Effects of loosing Aigamo ducks on the growth of rice plants, weeds, and the number of arthropods in paddy fields

Aigamo duck farming has been noticed as one of the techniques of environmental conservation agriculture. This study was carried out to investigate the effects of loosing Aigamo ducks on the growth and production of rice plants, the quantity of weeds and arthropods, and the balance of nitrogen (N) in paddy fields by changing the density of the Aigamo ducks. A paddy field was divided into three test plots: a 10-Aigamo-duck plot, a five-Aigamo-duck plot, and a weeding plot. The results show that the height, number of culms, and yield crops of the rice plants increased more in the 10-Aigamo-duck plot and the five-Aigamo-duck plot than that of the weeding plot. Millet ( Echinochloa oryzicola ) remained in both the Aigamo duck plots. The weeding plot was covered with monochoria ( Monochoria vaginalis ). In both the Aigamo duck plots, the outbreak of total arthropods was lower than that of the weeding plot, but the number of rice plants damaged by grass leaf rollers ( Cnaphalocrocis medinalis ) was increased. The number of spiders, regarded as useful insects, did not differ that much between the experimental plots. The N content of the soil did not differ as an effect of loosing the Aigamo ducks. The rice plants in the 10-Aigamo-duck plot absorbed more N than the rice plants in the other plots.     

Interannual variation in Neocalanus biomass in the Oyashio waters of the western North Pacific

We examined the interannual variation in Neocalanus copepod biomass in the Oyashio waters in spring and summer from 1972 to 1999. In the mid‐1970s, mesozooplankton biomass in spring was high; however, it decreased significantly in the late 1970s. The timing of the decrease in mesozooplankton biomass corresponded to the 1976/77 climatic regime shift. The biomass of N. flemingeri, which dominated the Neocalanus community, was roughly constant from 1980 to 1999. Although species‐level estimates of Neocalanus biomass were not available for the 1970s, a previous study reported that Neocalanus copepods were the predominant mesozooplankton in the Oyashio waters in spring during the 1970s. Neocalanus copepods dominated the mesozooplankton community throughout the 1970s, and their biomass decreased in the late 1970s. Springtime net community production, an index of new production, also decreased in the late 1970s. We suggest that the reduction in new production negatively affected Neocalanus food availability, resulting decreased copepod biomass. New production may have been limited by a combination of subsurface iron supplies, increased vertical density gradient, and reduced vertical water mixing in winter, which resulted in diminished iron entrainment in winter. In summer, mesozooplankton biomass significantly decreased and increased synchronously with the 1976/77 and 1988/89 climatic regime shifts. The biomass of N. plumchrus, which dominated the Neocalanus community, was low in the 1980s and increased in the early 1990s. The biomass of the second‐most dominant copepod, N. cristatus, also increased in the early 1990s. Neocalanus copepods were reported to be a dominant component of the mesozooplankton community in the 1970s; Neocalanus biomass was high in the mid‐1970s and decreased in the late 1970s. Japanese sardine (Sardinops melanostictus), an important predator of Neocalanus copepods, exhibited interannual variation in standing stock that was inversely related to mesozooplankton biomass. At their peak in 1984, sardines consumed 32–138% of the daily Neocalanus production during summer. Therefore, predation pressure on Neocalanus by Japanese sardine is likely to affect interannual variation in mesozooplankton biomass during the summer.     

Characterization of the digestive tract of wild ayu

ABSTRACT: The gut and gut contents of ayu Plecoglossus altivelis caught in the Ohta River in Hiroshima prefecture, Japan were examined. Relative intestine length (intestine length/body length) was almost constant. Except for relative intestine length, characteristics of the gut of wild ayu were not significantly different from those of cultured ayu. The height of intestinal folds increased and their width declined from stomach to anus. Cyanobacteria ( Homoeathrix sp. and Calothrix sp.) and diatoms ( Cymbella sp., Gomphonema sp., Melosira sp., Navicula sp., and Synedra sp.) were well digested during passage through the gut despite a lack of apparent destruction. In contrast, green algae ( Dictyosphearium sp., Coelastrum sp., and Pediastrum sp.) exhibited little degradation. The pH of stomach contents ranged from 2.8 to 7.4 (mean ± SD = 4.1 ± 1.0), whereas that of the posterior intestine was 7.0–8.5 (7.9 ± 0.4). Gut contents of wild ayu increased with bodyweight, and were more than threefold greater than those of cultured ayu, suggesting that wild ayu compensate for low nutrient content of algae through the continuous ingestion of large quantities of feed organisms.     

Acoustic identification of isada krill, Euphausia pacifica Hansen, off the Sanriku coast, north-eastern Japan

In this study, the feasibility of identification and abundance estimation of isada krill, Euphausia pacifica , was examined using a two-frequency (38 and 120 kHz) method. The acoustic survey and midwater trawling were conducted off the Sanriku coast, northern part of Honshu, Japan. In one pattern, the SV difference between the two frequencies was large, and in the other, the SV difference was small. These results were interpreted by scattering models, and showed that discrimination between isada krill and walleye pollock was possible.     

