The flood pulse and growth of floodplain fish in Bangladesh

The floodplain fisheries associated with the Compartmentalization Pilot Project, Tangail, Bangladesh, were monitored using a traditional length‐based fish stock assessment programme from 1992 to 1998. The growth of Colisa fasciatus (Bloch & Schneider) and Channa punctata (Bloch) was significantly higher in years of high floods. Further, the annual yields of Puntius sophore (Hamilton), C. punctata and C. fasciatus were significantly higher in years with high growth rates. The increased growth rate resulted in the presence of two cohorts in the catches during high floods instead of one cohort during years of low flooding. The species studied had relatively short life spans with longevity of 2.4–4.6 years. The majority of fishes did not survive the first year of their lives because of the low survival rate caused by high fishing mortality, which suggests that the fishes in the floodplains of Bangladesh exhibit an annual cycle. Annual fish yields in the flood plains of Bangladesh, appear to be maintained, despite the high fishing effort, by the annual flood pulse providing the nutrient‐rich environment needed for the remaining r‐strategists to survive.     

Conservation agriculture practice influences soil organic carbon pools in intensive rice-based systems of the Eastern Indo-Gangetic Plain

Studies of rice-based systems in the Indo-Gangetic Plain (IGP) have demonstrated the beneficial effects of Conservation Agriculture on soil organic carbon (SOC) status, along with increased soil health and crop productivity. However, it remains unclear as to the time for such treatments to have a positive effect. In this study of lentil-mung bean-rice and wheat-mung-rice rotations in Bangladesh positive effects of strip planting or bed planting, along with residue return, on SOC pools were apparent after 1.5 years, compared with intensive conventional tillage and limited residue return. Conventional tillage resulted in higher CO₂ emission compared with strip planting or bed planting as did high residue return. In the cereal-dominated rotation, the strip planting system sequestered carbon at a rate of 0.24–0.53 Mg C ha⁻¹ year⁻¹ (at 0–0.15 m depth) while conventional tillage was associated with a carbon loss of 0.52–0.82 Mg C ha⁻¹ year⁻¹. In the legume-dominated rotation, neither practice sequestered SOC. Under strip planting, a minimum annual crop residue input of 1.7 Mg C ha⁻¹ for the cereal-dominated system and 5.2 Mg C ha⁻¹ for the legume-dominated system was required to maintain SOC at equilibrium. We conclude that strip planting with high levels of crop residue return can be an effective and quick strategy in either slowing the loss of SOC or improving C sequestration in the intensive rice-based systems of the Eastern IGP.     

Soil degradation during the period 1967–1995 in Bangladesh

Long-term changes in carbon and nitrogen storage in the top 100 em layers of soils from different physiographic units in Bangladesh were evaluated using 460 soil samples from 43 profiles collected in 1967 and 1994/95. The study area consisted of ten physiographic units, viz.: Old Himalayan Piedmont Plain (OHP), Tista Floodplain (TF), Barind Tract (BT), Ganges Floodplain (GF), Madhupur Tract (MT), Brahmaputra Floodplain (BF), Meghna River and Estuarine Floodplain (MF), Surma-Kushiyara Floodplain (SKF), Northern and Eastern Piedmont Plain (NEP), and Chittagong Coastal Plain (CCP).

During the period 1967–1995, mean values of soil carbon and nitrogen declined by 16.2 t C ha^-1 and 1.38 t N ha^-1 in Bangladesh. The total carbon and nitrogen budgets showed a fall of 42.8 × 10⁶ t C and 3.36 × 10⁶ t N within the 27 y period in Bangladesh. All the physiographic units showed a decline in carbon and nitrogen contents except for BT which showed an increase of 3.76 t C ha^-1 and 0.77 t N ha^-1 for these elements. MT showed the highest decline in carbon (30.5 t C ha^-1) and nitrogen (3.25 t N ha^-1). The lowest decline in carbon was observed in SKF (7.18 t C ha^-1) while the same applied to nitrogen in GF (0.50 t N ha^-1). The other physiographic units showed a moderate decline in the contents of these elements.

