Changes in brain and pituitary GnRH levels during ovarian maturation in wild female Japanese flounder

To elucidate the role of gonadotropin-releasing hormone (GnRH) in gonadal maturation in wild female Japanese flounder Paralichthys olivaceus, we monitored changes in the levels of seabream GnRH (sbGnRH) in the olfactory bulb, telencephalon, hypothalamus, and pituitary during ovarian development together with changes in plasma levels of testosterone (T), estradiol-17β (E₂), and 17α, 20β-dihydroxy-4-pregnen-3-one (DHP). Fish were caught offshore of the northern mainland of Japan in the Pacific Ocean at 3- to 4-week intervals between April and September by gill net. The netted fish were categorized into six groups based on ovarian stages: previtellogenic (April–early May), early yolk (April–late May), late yolk (late May–June), early spawning (June–August), late spawning (September), and termination (September) stages. The gonadosomatic index significantly increased from the previtellogenic to early spawning stages and decreased thereafter. In the olfactory bulb, no significant differences were observed in sbGnRH levels among the developmental stages. In contrast, sbGnRH levels in the telencephalon and hypothalamus were very high in the previtellogenic stage, lower in the early spawning stage, and relatively high in latter stages. sbGnRH levels in the pituitary were high in the previtellogenic stage and low in the early spawning stage. In addition, the relatively high levels of pituitary sbGnRH were found together with high plasma T, E₂, and DHP levels in fish in the late yolk stage. These results indicate that sbGnRH in the telencephalon, hypothalamus, and pituitary is involved in ovarian maturation and that sbGnRH may play an important role in the initiation of ovarian recrudescence in wild Japanese flounder.     

Is yield enhancement by CO2 enrichment greater in genotypes with a higher capacity for nitrogen fixation?

Yield responsiveness to elevated CO₂ concentration [CO₂] was previously found to be greater when nitrogen (N) was supplied in adequate amounts; however, it remains unclear whether genotypic differences in N₂-fixing capacity affect yield responsiveness in soybean. We tested the hypothesis that yield responsiveness to elevated [CO₂] in soybean is greater in a genotype with a higher capacity for N₂ fixation. We used three near-isogenic genotypes with contrasting nodulation capacities: super-nodulating, normally nodulating and non-nodulating genotypes. Plants were subjected to two levels of [CO₂] (ambient or elevated: ambient + 200 μmol mol⁻¹) and two temperature regimes (low or high: low + ca. 4-5 °C) using temperature gradient chambers. The super-nodulating genotype exhibited a higher N content in leaves, regardless of [CO₂] and temperature. Photosynthetic rates were enhanced by CO₂ enrichment at earlier growth stages, but not at later growth stages, regardless of genotype. This photosynthetic acclimation was reflected in biomass production in all the genotypes examined. Yield responsiveness to elevated [CO₂] was greater in the nodulating genotypes than in the non-nodulating genotype, but the genotypic differences were obscured between the normally nodulating and super-nodulating genotype, thus our hypothesis was not fully verified.     

Development of new self-feeding system for mass rearing of ayu <Emphasis Type="Italic">Plecoglossus altivelis altivelis</Emphasis> under artificial and natural light-dark cycles

Self-feeding of grouped ayu Plecoglossus altivelis altivelis was examined under an artificial light-dark (LD) cycle and natural day length using a trigger with a photosensitive sensor. In Experiment 1, approximately 15 juvenile fish (mean body weight, 0.6 g) were kept in 60-L glass tanks (four tanks) under LD 12∶12 (lighting period 06∶00–18∶00 hours) and self-feeding and locomotor activities were simultaneously recorded. Self-feeding was detected within one day and feeding activities were strongly synchronized to the LD cycle, with almost strictly diurnal feeding (98.2%). Although locomotor activities in the upper part of the tank were also greatest during the light phase (76.8%), the activity profiles were different from those of self-feeding, suggesting the validity of the photosensitive sensor. In Experiment 2,25 fish (mean body weight, 15 g) were kept in outdoor 1000-L tanks (four tanks) under natural day length and water temperatures in May, and self-feeding was recorded from mid-August. Stable self-feeding was observed from early September in all the tanks. Nearly all food demands were diurnal, and usually crepuscular. Somatic growth was seen in all tanks. These results demonstrate that the self-feeding system using a photosensitive sensor is applicable for grouped juvenile ayu as small as 0.6 g and adult fish reared under natural conditions.     

Effects of feeding time on approaching behavior to food odor in goldfish

ABSTRACT:   Effects of feeding time on approaching behavior to food odor in goldfish Carassius auratus were examined using the Y-maze flow-through system to test whether the behavior differed according to feeding time and experimental time. Fish were fed at 08.00, 12.00 or 16.00 hours once a day or three times (08.00, 12.00 and 16.00 hours) a day for at least 3 weeks under a natural photoperiod, and at 22 ± 2°C, preference reactions to food odor were tested at 08.00, 10.00, 12.00, 14.00 and 16.00 hours. The fish fed once a day showed significant positive approaching behavior only at the time when they were normally fed. The fish fed three times a day showed no significant positive approaching behavior. These results suggest that goldfish can remember when food is available and/or that there exists a mechanism to inhibit approaching behavior when food is not available.     

