Uptake of orally administered polystyrene latex and poly(D,L-lactic/glycolic acid) microspheres into intestinal lymphoid tissues in chickens.

Fluorescein-labeled microspheres were orally administered to chickens and their distribution in intestinal lymphoid tissues was investigated. Polystyrene latex microspheres were observed in Peyer's patches, and also in the Meckel's diverticulum and the jejunum. Their density, however, seemed to be lower than that in Peyer's patches. Microspheres were rarely observed in the other intestinal tissues examined, including the bursa of Fabricius. Of note is that, although microspheres were present in the lumen, few, if any, were observed in the lamina propria of the caecal tonsil and caecum. Polystyrene latex microspheres of diameter 2.0 microm or 4.5 microm were also observed in Peyer's patches, but their density seemed to be lower as compared with the 0.75 microm microspheres. Poly(D,L-lactic/glycolic acid) (PLGA) microspheres were prepared using PLGAs of various molecular weights (MW) and their uptake into Peyer's patches was compared. Microspheres prepared with PLGA of average MW of 20000 were not taken up into Peyer's patches, but those prepared with PLGA of average MW of 61000 or 99 800 were taken up into Peyer's patches.     

Geographical variations in the trophic structure of the plankton community along a eutrophic–mesotrophic–oligotrophic transect

The geographical variations in trophic structure of the plankton community, as defined by total and relative carbon biomass of phytoplankton (PP), bacteria (BA), heterotrophic nanoflagellates (HNF), microzooplankton (MZ), and herbivorous (HNZ) and carnivorous net-zooplankton (CNZ), were investigated along an inshore–offshore transect from the innermost part of Osaka Bay to the Pacific Ocean off Kii Channel, Japan, in June 1991. Based on physico-chemical properties of the water and topographical features, the transect was divided into three trophic areas, i.e. eutrophic, mesotrophic and oligotrophic ones. The average carbon biomass of the total plankton community was highest (438 mg m⁻³) in the inshore eutrophic area, and declined steeply offshore (141 and 26.6 mg m⁻³ in the mesotrophic and oligotrophic areas, respectively). In the offshore oligotrophic area, the relative biomass of BA to PP and the relative biomass of small heterotrophs (i.e. BA, HNF and MZ) to the total heterotrophs were higher than in the other areas, indicating that the microbial food chain predominated. In the mesotrophic area, the biomass of HNZ (primarily copepods) was conspicuously high, even higher than that of PP, suggesting that the traditional grazing food chain prevailed. Because of this short food chain, a productive fishing ground is formed there. In the eutrophic area, the biomass of HNZ was much smaller relative to the enormous biomass of PP, indicating that a considerable amount of primary production was not utilized directly by the metazoan zooplankton. However, the relative contribution of the small heterotrophs to the total heterotrophs' biomass was higher in this area, as in the oligotrophic area.     

Can research on the early marine life stage of juvenile chum salmon <Emphasis Type="Italic">Oncorhynchus keta</Emphasis> forecast returns of adult salmon? A case study from eastern Hokkaido,Japan

To examine the efficacy of juvenile salmon research as a tool for forecasting adult returns, the results from a study on the early marine life stage of juvenile chum salmon, conducted in the Nemuro Strait during 1999–2002 (i.e., 1998–2001 brood years), were compared with the return rates of adult salmon. Among the four brood years, the 2000 brood year (i.e., salmon migrating to the sea in 2001) was previously reported as showing higher abundance, higher growth rate and better somatic condition during the coastal residency period. Consequently, we expected it to have the highest return rate, under a hypothesis that juvenile survival in coastal residency regulates brood-year strength. Contrary to this expectation, the 2000 brood year had almost the lowest return rate. Alternatively, a statistical model in which sea surface temperature during the first year of marine life and size at release were utilized as explanatory variables reconstructed the actual variability in return rates more accurately than that based on the early marine life stage. Possible reasons for the discrepancy between the results of the juvenile salmon research and adult returns are discussed, and we suggest improvements for future research on juvenile salmon.     

The differences in behavioral responses to a net obstacle between day and night in captive manatees; does entanglement happen at night?

Entanglement in fishing gear occurs in endangered manatees and may result in serious injury or death. Such incidents may happen more frequently at night when the animal’s visual sense is limited. In this study, we examined the differences in behavioral response of captive manatees to a net obstacle during light (day) and dark (night) periods. We used a plastic net as the obstacle, and video-recorded the manatees’ behavior. The experiments showed that captive manatees avoided the obstacle during the day more frequently than at night, which suggests that the manatees can perceive the obstacle more readily during light periods. However, there was no difference in the frequency of bumping or actively touching the obstacle between light and dark periods. The results suggest that the manatees can recognize the net obstacle even at night by purposely touching it, but they avoid it less frequently, and that entanglement during light periods may occur during accidental bumping, rather than from a failure to recognize it altogether.     

Otolith microstructure of brown sole <Emphasis Type="Italic">Pseudopleuronectes herzensteini</Emphasis>: validation of daily ring formation and the occurrence of microstructure denoting metamorphosis

Brown sole Pseudopleuronectes herzensteini larvae and juveniles were reared to validate daily otolith ring formation. At 15°C, a check (a distinct ring) formed on the sagittae and lapilli at 6 days after hatching, and clear increments regularly formed outside the check. For both otoliths, the relationship between the number of days after hatching and number of increments was linear, and the slope of the line was approximately 1; therefore, daily formation was validated. At 12°C, the check formed on the lapillus 8 days after hatching. Accessory primordia (AP) began forming on the sagittae of metamorphosing larvae, and the shape of the sagittae became complicated. AP were not formed on the lapillus; concentric rings were formed throughout larval and juvenile stages. Wide and obscure increments formed on the lapilli during metamorphosis (metamorphosing zone, MZ). Based on MZ, concentric rings that have formed on the lapilli of juveniles can be separated into larval and juvenile rings. The morphs of large juveniles’ lapilli were bilaterally asymmetric, and the blind-side lapilli were most suitable for otolith microstructure analysis. This study provides fundamental information for otolith microstructure analysis in wild brown sole.     

Plasmodium (Bennettinia) juxtanucleare infection in a captive white eared-pheasant (Crossoptilon crossoptilon) at a Japanese zoo

An adult male white eared-pheasant (Crossoptilon crossoptilon) at a Japanese zoo exhibited lethargy and emaciation. Microscopic examination of a blood smear revealed a haemosporidian parasitic infection. Based on the morphological characteristics and molecular analysis of the parasite, it was identified as Plasmodium (Bennettinia) juxtanucleare. This is the first report of P. juxtanucleare infection in bird species belonging to the genus Crossoptilon. Caution against avian malaria infection is required for the conservation of endangered bird species in zoos.