Based on the land area occupied by the sampled soil series of each physiographic unit, GF showed the highest decline of 13.7×10⁶ t C and a moderate decline of 0.52 × 10⁶ t N. Decrease in the carbon level for BF was moderate (9.31 × 10⁶ t C) but the decline in the nitrogen level was the highest (0.95 × 10⁶ t N). Decrease in the amount of carbon and nitrogen stored for the other physiographic units was: OHP (0.67 × 10⁶ t C, 0.03 × 10⁶ t N), TF (2.54 × 10⁶ t C, 0.25 × 10⁶ t N), MT (4.28 × 10⁶ t C, 0.45 × 10⁶ t N), MF (6.06 × 10⁶ t C, 0.61 × 10⁶ t N), SKF (2.87×10⁶ t C, 0.24×10⁶ t N), NEP (2.68×10⁶ t C, 0.22×10⁶ t N), and CCP (0.81 × 10⁶ t C, 0.11 × 10⁶ t N). Increase in carbon and nitrogen contents was only observed in BT (0.08 × 10⁶ t C, 0.02 × 10⁶ t N).     

Phosphorus status of some paddy soils in Bangladesh

Abstract

Phosphorus status of Bangladesh paddy soils covering the major paddy soil types was assessed in terms of parent materials and physiography. Total P concentration ranged from 172 to 604 mg kg^?1 in the topsoil and from 126 to 688 mg kg^?1 in the subsoil, and varied with the physiography to which the soils belonged. In most soils, the available P concentration was much higher for the topsoil than for the subsoil. The inorganic P concentration was higher than the organic P concentration, except for one soil series from the Old Himalayan Piedmont Plain, and was significantly and positively correlated with the total P concentration. Among the inorganic forms, only the concentration of Al-bound P showed a significant correlation with that of available P based on the Bray P-2 method in both topsoil and subsoil. In general, the P status was critically low in paddy soils of the terrace area. Normal growth of paddy rice in this area is expected to be difficult without application of P fertilizer.     

Effects of capture,loading density and transport stress on the mortality,physiological responses,bacterial density and growth of rohu <Emphasis Type="Italic">Labeo</Emphasis><Emphasis Type="Italic"> rohita</Emphasis> fingerlings

This study evaluated the effects of three levels of loading density (200, 300 and 400 g L⁻¹) and four levels of duration (1, 3, 6 and 9 h) on the mortality, plasma cortisol and chloride levels and growth of rohu Labeo rohita fingerlings in a transport simulation. While total immediate mortality was low (4–12%), delayed mortality was high (27–49%). Initial capture and handling were found to constitute the most stressful phase as indicated by elevated plasma cortisol. The levels of cortisol continued to rise at 6 and 9 h after transport, with the highest level observed at 9 h after transport. The level of plasma chloride fell after transport across all density levels and treatment durations. Specific growth rate (SGR, %/day) and total bacterial density (cfu/g) were not different between and within treatments, and between treatments and the controls. This study demonstrates that transport has a profound effect on the stress responses of rohu fingerlings. Although the level of immediate mortality was low, the higher level of delayed mortality has serious implications in terms of production inefficiency for grow-out farmers.     

Allozyme variation of hatchery and river populations of rohu (Labeo rohita, Hamilton) in Bangladesh

The genetic variations of rohu (Labeo rohita, Hamilton) sampled from five hatchery populations (Arabpur, Brahmaputra, Comilla, Kishorganj and Natore) and three major river populations (the Halda, the Jamuna and the Padma) were analysed by allozyme electrophoresis. Ten enzymes encoded by 11 loci were screened, and six were polymorphic. Alleles at three loci (Est‐1^*, Gpi‐1^* and Gpi‐2^*) proved variable for hatchery and river populations, and the Mdh‐2^* locus exhibited heterozygous genotypes for river populations only. Polymorphic loci per population (27.3±5.3%), heterozygous loci per individual (15.5±1.2%) and relative gene diversity (0.27±0.08) in river populations were higher than those for hatchery populations (25.5±1.8%, 10.7±1.6% and 0.25±0.01 respectively). Also, the observed heterozygosity (Ho) and expected heterozygosity (He) (0.09±0.03 and 0.14±0.04 respectively) in river populations were higher than those in hatchery populations (0.08±0.01 and 0.11±0.01 respectively). The lower levels of genetic variability in hatchery populations suggested the occurrence of inbreeding and/or genetic drift. The pairwise population differentiation (F_ST) values showed a lower level of genetic differentiation between hatchery and river population pairs. The unweighted pair‐group method with arithmetic mean dendrogram of Nei's genetic distances showed a relationship between the genetic distance and geographic distance. The populations were clustered into three groups: the Padma in one group, the Halda in second group and the Jamuna, including five hatcheries, in the third group. Highly diversified rohu individuals were observed in the Padma and Halda Rivers, whereas less genetically variable individuals were found in the Jamuna River and five hatcheries. These findings can be useful for rohu hatchery propagation to enhance the sustainable aquaculture production.     