Diel timing of molting and metamorphosis of Panulirus japonicus phyllosoma larvae under laboratory conditions

ABSTRACT:   The timing of molting and metamorphosis was monitored for Panulirus japonicus phyllosoma larvae cultured in the laboratory. Larvae cultured under natural light–dark cycle molted synchronously within approximately 1.0 h before and after sunrise, except for a short period after hatching; the timing of molting changed with time of sunrise. When three artificial light–dark cycles were introduced, larvae molted around the start of lighting, irrespective of the light–dark cycles. In the event of a sudden change in the start or end of lighting, molting was regulated by an endogenous rhythm. The start of lighting had a greater impact on the timing of molting than the end of lighting, suggesting that sunrise is probably the critical signal for phase-setting in molting rhythm. Metamorphosis to the puerulus stage occurred within 0.4 h before and 1.2 h after sunset under a natural light–dark cycle, and the timing of metamorphosis was also changed artificially by regulating the end of lighting.     

Environmental variability and growth histories of larval Japanese sardine (Sardinops melanostictus) and Japanese anchovy (Engraulis japonicus) near the frontal area of the Kuroshio

Environmental variability and growth‐rate histories from hatching to capture were investigated for larval Japanese sardine (Sardinops melanostictus) and Japanese anchovy (Engraulis japonicus). Larvae collected around the front of the Kuroshio Current were examined using otolith microstructure analysis, and their movement was estimated from numerical particle‐tracking experiments. Sardine larvae collected inshore of the Kuroshio front originated from a coastal area near the sampling site, while those collected in the offshore area originated from an area 500–800 km west‐southwest of the sampling site. Anchovy larvae collected both inshore and offshore had been transported from widely distributed spawning areas located west of the sampling area. At the age of 13–14 days for sardine and 19–20 days for anchovy, the offshore group exhibited significantly higher mean growth rates than did the inshore group. Although the offshore area was generally warmer than the inshore area, temporal variations in growth rate are not attributable solely to fluctuations in environmental temperature. While previous studies have examined the relationship between larval growth rates and environment based solely on data at capture, the methods used in the present study, combining otolith analysis and numerical particle‐tracking experiments, utilize data up until hatching. Although the relationship between growth rate and environment was not fully confirmed, this approach will greatly advance our understanding of fish population dynamics.     

Population assessment of sockeye salmon Oncorhynchus nerka caught by recreational angling and commercial fishery in Lake Toya, Japan

ABSTRACT: We carried out mail and access point surveys to estimate the catch numbers, angling effort of recreational angling and the population of sockeye salmon Oncorhynchus nerka in Lake Toya in 1998 and 1999. The mail survey questions in questionnaires distributed to anglers with a recreational angling license included date of angling, caught fish species and size, and catch number. In the access point survey we also asked anglers if they had a license. We measured the fork length and weight of caught fish. The catch rate (catch number in a day by each angler) from both surveys showed no significant difference, suggesting no bias for the catch rate between surveys. The estimated total angling effort was 1760 people (1998), and 1516 people (1999). The estimated recreational catch was 28 889 (1998) and 5455 (1999), that is, two or three times larger than the commercial catch. The fish population was estimated by using the DeLury method as 60 262 (1998) and 10 806 (1999). The total exploitation rate was 62% (1998) and 78% (1999). The size of caught fish was much larger in 1999 than 1998 because of the difference in age composition.     

太阳热处理对小白菜根肿病防治效果的研究

为探讨太阳热处理对小白菜根肿病的防治效果,以超级小黄白为供试材料,测定太阳热处理前后的土壤理化性质、根肿菌休眠孢子数量、土壤微生物多样性及发病率和病情指数,评价太阳热处理对小白菜根肿病的影响。研究表明:经太阳热处理后土壤0~10 cm处pH由4.96提高至5.60,根肿菌休眠孢子的浓度由1.09×10⁶ g^-1减少至5.74×10⁵ g^-1。变性梯度凝胶电泳(DGGE)结果证明,太阳热处理提高了土壤细菌微生物多样性,其中0~10 cm处和10~20 cm处土壤细菌微生物群落的香浓维纳指数分别由1.51、0.91提高到1.98、1.53,0~10 cm处根肿病的发病率由87.10%降低到49.12%,病情指数由45.24降低到16.96,防治效果明显。本研究为太阳热处理在实际农业生产中的应用及对根肿病的防治提供了理论基础。     

Experimental production of porcine gastroesophageal ulcers by betazole and reserpine

The ulcerogenic and secretogenic properties of betazole, (an H₂ agonist), and/or reserpine on pig stomachs were studied. (1) Betazole (50 mg/body) and reserpine (0.02 mg/kg) were successively injected (i.m.) for 5–10 days into starved animals. Gastroesophageal ulcers, pathologically similar to naturally occurring ulcers were observed in all pigs (10/10), whether a nutrient solution (5% glucose, 1 litre/day) was supplied or not. In the starved pigs given either betazole or reserpine, only a small ulcer or erosion was observed. (2) In four pigs which were given commercial mash at a rate of 3% of body weight per day and killed on the 6th or 10th day of successive injections of both drugs, the incidence of ulcers was 2/4. (3) The gastric secretogenic effect of betazole and/or reserpine was confirmed in pigs with Heidenhain gastric pouches. (4) From these data, a new method for the experimental induction of pig gastroesophageal ulcers, by means of simultaneous injections of betazole and reserpine for 5 days under the nutrient (glucose solution) drinking condition, is proposed. The authors consider that this method may be superior to the repository histamine method, with respect to the absence of adverse effects, practical convenience and pathological and etiological similarities with naturally occurring ulcers.