Effects of hypoxia on principal prey and growth of flathead flounder Hippoglossoides dubius in Funka Bay, Japan

ABSTRACT:   Effects of hypoxia on the principal prey and growth of flathead flounder Hippoglossoides dubius were studied in Funka Bay. Of the three dominant year-classes that occurred in recent years, the 1995 year-class was small in total length at age ≥ 3 and low in condition factor at age ≥ 2. Ophiuroids (almost Ophiura sarsi ), which were the dominant prey in the 1980s, were of little importance and instead, crustaceans such as mysids, natant decapods and pelagic amphipods, bivalves and fish were important prey items for H. dubius in 2000–2001. In addition, the feeding intensity of H. dubius in 2000–2001 was lower than that in the 1980s. These facts are closely related to a reduction of prey abundance, particularly ophiuroids. It seems that the hypoxia that occurred in the central part of the bay during the summer and autumn of 1995–1997 caused the poor food supply and low growth rate at ages 2–4 of the 1995 year-class.     

Synthesis of citrulline from ornithine by the small intestinal mucosa of cattle

Three segments of cattle small intestine (duodenum, upper jejuno‐ileum and lower jejuno‐ileum) were examined in an in vitro system for activity of ornithine carbamoyltransferase (OCT; EC 2.1.3.3) which is involved in the synthesis of citrulline (Cit) from ornithine (Orn). The mucosa of the three segments of small intestine was collected from Japanese black cattle, homogenized and then centrifuged. The supernatant fraction was used as the crude OCT enzyme solution. The OCT activity was assayed by the production of Cit from Orn determined directly by HPLC. The optimal pH and temperature for OCT activities in the duodenum, upper jejuno‐ileum and lower jejuno‐ileum of cattle small intestine were 7.47 and 39°C. Little difference was observed between the three segments. The OCT activity in cattle kidney was also examined for comparison, and almost no activity was found. The OCT activities in crude enzyme solutions of the three segments of small intestine were stable for up to one month of storage at ?20°C in Tris HCl buffer solution. Finally, the role of the small intestine in supplying Cit as a precursor for arginine synthesis in cattle kidney was discussed.     

Effect of oral administration of L-pipecolic acid on food intake in chicks and mice

It has been demonstrated that L-pipecolic acid (L-PA), a major metabolic intermediate of L-lysine (L-Lys) in the brain, is involved in the functioning of the γ-aminobutyric acid-ergic system. Previous study has shown that intracerebroventricular injection of L-PA suppressed feeding and induced sleep-like behavior in neonatal chicks. The present study examines whether the action of L-PA was induced by gavage in both chicks and mice. Oral administration of L-PA significantly inhibited food intake at 2 h after treatment in neonatal chicks, although no significant effect of L-Lys was detected. In mice, oral L-PA suppressed food intake compared to the control after 2 h of treatment. It was concluded that L-PA was effective for suppression of food intake after oral administration in both avian and mammalian species.     

Measurement of diurnal changes in stem and branch diameters using strain gauges

The applicability of a strain gauge for monitoring the diurnal changes of tree stem diameters and the differences in diurnal shrinkages between a stem and branches were investigated. Estimates of stem diameter changes obtained by a strain gauge were compared with changes obtained by a differential transformer. Patterns of strain changes obtained by a strain gauge were remarkably similar to the changes in the tree trunk diameter. This results demonstrated that a strain gauge is an effective technique for examining the behavior of changes in tree trunk diameter. Diurnal changes of diameter at various parts of the a tree were also measured with the help of several strain gauges. Diurnal strain changes of a stem and branches showed similar patterns of shrinkage during the day and swelling at night. However, the precise times at which the branches had their maximum and minimum strains differed from those observed in the stem, and the maximum rates of the strain changes lagged behind the stems in a day. These results lead us to believe that there is a time lag in the supply of water, which is required for compensating the water deficit between the stem and its branches. A part of this paper was presented at the 105th Annual Meeting of Japanese Forestry Society (1994).     

Water removal of wet veneer by roller pressing

High moisture content, flat sawn Japanese cedar (Cryptomeria japonica D. Don) veneer was compressed using a roller press to mechanically remove water. The amount of water removed depended on the amount of compression applied. At 60% compression, 400kg/m³ of water was removed. The process was not dependent on the size of the wood, the degree of compression, or the feed speed of the specimen. After compression, the remaining water contents were evenly distributed throughout the veneer regardless of the length of the specimen. The specimens did not completely recover to original thickness. High compression ratio and low temperature intensified the reduction of thickness. The bending strength after compression decreased in an inversely proportional manner with the thickness of the specimen and the compression degree.Part of this study was presented at the 50th Annual Meeting of the Japan Wood Research Society, Kyoto, April 2000