Seasonal changes in distribution and abundance of euphausiids in the coastal area of north-eastern Japan

ABSTRACT:   Seasonal changes in distribution and abundance of euphausiids off south-eastern Hokkaido (41°−43°N), Sanriku (38°−41°N), and Joban (36°−38°N) were investigated using cylindrical-conical nets every two months from March 1997 to February 1998. Twenty-six species of seven genera of euphausiids occurred during the survey. Among them, subarctic-transitional Euphausia pacifica was the most abundant throughout the year in coastal waters, as their relative contribution to the total abundance of euphausiids was 89–92%. This species occurred in each coastal water throughout the survey and was abundant from winter to early summer (February–June) off Sanriku and Joban and in autumn in south-eastern Hokkaido. Thysanoessa inspinata occurred off south-eastern Hokkaido and Sanriku throughout the survey, mainly in spring (April) but rarely occurred off Joban. Three other subarctic Thysanoessa species occurred mainly off south-eastern Hokkaido from winter to spring. Conversely, warm- and transitional-water epipelagic species occurred exclusively off Sanriku and Joban in autumn. The characteristics of seasonal distributional patterns of euphausiids are discussed in relation to the spatial and temporal changes of oceanographic conditions and several predators off north-eastern Japan.     

Biomass and production of the euphausiid Euphausia pacifica along the coastal waters off north-eastern Japan

ABSTRACT:   Biomass and production of Euphausia pacifica off south-eastern Hokkaido (41–43°N), Sanriku (38–41°N), and Joban (36–38°N) were investigated every two months from March 1997 to February 1998. High biomass was found in summer–autumn off south-eastern Hokkaido, and in the late winter–early summer off Sanriku and Joban. Annual mean biomass was 381, 314 and 258 mg C/m² off south-eastern Hokkaido, Sanriku, and Joban, respectively. The total production (sum of flesh, moults and eggs) during the survey period off south-eastern Hokkaido (3829 mg C/m²) was comparable with that off Sanriku (3872 mg C/m²); both were much higher than that off Joban (2243 mg C/m²). Somatic production during the survey period contributed the highest proportion (51.5–70.9%) to the total production in each coastal area. The somatic production–biomass ratio in each coastal area (5.2–6.9) was an intermediate value among 25 populations of 16 euphausiid species previously reported. This effect resulted from the negative factor of stagnated growth of adults during summer–winter, coupled with positive factors including continuous occurrence of larvae which show high growth rate throughout the year off Sanriku and Joban, and the numerous larvae occurring in October off south-eastern Hokkaido.     

孟加拉杂交水稻研究概况

孟加拉杂交水稻研究概况＊ＨｙｂｒｉｄｒｉｃｅｒｅｓｅａｒｃｈｉｎＢａｎｇｌａｄｅｓｈＡ．Ｗ．Ｊｕｌｆｉｑｕａｒ，Ｍ．ＭｏｈｉｕｌＨａｑｕｅ，Ａ．Ｋ．Ｇ．Ｍ．ＥｎａｍｕｌＨａｑｕｅ，Ｍ．ＡｌａｍｇｉｒＨｏｓａｉｎ（孟加拉水稻研究所Ｇａｚｉｐｕｒ１７０１...     

Homestead Agroforestry in Bangladesh: Dynamics of Stand Structure and Biodiversity

The cultivation of different plants around homesteads for subsistence and cash income has been a long tradition in Bangladesh. This study explores stand structure, composition, and biodiversity within the homestead agroforests of the drought-prone, northwestern region of Bangladesh. In 96 randomly selected homesteads within 3 study villages, we identified 56 tree species. Among those, Mangifera indica (mango) was the most popular fruit bearing species. Four non-parametric diversity indices were derived to provide a characterization of biodiversity. The Sørenson similarity index was also used to compare the similarity of species among different landholding size classes. The overall Shannon-Wiener biodiversity index and Pielou's evenness index values were 1.82 and 0.45, respectively. This study confirms that the farmers had strong preference for fruit species over timber yielding ones, and because of better growth performance natives were preferred over exotics.