Length-Weight Relationships and Relative Condition Factor of the Mullet, Rhinomugil Corsula (Hamilton, 1822) In the Sitakunda Coast of the Bay of Bengal, Bangladesh

This study deals with the length-weight relationship and relative condition factor (Kn) of 2480 specimens of Rhinomugil corsula (Hamilton, 1822), ranging from 3.5 cm to 29.5 cm total length and 0.40 g to 235.34 g weight, sampled monthly for two years period from March 2016 to February 2018 from the Sitakunda Coast of the Bay of Bengal, Bangladesh. Arithmetic form of equations for length (TL) and weight (W) of fish showed curvilinear relationships in male: W=0.0081TL3.016, female: W= 0.0083TL3.058 and combined sex: W=0.0076TL3.052, while logarithmic scale showed linear relationships in male: LogW=-2.122+3.016LogTL, female: LogW=-2.09+3.058 TL and combined sex: LogW=-2.121+3.052TL. In all the cases the coefficient of correlations between length and weight were positive and highly significant (P<0.01). The regression coefficient ‘b’ values were found to be 3.01±0.11, 3.06±0.12 and 3.05±0.12 for male, female and combined sexes, respectively for two years period together. When ‘t’ test was done, the growth was found to be isometric in case of male and combined sex and positive allometric in case of female. The relative condition factor (Kn) varied from 1.0003-1.009, 1.001-1.008 and 1.001-1.008, respectively, for male, female and combined sex in 2016-17, whereas 1.001-1.007, 1.003-1.006 and 0.992-1.008 respectively in 2017-18. The Kn values were always around ‘1’ or a little bit more than ‘1’ for length groups as well as monthly, indicating the excellent growth and robustness of fish due to favorable environmental condition prevailing in the habitat of the fish, in the Sitakunda coast of the Bay of Bengal. Bangladesh J. Zool. 49(1): 91-103, 2021

Investigating Spatiotemporal Variation of Heatwave and its Association with Blocking in the Northeastern Asia

&lt;p&gt;Severe heatwaves in recent decades caused tremendous financial loss and even deaths. And both the occurrence and characteristics of heatwave are changing under global warming. The spatiotemporal variation and characteristics of heatwave in Northeastern Asia are investigated on both grid and event bases in this study. We find that persistent, extensive and intense heatwave has become more frequent during the last four decades. Such trend is found significantly correlated with the increase of temperature.&lt;/p&gt;&lt;p&gt;As most dreadful heatwaves are reported to be accompanied by blocking, we also thoroughly analyze the association between heatwave and blocking using two leading blocking indices, examining 500hpa geopotential height (TM index) and vertically averaged potential vorticity anomaly (PV index), respectively. A discrepancy between blocking climatology of TM index and PV index is exhibited, with the former displaying two high-frequency zonal bands at the south and north regions, while the latter only showing one high frequency band in the north. However, grid-based concurrence analysis using the two blocking indices agreeably suggests that blocking favors the occurrence of heatwave, especially in the north region where blocking often occurs. We further explicitly investigate their extended temporal association with time lags, which has not been done before in the literatures. It reveals that heatwave mostly occurs after or on the onset day of blocking and ends after or at the end of blocking. It indicates that blocking is more of a favorable environmental condition to trigger heatwave than maintain it. Lastly, the impact of blocking on the characteristics of heatwave events is explored on an event basis, using the 3D object model newly proposed by this study. Blocking related heatwave events are more likely to be more persistent, extensive and intense than unrelated events.&lt;/p&gt;

ENVIRONMENTAL VARIABILITY ASSOCIATED WITH EASTERN LITTLE TUNA [Eutynnus affinis (Cantor, 1849)] CATCHES: A CASE FOR THE NORTH INDRAMAYU WATERS, JAVA SEA

Environmental variability during El Niño Southern Oscillation (ENSO) derived from satellite imagery of Sea Surface Temperature and Chlorophyll a were investigated during 2010 to 2014. This study investigates how ocean climate variability of ENSO affects environmental conditions and further addresses their relations with Eastern Little Tuna catches. Changes in environmental conditions during ENSO events resulted in perceivable variations in catches, with an average catches of 839.6 t during El Niño. The La Niña event, with an average catches of 602.6 t was less favorable for catches. Major fishing location located around 3.22-6.59ºS and 108.20-109.67ºE could have been suggested as the most favorable environmental condition to Eastern Little Tuna catch in the North Indramayu waters, Java Sea.

Role of Vibrio cholerae exochitinase ChiA2 in horizontal gene transfer

Vibrio cholerae exochitinase ChiA2 plays a key role in acquisition of nutrients by chitin hydrolysis in the natural environment as well as in pathogenesis in the intestinal milieu. In this study we demonstrate the importance of ChiA2 in horizontal gene transfer in the natural environment. We found that the expression of ChiA2 and TfoX, the central regulator of V. cholerae horizontal gene transfer, varied with changes in environmental conditions. The activity of ChiA2 was also dependent on these conditions. In 3 different environmental conditions tested here, we observed that the supporting environmental condition for maximum expression and activity of ChiA2 was 20 °C, pH 5.5, and 100 mmol/L salinity in the presence of chitin. The same condition also induced TfoX expression and was favorable for horizontal gene transfer in V. cholerae. High-performance liquid chromatography analysis showed that ChiA2 released a significant amount of (GlcNAc)2 from chitin hydrolysis under the favorable condition. We hypothesized that under the favorable environmental condition, ChiA2 was upregulated and maximally active to produce a significant amount of (GlcNAc)2 from chitin. The same environmental condition also induced tfoX expression, followed by its translational activation by the (GlcNAc)2 produced, leading to efficient horizontal gene transfer.

Nucleic Acid Content in Tissue of the Fish N. notopterus Collected from Different Aquatic Bodies

Nucleic acid content in brain, liver, kidney and gonads of the freshwater fish Notopterus notopterus collected from different aquatic bodies were studied during pre-spawning phase of the reproductive cycle. The three different aquatic bodies selected were Saradgi nala, Bennithora River and Bheema River and their physiochemical parameters also studied. The present study of nucleic acid content in brain, liver, kidney and gonads of the fish Notopterus notopterus collected from aquatic body Bennithora River shows normal levels of the nucleic acid as compared to that of fish from other two aquatic bodies. The normal content of nucleic acid content of N.notoptuers in the aquatic body Bennithora may be due to favorable environmental condition for survival, growth, distribution and reproductive activity.