 20 days and then transferred to normal condition and reared for 14 days. Changes in bone metabolism were studied by histomorphometry of the pharyngeal bone and measurements of calcium and phosphate contents of the opercular bone. 2. 2. Calcium deficiency activated bone resorption and decreased bone calcium and phosphate contents. 3. 3. Subsequent repletion of calcium markedly activated bone formation and suppressed bone resorption. The decreased contents of calcium and phosphate recovered to the control level. 4. 4. Results indicated that repletion of calcium restored the changes in bone metabolism induced by calcium deficiency.